Single platinum atoms embedded in nanoporous cobalt selenide as electrocatalyst for accelerating hydrogen evolution reaction

Co-doped NiFe carbonate hydroxide hydrate nanosheets with edge effect constructed from spent lithium-ion battery ternary cathodes for oxygen evolution reaction

The recycling of spent lithium-ion batteries (LIBs) has received increasing attention for environment and resource reclamation. Converting LIBs wastes into high-efficiency catalysts is a win-win strategy for realizing resource reclamation and addressing sustainable energy challenges. Herein, we developed a simple method to upcycle spent-LIBs cathode powder into Co-doped NiFe carbonate hydroxide hydrate (Co/NFCH-FF) as a low-cost and efficient oxygen evolution reaction (OER) electrocatalyst. The optimized Co/NFCH-FF electrode appears very competitive OER performances with low overpotentials of 201 and 249 mV at 10 and 100 mA cm-2, respectively, a small Tafel slope of 48.4 mV dec-1, and a high long-term stability. Moreover, we reveal that the existence of Co atoms leads to the formation of a crystalline/amorphous (c/a) interface at the Co/NFCH nanosheet edge, inducing the nanosheets possess a unique edge effect to enhance electric fields and accumulate hydroxide ions (OH-) at the edge during the OER process. Benefiting from edge effect, Co/NFCH-FF shows outstanding intrinsic activity. Furthermore, Co atoms as dopants stabilize the electronic structure of Co/NFCH-FF, enabling Co/NFCH-FF to exhibit excellent catalytic stability. This work provides an effective strategy for converting the end-life LIBs to high-performance multicomponent OER electrocatalysts and proposes new insights into the mechanism of enhanced catalytic activity of Co/NFCH.

Ruthenium-based single atom catalysts: synthesis and application in the electrocatalytic hydrogen evolution reaction

Electrocatalytic water splitting is a promising production method for green hydrogen; however, its practical application is limited by the lack of robust catalysts for the cathode hydrogen evolution reaction (HER). Recently, the use of Ru in electrocatalytic HER has become a research hotspot because Ru has a metal-hydrogen bond strength similar to that of Pt - known for its excellent HER activity - but has a lower cost than Pt. Numerous modification strategies are available to further improve the HER activity of metal Ru such as vulcanisation, phosphating and atomisation. The atomisation strategy has attracted much attention owing to its extremely high Ru atomic utilisation efficiency and tunable electronic structures. However, isolated studies could not effectively address the bottlenecks. Therefore, to promote the effective exploration of Ru-based single-atom catalysts and clarify the research status in this field, studies on related topics (e.g. Ru single-atom catalysts, Ru dual-atom catalysts, composite catalysts containing single-atom Ru and Ru nanoparticles) have been systematically and briefly summarised herein. Finally, the research challenges and prospects of Ru-based single-atom catalysts in the HER field have been discussed, which may provide valuable insights for further research.

Ru doping and interface engineering synergistically boost the electrocatalytic performance of a WP/WP2 nanosheet array for an efficient hydrogen evolution reaction

The surface electronic structure and morphology of catalysts have a crucial impact on the electrocatalytic hydrogen evolution reaction performance. This work reports on the fabrication of a Ru-doped WP/WP2 heterojunction nanosheet array electrode via a one-step phosphating treatment of a Ru-doped WO3 precursor. Benefitting from the large electrochemical active surface of nanosheet arrays, rich WP/WP2 heterojunction interface, and trace Ru atom doping, the catalyst has a fairly low overpotential of 58.0 mV at 10 mA cm-2 and a Tafel slope of 50.71 mV dec-1 in acid solution toward the electrocatalytic HER. Further, theoretical calculations unveil that Ru atom doping and interface effect synergistically optimized the electronic structure of the catalyst and hence weakened the adsorption capacity of the catalyst surface toward hydrogen (H), which lowered the Gibbs free energy (ΔGH*) and consequently effectively improved the HER performance. This work may open new avenues for developing advanced nanoarray electrodes with efficient electrochemical energy conversion.

Tunable Pt-NiO interaction-induced efficient electrocatalytic water oxidation and methanol oxidation

Metal-support interaction engineering is considered an efficient strategy for optimizing the catalytic activity. Nevertheless, the fine regulation of metal-support interactions as well as understanding the corresponding catalytic mechanisms (particularly those of non-carbon support-based counterparts) remains challenging. Herein, a controllable adsorption-impregnation strategy was proposed for the preparation of a porous nonlayered 2D NiO nanoflake support anchored with different forms of Pt nanoarchitectures, i.e. single atoms, clusters and nanoparticles. Benefiting from the unique porous architecture of NiO nanosheets, abundant active defect sites facilitated the immobilization of Pt single atoms onto the NiO crystal, resulting in NiO lattice distortion and thus changing the valence state of Pt, chemical bonding, and the coordination environment of the metal center. The synergy of the porous NiO support and the unexpected Pt single atom-NiO interactions effectively accelerated mass transfer and reduced the reaction kinetic barriers, contributing to a significantly enhanced mass activity of 5.59 A mgPt -1 at an overpotential of 0.274 V toward the electrocatalytic oxygen evolution reaction (OER) while 0.42 A mgPt -1 at a potential of 0.7 V vs. RHE for the methanol oxidation reaction (MOR) in an alkaline system, respectively. This work may offer fundamental guidance for developing metal-loaded/dispersed support nanomaterials toward electrocatalysis through the fine regulation of metal-support interactions.

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.

Synergistic Effect of P and Co Dual Doping Endows CuNi with High-Performance Hydrogen Evolution Reaction

The rational design of highly active and durable non-noble electrocatalysts for hydrogen evolution reaction (HER) is significantly important but technically challenging. Herein, a phosphor and cobalt dual doped copper-nickel alloy (P, Co-CuNi) electrocatalyst with high-efficient HER performance is prepared by one-step electrodeposition method and reported for the first time. As a result, P, Co-CuNi only requires an ultralow overpotential of 56 mV to drive the current density of 10 mA cm-2, with remarkable stability for over 360 h, surpassing most previously reported transition metal-based materials. It is discovered that the P doping can simultaneously increase the electrical conductivity and enhance the corrosion resistance, while the introduction of Co can precisely modulate the sub-nanosheets morphology to expose more accessible active sites. Moreover, XPS, UPS, and DFT calculations reveal that the synergistic effect of different dopants can achieve the most optimal electronic structure around Cu and Ni, causing a down-shifted d-band center, which reduces the hydrogen desorption free energy of the rate-determining step (H2O + e- + H* → H2 + OH-) and consequently enhances the intrinsic activity. This work provides a new cognition toward the development of excellent activity and stability HER electrocatalysts and spurs future study for other NiCu-based alloy materials.

Platinum-Ruthenium Dual-Atomic Sites Dispersed in Nanoporous Ni0.85Se Enabling Ampere-Level Current Density Hydrogen Production

Alkaline anion-exchange-membrane water electrolyzers (AEMWEs) using earth-abundant catalysts is a promising approach for the generation of green H2. However, the AEMWEs with alkaline electrolytes suffer from poor performance at high current density compared to proton exchange membrane electrolyzers. Here, atomically dispersed Pt-Ru dual sites co-embedded in nanoporous nickel selenides (np/Pt1Ru1-Ni0.85Se) are developed by a rapid melt-quenching approach to achieve highly-efficient alkaline hydrogen evolution reaction. The np/Pt1Ru1-Ni0.85Se catalyst shows ampere-level current density with a low overpotential (46 mV at 10 mA cm-2 and 225 mV at 1000 mA cm-2), low Tafel slope (32.4 mV dec-1), and excellent long-term durability, significantly outperforming the benchmark Pt/C catalyst and other advanced large-current catalysts. The remarkable HER performance of nanoporous Pt1Ru1-Ni0.85Se is attributed to the strong intracrystal electronic metal-support interaction (IEMSI) between Pt-Se-Ru sites and Ni0.85Se support which can greatly enlarge the charge redistribution density, reduce the energy barrier of water dissociation, and optimize the potential determining step. Furthermore, the assembled alkaline AEMWE with an ultralow Pt and Ru loading realizes an industrial-level current density of 1 A cm-2 at 1.84 volts with high durability.

