Strain Relaxation in Metal Alloy Catalysts Steers the Product Selectivity of Electrocatalytic CO2 Reduction

Tailoring competitive adsorption sites of hydroxide ion to enhance urea oxidation-assisted hydrogen production

Alloys with bimetallic electron modulation effect are promising catalysts for the electrooxidation of urea. However, the side reaction oxygen evolution reaction (OER) originating from the competitive adsorption of OH- and urea severely limited the urea oxidation reaction (UOR) activity on the alloy catalysts. This work successfully constructs the defect-rich NiCo alloy with lattice strain (PMo-NiCo/NF) by rapid pyrolysis and co-doping. By taking advantage of the compressive strain, the d-band center of NiCo is shifted downward, inhibiting OH- from adsorbing on the NiCo site and avoiding the detrimental OER. Meanwhile, the oxygenophilic P/Mo tailored specific adsorption sites to adsorb OH- preferentially, which further released the NiCo sites to ensure the enriched adsorption of urea, thus improving the UOR efficiency. As a result, PMo-NiCo/NF only requires 1.27 V and -57 mV to drive a current density of ±10 mA cm-2 for UOR and hydrogen evolution reaction (HER), respectively. With the guidance of this work, reactant competing adsorption sites could be tailored for effective electrocatalytic performance.

Bifunctional Catalysts for CO2 Reduction and O2 Evolution: A Pivotal for Aqueous Rechargeable Zn-CO2 Batteries

The quest for the advancement of green energy storage technologies and reduction of carbon footprint is determinedly rising toward carbon neutrality. Aqueous rechargeable Zn-CO2 batteries (ARZCBs) hold the great potential to encounter both the targets simultaneously, i.e., green energy storage and CO2 conversion to value-added chemicals/fuels. The major descriptor of ARZCBs efficiency is allied with the reactions occurring at cathode during discharging (CO2 reduction) and charging (O2 evolution) which own different fundamental mechanisms and hence mandate the employment of two different catalysts. This presents an overall complex and expensive battery system which requires a concrete solution, while the development and application of a bifunctional cathode catalyst toward both reactions could reduce the complexity and cost and thus can be a pivotal for ARZCBs. However, despite the increasing research interest and ongoing research, a systematic evaluation of bifunctional catalysts is rarely reported. In this review, the need of bifunctional cathode catalysts for ARZCBs and associated challenges with strategies have been critically assessed. A detailed progress examination and understanding toward designing of bifunctional catalyst for ARZCBs have been provided. This review will enlighten the future research approaching boosted performance of ARZCBs through the development of efficient bifunctional cathode catalysts.

In situ/Operando Synchrotron Radiation Analytical Techniques for CO2/CO Reduction Reaction: From Atomic Scales to Mesoscales

Electrocatalytic carbon dioxide/carbon monoxide reduction reaction (CO(2)RR) has emerged as a prospective and appealing strategy to realize carbon neutrality for manufacturing sustainable chemical products. Developing highly active electrocatalysts and stable devices has been demonstrated as effective approach to enhance the conversion efficiency of CO(2)RR. In order to rationally design electrocatalysts and devices, a comprehensive understanding of the intrinsic structure evolution within catalysts and micro-environment change around electrode interface, particularly under operation conditions, is indispensable. Synchrotron radiation has been recognized as a versatile characterization platform, garnering widespread attention owing to its high brightness, elevated flux, excellent directivity, strong polarization and exceptional stability. This review systematically introduces the applications of synchrotron radiation technologies classified by radiation sources with varying wavelengths in CO(2)RR. By virtue of in situ/operando synchrotron radiationanalytical techniques, we also summarize relevant dynamic evolution processes from electronic structure, atomic configuration, molecular adsorption, crystal lattice and devices, spanning scales from the angstrom to the micrometer. The merits and limitations of diverse synchrotron characterization techniques are summarized, and their applicable scenarios in CO(2)RR are further presented. On the basis of the state-of-the-art fourth-generation synchrotron facilities, a perspective for further deeper understanding of the CO(2)RR process using synchrotron radiation analytical techniques is proposed.

