Pt Single Atoms Supported on N-Doped Mesoporous Hollow Carbon Spheres with Enhanced Electrocatalytic H2 -Evolution Activity

Dual modification of cobalt silicate nanobelts by Co3O4 nanoparticles and phosphorization boosting oxygen evolution reaction properties

Oxygen evolution reaction (OER) process is the "bottleneck" of water splitting, and the low-cost and high-efficient OER catalysts are of great importance and attractive but they are still challenging. Herein, a dual modification strategy is developed to tune and enrich the structure of cobalt silicate (Co2SiO4) showing boosted OER properties. Cobalt oxide (Co3O4) decorated Co2SiO4 nanobelts, denoted as CS, is firstly prepared using a Co-based precursor by a facile hydrothermal reaction. Then, cobalt phosphide (CoP) nanoparticles are in-situ grown on CS (denoted as CS-P) by the phosphorization process, which provide many active sites and boost the surface reactivity. The experimental results and density function theory (DFT) calculations both reveal that the CoP on CS can improve the conductivity and ensure fast kinetics, thus leading to boost the OER properties of Co2SiO4. When the phosphorization temperature is at 400 °C (CS-P400), it gains the lowest overpotential of 297 mV, which is much lower than CS (340 mV) and Co2SiO4 (409 mV) at 10 mA·cm-2, and even superior to the state-of-the-art transition metal silicates. CS-P400 also achieves high electrochemical active surface area (ECSA) and small Tafel slope owing to its porous structures with large specific surface area and nanosheet-like structures which are good for exposing many active sites and favorable to the fast kinetics. This work not only provides a dual modification route to boost catalytic activity of Co2SiO4 (CS-P400), but also sheds light on a new avenue for developing highly dispersed CoP on silicates to boost OER performances.

Light-Promoted Extraction of Precious Metals Using a Porphyrin-Integrated One-Dimensional Covalent Organic Framework

Precious metals are valuable materials for the chemical industry, but they are scarce and pose a risk of supply disruption. Recycling precious metals from waste is a promising strategy, here we tactfully utilize light irradiation as an environmental-friendly and energy-saving adjunctive strategy to promote the reduction of precious metal ions, thereby improving the adsorption capacity and kinetics. A newly light-sensitive covalent organic framework (PP-COF) was synthesized to illustrate the effectiveness and feasibility of this light auxiliary strategy. The equilibrium adsorption capacities of PP-COF with light irradiation towards gold, platinum, and silver ions are 4729, 573, and 519 mg g-1, which are 3.3, 1.9, and 1.2 times the adsorption capacities under dark condition. Significantly, a filtration column with PP-COF can recover more than 99.8 % of the gold ions in the simulated e-waste leachates with light irradiation, and 1 gram of PP-COF can recover gold from up to 0.15 tonne of e-waste leachates. Interestingly, the captured precious metals by PP-COF with light irradiation mainly exist in the micron-sized particles, which can be easily separated by extraction. We believe this work can contribute to precious metal recovery and circular economy for recycling resources.

Recent progress of density functional theory studies on carbon-supported single-atom catalysts for energy storage and conversion

Single-atom catalysts (SACs) have become the forefront and hotspot in energy storage and conversion research, inheriting the advantages of both homogeneous and heterogeneous catalysts. In particular, carbon-supported SACs (CS-SACs) are excellent candidates for many energy storage and conversion applications, due to their maximum atomic efficiency, unique electronic and coordination structures, and beneficial synergistic effects between active catalytic sites and carbon substrates. In this review, we briefly review the atomic-level regulation strategies for optimizing CS-SACs for energy storage and conversion, including coordination structure control, nonmetallic elemental doping, axial coordination design, and polymetallic active site construction. Then we summarize the recent progress of density functional theory studies on designing CS-SACs by the above strategies for electrocatalysis, such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, CO2 reduction reaction, nitrogen reduction reaction, and electrosynthesis of urea, and electrochemical energy storage systems such as monovalent metal-sulfur batteries (Li-S and Na-S batteries). Finally, the current challenges and future opportunities in this emerging field are highlighted. This review will provide a helpful guideline for the rational design of the structure and functionality of CS-SACs, and contribute to material optimizations in applications of energy storage and conversion.

d-Band Center Engineering of Nickel Nanoparticles Accelerates Water Dissociation for Hydrogen Evolution in Neutral NaCl Solution

While Pt is highly efficient for hydrogen evolution reaction (HER), its widespread use is limited by scarcity and high cost. Herein, a vertically aligned electrocatalyst is present comprising Ni3S2 nanotube arrays (NTAs) and Ni nanoparticles (NPs) (Ni3S2/Ni NTAs) for neutral HER. In a neutral 4 wt.% NaCl solution (pH = 7), the Ni3S2/Ni NTAs achieves a current density of 100 mA cm-2 at a low overpotential of 540 mV, outperforming both Ni3S2 NTAs and Ni NTAs and even the commercial Pt plate. The hollow tubular structure offers ample mass transfer channels, and strong electronic interaction between Ni3S2 and Ni is observed. Theoretical studies reveal that the lowered d-band center (ɛd) of Ni 3d orbital significantly reduces the activation energy for H2O dissociation and facilitates the movement of an H atom in H2O away from OH to form a transition state, consequently promoting H2 evolution. When Ni3S2/Ni NTAs is used as the cathode in a two-electrode diaphragm-free electrolyzer with a RuSnTi anode, efficient H2 production and energy-saving Cl2 evolution are achieved. This work highlights the potential of uniquely structured electrocatalysts for HER in neutral NaCl solutions.

Insights into the roles of nitrogen and phosphorus co-doping for efficient methanol electrooxidation

Anchoring Pt onto multi-heteroatom doped carbon materials has been recognized as an effective approach to improve the performance of electrocatalytic methanol oxidation. However, distinct contributions and specific behavior mechanisms of different heteroatoms, notably N and P, the specific behavior mechanisms in synergistically promoting Pt NPs remain elusive. In this work, we construct 1D N and P co-doped carbon nanotube (N, P-CNTs) supports with abundant defect anchors for Pt. The as-prepared Pt/N, P-CNTs exhibit outstanding activity and exceptional stability in methanol oxidation reaction (MOR), achieving high mass activity up to 6481.3 mA mg-1Pt. Moreover, they can retain 90.5 % of their initial current density even after 800 cycles tests. Detailed characterizations and theoretical calculations indicate that the robust strong metal-support interactions (SMSI) effect caused by N doping within the unique N and P co-doped coordination structure controllably regulate the coordination environment of Pt, reduce the d-band center of Pt, thus promoting the adsorption and decomposition of CH3OH. However, P doping weakens the adsorption strength of CO on the Pt active site by sacrificing partial electron transfer, accelerating the oxidative conversion of the CO-like poisoning species (COads). Significantly, the synergistic mechanism of N and P species on the modification of Pt's electronic structure and its subsequent impact on the electrocatalytic methanol oxidation behaviors on the Pt surface was thoroughly elucidated, providing a constructive route for designing robust MOR electrocatalysts with high MOR activity and durability.

Shell-induced enhancement of Fenton-like catalytic performance towards advanced oxidation processes: Concept, mechanism, and properties

Fenton-like advanced oxidation processes (AOPs) are commonly used to eliminate recalcitrant organic pollutants as they produce highly reactive oxygen species through the reactions between the catalysts and oxidants. Recently, considerable attention has been directed towards shell-structured Fenton-like catalysts that offer high stability, maximum utilization of active sites, and exceptional catalytic performance. In this review, we have introduced the concept of several typical shell-forming architectures (e.g., hollow structure, core-shell structure, yolk-shell structure, particle-in-tube structure, and multi-shelled structure), elucidating their role in promoting Fenton-like reaction catalysis through the nanoconfinement mechanism. In each aspect, the correlation between the shell-induced effects and the Fenton-like catalytic performance is highlighted. Finally, future challenges and opportunities for the development of shell-structured Fenton-like catalysts towards AOPs are presented, offering bright practical application prospects.