Hydrogen Evolution in Neutral Media by Differential Intermediate Binding at Charge-Modulated Sites of a Bimetallic Alloy Electrocatalyst

The energy barrier to dissociate neutral water has been lowered by the differential intermediate binding on the charge-modulated metal centers of Co85Mo15 sheets supported on Ni-foam (NF), where the overpotential for hydrogen evolution reaction (HER) in 1 M phosphate buffer solution (PBS) is only 50±9 mV at -10 mA cm-2. It has a turnover frequency (TOF) of 0.18 s-1, mass activity of 13.2 A g-1 at -200 mV vs. reversible hydrogen electrode (RHE), and produces 16 ml H2 h-1 at -300 mV vs. RHE, more than double that of 20 % Pt/C. The Moδ+ and Coδ- sites adsorb OH*, and H*, respectively, and the electron injection from Co to H-O-H cleaves the O-H bond to form the Mo-OH* intermediate. Operando spectral analyses indicate a weak H-bonded network for facilitating the H2O*/OH* transport, and a potential-induced reversal of the charge density from Co to the more electronegative Mo, because of the electron withdrawing Co-H* and Mo-OH* species. Co85Mo15/NF can also drive the complete electrolysis of neutral water at only 1.73 V (10 mA cm-2). In alkaline, and acidic media, it demonstrates a Pt-like HER activity, accomplishing -1000 mA cm-2 at overpotentials of 161±7, and 175±22 mV, respectively.

Solvothermal Fabrication of Mesoporous Pd Nano-Corals at Mild Temperature for Alkaline Hydrogen Evolution Reaction

Porous metallic nanomaterials exhibit interesting physical and chemical properties, and are widely used in various fields. Traditional fabrication techniques are limited to metallurgy, sintering, electrodeposition, etc., which limit the control of pore size and distribution, and make it difficult to achieve materials with high surface areas. On the other hand, the chemical preparation of metallic nanoparticles is usually carried out with strong reducing agents or at high temperature, resulting in the formation of dispersed particles which cannot evolve into porous metal. In this study, we reported the simple fabrication of coral-like mesoporous Pd nanomaterial (Pd NC) with a ligament size of 4.1 nm. The fabrication was carried out by simple solvothermal reduction at a mild temperature of 135 °C, without using any templates. The control experiments suggested that tetrabutylammonium bromide (TBAB) played a critical role in the Pd(II) reduction into Pd nanoclusters and their subsequent aggregation to form Pd NC, and another key point for the formation of Pd NC is not to use a strong reducing agent. In alkaline water electrolysis, the Pd NC outperforms the monodisperse Pd NPs and the state-of-the-art Pt (under large potentials) for H2 evolution reaction, probably due to its mesoporous structure and large surface area. This work reports a simple and novel method for producing porous metallic nanomaterials with a high utilization efficiency of metal atoms, and it is expected to contribute to the practical preparation of porous metallic nanomaterials by solvothermal reductions.

Gram-scale synthesis of small-sized PtM intermetallics as high-performance catalysts for the hydrogen evolution reaction

Pt-based intermetallics exhibit excellent activity in electrocatalysis. However, their controlled syntheses remain difficult. Herein, carbon-supported PtM (M = Fe, Co, Ni, Zn and Mn) intermetallics with small size (3 nm) were prepared at the gramscale and applied as a highly effective electrocatalyst for the hydrogen evolution reaction.

Recent Progress on Potentiometric Sensor Applications Based on Nanoscale Metal Oxides: A Comprehensive Review

Electrochemical sensors have been the subject of much research and development as of late, with several publications detailing new designs boasting enhanced performance metrics. That is, without a doubt, because such sensors stand out from other analytical tools thanks to their excellent analytical characteristics, low cost, and ease of use. Their progress has shown a trend toward seeking out novel useful nano structure materials. A variety of nanostructure metal oxides have been utilized in the creation of potentiometric sensors, which are the subject of this article. For screen-printed pH sensors, metal oxides have been utilized as sensing layers due to their mixed ion-electron conductivity and as paste-ion-selective electrode components and in solid-contact electrodes. Further significant uses include solid-contact layers. All the metal oxide uses mentioned are within the purview of this article. Nanoscale metal oxides have several potential uses in the potentiometry method, and this paper summarizes such uses, including hybrid materials and single-component layers. Potentiometric sensors with outstanding analytical properties can be manufactured entirely from metal oxides. These novel sensors outperform the more traditional, conventional electrodes in terms of useful characteristics. In this review, we looked at the potentiometric analytical properties of different building solutions with various nanoscale metal oxides.

Structural engineering of atomic catalysts for electrocatalysis

As a burgeoning category of heterogeneous catalysts, atomic catalysts have been extensively researched in the field of electrocatalysis. To satisfy different electrocatalytic reactions, single-atom catalysts (SACs), diatomic catalysts (DACs) and triatomic catalysts (TACs) have been successfully designed and synthesized, in which microenvironment structure regulation is the core to achieve high-efficiency catalytic activity and selectivity. In this review, the effect of the geometric and electronic structure of metal active centers on catalytic performance is systematically introduced, including substrates, central metal atoms, and the coordination environment. Then theoretical understanding of atomic catalysts for electrocatalysis is innovatively discussed, including synergistic effects, defect coupled spin state change and crystal field distortion spin state change. In addition, we propose the challenges to optimize atomic catalysts for electrocatalysis applications, including controlled synthesis, increasing the density of active sites, enhancing intrinsic activity, and improving the stability. Moreover, the structure-function relationships of atomic catalysts in the CO2 reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, hydrogen evolution reaction, and oxygen evolution reaction are highlighted. To facilitate the development of high-performance atomic catalysts, several technical challenges and research orientations are put forward.

Surface Engineered Single-atom Systems for Energy Conversion

Single-atom catalysts (SACs) are demonstrated to show exceptional reactivity and selectivity in catalytic reactions by effectively utilizing metal species, making them a favorable choice among the different active materials for energy conversion. However, SACs are still in the early stages of energy conversion, and problems like agglomeration and low energy conversion efficiency are hampering their practical applications. Substantial research focus on support modifications, which are vital for SAC reactivity and stability due to the intimate relationship between metal atoms and support. In this review, a category of supports and a variety of surface engineering strategies employed in SA systems are summarized, including surface site engineering (heteroatom doping, vacancy introducing, surface groups grafting, and coordination tunning) and surface structure engineering (size/morphology control, cocatalyst deposition, facet engineering, and crystallinity control). Also, the merits of support surface engineering in single-atom systems are systematically introduced. Highlights are the comprehensive summary and discussions on the utilization of surface-engineered SACs in diversified energy conversion applications including photocatalysis, electrocatalysis, thermocatalysis, and energy conversion devices. At the end of this review, the potential and obstacles of using surface-engineered SACs in the field of energy conversion are discussed. This review aims to guide the rational design and manipulation of SACs for target-specific applications by capitalizing on the characteristic benefits of support surface engineering.

Single-atom platinum with asymmetric coordination environment on fully conjugated covalent organic framework for efficient electrocatalysis

Two-dimensional (2D) covalent organic frameworks (COFs) and their derivatives have been widely applied as electrocatalysts owing to their unique nanoscale pore configurations, stable periodic structures, abundant coordination sites and high surface area. This work aims to construct a non-thermodynamically stable Pt-N2 coordination active site by electrochemically modifying platinum (Pt) single atoms into a fully conjugated 2D COF as conductive agent-free and pyrolysis-free electrocatalyst for the hydrogen evolution reaction (HER). In addition to maximizing atomic utilization, single-atom catalysts with definite structures can be used to investigate catalytic mechanisms and structure-activity relationships. In this work, in-situ characterizations and theoretical calculations reveal that a nitrogen-rich graphene analogue COF not only exhibits a favorable metal-support effect for Pt, adjusting the binding energy between Pt sites to H* intermediates by forming unique Pt-N2 instead of the typical Pt-N4 coordination environment, but also enhances electron transport ability and structural stability, showing both conductivity and stability in acidic environments.