Regulating the Critical Intermediates of Dual-Atom Catalysts for CO2 Electroreduction

Electrocatalysis is a very attractive way to achieve a sustainable carbon cycle by converting CO2 into organic fuels and feedstocks. Therefore, it is crucial to design advanced electrocatalysts by understanding the reaction mechanism of electrochemical CO2 reduction reaction (eCO2RR) with multiple electron transfers. Among electrocatalysts, dual-atom catalysts (DACs) are promising candidates due to their distinct electronic structures and extremely high atomic utilization efficiency. Herein, the eCO2RR mechanism and the identification of intermediates using advanced characterization techniques, with a particular focus on regulating the critical intermediates are systematically summarized. Further, the insightful understanding of the functionality of DACs originates from the variable metrics of electronic structures including orbital structure, charge distribution, and electron spin state, which influences the active sites and critical intermediates in eCO2RR processes. Based on the intrinsic relationship between variable metrics and critical intermediates, the optimized strategies of DACs are summarized containing the participation of synergistic atoms, engineering of the atomic coordination environment, regulation of the diversity of central metal atoms, and modulation of metal-support interaction. Finally, the challenges and future opportunities of atomically dispersed catalysts for eCO2RR processes are discussed.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Rare-earth Element-based Electrocatalysts Designed for CO2 Electro-reduction

Electrochemical CO2 reduction presents a promising approach for synthesizing fuels and chemical feedstocks using renewable energy sources. Although significant advancements have been made in the design of catalysts for CO2 reduction reaction (CO2RR) in recent years, the linear scaling relationship of key intermediates, selectivity, stability, and economical efficiency are still required to be improved. Rare earth (RE) elements, recognized as pivotal components in various industrial applications, have been widely used in catalysis due to their unique properties such as redox characteristics, orbital structure, oxygen affinity, large ion radius, and electronic configuration. Furthermore, RE elements could effectively modulate the adsorption strength of intermediates and provide abundant metal active sites for CO2RR. Despite their potential, there is still a shortage of comprehensive and systematic analysis of RE elements employed in the design of electrocatalysts of CO2RR. Therefore, the current approaches for the design of RE element-based electrocatalysts and their applications in CO2RR are thoroughly summarized in this review. The review starts by outlining the characteristics of CO2RR and RE elements, followed by a summary of design strategies and synthetic methods for RE element-based electrocatalysts. Finally, an overview of current limitations in research and an outline of the prospects for future investigations are proposed.

Strongly Coupled Ag/Sn-SnO2 Nanosheets Toward CO2 Electroreduction to Pure HCOOH Solutions at Ampere-Level Current

Electrocatalytic reduction of CO2 converts intermittent renewable electricity into value-added liquid products with an enticing prospect, but its practical application is hampered due to the lack of high-performance electrocatalysts. Herein, we elaborately design and develop strongly coupled nanosheets composed of Ag nanoparticles and Sn-SnO2 grains, designated as Ag/Sn-SnO2 nanosheets (NSs), which possess optimized electronic structure, high electrical conductivity, and more accessible sites. As a result, such a catalyst exhibits unprecedented catalytic performance toward CO2-to-formate conversion with near-unity faradaic efficiency (≥ 90%), ultrahigh partial current density (2,000 mA cm-2), and superior long-term stability (200 mA cm-2, 200 h), surpassing the reported catalysts of CO2 electroreduction to formate. Additionally, in situ attenuated total reflection-infrared spectra combined with theoretical calculations revealed that electron-enriched Sn sites on Ag/Sn-SnO2 NSs not only promote the formation of *OCHO and alleviate the energy barriers of *OCHO to *HCOOH, but also impede the desorption of H*. Notably, the Ag/Sn-SnO2 NSs as the cathode in a membrane electrode assembly with porous solid electrolyte layer reactor can continuously produce ~ 0.12 M pure HCOOH solution at 100 mA cm-2 over 200 h. This work may inspire further development of advanced electrocatalysts and innovative device systems for promoting practical application of producing liquid fuels from CO2.

Chlorine-Coordinated Unsaturated Ni-N2 Sites for Efficient Electrochemical Carbon Dioxide Reduction

Heteroatom-doping is an effective method for modifying the geometric symmetry of metal-nitrogen-carbon (M-N-C) single-atom catalysts and thereby tuning the electronic structure. Up to now, most of the current reports have concentrated on introducing heteroatoms into the highly symmetrical M-N4 structure. The coordination-unsaturated M-N2 structure is more sterically favorable for the insertion of alien atoms to optimize the electronic structure. Herein, a Ni-N2 catalyst with out-of-plane coordinated chlorine (Cl) atoms (Ni-N2 Cl/C) is successfully constructed on chlorine-functionalized carbon supports (C-Cl) for an efficient carbon dioxide reduction reaction (CO2 RR). Density functional theory calculations demonstrate that the prepared Ni-N2 Cl/C catalyst exhibits a higher capability in balancing COOH* formation and CO* desorption. In addition, in situ Raman spectra confirm that the lower CO binding energy on the Ni-N2 Cl/C facilitates CO escape, leading to excellent CO2 RR performance. A high CO Faradaic efficiency (FECO ) of more than 80% is achieved from -0.6 to -1.2 V versus reversible hydrogen electrode on the Ni-N2 Cl/C and it exhibits negligible FECO and current declination over a 40-h stability test. Furthermore, a high turnover frequency (TOF) value of 15 808 h-1 is obtained, which is more than ten times that of Ni-N2 /C (1476 h-1 ) without coordinated Cl atoms.

