Breaking scaling relations for efficient CO2 electrochemical reduction through dual-atom catalysts

Secondary Coordination Effects of Adjacent Metal Center in Metal-Nitrogen-Carbon Improve Scaling Relation of Oxygen Electrocatalysis

Heterogenous single-atom catalysts (SACs) are reminiscent of homogeneous catalysts because of the similarity of structural motif of active sites, showing the potential of using the advantage of homogeneous catalysts to tackle challenges in hetereogenous catalysis. In heterogeneous oxygen electrocatalysis, the homogeneity of adsorption patterns of reaction intermediates leads to scaling relationships that limit their activities. In contrast, homogeneous catalysts can circumvent such limits by selectively altering the adsorption of intermediates through secondary coordination effects (SCEs). This inspired us to explore potential SCEs in metal-nitrogen-carbon (M-N-C), a promising type of oxygen evolution electrocatalyst. We introduced SCEs with a neighboring metal site that can modulate the adsorption strengths of oxygen-containing intermediates. First-principles calculations show that the second site in the heteronuclear duo four-nitrogen-coordinated metal center can induce SCEs that selectively stabilize the OOH intermediate but with minor effects on the OH intermediate and, thereby, disrupt the scaling relation between oxygen species and eventually increase the catalytic activity in oxygen evolution reactions. Additionally, the activity of oxygen reduction reaction of selected M-N-C is also enhanced by such SCE. Our computational work underscored the critical role SCEs can have in shaping activities of SACs, particularly in favorably altering scaling relationships, and demonstrated its potential to address catalytic challenges in heterogeneous catalysis.

Strategies for Achieving Carbon Neutrality: Dual-Atom Catalysts in Focus

Carbon neutrality is a fundamental strategy for achieving the sustainable development of human society. Catalyzing CO2 reduction into various high-value-added fuels serves as an effective pathway to achieve this strategic objective. Atom-dispersed catalysts have received extensive attention due to their maximum atomic utilization, high catalytic selectivity, and exceptional catalytic performance. Dual-atom catalysts (DACs), as an extension of single-atom catalysts (SACs), not only retain the advantages of SACs, but also produce many new properties. This review initiates its exploration by elucidating the mechanism of CO2 reduction reaction (CO2RR) from CO2 adsorption and CO2 activation. Then, a comprehensive summary of recently developed preparation methods of DACs is presented. Importantly, the mechanisms underlying the promoted catalytic performance of DACs in comparison to SACs are subjected to a comprehensive analysis from adjustable adsorption capacity, tunable electronic structure, strong synergistic effect, and enhanced spacing effect, elucidating their respective superiorities in CO2RR. Subsequently, the application of DACs in CO2RR is discussed in detail. Conclusively, the prospective trajectories and inherent challenges of CO2RR are expounded upon concerning the continued advancement of DACs. This thorough review not only enhances the comprehension of DACs within CO2RR but also accentuates the prospective developments in the design of sophisticated catalytic materials.

Experimental and Theoretical Insights into Single Atoms, Dual Atoms, and Sub-Nanocluster Catalysts for Electrochemical CO2 Reduction (CO2RR) to High-Value Products

Electrocatalytic carbon dioxide (CO2) conversion into valuable chemicals paves the way for the realization of carbon recycling. Downsizing catalysts to single-atom catalysts (SACs), dual-atom catalysts (DACs), and sub-nanocluster catalysts (SNCCs) has generated highly active and selective CO2 transformation into highly reduced products. This is due to the introduction of numerous active sites, highly unsaturated coordination environments, efficient atom utilization, and confinement effect compared to their nanoparticle counterparts. Herein, recent Cu-based SACs are first reviewed and the newly emerged DACs and SNCCs expanding the catalysis of SACs to electrocatalytic CO2 reduction (CO2RR) to high-value products are discussed. Tandem Cu-based SAC-nanocatalysts (NCs) (SAC-NCs) are also discussed for the CO2RR to high-value products. Then, the non-Cu-based SACs, DACs, SAC-NCs, and SNCCs and theoretical calculations of various transition-metal catalysts for CO2RR to high-value products are summarized. Compared to previous achievements of less-reduced products, this review focuses on the double objective of achieving full CO2 reduction and increasing the selectivity and formation rate toward C-C coupled products with additional emphasis on the stability of the catalysts. Finally, through combined theoretical and experimental research, future outlooks are offered to further develop the CO2RR into high-value products over isolated atoms and sub-nanometal clusters.