A universal and scalable transformation of bulk metals into single-atom catalysts in ionic liquids

Single-atom catalysts (SACs) with maximized metal atom utilization and intriguing properties are of utmost importance for energy conversion and catalysis science. However, the lack of a straightforward and scalable synthesis strategy of SACs on diverse support materials remains the bottleneck for their large-scale industrial applications. Herein, we report a general approach to directly transform bulk metals into single atoms through the precise control of the electrodissolution-electrodeposition kinetics in ionic liquids and demonstrate the successful applicability of up to twenty different monometallic SACs and one multimetallic SAC with five distinct elements. As a case study, the atomically dispersed Pt was electrodeposited onto Ni3N/Ni-Co-graphene oxide heterostructures in varied scales (up to 5 cm × 5 cm) as bifunctional catalysts with the electronic metal-support interaction, which exhibits low overpotentials at 10 mA cm-2 for hydrogen evolution reaction (HER, 30 mV) and oxygen evolution reaction (OER, 263 mV) with a relatively low Pt loading (0.98 wt%). This work provides a simple and practical route for large-scale synthesis of various SACs with favorable catalytic properties on diversified supports using alternative ionic liquids and inspires the methodology on precise synthesis of multimetallic single-atom materials with tunable compositions.

Atomically-Thin Holey 2D Nanosheets of Defect-Engineered MoN-Mo5 N6 Composites as Effective Hybridization Matrices

The defect engineering of inorganic solids has received significant attention because of its high efficacy in optimizing energy-related functionalities. Consequently, this approach is effectively leveraged in the present study to synthesize atomically-thin holey 2D nanosheets of a MoN-Mo5 N6 composite. This is achieved by controlled nitridation of assembled MoS2 monolayers, which induced sequential cation/anion migration and a gradual decrease in the Mo valency. Precise control of the interlayer distance of the MoS2 monolayers via assembly with various tetraalkylammonium ions is found to be crucial for synthesizing sub-nanometer-thick holey MoN-Mo5 N6 nanosheets with a tunable anion/cation vacancy content. The holey MoN-Mo5 N6 nanosheets are employed as efficient immobilization matrices for Pt single atoms to achieve high electrocatalytic mass activity, decent durability, and low overpotential for the hydrogen evolution reaction (HER). In situ/ex situ spectroscopy and density functional theory (DFT) calculations reveal that the presence of cation-deficient Mo5 N6 domain is crucial for enhancing the interfacial interactions between the conductive molybdenum nitride substrate and Pt single atoms, leading to enhanced electron injection efficiency and electrochemical stability. The beneficial effects of the Pt-immobilizing holey MoN-Mo5 N6 nanosheets are associated with enhanced electronic coupling, resulting in improvements in HER kinetics and interfacial charge transfer.

Facilitating alkaline hydrogen evolution reaction on the hetero-interfaced Ru/RuO2 through Pt single atoms doping

Exploring an active and cost-effective electrocatalyst alternative to carbon-supported platinum nanoparticles for alkaline hydrogen evolution reaction (HER) have remained elusive to date. Here, we report a catalyst based on platinum single atoms (SAs) doped into the hetero-interfaced Ru/RuO2 support (referred to as Pt-Ru/RuO2), which features a low HER overpotential, an excellent stability and a distinctly enhanced cost-based activity compared to commercial Pt/C and Ru/C in 1 M KOH. Advanced physico-chemical characterizations disclose that the sluggish water dissociation is accelerated by RuO2 while Pt SAs and the metallic Ru facilitate the subsequent H* combination. Theoretical calculations correlate with the experimental findings. Furthermore, Pt-Ru/RuO2 only requires 1.90 V to reach 1 A cm-2 and delivers a high price activity in the anion exchange membrane water electrolyzer, outperforming the benchmark Pt/C. This research offers a feasible guidance for developing the noble metal-based catalysts with high performance and low cost toward practical H2 production.

Electronic and Geometric Effects Endow PtRh Jagged Nanowires with Superior Ethanol Oxidation Catalysis

Complete ethanol oxidation reaction (EOR) in C1 pathway with 12 transferred electrons is highly desirable yet challenging in direct ethanol fuel cells. Herein, PtRh jagged nanowires synthesized via a simple wet-chemical approach exhibit exceptional EOR mass activity of 1.63 A mgPt-1 and specific activity of 4.07 mA cm-2 , 3.62-fold and 4.28-folds increments relative to Pt/C, respectively. High proportions of 69.33% and 73.42% of initial activity are also retained after chronoamperometric test (80 000 s) and 1500 consecutive potential cycles, respectively. More importantly, it is found that PtRh jagged nanowires possess superb anti-CO poisoning capability. Combining X-ray absorption spectroscopy, X-ray photoelectron spectroscopy as well as density functional theory calculations unveil that the remarkable catalytic activity and CO tolerance stem from both the Rh-induced electronic effect and geometric effect (manifested by shortened Pt─Pt bond length and shrinkage of lattice constants), which facilitates EOR catalysis in C1 pathway and improves reaction kinetics by reducing energy barriers of rate-determining steps (such as *CO → *COOH). The C1 pathway efficiency of PtRh jagged nanowires is further verified by the high intensity of CO2 relative to CH3 COOH/CH3 CHO in infrared reflection absorption spectroscopy.

Advancements in Microwave Absorption Motivated by Interdisciplinary Research

Microwave absorption materials (MAMs) are originally developed for military purposes, but have since evolved into versatile materials with promising applications in modern technologies, including household use. Despite significant progress in bench-side research over the past decade, MAMs remain limited in their scope and have yet to be widely adopted. This review explores the history of MAMs from first-generation coatings to second-generation functional absorbers, identifies bottlenecks hindering their maturation. It also presents potential solutions such as exploring broader spatial scales, advanced characterization, introducing liquid media, utilizing novel toolbox (machine learning, ML), and proximity of lab to end-user. Additionally, it meticulously presents compelling applications of MAMs in medicine, mechanics, energy, optics, and sensing, which go beyond absorption efficiency, along with their current development status and prospects. This interdisciplinary research direction differs from previous research which primarily focused on meeting traditional requirements (i.e., thin, lightweight, wide, and strong), and can be defined as the next generation of smart absorbers. Ultimately, the effective utilization of ubiquitous electromagnetic (EM) waves, aided by third-generation MAMs, should be better aligned with future expectations.

Local Electron Environment Regulation of Spinel CoMn2O4 Induced Effective Reactant Adsorption and Transformation of Lattice Oxygen for Toluene Oxidation

In contrast to numerous studies on oxygen species, the interaction of volatile organic compounds (VOCs) with oxides is also critical to the catalytic reaction but has hardly been considered. Herein, we develop a highly efficient Pt atom doped spinel CoMn2O4 (Pt-CoMn) for oxidation of toluene at low temperature, and the toluene conversion rate increased by 18.3 times (129.7 versus 7.1 × 10-11 mol/(m2·s)) at 160 °C compared to that of CoMn2O4. Detailed characterizations and density functional theory calculations reveal that the local electron environment of the Co sites is changed after Pt doping, and the formed electron-deficient Co sites in turn strengthen the interaction with toluene. Adsorbed toluene will react with lattice oxygen in Pt-CoMn and CoMn catalysts and convert into benzoate intermediates, and the consumption rate of benzoate is closely related to the activation of gaseous oxygen. Significantly, the abundant bulk defects of Pt-CoMn help to open the reaction channel in the CoMn spinel, which acts as an oxygen pump to promote the transformation of bulk lattice oxygen into surface lattice oxygen at lower temperatures, thus accelerating the conversion rate of benzoate intermediates into CO2 and enhancing low-temperature combustion of toluene. Pt-CoMn developed here emphasizes the regulation of VOCs adsorption strength and lattice oxygen transformation processes on CoMn2O4 by adjusting the local electron environment, which will provide new guidance for the design of efficient oxide catalysts for catalytic oxidation.