Insights into the mechanism in electrochemical CO2 reduction over single-atom copper alloy catalysts: A DFT study

Copper single-atom alloy catalysts (M@Cu SAAs) have shown great promise for electrochemical CO2 reduction reaction (CO2RR). However, a clear understanding of the CO2RR process on M@Cu SAAs is still lacking. This study uses density functional theoretical (DFT) calculations to obtain a comprehensive mechanism and the origin of activity of M@Cu SAAs. The importance of the adsorption mode of M@Cu is revealed: key intermediates either adsorbed in the adjacent hollow site around Cu atoms (AD mode) or adsorbed directly on the top site of M (SE mode). AD mode generally exhibits finely tuned binding strengths of key intermediates, which significantly enhances the activity of the catalysts. Increasing the coverage of ∗CO on the M@Cu with SE mode leads to relocation of the active site, resulting in improved activity of C2 products. The insights gained in this work have significant implications for rational design strategy toward efficient CO2RR electrocatalysts.

Lattice Compression Revealed at the ≈1 nm Scale

Lattice tuning at the ≈1 nm scale is fascinating and challenging; for instance, lattice compression at such a minuscule scale has not been observed. The lattice compression might also bring about some unusual properties, which waits to be verified. Through ligand induction, we herein achieve the lattice compression in a ≈1 nm gold nanocluster for the first time, as detected by the single-crystal X-ray crystallography. In a freshly synthesized Au52 (CHT)28 (CHT=S-c-C6 H11 ) nanocluster, the lattice distance of the (110) facet is found to be compressed from 4.51 to 3.58 Å at the near end. However, the lattice distances of the (111) and (100) facets show no change in different positions. The lattice-compressed nanocluster exhibits superior electrocatalytic activity for the CO2 reduction reaction (CO2 RR) compared to that exhibited by the same-sized Au52 (TBBT)32 (TBBT=4-tert-butyl-benzenethiolate) nanocluster and larger Au nanocrystals without lattice variation, indicating that lattice tuning is an efficient method for tailoring the properties of metal nanoclusters. Further theoretical calculations explain the high CO2 RR performance of the lattice-compressed Au52 (CHT)28 and provide a correlation between its structure and catalytic activity.

Lattice-Strain Engineering for Heterogenous Electrocatalytic Oxygen Evolution Reaction

The energy efficiency of metal-air batteries and water-splitting techniques is severely constrained by multiple electronic transfers in the heterogenous oxygen evolution reaction (OER), and the high overpotential induced by the sluggish kinetics has become an uppermost scientific challenge. Numerous attempts are devoted to enabling high activity, selectivity, and stability via tailoring the surface physicochemical properties of nanocatalysts. Lattice-strain engineering as a cutting-edge method for tuning the electronic and geometric configuration of metal sites plays a pivotal role in regulating the interaction of catalytic surfaces with adsorbate molecules. By defining the d-band center as a descriptor of the structure-activity relationship, the individual contribution of strain effects within state-of-the-art electrocatalysts can be systematically elucidated in the OER optimization mechanism. In this review, the fundamentals of the OER and the advancements of strain-catalysts are showcased and the innovative trigger strategies are enumerated, with particular emphasis on the feedback mechanism between the precise regulation of lattice-strain and optimal activity. Subsequently, the modulation of electrocatalysts with various attributes is categorized and the impediments encountered in the practicalization of strained effect are discussed, ending with an outlook on future research directions for this burgeoning field.

Tuning the Coordination Environment of Carbon-Based Single-Atom Catalysts via Doping with Multiple Heteroatoms and Their Applications in Electrocatalysis

Carbon-based single-atom catalysts (SACs) are considered to be a perfect platform for studying the structure-activity relationship of different reactions due to the adjustability of their coordination environment. Multi-heteroatom doping has been demonstrated as an effective strategy for tuning the coordination environment of carbon-based SACs and enhancing catalytic performance in electrochemical reactions. Herein, recently developed strategies for multi-heteroatom doping, focusing on the regulation of single-atom active sites by heteroatoms in different coordination shells, are summarized. In addition, the correlation between the coordination environment and the catalytic activity of carbon-based SACs are investigated through representative experiments and theoretical calculations for various electrochemical reactions. Finally, concerning certain shortcomings of the current strategies of doping multi-heteroatoms, some suggestions are put forward to promote the development of carbon-based SACs in the field of electrocatalysis.