Understanding Pt Active Sites on Nitrogen-Doped Carbon Nanocages for Industrial Hydrogen Evolution with Ultralow Pt Usage

Engineering microstructures of Pt and understanding the related catalytic mechanism are critical to optimizing the performance for hydrogen evolution reaction (HER). Herein, Pt dispersion and coordination are precisely regulated on hierarchical nitrogen-doped carbon nanocages (hNCNCs) by a thermal-driven Pt migration, from edge-hosted Pt-N2Cl2 single sites in the initial Pt1/hNCNC-70 °C catalyst to Pt clusters/nanoparticles and back to in-plane Pt-NxC4-x single sites. Thereinto, Pt-N2Cl2 presents the optimal HER activity (6 mV@10 mA cm-2) while Pt-NxC4-x shows poor HER activity (321 mV@10 mA cm-2) due to their different Pt coordination. Operando characterizations demonstrate that the low-coordinated Pt-N2 intermediates derived from Pt-N2Cl2 under the working condition are the real active sites for HER, which enable the multi-H adsorption mechanism with an ideal H* adsorption energy of nearly 0 eV, thereby the high activity, as revealed by theoretical calculations. In contrast, the high-coordinated Pt-NxC4-x sites only allow the single-H adsorption with a positive adsorption energy and thereby the low HER activity. Accordingly, with an ultralow Pt loading of only 25 μgPt cm-2, the proton exchange membrane water electrolyzer assembled using Pt1/hNCNC-70 °C as the cathodic catalyst achieves an industrial-level current density of 1.0 A cm-2 at a low cell voltage of 1.66 V and high durability, showing great potential applications.

Subnanometric Pt-W Bimetallic Clusters for Efficient Alkaline Hydrogen Evolution Electrocatalysis

Rational design and synthesis of subnanometric bimetallic clusters (SBCs) within a narrow size distribution, along with achieving full SBCs exposure on supporting materials, are formidable challenges that must be overcome to realize potential applications. This work details a facile strategy to synthesize fully exposed PtW SBCs with an average size of 0.81 nm on the surface of spherical N-doped carbon (PtW/NC), which is underpinned by the electrostatic interactions between the negatively charged [H3PtW6O24]5- polyanions and the positively charged closed-pore metal-organic framework (MOF) [Zn5(OH)2(AmTRZ)6]2+. The PtW/NC exhibits significant electrocatalytic performance and stability for the alkaline hydrogen evolution reaction with an ultralow overpotential of 4 mV at 10 mA cm-2, a low Tafel slope of 29 mV dec-1, and a long-term electrolysis stability exceeding 140 h. The Pt mass activity of PtW/NC is 34 times higher than that of commercial 20 wt % Pt/C at the 100 mV overpotential. Both theoretical calculations and electrochemical measurements indicate that a synergistic effect between Pt and W is responsible for this notable catalytic performance. The synthetic approach outlined in this work can be applied to other MOFs and coordination networks that lack pores or have limited porosity.

Electronic Structure Regulated Carbon-Based Single-Atom Catalysts for Highly Efficient and Stable Electrocatalysis

Single-atom-catalysts (SACs) with atomically dispersed sites on carbon substrates have attained great advancements in electrocatalysis regarding maximum atomic utilization, unique chemical properties, and high catalytic performance. Precisely regulating the electronic structure of single-atom sites offers a rational strategy to optimize reaction processes associated with the activation of reactive intermediates with enhanced electrocatalytic activities of SACs. Although several approaches are proposed in terms of charge transfer, band structure, orbital occupancy, and the spin state, the principles for how electronic structure controls the intrinsic electrocatalytic activity of SACs have not been sufficiently investigated. Herein, strategies for regulating the electronic structure of carbon-based SACs are first summarized, including nonmetal heteroatom doping, coordination number regulating, defect engineering, strain designing, and dual-metal-sites scheming. Second, the impacts of electronic structure on the activation behaviors of reactive intermediates and the electrocatalytic activities of water splitting, oxygen reduction reaction, and CO2/N2 electroreduction reactions are thoroughly discussed. The electronic structure-performance relationships are meticulously understood by combining key characterization techniques with density functional theory (DFT) calculations. Finally, a conclusion of this paper and insights into the challenges and future prospects in this field are proposed. This review highlights the understanding of electronic structure-correlated electrocatalytic activity for SACs and guides their progress in electrochemical applications.

S-Modified Graphitic Carbon Nitride with Double Defect Sites For Efficient Photocatalytic Hydrogen Evolution

Graphitic carbon nitride (gC3N4) is an attractive photocatalyst for solar energy conversion due to its unique electronic structure and chemical stability. However, gC3N4 generally suffers from insufficient light absorption and rapid compounding of photogenerated charges. The introduction of defects and atomic doping can optimize the electronic structure of gC3N4 and improve the light absorption and carrier separation efficiency. Herein, the high efficiency of carbon nitride photocatalysis for hydrogen evolution in visible light is achieved by an S-modified double-deficient site strategy. Defect engineering forms abundant unsaturated sites and cyano (─C≡N), which promotes strong interlayer C─N bonding interactions and accelerates charge transport in gC3N4. S doping tunes the electronic structure of the semiconductors, and the formation of C─S─C bonds optimizes the electron-transfer paths of the C─N bonding, which enhances the absorption of visible light. Meanwhile,C≡N acts as an electron trap to capture photoexcited electrons, providing the active site for the reduction of H+ to hydrogen. The photocatalytic hydrogen evolution efficiency of SDCN (1613.5 µmol g-1 h-1) is 31.5 times higher than that of pristine MCN (51.2 µmol g-1 h-1). The charge separation situation and charge transfer mechanism of the photocatalysts are investigated in detail by a combination of experimental and theoretical calculations.

Design, Synthesis, Magnetic Properties, and Hydrogen Evolution Reaction of a Butterfly-like Heterometallic Trinuclear [CuII2MnII] Cluster

A novel heterometallic trinuclear cluster [CuII2MnII(cpdp)(NO3)2(Cl)] (1) has been designed and synthesized by employing a molecular library approach that uses CuCl2·2H2O and Mn(NO3)2·4H2O as inorganic metal salts and H3cpdp as a multifunctional organic scaffold (H3cpdp = N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol). This heterometallic cluster has emerged as an unusual ferromagnetic material and promising electrocatalyst for hydrogen evolution reaction (HER) in the domain of inorganic and materials chemistry. Crystal structure analysis establishes the structural arrangement of 1, revealing a butterfly-like topology with an unusual seven-coordinated Mn(II) center. Formation of this cluster is accomplished by a self-assembly process through functionalization of 1 with one μ2:η1:η1-nitrate and two μ2:η2:η1-benzoate groups via the CuII(μ2-NO3)CuII} and {CuII(μ2-O2CC6H5)MnII} linkages, respectively. Variable-temperature SQUID magnetometry revealed the coexistence of ferromagnetic and antiferromagnetic interactions in 1. The observed magnetic behavior in 1 is unexpected because of a large Cu-O-Mn angle with a value of 132.05°, indicating that the correlation between coupling constants and the structural parameters is a multifactor problem. This cluster shows excellent electrocatalytic performance for the HER attaining a current density of 10 mA/cm2 with a Tafel slope of 183 mV dec-1 at a 310 mV overpotential value. Essentially, cluster 1 shows exceptional electrochemical stability at ambient temperature, accompanied by minimal degradation of the current density as examined by chronoamperometric studies. Density functional theory calculations establish the mechanistic insight into the HER process, indicating that the CuII-OCO-MnII site is the active site for formation of molecular hydrogen.

Engineering MXene Surface via Oxygen Functionalization and Au Nanoparticle Deposition for Enhanced Electrocatalytic Hydrogen Evolution Reaction

MXene, a family of 2D transition metal carbides and nitrides, presents promising applications in electrocatalysis. Maximizing its large surface area is key to developing efficient non-noble-metal catalysts for the hydrogen evolution reaction (HER). In this study, oxygen-functionalized Ti3C2Tx MXene (Ti3C2Ox) is synthesized and deposited gold nanoparticles (Au NPs) onto it, forming a novel composite material, Au-Ti3C2Ox. By selectively removing other functional groups, mainly -O functional groups are retained on the surface, directing electron transfer from Au NPs to MXene due to electronic metal-support interaction (EMSI), thereby improving the catalytic activity of the MXene surface. Additionally, the interaction between Au NPs and -O functional groups further enhanced the overall catalytic activity, achieving an overpotential of 62 mV and a Tafel slope of 40.1 mV dec-1 at a current density of -10 mA cm-2 in 0.5 m H2SO4 solution. Density functional theory calculations and scanning electrochemical microscopy with ≤150 nm resolution confirmed the enhanced catalytic efficiency due to the specific interaction between Au NPs and Ti3C2Ox. This work provides a surface modification strategy to fully utilize the MXene surface and enhance the overall catalytic activity of MXene-based catalysts.