Ultralow Ru Single Atoms Confined in Cerium Oxide Nanoglues for Highly-Sensitive and Robust H2 O2 -Related Biocatalytic Diagnosis

Exploring highly efficient, portable, and robust biocatalysts is a great challenge in colorimetric biosensors. To overcome the challenging states in creating single-atom biocatalysts, such as insufficient activity and stability, here, this work has engineered a unique CeO2 support as nanoglue to tightly anchor the Ru single-atom sites (CeO2 -Ru) with strong electronic coupling for achieving highly sensitive and robust H2 O2 -related biocatalytic diagnosis. The morphology and chemical/electronic structure analysis demonstrates that the Ru atoms are well-dispersed on CeO2 surface to form high-density active sites. Benefiting from the unique structure, the prepared CeO2 -Ru exhibits outstanding peroxidase (POD) like catalytic activity and selectivity to H2 O2 . Steady-state kinetic study results show that the CeO2 -Ru presents the highest Vmax and turnover number than the state-of-the-art POD-like biocatalysts. Consequently, the CeO2 -Ru discloses a high efficiency, good selectivity, and robust stability in the colorimetric detection of L-cysteine, glucose, and uric acid. Notably, the limit of detection (LOD) can reach 0.176 × 10-3 m for the L-cysteine, 0.095 × 10-3 m for the glucose, and 0.088 × 10-3 m for the uric acid via cascade reaction. This work suggests that the proposed unique CeO2 nanoglue will offer a new path to create single-atom noble metal biocatalysts and take a step closer to future biotherapeutic and biocatalytic applications.

Sulfur-Stabilizing Ultrafine High-Entropy Alloy Nanoparticles on MXene for Highly Efficient Ethanol Electrooxidation

High-entropy alloys (HEAs) are significantly promising candidates for heterogeneous catalysis, yet the controllable synthesis of ultrafine HEA nanoparticles (NPs) remains a formidable challenge due to severe thermal sintering during the high-temperature fabrication process. Herein, we report a sulfur-stabilizing strategy to construct ultrafine HEA NPs with an average diameter of 4.02 nm supported on sulfur-modified Ti3C2Tx (S-Ti3C2Tx) MXene, on which the strong interfacial metal-sulfur interactions between HEA NPs and the S-Ti3C2Tx supports significantly increase the interfacial adhesion strength, thus greatly suppressing nanoparticle sintering by retarding both particle migration and metal atom diffusion. The representative quinary PtPdCuNiCo HEA-S-Ti3C2Tx exhibits excellent catalytic performance toward alkaline ethanol oxidation reaction (EOR) with an ultrahigh mass activity of 7.03 A mgPt+Pd-1, which is 4.34 and 5.17 times higher than those of the commercial Pt/C and Pd/C catalysts, respectively. In situ attenuated total reflection-infrared spectroscopy studies reveal that the high intrinsic catalytic activity for the EOR can be ascribed to the synergy of different catalytically active sites of HEA NPs and the well-designed interfacial metal-sulfur interactions.

Improved Electrocatalytic Activity and Stability by Single Iridium Atoms on Iron-based Layered Double Hydroxides for Oxygen Evolution

Full understanding to the origin of the catalytic performance of a supported nanocatalyst from the points of view of both the active component and support is significant for the achievement of high performance. Herein, based on a model electrocatalyst of single-iridium-atom-doped iron (Fe)-based layered double hydroxides (LDH) for oxygen evolution reaction (OER), we reveal the first completed origin of the catalytic performance of such supported nanocatalysts. Specially, besides the activity enhancement of Ir sites by LDH support, the stability of surface Fe sites is enhanced by doped Ir sites: DFT calculation shows that the Ir sites can reduce the activity and enhance the stability of the nearby Fe sites; while further finite element simulations indicate, the stability enhancement of distant Fe sites could be attributed to the much low concentration of OER reactant (hydroxyl ions, OH- ) around them induced by the much fast consumption of OH- on highly active Ir sites. These new findings about the interaction between the main active components and supports are applicable in principle to other heterogeneous nanocatalysts and provide a completed understanding to the catalytic performance of heterogeneous nanocatalysts.

Single-Atom Cr-N4 Sites with High Oxophilicity Interfaced with Pt Atomic Clusters for Practical Alkaline Hydrogen Evolution Catalysis

Although dispersing Pt atomic clusters (ACs) on a conducting support is a promising way to minimize the Pt amount required in hydrogen evolution reaction (HER), the catalytic mass activity and durability of Pt ACs are often unsatisfactory for alkaline HER due to their unfavorable water dissociation and challenges in stabilizing them against agglomeration and detachment. Herein, we report a class of single-atom Cr-N4 sites with high oxophilicity interfaced with Pt ACs on mesoporous carbon for achieving a highly active and stable alkaline HER in an anion-exchange-membrane water electrolyzer (AEMWE). The as-made catalyst achieves the highest reported Pt mass activity (37.6 times higher than commercial Pt/C) and outstanding operational stability. Experimental and theoretical studies elucidate that the formation of a unique Pt-Cr quasi-covalent bonding interaction at the interface of Cr-N4 sites and Pt ACs effectively suppresses the migration and thermal vibration of Pt atoms to stabilize Pt ACs and contributes to the greatly enhanced catalytic stability. Moreover, oxophilic Cr-N4 sites adjacent to Pt ACs with favorable adsorption of hydroxyl species facilitate nearly barrierless water dissociation and thus enhance the HER activity. An AEMWE using this catalyst (with only 50 μgPt cm-2) can operate stably at an industrial-level current density of 500 mA cm-2 at 1.8 V for >100 h with a small degradation rate of 90 μV h-1.

Single-Atom Pt Doping Induced p-Type to n-Type Transition in NiO Nanosheets toward Self-Gating Modulated Electrocatalytic Hydrogen Evolution Reaction

Exploring highly efficient single atom catalysts with defined active centers and tunable electronic structures is highly desirable. Herein, we developed an efficient hydrogen evolution reaction (HER) electrocatalyst through a self-gating phenomenon induced by Pt single atoms (SAs) supported on ultrathin NiO nanosheets (PtSA-NiO). The Ni atoms in NiO are partially replaced by the atomically dispersed Pt atoms, leading to a transition from p-type NiO into n-type PtSA-NiO. When the n-type PtSA-NiO serves as HER electrocatalyst, the self-gating phenomenon occurs in the ultrathin nanosheets, resulting in a mixture of leakage ("active") and metal-insulator-semiconductor ("inert") regions. The "inert" region induced by the ionic gating and reverse potential is capable of accumulating relatively high surface charge carrier concentration with an ultrahigh electric field, making the PtSA-NiO highly conductive; meanwhile, the HER process occurs at the Pt SAs sites (active region) in the PtSA-NiO nanosheets. As a result, the PtSA-NiO requires only 55 mV to deliver 10 mA/cm2 in an alkaline solution with good stability.

Stabilizing Pt Single Atoms through Pt-Se Electron Bridges on Vacancy-enriched Nickel Selenide for Efficient Electrocatalytic Hydrogen Evolution

Rational design of Pt single-atom catalysts provides a promising strategy to significantly improve the electrocatalytic activity for hydrogen evolution reaction. In this work, we presented a novel and efficient strategy for utilizing the low electron-density region of substrate to effectively trap and confine high electron-density metal atoms. The Pt single-atom catalyst supported by nickel selenide with rich vacancies was prepared via a hydrothermal-impregnation stepwise approach. Through experimental testation and DFT theoretical calculation, we confirm that Pt single atoms are well distributed at cationic vacancies of nickel selenide with loading amount of 3.2 wt. %. Moreover, the atomic Pt combined with the high electronegative Se to form Pt-Se bond as a "bridge" between single atoms and substrate for fast electron translation. This novel catalyst shows an extremely low overpotential of 45 mV at 10 mA cm-2 and an excellent stability over 120 h. Furthermore, the nickel selenide supported Pt SACs exhibits long-term stability for practical application, which maintains a high current density of 390 mA cm-2 over 80 h with a retention of 99 %. This work points a promising direction for designing single atoms catalysts with high catalytic activity and stability for advanced green energy conversion technologies.