Competitive Trapping of Single Atoms onto a Metal Carbide Surface

Controlling atomic adjustment of single-atom catalysts (SACs) can directly change its local configuration, regulate the energy barrier of intermediates, and further optimize reaction pathways. Herein, we report an atom manipulating process to synthesize Ni atoms stabilized on vanadium carbide (Ni_SA-VC) through a nanofiber-medium thermodynamically driven atomic migration strategy. Experimental and theoretical results systematically reveal the tunable migration pathway of Ni atom from Ni nanoparticles to neighboring N-doped carbon (NC) and finally to metal carbide that was obtained by regulating the competitive adsorption energies between VC and NC for capturing Ni atoms. For CO₂-to-CO electroreduction, Ni_SA-VC exhibits an industrial current density of -180 mA cm^-2 at -1.0 V vs reversible hydrogen electrode and the highest Faradaic efficiency for CO production (FE_CO) of 96.8% at -0.4 V vs RHE in a flow cell. Significant electron transfers occurring in Ni_SA-VC structures contribute to the activation of CO₂, facilitate the reaction free energy, regulate *CO desorption as the rate-determining step, and promote the activity and selectivity. This study provides an understanding on how to design powerful SACs for electrocatalysis.

Engineering the Electronic Interaction between Atomically Dispersed Fe and RuO2 Attaining High Catalytic Activity and Durability Catalyst for Li-O2 Battery

It is significant to develop catalysts with high catalytic activity and durability to improve the electrochemical performances of lithium-oxygen batteries (LOBs). While electronic metal-support interaction (EMSI) between metal atoms and support has shown great potential in catalytic field. Hence, to effectively improve the electrochemical performance of LOBs, atomically dispersed Fe modified RuO₂ nanoparticles are designed to be loaded on hierarchical porous carbon shells (Fe_SA -RuO₂ /HPCS) based on EMSI criterion. It is revealed that the Ru-O-Fe₁ structure is formed between the atomically dispersed Fe atoms and the surrounding Ru sites through electron interaction, and this structure could act as the ultra-high activity driving force center of oxygen reduction/evolution reaction (ORR/OER). Specifically, the Ru-O-Fe₁ structure enhances the reaction kinetics of ORR to a certain extent, and optimizes the morphology of discharge products by reducing the adsorption energy of catalyst for O₂ and LiO₂ ; while during the OER process, the Ru-O-Fe₁ structure not only greatly enhances the reaction kinetics of OER, but also catalyzes the efficient decomposition of the discharge products Li₂ O₂ by the favorable electron transfer between the active sites and the discharge products. Hence, LOBs based on FeSA-RuO₂ /HPCS cathodes show an ultra-low over-potential, high discharge capacity and superior durability.

Metal-Organic Frameworks as Electrocatalysts

Transition metal complexes are well-known homogeneous electrocatalysts. In this regard, metal-organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF-derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

Revealing the stochastic kinetics evolution of photocatalytic CO2 reduction

Investigating kinetic mechanisms to design efficient photocatalysts is critical for improving photocatalytic CO₂ reduction, but the stochastic photo-physical/chemical properties of kinetics remain unclear. Herein, we propose a statistical study to discuss the stochastic feature evolution of photocatalytic systems. The uncertainties of light absorption, charge carrier migration, and surface reaction are described by nonparametric estimation methods in the proposed model, which includes the effect of operational and material parameters. The density distribution of surface electrons shifts from a skewed distribution to an approximate uniform distribution as incident photon density increases. The system temperature rising induces the rate-determining step of surface reactions to change from charge carrier kinetics to reactant activation processes. Benefiting from the synergistic optimization between the operational parameter and active site density, the electron-capturing probability of active sites is boosted from 0.06 to 0.17. The modified reaction kinetic equation is constructed based on the distribution function of charge carrier kinetics. Furthermore, the experimental photoactivity results are consistent with the statistical analysis, which proves the feasibility of the established model. The characterization tests show that the gap between testing activities and theoretical efficiency is caused by a mismatch between charge carrier supply and mass transfer. Our work unveils the stochastic features in photocatalytic CO₂ reduction, offering a comprehensive analytical framework for photocatalytic system optimization.