Pyrolysis-Free Synthesis of Synergistic Single-Atom/Nanocluster Electrocatalysts for Hydrogen Evolution

Constructing catalysts that simultaneously contain single atom/metal nanocluster active sites is a promising strategy to enhance the original catalytic behavior and accelerate the catalysis involving multi-electron reactions or multi-intermediates. Herein, the pyrolysis-free synthetic method is developed to integrate single atoms and nanoclusters towards highly satisfactory catalytic performances for both acidic and alkaline hydrogen electrocatalysis. The controllable pyrolysis-free strategy allows the precise modulation of the active centers, realizing the optimization of the adsorption energy and the regulation of the synergistic active components. Specially, the as-prepared catalysts with hybrid single-atom/nanocluster sites exhibited superior catalytic activities for hydrogen evolution in both acidic and alkaline media with low over-potentials at -10 mA cm-2 of 25 mV and 8.6 mV, respectively, combining with outstanding durability towards high current density and methanol poisoning. This work developed a universal synthetic strategy for the single atom/nanocluster synergy systems and addressed the superiority of hybrid single-atom/nanocluster sites.

Balancing Edge Defects and Graphitization in a Pt-Fe/Carbon Electrocatalyst for High-Power-Density and Durable Flow Seawater-Al/Acid Hybrid Fuel Cells and Zn-Air Batteries

Overcoming the trade-off between the graphitization of the carbon substrate and enhanced electronic metal-support interaction (EMSI) and intrinsic activity of Pt-C catalysts remains a major challenge for ensuring the durable operation of energy conversion devices. This article presents a hybrid catalyst consisting of PtFe nanoparticles and single Pt and Fe atoms supported on N-doped carbon (PtFeNPs@PtFeSAs-N-C), which exhibits improved activities in hydrogen evolution and oxygen reduction reactions (HER and ORR, respectively) and has excellent durability owing to the high graphitization, rich edge defects, and porosity of the carbon in PtFeNPs@PtFeSAs-N-C, as well as strong EMSI between the PtFe nanoparticles and edge-defective carbon embedded with Pt and Fe atoms. According to theoretical calculations, the strong EMSI optimizes the H* adsorption-desorption and facilitates the adsorption OOH*, accelerating the HER and ORR processes. A novel flow seawater-Al/acid hybrid fuel cell using the PtFeNPs@PtFeSAs-N-C cathode can serve as a high-efficiency energy conversion device that delivers a high power density of 109.5 mW cm-2 while producing H2 at a significantly high rate of 271.6 L m-2 h-1. Moreover, PtFeNPs@PtFeSAs-N-C exhibits a remarkable performance (high power density of 298.0 mW cm-2 and long-term durability of 1000 h) in a flow Zn-air battery.

A supported Ni2 dual-atoms site hollow urchin-like carbon catalyst for synergistic CO2 electroreduction

Dual-atoms catalysts (DACs), while inheriting the advantages of maximum atom utilization ratio and excellent selectivity of single-atom catalysts (SACs), can better enhance the catalytic activity through the synergy of adjacent atoms. Therefore, DACs are considered to be very potential catalysts for CO2 to CO conversion. Its catalytic activity is greatly influenced by the coordination environment and morphology. Here, hollow urchin-like NiNC catalysts (Ni-NC(HU)-x, x = 100, 50, 25, 0) were synthesized using urchin-like nickel particles as template. By adjusting the amount of additional nitrogen source, the percentage content of pyridinic-N was adjusted as well as further affecting the coordination environment. Among them, Ni-NC(HU)-50, which had the highest content of pyridinic-N, formed a dual-atoms coordination structure and had the best catalytic performance that the CO Faradaic efficiency (FECO) reached 97.2 % at -0.9 V vs. reversible hydrogen electrode (RHE) and sustained above 95 % within 50 h. In-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and density functional theory (DFT) calculations showed that Ni-NC(HU)-50 exhibited the best performance of CO2 reduction reaction (CO2RR) by lowering the *COOH formation free energy barrier and its favorable dual desorption mechanism of *COL and *COB.

Applications of metal nanoclusters supported on the two-dimensional material graphene in electrocatalytic carbon dioxide reduction

Metal nanoclusters (MNCs) have been demonstrated to exhibit superior catalytic performance compared to single nanoparticles. This is attributed to their quantized electronic structure, unique geometrical stacking and abundant active sites. While the exposed metal atoms can markedly enhance the efficiency of catalysis, unfortunately, MNCs are susceptible to agglomeration, which impairs their catalytic activity and stability. Graphene is a two-dimensional material consisting of a single atomic layer formed by the hybridization of the s and p orbitals of carbon atoms. It exhibits stable physical and chemical properties and has an easily controllable structure, making it an ideal carrier for MNCs. When metal nanoclusters (MNCs) are loaded on a graphene substrate, the MNCs can form a stable binding site on the graphene substrate. Furthermore, the construction of a defective structure on the graphene substrate enables the formation of robust interactions between the metal atoms of the MNCs and the substrate, facilitating the rapid establishment of electron conduction pathways and markedly enhancing the electrocatalytic performance. This paper presents a review of the applications of metal nanoclusters supported on graphene skeletons in the field of the electrocatalytic CO2 reduction reaction (CO2RR). Firstly, we briefly introduce the reaction mechanism of the CO2RR, then we systematically discuss the synthesis strategies, properties and applications of metal nanoclusters in electrocatalytic carbon dioxide reduction from both experimental and theoretical perspectives, and lastly, we discuss the opportunities and challenges of metal nanocluster catalysts supported on carbon materials.

Reducing Dielectric Confinement Effect Enhances Carrier Separation in Two-Dimensional Hybrid Perovskite Photocatalysts

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) with alternating structure of the organic and inorganic layers have a natural quantum well structure. The difference of dielectric constants between organic and inorganic layers in this structure results in the enhancement of dielectric confinement effect, which exhibits a large exciton binding energy and hinders the separation of electron-hole pairs. Herein, a strategy to reduce the dielectric confinement effect by narrowing the dielectric difference between organic amine molecule and [PbBr6]4- octahedron is put forward. The Ethanolamine (EOA) contains hydroxyl groups, resulting in the positive and negative charge centers of O and H non-overlapping, which generated a larger polarity and dielectric constant. The reduced dielectric constant produces a smaller exciton binding energy (71.03 meV) of (C2H7NO)2PbBr4 ((EOA)2PbBr4) than (C8H11N)2PbBr4 ((PEA)2PbBr4 (156.07 meV), and promotes the dissociation of electrons and holes. The increasing of lifetime of photogenerated carrier in (EOA)2PbBr4 are proved by femtosecond transient absorption spectra. Density functional theory (DFT) calculations have also indicated that the small energy shift of the total density of states (DOS) between the C/H/N and the Pb/Br in (EOA)2PbBr4 favors the separation of electrons and holes. In addition, this work demonstrates the application of (PEA)2PbBr4 and (EOA)2PbBr4 in the field of photocatalytic CO2 reduction.

Engineering antibonding orbital occupancy of NiMoO4-supported Ru nanoparticles for enhanced chlorine evolution reaction

Chlorine evolution reaction (CER) is crucial for industrial-scale production of high-purity Cl2. Despite the development of classical dimensionally stable anodes to enhance CER efficiency, the competitive oxygen evolution reaction (OER) remains a barrier to achieving high Cl2 selectivity. Herein, a binder-free electrode, Ru nanoparticles (NPs)-decorated NiMoO4 nanorod arrays (NRAs) supported on Ti foam (Ru-NiMoO4/Ti), was designed for active CER in saturated NaCl solution (pH = 2). The Ru-NiMoO4/Ti electrode exhibits a low overpotential of 20 mV at 10 mA cm-2 current density, a high Cl2 selectivity exceeding 90%, and robust durability for 90h operation. The marked difference in Tafel slopes between CER and OER indicates the high Cl2 selectivity and superior reaction kinetics of Ru-NiMoO4/Ti electrode. Further studies reveal a strong metal-support interaction (SMSI) between Ru and NiMoO4, facilitating electron transfer through the Ru-O bridge bond and increasing the Ru 3d-Cl 2p antibonding orbital occupancy, which eventually results in weakened Ru-Cl bonding, promoted Cl desorption, and enhanced Cl2 evolution. Our findings provide new insights into developing electrodes with enhanced CER performance through antibonding orbital occupancy engineering.