High Valence State Sites as Favorable Reductive Centers for High-Current-Density Water Splitting

Electrochemical water splitting is a promising approach for producing sustainable and clean hydrogen. Typically, high valence state sites are favorable for oxidation evolution reaction (OER), while low valence states can facilitate hydrogen evolution reaction (HER). However, here we proposed a high valence state of Co3+ in Ni9.5 Co0.5 -S-FeOx hybrid as the favorable center for efficient and stable HER, while structural analogues with low chemical states showed much worse performance. As a result, the Ni9.5 Co0.5 -S-FeOx catalyst could drive alkaline HER with an ultra-low overpotential of 22 mV for 10 mA cm-2 , and 175 mV for 1000 mA cm-2 at the industrial temperature of 60 °C, with an excellent stability over 300 h. Moreover, this material could work for both OER and HER, with a low cell voltage being 1.730 V to achieve 1000 mA cm-2 for overall water splitting at 60 °C. X-ray absorption spectroscopy (XAS) clearly identified the high valence Co3+ sites, while in situ XAS during HER and theoretical calculations revealed the favorable electron capture at Co3+ and suitable H adsorption/desorption energy around Co3+ , which could accelerate the HER. The understanding of high valence states to drive reductive reactions may pave the way for the rational design of energy-related catalysts.

Tailored Lattice Compressive Strain of Pt-Skins by the L12 -Pt3 M Intermetallic Core for Highly Efficient Oxygen Reduction

The sluggish kinetics of oxygen reduction reaction (ORR) and unsatisfactory durability of Pt-based catalysts are severely hindering the commercialization of proton-exchange-membrane fuel cells (PEMFCs). In this work, the lattice compressive strain of Pt-skins imposed by Pt-based intermetallic cores is tailored for highly effective ORR through the confinement effect of the activated nitrogen-doped porous carbon (a-NPC). The modulated pores of a-NPC not only promote Pt-based intermetallics with ultrasmall size (average size of <4 nm), but also efficiently stabilizes intermetallic nanoparticles and sufficient exposure of active sites during the ORR process. The optimized catalyst (L12 -Pt3 Co@ML-Pt/NPC10 ) achieves excellent mass activity (1.72 A mgPt -1 ) and specific activity (3.49 mA cmPt -2 ), which are 11- and 15-fold that of commercial Pt/C, respectively. Besides, owing to the confinement effect of a-NPC and protection of Pt-skins, L12 -Pt3 Co@ML-Pt/NPC10 retains 98.1% mass activity after 30 000 cycles, and even 95% for 100 000 cycles, while Pt/C retains only 51.2% for 30 000 cycles. Rationalized by density functional theory, compared with other metals (Cr, Mn, Fe, and Zn), L12 -Pt3 Co closer to the top of "volcano" induces a more suitable compressive strain and electronic structure on Pt-skin, leading to an optimal oxygen adsorption energy and a remarkable ORR performance.

Diatomite-Templated Synthesis of Single-Atom Cobalt-Doped MoS2 /Carbon Composites to Boost Sodium Storage

2D transition metal dichalcogenides (TMDCs) and single-atom catalysts (SACs) are promising electrodes for energy conversion/storage because of the layered structure and maximum atom utilization efficiency. However, the integration of such two type materials and the relevant sodium storage applications remain daunting challenges. Here, an ingenious diatomite-templated synthetic strategy is designed to fabricate single-atom cobalt-doped MoS2 /carbon (SA Co-MoS2 /C) composites toward the high-performance sodium storage. Benefiting from the unique hierarchical structure, high electron/sodium-ion conductivity, and abundant active sites, the obtained SA Co-MoS2 /C reveals remarkable specific capacity (≈604.0 mAh g-1 at 0.1 A g-1 ), high rate performance, and outstanding long cyclic stability. Particularly, the sodium-ion full cell composed of SA Co-MoS2 /C anode and Na3 V2 (PO4 )3 cathode demonstrates unexpected stability with the cycle number exceeded 1200. The internal sodium storage mechanism is clarified with the aid of density functional theory calculations and in situ experimental characterizations. This work not only represents a substantial leap in terms of synthesizing SACs on 2D TMDCs but also provides a crucial step toward the practical sodium-ion battery applications.

Nanoflower-like FeVNi3S2-xas efficient electrocatalyst for alkaline oxygen evolution reaction

The development of low cost efficient catalysts for oxygen evolution reaction (OER) is still a obstacle to realize the commercialization of electrocatalytic water splitting. Herein, interface engineering and heteroatom doping is adopted to synthesize iron and vanadium doped nickel sulfide on nickel foam via hydrothermal method followed by hydrogen treatment to create sulfur defects. The optimized nanoflower-like FeVNi3S2-x/NF is an efficient OER electrocatalyst that outperforms many of the reported transition metals catalysts. Benefiting from abundant sulfur defects and the synergistic effect of heteroatom doping, FeVNi3S2-x/NF exhibits an ultralow overpotential of 230 mV to reach a current density of 100 mA cm-2, a rapid reaction kinetics with a small Tafel slope of 46.6 mV dec-1, and a stable long-term durability in 1 M KOH. Experimental results and characterizations confirm that sulfur vacancies together with the synergistic effect from multiple heteroatom doping can effectively regulate the electronic structure, resulting in increased electrical conductivity and electrochemically active surface area, thus enhancing OER performance. Furthermore,in situRaman spectroscopy reveals that, the reconstitution amorphous nickel oxyhydroxide (NiOOH) on the catalyst surface is responsible for catalyzing the OER reaction. This work represents a promising methodology to synthesize low-cost and highly active OER electrocatalysts.

Pt single atoms meet metal-organic frameworks to enhance electrocatalytic hydrogen evolution activity

The electrochemical hydrogen evolution reaction (HER) effectively produces clean, renewable, and sustainable hydrogen; however, the development of efficient electrocatalysts is required to reduce the high energy barrier of the HER. Herein, we report two excellent single-atom (SA)/metal-organic framework (MOF) composite electrocatalysts (PtSA-MIL100(Fe) and PtSA-MIL101(Cr)) for HER. The obtained PtSA-MIL100(Fe) and PtSA-MIL101(Cr) electrocatalysts exhibit overpotentials of 60 and 61 mV at 10 mA cm-2, respectively, which are close to that of commercial Pt/C (38 mV); they exhibit overpotentials of 310 and 288 mV at 200 mA cm-2, respectively, which are comparable to that of commercial Pt/C (270 mV). Theoretical simulations reveal that Pt SAs modulate the electronic structures of the MOFs, leading to the optimization of the binding strength for H* and significant enhancement of the HER activity. This study describes a novel strategy for preparing desirable HER electrocatalysts based on the synergy between SAs and MIL-series MOFs. Using MIL-series MOFs to support SAs could be valuable for future catalyst design.

Cooperative Rh-O5/Ni(Fe) Site for Efficient Biomass Upgrading Coupled with H2 Production

Designing efficient and durable bifunctional catalysts for 5-hydroxymethylfurfural (HMF) oxidation reaction (HMFOR) and hydrogen evolution reaction (HER) is desirable for the co-production of biomass-upgraded chemicals and sustainable hydrogen, which is limited by the competitive adsorption of hydroxyl species (OHads) and HMF molecules. Here, we report a class of Rh-O5/Ni(Fe) atomic site on nanoporous mesh-type layered double hydroxides with atomic-scale cooperative adsorption centers for highly active and stable alkaline HMFOR and HER catalysis. A low cell voltage of 1.48 V is required to achieve 100 mA cm-2 in an integrated electrolysis system along with excellent stability (>100 h). Operando infrared and X-ray absorption spectroscopic probes unveil that HMF molecules are selectively adsorbed and activated over the single-atom Rh sites and oxidized by in situ-formed electrophilic OHads species on neighboring Ni sites. Theoretical studies further demonstrate that the strong d-d orbital coupling interactions between atomic-level Rh and surrounding Ni atoms in the special Rh-O5/Ni(Fe) structure can greatly facilitate surface electronic exchange-and-transfer capabilities with the adsorbates (OHads and HMF molecules) and intermediates for efficient HMFOR and HER. We also reveal that the Fe sites in Rh-O5/Ni(Fe) structure can promote the electrocatalytic stability of the catalyst. Our findings provide new insights into catalyst design for complex reactions involving competitive adsorptions of multiple intermediates.