Designing a Built-In Electric Field for Efficient Energy Electrocatalysis

To utilize intermittent renewable energy as well as achieve the goals of peak carbon dioxide emissions and carbon neutrality, various electrocatalytic devices have been developed. However, the electrocatalytic reactions, e.g., hydrogen evolution reaction/oxygen evolution reaction in overall water splitting, polysulfide conversion in lithium-sulfur batteries, formation/decomposition of lithium peroxide in lithium-oxygen batteries, and nitrate reduction reaction to degrade sewage, suffer from sluggish kinetics caused by multielectron transfer processes. Owing to the merits of accelerated charge transport, optimized adsorption/desorption of intermediates, raised conductivity, regulation of the reaction microenvironment, as well as ease to combine with geometric characteristics, the built-in electric field (BIEF) is expected to overcome the above problems. Here, we give a Review about the very recent progress of BIEF for efficient energy electrocatalysis. First, the construction strategies and the characterization methods (qualitative and quantitative analysis) of BIEF are summarized. Then, the up-to-date overviews of BIEF engineering in electrocatalysis, with attention on the electron structure optimization and reaction microenvironment modulation, are analyzed and discussed in detail. In the end, the challenges and perspectives of BIEF engineering are proposed. This Review gives a deep understanding on the design of electrocatalysts with BIEF for next-generation energy storage and electrocatalytic devices.

Engineering the degree of concavity of one-dimensional Au-Cu alloy nanorods with partial intermetallic compounds by facile wet chemical synthesis

Finely modulating the morphology of bimetallic nanomaterials plays a vital role in enhancing their catalytic activities. Among the various morphologies, concave structures have received considerable attention due to the three advantageous features of high-index facets, high surface areas, and high curvatures, which contribute greatly to enhancing the catalytic performance. However, concave morphologies are not the products generated from thermodynamically controlled growth with minimized surface energy. Additionally, most nanocrystals with concave shapes are currently in the state of mono-metals or alloys with disordered arrangements of atoms. The synthesis of alloy structures with ordered atom arrangements, intermetallic compounds, which tend to display superior catalytic performance on account of their optimal geometric and electronic effects, has rarely been reported as high-temperature annealing is usually needed, which constrains the modulation of morphology and surface structure. In this work, concave one-dimensional Au-Cu nanorods with a partially ordered intermetallic structure were synthesized via a facile wet chemical method. By simply adjusting the reaction kinetics via the concentrations of the corresponding metal precursors, the degree of concavity of the one-dimensional Au-Cu nanorods could be regulated. In both the p-nitrophenol reduction and CO₂ electro-reduction reactions, the concave-shaped Au-Cu nanorods demonstrated superior catalytic activity compared to corresponding non-concave samples with the same structure due to the morphological advantages provided by the concave structure.

Defective CuO-rich CuFe2O4 nanofibers enable the efficient synergistic electrochemical reduction of nitrate to ammonia

CuO-rich CuFe2O4 nanofibers with oxygen vacancies as a NO3−RR catalyst achieve a high Faradaic efficiency of 91.08% and a large NH3 yield of 9296.21 μg h−1 cm−2 at −1.0 V vs. RHE in 0.1 M PBS with 0.1 M NO3−.

Co doped MoS2 nanosheet: a stable and pH-universal electrocatalyst for efficient hydrogen evolution reaction

Generally, the hydrogen generation of non-noble metal based electrocatalysts is limited by the high overpotential and acid-base environment of electrolyte. Therefore, it is essential to develop hydrogen evolution reaction (HER)...

Facile synthesis of a novel 0D/2D CdS/Bi4TaO8Br heterojunction for enhanced photocatalytic tetracycline hydrochloride degradation under visible light

A novel visible light-responsive 0D/2D CdS/Bi4TaO8Br nanocomposite photocatalyst with enhanced activity was synthesized by the in situ deposition of CdS quantum dots (QDs) on the surface of 2D Bi4TaO8Br nanoplates.

An electrochemical modification strategy to fabricate NiFeCuPt polymetallic carbon matrices on nickel foam as stable electrocatalysts for water splitting

Electrochemical modification is a mild and economical way to prepare electrocatalytic materials with abundant active sites and high atom efficiency. In this work, a stable NiFeCuPt carbon matrix deposited on nickel foam (NFFeCuPt) was fabricated with an extremely low Pt load (∼28 μg cm⁻²) using one-step electrochemical co-deposition modification, and it serves as a bifunctional catalyst for overall water splitting and achieves 100 mA cm⁻² current density at a low cell voltage of 1.54 V in acidic solution and 1.63 V in alkaline solution, respectively. In addition, a novel electrolyte was developed to stabilize the catalyst under acidic conditions, which provides inspiration for the development of highly efficient, highly stable, and cost-effective ways to synthesize electrocatalysts.

Multiple metal elements immobilized into a carbon matrix to fabricate an ultra-stable water splitting electrocatalyst by one-step electrochemical modification.