Second-shell modulation on porphyrin-like Pt single atom catalysts for boosting oxygen reduction reaction

The first coordination shell is considered crucial in determining the performance of single atom catalysts (SACs), but the significance of the second coordination shell has been overlooked. In this study, we developed a post-doping strategy to realize predictable and controlled modulation on the second coordination shell. By incorporating a P atom into the second coordination shell of a porphyrin-like Pt SAC, the charge density at the Fermi level of Pt single atom increases, enhancing its intrinsic activity. Moreover, the P atom shows stronger adsorption towards large size anions (ClO4 -) than Pt atoms, preventing the Pt site poisoning in acid. As a result, the Pt-N4P-C catalyst exhibits significantly higher activity than the Pt-N4-C catalyst. It even outperforms commercial Pt/C (20 wt% Pt) with a Pt content of only 0.22 wt% in both alkaline and acidic solutions. This work indicates the second coordination shell modulation also greatly impacts the performance of SACs.

First-Principles Calculations and Machine Learning of Hydrogen Evolution Reaction Activity of Nonmetallic Doped β-Mo2C Support Pt Single-Atom Catalysts

The most widely used catalyst for the hydrogen evolution reaction (HER) is Pt, but the high cost and low abundance of Pt need to be urgently addressed. Single-atom catalysts (SACs) have been an effective means of improving the utilization of Pt atoms. In this work, we used a nonmetal (NM = B, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and I) doped β-Mo2C (100) C-termination surface as the support, with Pt atoms dispersed on the support surface to construct Pt@NM-Mo2C. Using density functional theory (DFT) calculations, we selected catalysts with excellent HER activity. Among 117 candidate catalysts, 49 catalysts exhibited ideal catalytic performance with Gibbs free energy of hydrogen intermediate (H*) adsorption (ΔGH*) values less than 0.2 eV. The ΔGH* values of 16 catalysts were even lower than that of Pt (ΔGH* ≈ 0.09 eV), with PtI@N2/4-a-Mo2C demonstrating the best performance (ΔGH* = -0.01 eV). Combined with electronic structure analysis, we could understand the impact of charge transfer between Pt and the underlying NM atoms on the strength of the Pt-H bond, thereby promoting HER activity. Using machine learning (ML), we identified that the primary influencing factors of the HER catalytic activity in the Pt@NM-Mo2C system were the Bader charge transfer of Pt (NePt), the d-band center of Pt (εdPt), and the atomic radius of NM (RNM), with NePt having the greatest impact on the HER catalytic activity.

Amino-Induced CO2 Spillover to Boost the Electrochemical Reduction Activity of CdS for CO Production

A considerable challenge in CO2 reduction reaction (CO2RR) to produce high-value-added chemicals comes from the adsorption and activation of CO2 to form intermediates. Herein, an amino-induced spillover strategy aimed at significantly enhancing the CO2 adsorption and activation capabilities of CdS supported on N-doped mesoporous hollow carbon sphere (NH2-CdS/NMHCS) for highly efficient CO2RR is presented. The prepared NH2-CdS/NMHCS exhibits a high CO Faradaic efficiency (FECO) exceeding 90% from -0.8 to -1.1 V versus reversible hydrogen electrode (RHE) with the highest FECO of 95% at -0.9 V versus RHE in H cell. Additional experimental and theoretical investigations demonstrate that the alkaline -NH2 group functions as a potent trapping site, effectively adsorbing the acidic CO2, and subsequently triggering CO2 spillover to CdS. The amino modification-induced CO2 spillover, combined with electron redistribution between CdS and NMHCS, not only readily achieves the spontaneous activation of CO2 to *COOH but also greatly reduces the energy required for the conversion of *COOH to *CO intermediate, thus endowing NH2-CdS/NMHCS with significantly improved reaction kinetics and reduced overpotential for CO2-to-CO conversion. It is believed that this research can provide valuable insights into the development of electrocatalysts with superior CO2 adsorption and activation capabilities for CO2RR application.

Edge-Rich Pt-O-Ce Sites in CeO2 Supported Patchy Atomic-Layer Pt Enable a Non-CO Pathway for Efficient Methanol Oxidation

Rational design of efficient methanol oxidation reaction (MOR) catalyst that undergo non-CO pathway is essential to resolve the long-standing poisoning issue. However, it remains a huge challenge due to the rather difficulty in maximizing the non-CO pathway by the selective coupling between the key *CHO and *OH intermediates. Here, we report a high-performance electrocatalyst of patchy atomic-layer Pt epitaxial growth on CeO2 nanocube (Pt ALs/CeO2) with maximum electronic metal-support interaction for enhancing the coupling selectively. The small-size monolayer material achieves an optimal geometrical distance between edge Pt-O-Ce sites and *OH absorbed on CeO2, which well restrains the dehydrogenation of *CHO, resulting in the non-CO pathway. Meanwhile, the *CHO/*CO intermediate generated at inner Pt-O-Ce sites can migrate to edge, inducing the subsequent coupling reaction, thus avoiding poisoning while promoting reaction efficiency. Consequently, Pt ALs/CeO2 exhibits exceptionally catalytic stability with negligible degradation even under 1000 s pure CO poisoning operation and high mass activity (14.87 A/mgPt), enabling it one of the best-performing alkali-stable MOR catalysts.

Indium Oxide Layer Dual Functional Modified Bismuth Vanadate Photoanode Promotes Photoelectrochemical Oxidation of Water to Hydrogen Peroxide

The photoelectrochemical (PEC) dual-electron pathway for water oxidation to produce hydrogen peroxide (H2O2) shows promising prospects. However, the dominance of the four-electron pathway leading to O2 evolution competes with this reaction, severely limiting the efficiency of H2O2 production. Here, we report a In2O3 passivator-coated BiVO4 (BVO) photoanode, which effectively enhances the selectivity and yield of H2O2 production via PEC water oxidation. Based on XPS spectra and DFT calculations, a heterojunction is formed between In2O3 and BVO, promoting the effective separation of interface and surface charges. More importantly, Mott-Schottky analysis and open-circuit potential measurements demonstrate that the In2O3 passivation layer on the BVO photoanode shifts the hole quasi-Fermi level towards the anodic direction, enhancing the oxidation level of holes. Additionally, the widening of the depletion layer and the flattening of the band bending on the In2O3-coated BVO photoanode favor the generation of H2O2 while suppressing the competitive O2 evolution reaction. In addition, the coating of In2O3 can also inhibit the decomposition of H2O2 and improve the stability of the photoanode. This work provides new perspectives on regulating PEC two/four-electron transfer for selective H2O2 production via water oxidation.

Platinum/Platinum Sulfide on Sulfur-Doped Carbon Nanosheets with Multiple Interfaces toward High Hydrogen Evolution Activity

Platinum (Pt)-based materials are among the most competitive electrocatalysts for the hydrogen evolution reaction (HER) due to suitable hydrogen adsorption energy. Due to the rarity of Pt, it is desirable to develop cost-effective Pt-based electrocatalysts with low Pt loading. Herein, Pt/PtS electrocatalysts on S-doped carbon nanofilms (PPS/C) have been successfully fabricated through a precursor reduction route with a complex of Pt and 1-dodecanethiol (1-DDT) as the precursor. The PPS/C achieved at 400 °C (PPS/C-400) exhibits excellent HER performances with an ultralow overpotential of 41.3 mV, a low Tafel slope of 43.1 mV dec-1 at a current density of 10 mA cm-2, and a long-term stability of 10 h, superior to many recently reported Pt-based HER electrocatalysts. More importantly, PPS/C-400 shows a high mass-specific activity of 0.362 A mgPt-1 at 30 mV, which is 1.88 times of that of commercial 20% Pt/C (0.193 A mgPt-1). The introduction of sulfur leads to the formation of PtS, which not only reduces the content of Pt but also realizes the interface regulation of Pt/PtS, as well as the doping of carbon. Both regulations make the resulting catalyst have abundant active centers and rapid electron transfer/transport, which is conducive to balancing the adsorption and resolution of intermediate products, and finally achieving great mass-specific activity and stability. The research work may provide ideas for designing effective Pt-based multi-interface electrocatalysts.