Relationship between Structure and Performance of Atomic-Scale Electrocatalysts for Water Splitting

Atomic-scale electrocatalysts greatly improve the performance and efficiency of water splitting but require special adjustments of the supporting structures for anchoring and dispersing metal single atoms. Here, the structural evolution of atomic-scale electrocatalysts for water splitting is reviewed based on different synthetic methods and structural properties that create different environments for electrocatalytic activity. The rate-determining step or intermediate state for hydrogen or oxygen evolution reactions is energetically stabilized by the coordination environment to the single-atom active site from the supporting material. In large-scale practical use, maximizing the loading amount of metal single atoms increases the efficiency of the electrocatalyst and reduces the economic cost. Dual-atom electrocatalysts with two different single-atom active sites react with an increased number of water molecules and reduce the adsorption energy of water derived from the difference in electronegativity between the two metal atoms. In particular, single-atom dimers induce asymmetric active sites that promote the degradation of H2 O to H2 or O2 evolution. Consequently, the structural properties of atomic-scale electrocatalysts clarify the atomic interrelation between the catalytic active sites and the supporting material to achieve maximum efficiency.

2D Cobalt Chalcogenide Heteronanostructures Enable Efficient Alkaline Hydrogen Evolution Reaction

The development of high-efficiency non-precious metal electrocatalysts for alkaline electrolyte hydrogen evolution reactions (HER) is of great significance in energy conversion to overcome the limited supply of fossil fuels and carbon emission. Here, a highly active electrocatalyst is presented for hydrogen production, consisting of 2D CoSe2 /Co3 S4 heterostructured nanosheets along Co3 O4 nanofibers. The different reaction rate between the ion exchange reaction and redox reaction leads to the heterogeneous volume swelling, promoting the growth of 2D structure. The 2D/1D heteronanostructures enable the improved the electrochemical active area, the number of active sites, and more favorable H binding energy compared to individual cobalt chalcogenides. The roles of the different composition of the heterojunction are investigated, and the electrocatalysts based on the CoSe2 /Co3 S4 @Co3 O4 exhibited an overpotential as low as 165 mV for 10 mA cm-2 and 393 mV for 200 mA cm-2 in 1 m KOH electrolyte. The as-prepared electrocatalysts remained active after 55 h operation without any significant decrease, indicating the excellent long-term operation stability of the electrode. The Faradaic efficiency of hydrogen production is close to 100% at different voltages. This work provides a new design strategy toward Co-based catalysts for efficient alkaline HER.

Balancing Volmer Step by Superhydrophilic Dual-Active Domains for Enhanced Hydrogen Evolution

The reaction kinetics of hydrogen evolution reaction (HER) is largely determined by balancing the Volmer step in alkaline media. Bifunctionality as a proposed strategy can divide the work of water dissociation and intermediates (OH* and H*) adsorption/desorption. However, sluggish OH* desorption plagues water re-adsorption, which leads to poisoning effects of active sites. Some active sites may even directly act as spectators and do not participate in the reaction. Furthermore, the activity comparison under approximate nanostructure between bifunctional effect and single-exposed active sites is not fully understood. Here, a facile three-step strategy is adopted to successfully grow molybdenum disulfide (MoS2 ) on cobalt-containing nitrogen-doped carbon nanotubes (Co-NCNTs), forming obvious dual active domains. The active sites on domains of Co-NCNTs and MoS2  and the tuned electronic structure at the heterointerface trigger the bifunctional effect to balance the Volmer step and improve the catalytic activity. The HER driven by the bifunctional effect can significantly optimize the Gibbs free energy of water dissociation and hydrogen adsorption, resulting in fast reaction kinetics and superior catalytic performance. As a result, the Co-NCNTs/MoS2  catalyst outperforms other HER electrocatalysts with low overpotential (58 and 84 mV at 10 mA cm-2  in alkaline and neutral conditions, respectively), exceptional stability, and negligible degradation.

Dual roles of sub-nanometer NiO in alkaline hydrogen evolution reaction: breaking the Volmer limitation and optimizing d-orbital electronic configuration

Pt-based nanoclusters toward the hydrogen evolution reaction (HER) remain the most promising electrocatalysts. However, the sluggish alkaline Volmer-step kinetics and the high-cost have hampered progress in developing high-performance HER catalysts. Herein, we propose to construct sub-nanometer NiO to tune the d-orbital electronic structure of nanocluster-level Pt for breaking the Volmer-step limitation and reducing the Pt-loading. Theoretical simulations firstly suggest that electron transfer from NiO to Pt nanoclusters could downshift the Ed-band of Pt and result in the well-optimized adsorption/desorption strength of the hydrogen intermediate (H*), therefore accelerating the hydrogen generation rate. NiO and Pt nanoclusters confined into the inherent pores of N-doped carbon derived from ZIF-8 (Pt/NiO/NPC) were designed to realize the structure of computational prediction and boost the alkaline hydrogen evolution. The optimal 1.5%Pt/NiO/NPC exhibited an excellent HER performance and stability with a low Tafel slope (only 22.5 mv dec-1) and an overpotential of 25.2 mV at 10 mA cm-2. Importantly, the 1.5%Pt/NiO/NPC possesses a mass activity of 17.37 A mg-1 at the overpotential of 20 mV, over 54 times higher than the benchmark 20 wt% Pt/C. Furthermore, DFT calculations illustrate that the Volmer-step could be accelerated owing to the high OH- attraction of NiO nanoclusters, leading to the Pt nanoclusters exhibiting a balance of H* adsorption and desorption (ΔGH* = -0.082 eV). Our findings provide new insights into breaking the water dissociation limit of Pt-based catalysts by coupling with a metal oxide.

Performance Regulation of Single-Atom Catalyst by Modulating the Microenvironment of Metal Sites

Metal-based catalysts, encompassing both homogeneous and heterogeneous types, play a vital role in the modern chemical industry. Heterogeneous metal-based catalysts usually possess more varied catalytically active centers than homogeneous catalysts, making it challenging to regulate their catalytic performance. In contrast, homogeneous catalysts have defined active-site structures, and their performance can be easily adjusted by modifying the ligand. These characteristics lead to remarkable conceptual and technical differences between homogeneous and heterogeneous catalysts. As a recently emerging class of catalytic material, single-atom catalysts (SACs) have become one of the most active new frontiers in the catalysis field and show great potential to bridge homogeneous and heterogeneous catalytic processes. This review documents a brief introduction to SACs and their role in a range of reactions involving single-atom catalysis. To fully understand process-structure-property relationships of single-atom catalysis in chemical reactions, active sites or coordination structure and performance regulation strategies (e.g., tuning chemical and physical environment of single atoms) of SACs are comprehensively summarized. Furthermore, we discuss the application limitations, development trends and future challenges of single-atom catalysis and present a perspective on further constructing a highly efficient (e.g., activity, selectivity and stability), single-atom catalytic system for a broader scope of reactions.

Location-selective immobilisation of single-atom catalysts on the surface or within the interior of ionic nanocrystals using coordination chemistry

Single-atom catalysts dispersed on support materials show excellent heterogeneous catalytic properties that can be tuned using the interactions between the single atoms and the support. Such interactions depend on whether the single atoms are located on the surface or within the interior of the support. However, little is known about immobilising single atoms on the surface or within the interior of supports deliberately and selectively. Herein, such location-selective placement of single atoms is achieved through the choice of metal complex precursor, solvent, and workup procedure. Using CdSe nanoplatelets as a support, a cis-[PtCl₂(SO(CH₃)₂)₂] precursor in an aprotic solvent exclusively attaches single Pt atoms on the surface of the support. In contrast, a [PtCl₄]^2- precursor in a protic solvent followed by amine treatment places 60% of the single Pt atoms inside the support by cation substitution. The surface-adsorbed single Pt atoms show higher stability in photocatalytic hydrogen evolution than the substituted ones, and the preclusion of substitution as internal Pt maximises the activity. Thus, this study provides a viable strategy for the structurally precise synthesis and design of single-atom catalysts.

High-Performance Alkali Metal Ion Storage in Bi2Se3 Enabled by Suppression of Polyselenide Shuttling Through Intrinsic Sb-Substitution Engineering

Bismuth selenide holds great promise as a kind of conversion-alloying-type anode material for alkali metal ion storage because of its layered structure with large interlayer spacing and high theoretical specific capacity. Nonetheless, its commercial development has been significantly hammered by the poor kinetics, severe pulverization, and polyselenide shuttle during the charge/discharge process. Herein, Sb-substitution and carbon encapsulation strategies are simultaneously employed to synthesize Sb_xBi_2-xSe₃ nanoparticles decorated on Ti₃C₂T_x MXene with encapsulation of N-doped carbon (Sb_xBi_2-xSe₃/MX⊂NC) as anodes for alkali metal ion storage. The superb electrochemical performances could be assigned to the cationic displacement of Sb³⁺ that effectively inhibits the shuttling effect of soluble polyselenides and the confinement engineering that alleviates the volume change during the sodiation/desodiation process. When used as anodes for sodium- and lithium-ion batteries, the Sb_0.4Bi_1.6Se₃/MX⊂NC composite exhibits superior electrochemical performances. This work offers valuable guidance to suppress the shuttling of polyselenides/polysulfides in high-performance alkali metal ion batteries with conversion/alloying-type transition metal sulfide/selenide anode materials.

Cobalt selenide with ordered cation vacancies for efficient oxygen reduction and frigostable Al-air batteries

Aluminum-air batteries are still inhibited by the sluggish cathodic oxygen reduction reactions, especially in low temperature conditions. Thus, it is urgent to develop efficient electrocatalysts for Al-air batteries to allow their use in extreme weather conditions. In this work, hexagonal Co0.85Se-decorated N,Se co-doped carbon nanofibers (Co0.85Se@N,Se-CNFs) were synthesized via facile carbonization/selenization of electrospun ZIF-67 nanocubes. The as-prepared metallic Co0.85Se with ordered structural cation vacancies endows Co0.85Se@N,Se-CNFs with remarkable oxygen reduction reaction activity, including high onset and half-wave potentials (0.93 V and 0.87 V vs. RHE, respectively). Consequently, the corresponding Al-air battery exhibits superior performance in a wide range of operating temperatures (-40-50 °C). For instance, this Al-air battery exhibits a voltage from 0.15-1.2 V with a peak power density of about 0.7 mW cm-2 at -40 °C. It is expected that TMSe-decorated N,Se co-doped carbon nanofibers could be applied in extensive energy fields.

Dynamic active-site induced by host-guest interactions boost the Fenton-like reaction for organic wastewater treatment

In heterogeneous catalysis, uncovering the dynamic evolution of active sites in the working conditions is crucial to realizing increased activity and enhanced stability of catalyst in Fenton-like activation. Herein, we capture the dynamic changes in the unit cell of Co/La-SrTiO₃ catalyst during the exemplary peroxymonosulfate activation process using X-ray absorption spectroscopy and in situ Raman spectroscopy, revealing the substrate tuned its structural evolution, which is the reversible stretching vibration of O-Sr-O and Co/Ti-O bonds in different orientations. This process effectively promotes the generation of key SO₅* intermediates, which is beneficial to the formation of ¹O₂ and SO₄^•- from persulfate on the Co active site. Density functional theory and X-ray absorption spectroscopy show that the optimized structural distortion enhanced the metal-oxygen bond strength by tuning the e_g orbitals and increased the number of transferred electrons to peroxymonosulfate by about 3-fold, achieving excellent efficiency and stability in removing organic pollutants.

Cascade Anchoring Strategy for Fabricating High-Loading Pt Single Atoms as Bifunctional Catalysts for Electrocatalytic Hydrogen Evolution and Oxygen Reduction Reactions

Carbon supports containing single-atomically dispersed metal-N_x (denoted as M_SAC-N_xC_y, x, y: coordination number) have attracted increasing attention due to their superb performance in heterogeneous catalysis. However, large-scale controllable preparation of single-atom catalysts (SACs) with high concentration of supported metal-N_x is still a big challenge because of the metal atom agglomeration during synthesis at high density and temperatures. Herein, we report a stepwise anchoring strategy from a 1,10-o-phenanthroline Pt chelate to an N_x-doped carbon (N_xC_y) with isolated Pt single-atom catalysts (Pt_SAC-N_xC_y) containing Pt loadings up to 5.31 wt % measured via energy-dispersive X-ray spectroscopy (EDS). The results show that 1,10-o-phenanthroline Pt chelate predominantly contributes to the formation of chelate single metal sites that bind tightly to platinum ions to prevent metal atoms from aggregating, resulting in high metal loading. The high-loading Pt_SAC-N_xC_y exhibits a low hydrogen evolution (HER) overpotential of 24 mV at 0.010 A cm^-2 current density with a relatively small Tafel gradient of 60.25 mV dec^-1 and excellent stable performance. In addition, the Pt_SAC-N_xC_y catalyst shows excellent oxygen reduction reaction (ORR) catalytic activity with good stability, represented by the fast ORR kinetics under high-potential conditions. Theoretical calculations show that Pt_SAC-NC₃ (x = 1, y = 3) offers a lower H₂O activation energy barrier than Pt nanoparticles. The adsorption free energy of a H atom on a Pt single-atom site is lower than that on a Pt cluster, which is easier for H₂ desorption. This study provides a potentially powerful cascade anchoring strategy in the design of other stable M_SAC-N_xC_y catalysts with high-density metal-N_x sites for the HER and ORR.

N, P co-doped Ni/Mo-based multicomponent electrocatalysts in situ decorated on Ni foam for overall water splitting

Developing the robust non-precious metal bifunctional electrocatalyst is highly imperative for the hydrogen evolution from overall water splitting. Herein, a Ni foam (NF)-supported ternary Ni/Mo bimetallic complex (Ni/Mo-TEC@NF), hierarchically constructed by coupling the in-situ formed MoNi₄ alloys and Ni₂Mo₃O₈ with Ni₃Mo₃C on NF, has been developed through a facile method involving the in-situ hydrothermal growth of the Ni-Mo oxides/polydopamine (NiMoO_x/PDA) complex on NF and a subsequent annealing in a reduction atmosphere. Synchronously, N and P atoms are co-doped into Ni/Mo-TEC during the annealing procedure using phosphomolybdic acid and PDA raw materials as P and N sources, respectively. The resultant N, P-Ni/Mo-TEC@NF shows outstanding electrocatalytic activities and tremendous stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), due to the multiple heterojunction effect-promoted electron transfer, the large number of exposed active sites, and the modulated electronic structure by the N and P co-doping. It only needs a low overpotential of 22 mV to afford the current density of 10 mA·cm^-2 for HER in alkaline electrolyte. More importantly, as the anode and cathode, it requires only 1.59 and 1.65 V to achieve 50 and 100 mA·cm^-2 for overall water splitting, respectively, comparable to the benchmark Pt/C@NF//RuO₂@NF couple. This work could spur the search for economical and efficient electrodes by in situ constructing multiple bimetallic components on 3D conductive substrates for practical hydrogen generation.