Substrate-Assisted Atomic Dispersion of Cobalt for Alkaline Water Electrolysis

Atomically dispersed single-atom catalysts have recently attracted broad research interest due to their high atom efficiency and unique catalytic performance. In this study, atomic dispersion of cobalt is achieved using a chemical bath deposition method on a highly stable alkali titanate film (Ti/KTiO). These films were characterized using a variety of techniques, with atomic dispersion confirmed via grazing incidence X-ray absorption spectroscopy and ab initio modeling of single-atom systems. This modeling indicated that the alkali ion incorporated into the film facilitates atomic dispersion. Experimentally, the Ti/KTiO-supported Co(OH)2 catalysts exhibited remarkable electrochemical performance, with an overpotential of 163 mV to achieve a current density of 10 mA cm-2 with a catalyst loading of ∼0.1 mg cm-2 and high stability. These results show the potential of Ti/KTiO/Co(OH)2 catalysts for atomically efficient hydrogen production.

From Charge to Spin: An In-Depth Exploration of Electron Transfer in Energy Electrocatalysis

Catalytic materials play crucial roles in various energy-related processes, ranging from large-scale chemical production to advancements in renewable energy technologies. Despite a century of dedicated research, major enduring challenges associated with enhancing catalyst efficiency and durability, particularly in green energy-related electrochemical reactions, remain. Focusing only on either the crystal structure or electronic structure of a catalyst is deemed insufficient to break the linear scaling relationship (LSR), which is the golden rule for the design of advanced catalysts. The discourse in this review intricately outlines the essence of heterogeneous catalysis reactions by highlighting the vital roles played by electron properties. The physical and electrochemical properties of electron charge and spin that govern catalysis efficiencies are analyzed. Emphasis is placed on the pronounced influence of external fields in perturbing the LSR, underscoring the vital role that electron spin plays in advancing high-performance catalyst design. The review culminates by proffering insights into the potential applications of spin catalysis, concluding with a discussion of extant challenges and inherent limitations.

Elucidating the Discrepancy between the Intrinsic Structural Instability and the Apparent Catalytic Steadiness of M-N-C Catalysts toward Oxygen Evolution Reaction

Despite the widespread investigations on the M-N-C type single atom catalysts (SACs) for oxygen evolution reaction (OER), an internal conflict between its intrinsic thermodynamically structural instability and apparent catalytic steadiness has long been ignored. Clearly unfolding this contradiction is necessary and meaningful for understanding the real structure-property relation of SACs. Herein, by using the well-designed pH-dependent metal leaching experiments and X-ray absorption spectroscopy, an unconventional structure reconstruction of M-N-C catalyst during OER process was observed. Combining with density functional theory calculations, the initial Ni-N coordination is easily broken in the presence of adsorbed OH*, leading to favorable formation of Ni-O coordination. The formed Ni-O works stably as the real active center for OER catalysis in alkaline media but unstably in acid, which clearly explains the existing conflict. Unveiling the internal contradiction between structural instability and catalytic steadiness provides valuable insights for rational design of single atom OER catalysts.

Atom-pair engineering of single-atom nanozyme for boosting peroxidase-like activity

Constructing atom-pair engineering and improving the activity of metal single-atom nanozyme (SAzyme) is significant but challenging. Herein, we design the atom-pair engineering of Zn-SA/CNCl SAzyme by simultaneously constructing Zn-N4 sites as catalytic sites and Zn-N4Cl1 sites as catalytic regulator. The Zn-N4Cl1 catalytic regulators effectively boost the peroxidase-like activities of Zn-N4 catalytic sites, resulting in a 346-fold, 1496-fold, and 133-fold increase in the maximal reaction velocity, the catalytic constant and the catalytic efficiency, compared to Zn-SA/CN SAzyme without the Zn-N4Cl1 catalytic regulator. The Zn-SA/CNCl SAzyme with excellent peroxidase-like activity effectively inhibits tumor cell growth in vitro and in vivo. The density functional theory (DFT) calculations reveal that the Zn-N4Cl1 catalytic regulators facilitate the adsorption of *H2O2 and re-exposure of Zn-N4 catalytic sites, and thus improve the reaction rate. This work provides a rational and effective strategy for improving the peroxidase-like activity of metal SAzyme by atom-pair engineering.

Defect Engineering Simultaneously Regulating Exciton Dissociation in Carbon Nitride and Local Electron Density in Pt Single Atoms Toward Highly Efficient Photocatalytic Hydrogen Production

The high exciton binding energy (Eb) and sluggish surface reaction kinetics have severely limited the photocatalytic hydrogen production activity of carbon nitride (CN). Herein, a hybrid system consisting of nitrogen defects and Pt single atoms is constructed through a facile self-assembly and photodeposition strategy. Due to the acceleration of exciton dissociation and regulation of local electron density of Pt single atoms along with the introduction of nitrogen defects, the optimized Pt-MCT-3 exhibits a hydrogen production rate of 172.0 µmol h-1 (λ ≥ 420 nm), ≈41 times higher than pristine CN. The apparent quantum yield for the hydrogen production is determined to be 27.1% at 420 nm. The experimental characterizations and theoretical calculations demonstrate that the nitrogen defects act as the electron traps for the exciton dissociation, resulting in a decrease of Eb from 86.92 to 43.20 meV. Simultaneously, the stronger interaction between neighboring nitrogen defects and Pt single atoms directionally drives free electrons to aggregate around Pt single atoms, and tailors the d-band electrons of Pt, forming a moderate binding strength between Pt atoms and H* intermediates.

Ultrasmall and Highly Dispersed Pt Entities Deposited on Mesoporous N-doped Carbon Nanospheres by Pulsed CVD for Improved HER

Vapor-based deposition techniques are emerging approaches for the design of carbon-supported metal powder electrocatalysts with tailored catalyst entities, sizes, and dispersions. Herein, a pulsed CVD (Pt-pCVD) approach is employed to deposit different Pt entities on mesoporous N-doped carbon (MPNC) nanospheres to design high-performance hydrogen evolution reaction (HER) electrocatalysts. The influence of consecutive precursor pulse number (50-250) and deposition temperature (225-300 °C) are investigated. The Pt-pCVD process results in highly dispersed ultrasmall Pt clusters (≈1 nm in size) and Pt single atoms, while under certain conditions few larger Pt nanoparticles are formed. The best MPNC-Pt-pCVD electrocatalyst prepared in this work (250 pulses, 250 °C) reveals a Pt HER mass activity of 22.2 ± 1.2 A mg-1 Pt at -50 mV versus the reversible hydrogen electrode (RHE), thereby outperforming a commercially available Pt/C electrocatalyst by 40% as a result of the increased Pt utilization. Remarkably, after optimization of the Pt electrode loading, an ultrahigh Pt mass activity of 56 ± 2 A mg-1 Pt at -50 mV versus RHE is found, which is among the highest Pt mass activities of Pt single atom and cluster-based electrocatalysts reported so far.

Modulating Ni-S coordination in Ni3S2 to promote electrocatalytic oxidation of 5-hydroxymethylfurfural at ampere-level current density

Electricity-driven oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a highly attractive strategy for biomass transformation. However, achieving industrial-grade current densities remains a great challenge. Herein, by modulating the water content in a solvothermal system, Ni3S2/NF with stabilized and shorter Ni-S bonds as well as a tunable coordination environment of Ni sites was fabricated. The prepared Ni3S2/NF was highly efficient for electrocatalytic oxidation of HMF to produce FDCA, and the FDCA yield and Faraday efficiency could reach 98.8% and 97.6% at the HMF complete conversion. More importantly, an industrial-grade current density of 1000 mA cm-2 could be achieved at a potential of only 1.45 V vs. RHE for HMFOR and the current density could exceed 500 mA cm-2 with other bio-based compounds as the reactants. The excellent performance of Ni3S2/NF originated from the shorter Ni-S bonds and its better electrochemical properties, which significantly promoted the dehydrogenation step of oxidizing HMF. Besides, the gram-scale FDCA production could be realized on Ni3S2/NF in a MEA reactor. This work provides a robust electrocatalyst with high potential for practical applications for the electrocatalytic oxidation of biomass-derived compounds.

Immobilizing Ordered Oxophilic Indium Sites on Platinum Enabling Efficient Hydrogen Oxidation in Alkaline Electrolyte

Addressing the sluggish kinetics in the alkaline hydrogen oxidation reaction (HOR) is a pivotal yet challenging step toward the commercialization of anion-exchange membrane fuel cells (AEMFCs). Here, we have successfully immobilized indium (In) atoms in an orderly fashion into platinum (Pt) nanoparticles supported by reduced graphene oxide (denoted as O-Pt3In/rGO), significantly enhancing alkaline HOR kinetics. We have revealed that the ordered atomic matrix enables uniform and optimized hydrogen binding energy (HBE), hydroxyl binding energy (OHBE), and carbon monoxide binding energy (COBE) across the catalyst. With a mass activity of 2.3066 A mg-1 at an overpotential of 50 mV, over 10 times greater than that of Pt/C, the catalyst also demonstrates admirable CO resistance and stability. Importantly, the AEMFC implementing this catalyst as the anode catalyst has achieved an impressive power output compared to Pt/C. This work not only highlights the significance of constructing ordered oxophilic sites for alkaline HOR but also sheds light on the design of well-structured catalysts for energy conversion.