Electrosynthesis of chlorine from seawater-like solution through single-atom catalysts

The chlor-alkali process plays an essential and irreplaceable role in the modern chemical industry due to the wide-ranging applications of chlorine gas. However, the large overpotential and low selectivity of current chlorine evolution reaction (CER) electrocatalysts result in significant energy consumption during chlorine production. Herein, we report a highly active oxygen-coordinated ruthenium single-atom catalyst for the electrosynthesis of chlorine in seawater-like solutions. As a result, the as-prepared single-atom catalyst with Ru-O₄ moiety (Ru-O₄ SAM) exhibits an overpotential of only ~30 mV to achieve a current density of 10 mA cm^-2 in an acidic medium (pH = 1) containing 1 M NaCl. Impressively, the flow cell equipped with Ru-O₄ SAM electrode displays excellent stability and Cl₂ selectivity over 1000 h continuous electrocatalysis at a high current density of 1000 mA cm^-2. Operando characterizations and computational analysis reveal that compared with the benchmark RuO₂ electrode, chloride ions preferentially adsorb directly onto the surface of Ru atoms on Ru-O₄ SAM, thereby leading to a reduction in Gibbs free-energy barrier and an improvement in Cl₂ selectivity during CER. This finding not only offers fundamental insights into the mechanisms of electrocatalysis but also provides a promising avenue for the electrochemical synthesis of chlorine from seawater electrocatalysis.

Photothermal-enabled single-atom catalysts for high-efficiency hydrogen peroxide photosynthesis from natural seawater

Hydrogen peroxide (H₂O₂) is a powerful industrial oxidant and potential carbon-neutral liquid energy carrier. Sunlight-driven synthesis of H₂O₂ from the most earth-abundant O₂ and seawater is highly desirable. However, the solar-to-chemical efficiency of H₂O₂ synthesis in particulate photocatalysis systems is low. Here, we present a cooperative sunlight-driven photothermal-photocatalytic system based on cobalt single-atom supported on sulfur doped graphitic carbon nitride/reduced graphene oxide heterostructure (Co-CN@G) to boost H₂O₂ photosynthesis from natural seawater. By virtue of the photothermal effect and synergy between Co single atoms and the heterostructure, Co-CN@G enables a solar-to-chemical efficiency of more than 0.7% under simulated sunlight irradiation. Theoretical calculations verify that the single atoms combined with heterostructure significantly promote the charge separation, facilitate O₂ absorption and reduce the energy barriers for O₂ reduction and water oxidation, eventually boosting H₂O₂ photoproduction. The single-atom photothermal-photocatalytic materials may provide possibility of large-scale H₂O₂ production from inexhaustible seawater in a sustainable way.

Single-atomic platinum on fullerene C60 surfaces for accelerated alkaline hydrogen evolution

The electrocatalytic hydrogen evolution reaction (HER) is one of the most studied and promising processes for hydrogen fuel generation. Single-atom catalysts have been shown to exhibit ultra-high HER catalytic activity, but the harsh preparation conditions and the low single-atom loading hinder their practical applications. Furthermore, promoting hydrogen evolution reaction kinetics, especially in alkaline electrolytes, remains as an important challenge. Herein, Pt/C₆₀ catalysts with high-loading, high-dispersion single-atomic platinum anchored on C₆₀ are achieved through a room-temperature synthetic strategy. Pt/C₆₀-2 exhibits high HER catalytic performance with a low overpotential (η₁₀) of 25 mV at 10 mA cm^-2. Density functional theory calculations reveal that the Pt-C₆₀ polymeric structures in Pt/C₆₀-2 favors water adsorption, and the shell-like charge redistribution around the Pt-bonding region induced by the curved surfaces of two adjacent C₆₀ facilitates the desorption of hydrogen, thus favoring fast reaction kinetics for hydrogen evolution.

Dopant triggered atomic configuration activates water splitting to hydrogen

Finding highly efficient hydrogen evolution reaction (HER) catalysts is pertinent to the ultimate goal of transformation into a net-zero carbon emission society. The design principles for such HER catalysts lie in the well-known structure-property relationship, which guides the synthesis procedure that creates catalyst with target properties such as catalytic activity. Here we report a general strategy to synthesize 10 kinds of single-atom-doped CoSe₂-DETA (DETA = diethylenetriamine) nanobelts. By systematically analyzing these products, we demonstrate a volcano-shape correlation between HER activity and Co atomic configuration (ratio of Co-N bonds to Co-Se bonds). Specifically, Pb-CoSe₂-DETA catalyst reaches current density of 10 mA cm^-2 at 74 mV in acidic electrolyte (0.5 M H₂SO₄, pH ~0.35). This striking catalytic performance can be attributed to its optimized Co atomic configuration induced by single-atom doping.

Ambient Electrosynthesis toward Single-Atom Sites for Electrocatalytic Green Hydrogen Cycling

With the ultimate atomic utilization, well-defined configuration of active sites and unique electronic properties, catalysts with single-atom sites (SASs) exhibit appealing performance for electrocatalytic green hydrogen generation from water splitting and further utilization via hydrogen-oxygen fuel cells, such that a vast majority of synthetic strategies toward SAS-based catalysts (SASCs) are exploited. In particular, room-temperature electrosynthesis under atmospheric pressure offers a novel, safe, and effective route to access SASs. Herein, the recent progress in ambient electrosynthesis toward SASs for electrocatalytic sustainable hydrogen generation and utilization, and future opportunities are discussed. A systematic summary is started on three kinds of ambient electrochemically synthetic routes for SASs, including electrochemical etching (ECE), direct electrodeposition (DED), and electrochemical leaching-redeposition (ELR), associated with advanced characterization techniques. Next, their electrocatalytic applications for hydrogen energy conversion including hydrogen evolution reaction, oxygen evolution reaction, overall water splitting, and oxygen reduction reaction are reviewed. Finally, a brief conclusion and remarks on future challenges regarding further development of ambient electrosynthesis of high-performance and cost-effective SASCs for many other electrocatalytic applications are presented.

Ensemble Effect of Ruthenium Single-Atom and Nanoparticle Catalysts for Efficient Hydrogen Evolution in Neutral Media

Hydrogen evolution reaction (HER) plays a key role in electrochemical water splitting, which is a sustainable way for hydrogen production. The kinetics of HER is sluggish in neutral media that requires noble metal catalysts to alleviate energy consumption during the HER process. Here, we present a catalyst comprising a ruthenium single atom (Ru₁) and nanoparticle (Ru_n) loaded on the nitrogen-doped carbon substrate (Ru₁-Ru_n/CN), which exhibits excellent activity and superior durability for neutral HER. Benefiting from the synergistic effect between single atoms and nanoparticles in the Ru₁-Ru_n/CN, the catalyst exhibits a very low overpotential down to 32 mV at a current density of 10 mA cm^-2 while maintaining excellent stability up to 700 h at a current density of 20 mA cm^-2 during the long-term test. Computational calculations reveal that, in the Ru₁-Ru_n/CN catalyst, the existence of Ru nanoparticles affects the interactions between Ru single-atom sites and reactants and thus improves the catalytic activity of HER. This work highlights the ensemble effect of electrocatalysts for HER and could shed light on the rational design of efficient catalysts for other multistep electrochemical reactions.

Self-Tandem Electrocatalytic NO Reduction to NH3 on a W Single-Atom Catalyst

We design single-atom W confined in MoO_3-x amorphous nanosheets (W₁/MoO_3-x) comprising W₁-O₅ motifs as a highly active and durable NORR catalyst. Theoretical and operando spectroscopic investigations reveal the dual functions of W₁-O₅ motifs to (1) facilitate the activation and protonation of NO molecules and (2) promote H₂O dissociation while suppressing *H dimerization to increase the proton supply, eventually resulting in a self-tandem NORR mechanism of W₁/MoO_3-x to greatly accelerate the protonation energetics of the NO-to-NH₃ pathway. As a result, W₁/MoO_3-x exhibits the highest NH₃-Faradaic efficiency of 91.2% and NH₃ yield rate of 308.6 μmol h^-1 cm^-2, surpassing that of most previously reported NORR catalysts.