Platinum Cluster Decoration on Hollow Carbon Spheres for High-Efficiency Hydrogen Evolution Reaction

Currently, platinum (Pt)/carbon support composite materials have tremendous application prospects in the hydrogen evolution reaction (HER). However, one of the primary challenges for boosting their performance is designing a substrate with the desired microstructure. Herein, the intact hollow carbon spheres (HCSs) were prepared via template method. Based on the morphology variation of the as-prepared HCSs-x, we conjectured that the polydopamine (PDA) core was generated first and then slowly grew into a complete overburden (SiO2@PDA). Afterward, Pt atomic clusters were anchored on the outer shells of HCSs-4 to construct composite electrocatalysts (Pty/HCSs-4) by a chemical reduction method. Due to the low charge-transfer resistance, the HCSs have a large electrochemical surface area and provide a continuous electron transport pathway, boosting the atom utilization efficiency during hydrogen production and release. The synthesized Pt2.5/HCSs-4 electrocatalysts exhibit excellent HER activity in acidic media, which can be ascribed to the compositional modulation and delicate structural design. Specifically, when the overpotential is 10 A g-1, the overpotential can achieve 92 mV. This work opens a new route to fabricate Pt-based electrocatalysts and brings a new understanding of the formation mechanism of HCSs.

General negative pressure annealing approach for creating ultra-high-loading single atom catalyst libraries

Catalyst systems populated by high-density single atoms are crucial for improving catalytic activity and selectivity, which can potentially maximize the industrial prospects of heterogeneous single-atom catalysts (SACs). However, achieving high-loading SACs with metal contents above 10 wt% remains challenging. Here we describe a general negative pressure annealing strategy to fabricate ultrahigh-loading SACs with metal contents up to 27.3-44.8 wt% for 13 different metals on a typical carbon nitride matrix. Furthermore, our approach enables the synthesis of high-entropy single-atom catalysts (HESACs) that exhibit the coexistence of multiple metal single atoms with high metal contents. In-situ aberration-corrected HAADF-STEM (AC-STEM) combined with ex-situ X-ray absorption fine structure (XAFS) demonstrate that the negative pressure annealing treatment accelerates the removal of anionic ligand in metal precursors and boosts the bonding of metal species with N defective sites, enabling the formation of dense N-coordinated metal sites. Increasing metal loading on a platinum (Pt) SAC to 41.8 wt% significantly enhances the activity of propane oxidation towards liquid products, including acetone, methanol, and acetic acid et al. This work presents a straightforward and universal approach for achieving many low-cost and high-density SACs for efficient catalytic transformations.

Single-Atom Iron Catalyst as an Advanced Redox Mediator for Anodic Oxidation of Organic Electrosynthesis

Homogeneous electrocatalysts can indirect oxidate the high overpotential substrates through single-electron transfer on the electrode surface, enabling efficient operation of organic electrosynthesis catalytic cycles. However, the problems of this chemistry still exist such as high dosage, difficult recovery, and low catalytic efficiency. Single-atom catalysts (SACs) exhibit high atom utilization and excellent catalytic activity, hold great promise in addressing the limitations of homogeneous catalysts. In view of this, we have employed Fe-SA@NC as an advanced redox mediator to try to change this situation. Fe-SA@NC was synthesized using an encapsulation-pyrolysis method, and it demonstrated remarkable performance as a redox mediator in a range of reported organic electrosynthesis reactions, and enabling the construction of various C-C/C-X bonds. Moreover, Fe-SA@NC demonstrated a great potential in exploring new synthetic method for organic electrosynthesis. We employed it to develop a new electro-oxidative ring-opening transformation of cyclopropyl amides. In this new reaction system, Fe-SA@NC showed good tolerance to drug molecules with complex structures, as well as enabling flow electrochemical syntheses and gram-scale transformations. This work highlights the great potential of SACs in organic electrosynthesis, thereby opening a new avenue in synthetic chemistry.

Ni─Co─O─S Derived Catalysts on Hierarchical N-doped Carbon Supports with Strong Interfacial Interactions for Improved Hybrid Water Splitting Performance

Simultaneously improving electrochemical activity and stability is a long-term goal for water splitting. Herein, hierarchical N-doped carbon nanotubes on carbon nanowires derived from PPy are grown on carbon cloth, serving as a support for NiCo oxides/sulfides. The hierarchical electrodes annealed in N2 or H2/N2 display improved intrinsic activity and stability for hydrogen evolution reaction (HER) and glucose oxidation reaction. Compared with Pt/C||Ir/C in alkaline media, the glucose electrolysis assembled with electrodes exhibits a cell voltage of 1.38 V at 10 mA cm-2, durability for >12 h at 50 mA cm-2, and resistance to glucose/gluconic acid poisoning. In addition, electrocatalysts can also be applied in ethanol oxidation reactions. Systematic characterizations reveal the strong interactions between NiCo and N-doped carbon support-induced partial charge transfer at the interface and regulate the local electronic structure of active sites. Density functional theory calculations demonstrate that the synergistic effect between N-doped carbon supports, metallic NiCo, and NiCo oxides/sulfides optimize the adsorption energy of H2O and the H* free energy for HER. The energy barrier of the dehydrogenation of glucose effectively decreased. This work will attract attention to the role of metal-support interactions in enhancing the intrinsic activity and stability of electrocatalysts.

Iron Active Center Coordination Reconstruction in Iron Carbide Modified on Porous Carbon for Superior Overall Water Splitting

In this work, a novel liquid nitrogen quenching strategy is engineered to fulfill iron active center coordination reconstruction within iron carbide (Fe3C) modified on biomass-derived nitrogen-doped porous carbon (NC) for initiating rapid hydrogen and oxygen evolution, where the chrysanthemum tea (elm seeds, corn leaves, and shaddock peel, etc.) is treated as biomass carbon source within Fe3C and NC. Moreover, the original thermodynamic stability is changed through the corresponding force generated by liquid nitrogen quenching and the phase transformation is induced with rich carbon vacancies with the increasing instantaneous temperature drop amplitude. Noteworthy, the optimizing intermediate absorption/desorption is achieved by new phases, Fe coordination, and carbon vacancies. The Fe3C/NC-550 (550 refers to quenching temperature) demonstrates outstanding overpotential for hydrogen evolution reaction (26.3 mV at -10 mA cm-2) and oxygen evolution reaction (281.4 mV at 10 mA cm-2), favorable overall water splitting activity (1.57 V at 10 mA cm-2). Density functional theory (DFT) calculations further confirm that liquid nitrogen quenching treatment can enhance the intrinsic electrocatalytic activity efficiently by optimizing the adsorption free energy of reaction intermediates. Overall, the above results authenticate that liquid nitrogen quenching strategy open up new possibilities for obtaining highly active electrocatalysts for the new generation of green energy conversion systems.

d-band center engineering of single Cu atom and atomic Ni clusters for enhancing electrochemical CO2 reduction to CO

The rational design of catalysts with atomic dispersion and a deep understanding of the catalytic mechanism is crucial for achieving high performance in CO2 reduction reaction (CO2RR). Herein, we present an atomically dispersed electrocatalyst with single Cu atom and atomic Ni clusters supported on N-doped mesoporous hollow carbon sphere (CuSANiAC/NMHCS) for highly efficient CO2RR. CuSANiAC/NMHCS demonstrates a remarkable CO Faradaic efficiency (FECO) exceeding 90% across a potential range of -0.6 to -1.2 V vs. reversible hydrogen electrode (RHE) and achieves its peak FECO of 98% at -0.9 V vs. RHE. Theoretical studies reveal that the electron redistribution and modulated electronic structure-notably the positive shift in d-band center of Ni 3d orbital-resulting from the combination of single Cu atom and atomic Ni clusters markedly enhance the CO2 adsorption, facilitate the formation of *COOH intermediate, and thus promote the CO production activity. This study offers fresh perspectives on fabricating atomically dispersed catalysts with superior CO2RR performance.

Mesoporous amorphous non-noble metals as versatile substrates for high loading and uniform dispersion of Pt-group single atoms

Atomically dispersed Pt-group metals are promising as nanocatalysts because of their unique geometric structures and ultrahigh atomic utilization. However, loading isolated Pt-group metals in single-atom alloys (SAAs) with distinctive bimetallic sites is challenging. In this study, we present amorphous mesoporous Ni boride (Ni-B) as an ideal substrate to uniformly disperse Pt atoms with tunable loadings (1.7 to 12.2 wt %). The effect of the morphology, composition, and crystal phase of the Ni-B host on the growth and dispersion of Pt atoms is discussed. The resulting amorphous Pt-Ni-B mesoporous nanospheres exhibit superior electrocatalytic H2 evolution performance in acidic media. This strategy holds the potential to synthesize a diverse library of mesoporous amorphous Pt-group SAAs, by leveraging functional amorphous nanostructured 3d transition-metal borides as substrates, thereby proposing a comprehensive strategy to control atomically dispersed Pt-group metals.

Pt Single-Atoms on Structurally-Integrated 3D N-Doped Carbon Tubes Grid for Ampere-Level Current Density Hydrogen Evolution

To date, the excellent mass-catalytic activities of Pt single-atoms catalysts (Pt-SACs) toward hydrogen evolution reaction (HER) are categorically confirmed; however, their high current density performance remains a challenge for practical applications. Here, a binder-free approach is exemplified to fabricate self-standing superhydrophilic-superaerphobic Pt-SACs cathodes by directly anchoring Pt-SAs via Pt-NxC4-x coordination bonds to the structurally-integrated 3D nitrogen-doped carbon tubes (N-CTs) array grid (denoted as Pt@N-CTs). The 3D Pt@N-CTs cathode with optimal Pt-SACs loading is capable of operating at a high current density of 1000 mA cm-2 with an ultralow overpotential of 157.9 mV with remarkable long-term stability over 11 days at 500 mA cm-2. The 3D super-wettable free-standing Pt@N-CTs possess interconnected vertical and lateral N-CTs with hierarchical-sized open channels, which facilitates the mass transfer. The binder-free immobilization adding to the large surface area and 3D-interconnected open channels endow Pt@N-CTs cathodes with high accessible active sites, electrical conductivity, and structural stability that maximize the utilization efficiency of Pt-SAs to achieve ampere-level current density HER at low overpotentials.

A Versatile Nanozyme-Based NADH Circulating Oxidation Reactor for Tumor Therapy through Triple Cellular Metabolism Disruption

Nanozyme-based metabolic regulation triggered by tumor-specific endogenous stimuli has emerged as a promising therapeutic strategy for tumors. The current efficacy, however, is constrained by the limited concentration of endogenous substrates and the metabolic plasticity of tumors. Consequently, the implementation of efficient metabolic regulation in tumor therapy is urgently needed. Herein, a versatile nanozyme-based nicotinamide adenine dinucleotide (NADH) circulating oxidation nanoreactor is reported. First, the synthesized cobalt-doped hollow carbon spheres (Co-HCS) possess NADH oxidase (NOX)-mimicking activity for the NADH oxidation to disrupt oxidative phosphorylation (OXPHOS) pathway of tumor cells. Second, the substrate-cycle manner of Co-HCS can be used for NADH circulating oxidation to overcome the limitation of substrate deficiency. Finally, 2-Deoxy-D-glucose (2-DG) and 6-aminonicotinamide (6-AN) are introduced to block glycolysis and pentose phosphate pathway (PPP), thus creating a versatile nanozyme-based NADH circulating oxidation nanoreactor (Co-HCS/D/A) for tumor therapy through triple cellular metabolism disruption. In vitro and in vivo results demonstrate that the designed nanoreactor not only enhances the catalytic efficiency but also disrupts the tumor metabolic homeostasis, leading to efficient therapy outcome. This study develops a novel NADH circulating oxidation nanoreactor for tumor therapy through triple cellular metabolism disruption, which addresses the limitations of current nanozyme-based metabolism regulation for tumor therapy.

Achieving Negatively Charged Pt Single Atoms on Amorphous Ni(OH)2 Nanosheets with Promoted Hydrogen Absorption in Hydrogen Evolution

Single-atom (SA) catalysts with nearly 100% atom utilization have been widely employed in electrolysis for decades, due to the outperforming catalytic activity and selectivity. However, most of the reported SA catalysts are fixed through the strong bonding between the dispersed single metallic atoms with nonmetallic atoms of the substrates, which greatly limits the controllable regulation of electrocatalytic activity of SA catalysts. In this work, Pt-Ni bonded Pt SA catalyst with adjustable electronic states was successfully constructed through a controllable electrochemical reduction on the coordination unsaturated amorphous Ni(OH)2 nanosheet arrays. Based on the X-ray absorption fine structure analysis and first-principles calculations, Pt SA was bonded with Ni sites of amorphous Ni(OH)2, rather than conventional O sites, resulting in negatively charged Ptδ-. In situ Raman spectroscopy revealed that the changed configuration and electronic states greatly enhanced absorbability for activated hydrogen atoms, which were the essential intermediate for alkaline hydrogen evolution reaction. The hydrogen spillover process was revealed from amorphous Ni(OH)2 that effectively cleave the H-O-H bond of H2O and produce H atom to the Pt SA sites, leading to a low overpotential of 48 mV in alkaline electrolyte at -1000 mA cm-2 mg-1Pt, evidently better than commercial Pt/C catalysts. This work provided new strategy for the controllable modulation of the local structure of SA catalysts and the systematic regulation of the electronic states.

Effects of Intrinsic Defects in Pt-Based Carbon Supports on Alkaline Hydrogen Evolution Reaction

Carbon material has widely been utilized in the synthesis of efficient carbon-supported Pt (Pt/C) catalysts, in which the structural properties greatly influence the electrocatalytic performances of Pt/C catalysts. However, the effects of intrinsic defects in carbon supports on the performance of the alkaline hydrogen evolution reaction (HER) have not been systematically investigated. Herein, porous carbon supports with different degrees of intrinsic defects were prepared by a simple template-assisted strategy, and the resulting samples were systematically studied by various analytical methods. The results suggested that the presence of abundant intrinsic defects (vacancy and topological defects) in the carbon support was advantageous in terms of favoring the dispersion and anchoring of Pt species, promoting electron transfer between Pt atoms and the carbon support, and tuning the electronic states of Pt species. These features improved the HER performance of Pt/C catalysts. Compared to the nontemplate-assisted carbon-supported Pt catalyst (Pt/NTC) with an overpotential of 178 mV, the optimized template-assisted carbon-supported Pt catalyst (Pt/TC) exhibited a lower overpotential of 58 mV at 10 mA cm-2. Besides, the Pt/TC catalyst displayed better HER durability than the Pt/NTC catalyst owing to its strong metal-support interaction. The DFT calculations confirmed the important role played by intrinsic defects (vacancy and topological defects) in stabilizing Pt atoms, with Pt-C3 coordination identified as the most favorable structure for improving the HER performance of Pt. Overall, novel insights on the significant contribution of intrinsic defects in porous carbon supports on the HER performances of Pt/C catalysts were provided, useful for future design and fabrication of advanced carbon-supported catalysts or other carbon-based electrode materials.

Strategies Toward High Selectivity, Activity, and Stability of Single-Atom Catalysts

Single-atom catalysts (SACs) hold immense promise in facilitating the rational use of metal resources and achieving atomic economy due to their exceptional atom-utilization efficiency and distinct characteristics. Despite the growing interest in SACs, only limited reviews have holistically summarized their advancements centering on performance metrics. In this review, first, a thorough overview on the research progress in SACs is presented from a performance perspective and the strategies, advancements, and intriguing approaches employed to enhance the critical attributes in SACs are discussed. Subsequently, a comprehensive summary and critical analysis of the electrochemical applications of SACs are provided, with a particular focus on their efficacy in the oxygen reduction reaction , oxygen evolution reaction, hydrogen evolution reaction , CO2 reduction reaction, and N2 reduction reaction . Finally, the outline future research directions on SACs by concentrating on performance-driven investigation, where potential areas for improvement are identified and promising avenues for further study are highlighted, addressing challenges to unlock the full potential of SACs as high-performance catalysts.

Directed Dual Charge Pumping Tunes the d-Orbital Configuration of Pt Cluster Boosting Hydrogen Evolution Kinetic

Achieving high catalytic activity with a minimum amount of platinum (Pt) is crucial for accelerating the cathodic hydrogen evolution reaction (HER) in proton exchange membrane (PEM) water electrolysis, yet it remains a significant challenge. Herein, a directed dual-charge pumping strategy to tune the d-orbital electronic distribution of Pt nanoclusters for efficient HER catalysis is proposed. Theoretical analysis reveals that the ligand effect and electronic metal-support interactions (EMSI) create an effective directional electron transfer channel for the d-orbital electrons of Pt, which in turn optimizes the binding strength to H*, thereby significantly enhancing HER efficiency of the Pt site. Experimentally, this directed dual-charge pumping strategy is validated by elaborating Sb-doped SnO2 (ATO) supported Fe-doped PtSn heterostructure catalysts (Fe-PtSn/ATO). The synthesized 3%Fe-PtSn/ATO catalysts exhibit lower overpotential (requiring only 10.5 mV to reach a current density of 10 mA cm- 2), higher mass activity (28.6 times higher than commercial 20 wt.% Pt/C), and stability in the HER process in acidic media. This innovative strategy presents a promising pathway for the development of highly efficient HER catalysts with low Pt loading.

Pt nanoparticles anchored by oxygen vacancies in MXenes for efficient electrocatalytic hydrogen evolution reaction

The improvement of the hydrogen evolution reaction (HER) performance of nanomaterials is associated with the interfacial synergistic interaction and their hydrogen adsorption kinetics. Nevertheless, it is still a challenge to accelerate the proton transfer and optimize the HER kinetics by constructing Pt-supported heterostructures based on the hydrogen spillover phenomenon. Herein, oxygen vacancies on the surface of MXene nanosheets were constructed via a high-temperature annealing method, which was employed to anchor/stabilize Pt nanoparticles and fabricate a Pt/MXene heterostructure. EPR and XPS analyses verified the presence of oxygen vacancies, which could enhance the intrinsic HER activity of the MXene. The HER catalytic performance was investigated by taking into account the surface structure of the MXene affected by the annealing temperature, the concentration of Pt and the number of deposition cycles. Electrochemical results showed that Pt/MXene with higher utilization of Pt was obtained at 900 °C and 0.05 mgPt mL-1. The 0.05-Pt/MXene-900 obtained at deposition of 60 cycles in 0.5 M H2SO4 solution exhibited the optimized HER activity. The overpotential was 22 mV at a current density of 10 mA cm-2 and the Tafel slope was 42.41 mV dec-1. Furthermore, the accelerated HER kinetics was mainly due to the electron trapping ability of the MXene, small particles of Pt, as well as the enhanced charge transfer between the oxygen vacancies of the MXene and Pt. This strategy for constructing Pt-supported heterostructures based on the vacancy anchoring effects provides new ideas for the design of well-defined electrocatalysts toward the HER.

Correlation between Heteroatom Coordination and Hydrogen Evolution for Single-site Pt on Carbon-based Nanocages

The electrocatalytic performance of single-site catalysts (SSCs) is closely correlated with the electronic structure of metal atoms. Herein we construct a series of Pt SSCs on heteroatom-doped hierarchical carbon nanocages, which exhibit increasing hydrogen evolution reaction (HER) activities along S-doped, P-doped, undoped and N-doped supports. Theoretical simulation indicates a multi-H-atom adsorption process on Pt SSCs due to the low coordination, and a reasonable descriptor is figured out to evaluate the HER activities. Relative to C-coordinated Pt, N-coordinated Pt has higher reactivity due to the electron transfer of N-to-Pt, which enriches the density of states of Pt 5d orbital near the Fermi level and facilitates the capturing of protons, just the opposite to the situations for P- and S-coordinated ones. The stable N-coordinated Pt originates from the kinetic stability throughout the multi-H-atom adsorption process. This finding provides a significant guidance for rational design of advanced Pt SSCs on carbon-based supports.

Recent advances in catalytic oxidation of VOCs by two-dimensional ultra-thin nanomaterials

Catalytic oxidation, an end-of-pipe treatment technology for effectively purifying volatile organic compounds (VOCs), has received widespread attention. The crux of catalytic oxidation lies in the development of efficient catalysts, with their optimization necessitating a comprehensive analysis of the catalytic reaction mechanism. Two-dimensional (2D) ultra-thin nanomaterials offer significant advantages in exploring the catalytic oxidation mechanism of VOCs due to their unique structure and properties. This review classifies strategies for regulating catalytic properties and typical applications of 2D materials in VOCs catalytic oxidation, in addition to their characteristics and typical characterization techniques. Furthermore, the possible reaction mechanism of 2D Co-based and Mn-based oxides in the catalytic oxidation of VOCs is analyzed, with a special focus on the synergistic effect between oxygen and metal vacancies. The objective of this review is to provide valuable references for scholars in the field.

Bottom-Up Construction of Mesoporous Cerium-Doped Titania with Stably Dispersed Pt Nanocluster for Efficient Hydrogen Evolution

Hydrogen generation is one of the crucial technologies to realize sustainable energy development, and the design of advanced catalysts with efficient interfacial sites and fast mass transfer is significant for hydrogen evolution. Herein, an in situ coassembly strategy was proposed to engineer a cerium-doped ordered mesoporous titanium oxide (mpCe/TiO2), of which the abundant oxygen vacancies (Ov) and highly exposed active pore walls contribute to good stability of ultrasmall Pt nanoclusters (NCs, ∼ 1.0 nm in diameter) anchored in the uniform mesopores (ca. 20 nm). Consequently, the tailored mpCe/TiO2 with 0.5 mol % Ce-doping-supported Pt NCs (Pt-mpCe/TiO2-0.5) exhibits superior H2 evolution performance toward the water-gas shift reaction with a 0.73 molH2·s-1·molPt-1 H2 evolution rate at 200 °C, which is almost 6-fold higher than the Pt-mpTiO2 (0.13 molH2·s-1·molPt-1 H2). Density functional theory calculations confirm that the structure of Ce-doped TiO2 with Ce coordinated to six O atoms by substituting Ti atoms is thermodynamically favorable without the deformation of Ti-O bonds. The Ov generated by the six O atom-coordinated Ce doping is highly active for H2O dissociation with an energy barrier of 2.18 eV, which is obviously lower than the 2.37 eV for the control TiO2. In comparison with TiO2, the resultant Ce/TiO2 support acts as a superior electron acceptor for Pt NCs and causes electron deficiency at the Pt/support interface with a 0.17 eV downshift of the Pt d-band center, showing extremely obvious electronic metal-support interaction (EMSI). As a result, abundant and hyperactive Ti3+-Ov(-Ce3+)-Ptδ+ interfacial sites are formed to significantly promote the generation of CO2 and H2 evolution. In addition, the stronger EMSI between Pt NCs and mpCe/TiO2-0.5 than that between Pt and mpTiO2 contributes to the superior self-enhanced catalytic performance during the cyclic test, where the CO conversion at 200 °C increases from 72% for the fresh catalyst to 99% for the used one. These findings reveal the subtle relationship between the mesoporous metal oxide-metal composite catalysts with unique chemical microenvironments and their catalytic performance, which is expected to inspire the design of efficient heterogeneous catalysts.

Facile Fabrication of Hollow Nanoporous Carbon Architectures by Controlling MOF Crystalline Inhomogeneity for Ultra-Stable Na-Ion Storage

Hollow nanoporous carbon architectures (HNCs) present significant utilitarian value for a wide variety of applications. Facile and efficient preparation of HNCs has long been pursued but still remains challenging. Herein, we for the first time demonstrate that single-component metal-organic frameworks (MOFs) crystals, rather than the widely reported hybrid ones which necessitate tedious operations for preparation, could enable the facile and versatile syntheses of functional HNCs. By controlling the growth kinetics, the MOFs crystals (STU-1) are readily engineered into different shapes with designated styles of crystalline inhomogeneity. A subsequent one-step pyrolysis of these MOFs with intraparticle difference can induce a simultaneous self-hollowing and carbonization process, thereby producing various functional HNCs including yolk-shell polyhedrons, hollow microspheres, mesoporous architectures, and superstructures. Superior to the existing methods, this synthetic strategy relies only on the complex nature of single-component MOFs crystals without involving tedious operations like coating, etching, or ligand exchange, making it convenient, efficient, and easy to scale up. An ultra-stable Na-ion battery anode is demonstrated by the HNCs with extraordinary cyclability (93 % capacity retention over 8000 cycles), highlighting a high level of functionality of the HNCs.