Towards superior CO2RR catalysts: Deciphering the selectivity puzzle over dual-atom catalyst

The electrocatalytic CO2 reduction reaction (CO2RR) is one of the most important electrocatalytic reactions. Starting from a well-defined *CO intermediate, the CO2RR can bifurcate into two pathways, either forming a hydrogenation product by *CO bond hydrogenation or leading to CO desorption by *C bond cleavage. However, it is perplexing why many dual-atom catalysts (DACs) exhibit high CO selectivity in experiments, despite previous theoretical studies arguing that the *CO bond hydrogenation is thermodynamically more favorable than the *C bond breaking. Furthermore, the selectivity is contingent upon the potential and is perturbed by the hydrogen evolution reaction (HER), which is far from clear. Using ab initio molecular dynamics and a "slow-growth" sampling method to evaluate the potential-dependent kinetics, we uncover the selectivity origin of CO2RR to CO on a typical NC-based DAC (CuFe-N6-C). Importantly, the results show that at higher CO* coverage, CO* desorption kinetics are accelerated, while the competing *CO bond hydrogenation reaction is inhibited at varying potentials. Furthermore, the selectivity of the HER is observed to increase as the potential decreases. However, at higher CO* coverage, the energy barrier for the *C bond cleavage is lower than that for HER, suggesting that HER is suppressed on CuFe-N6-C. Our work unlocks a long-standing puzzle about the selectivity of important DAC catalysts for CO2RR and provides insights for more effective catalyst design.

Single and dual-atom catalysts towards electrosynthesis of ammonia and urea: a review

Ammonia and urea represent two important chemicals that have contributed to the rapid development of humanity. However, their industrial production requires harsh conditions, consuming excessive energy and resulting in significant greenhouse gas emission. Therefore, there is growing interest in the electrocatalytic synthesis of ammonia and urea as it can be carried out under ambient conditions. Recently, atomic catalysts (ACs) have gained increased attention for their superior catalytic properties, being able to outperform their micro and nano counterparts. This review examines the advantages and disadvantages of ACs and summarises the advancement of ACs in the electrocatalytic synthesis of ammonia and urea. The focus is on two types of AC - single-atom catalysts (SACs) and diatom catalysts (DACs). SACs offer various advantages, including the 100% atom utilization that allows for low material mass loading, suppression of competitive reactions such as hydrogen evolution reaction (HER), and alternative reaction pathways allowing for efficient synthesis of ammonia and urea. DACs inherit these advantages, possessing further benefits of synergistic effects between the two catalytic centers at close proximity, particularly matching the NN bond for N2 reduction and boosting C-N coupling for urea synthesis. DACs also possess the ability to break the linear scaling relation of adsorption energy of reactants and intermediates, allowing for tuning of intermediate adsorption energies. Finally, possible future research directions using ACs are proposed.

Rigidly Axial O Coordination-Induced Spin Polarization on Single Ni-N4-C Site by MXene Coupling for Boosting Electrochemical CO2 Reduction to CO

Regulating the spin states in transition-metal (TM)-based single-atom catalysts (SACs), such as the TM-Nx-C configurations, is crucial for improving the catalytic activity. However, the role of spin in single Ni atoms facilitating the electrochemical CO2 reduction reaction (CO2RR) has been largely overlooked. Using first-principles simulations, we investigated the electrocatalytic performance of Ni-N4-C SACs vertically stacked on the O-terminated MXene nanosheets for the CO2RR. The terminated O atoms on MXene axially interact with the Ni atom due to significant charge transfer between them. Unlike the pure Ni-N4 site, which lacks spin polarization, the newly formed Ni-N4O configuration breaks the spin degeneracy of Ni d orbitals, dramatically lifting the energy level of spin-down d orbitals relative to that of spin-up d orbitals. As a result, the d electrons of Ni in the two spin channels are rearranged, leading to large net spin moments of 1.4 μB. Compared to the Ni-N4 site, the partially filled minority-spin dz2 orbitals of Ni on Ni-N4O weaken the occupied d-π* orbitals between Ni and *COOH, significantly stabilizing the key intermediate. The detailed reaction mechanisms and energetics show that four MXenes, namely, Hf3C2, Zr3C2, Hf2C, and Zr2C, can induce a large spin on the Ni site, thereby improving catalytic activity for CO2 reduction to CO, with a lower onset potential of about -0.75 V vs SHE compared to pure Ni SACs (-1.17 V) according to the potential-constant model with an explicit solvent environment.

Asymmetric Microenvironment Tailoring Strategies of Atomically Dispersed Dual-Site Catalysts for Oxygen Reduction and CO2 Reduction Reactions

Dual-atom catalysts (DACs) with atomically dispersed dual-sites, as an extension of single-atom catalysts (SACs), have recently become a new hot topic in heterogeneous catalysis due to their maximized atom efficiency and dual-site diverse synergy, because the synergistic diversity of dual-sites achieved by asymmetric microenvironment tailoring can efficiently boost the catalytic activity by optimizing the electronic structure of DACs. Here, this work first summarizes the frequently-used experimental synthesis and characterization methods of DACs. Then, four synergistic catalytic mechanisms (cascade mechanism, assistance mechanism, co-adsorption mechanism and bifunction mechanism) and four key modulating methods (active site asymmetric strategy, transverse/axial-modification engineering, distance engineering and strain engineering) are elaborated comprehensively. The emphasis is placed on the effects of asymmetric microenvironment of DACs on oxygen/carbon dioxide reduction reaction. Finally, some perspectives and outlooks are also addressed. In short, the review summarizes a useful asymmetric microenvironment tailoring strategy to speed up synthesis of high-performance electrocatalysts for different reactions.

Nonbonding Metal-Metal Interaction in Metal-Nitrogen-Carbon Single-Atom Catalysts Boosts CO Electroreduction

Metal-nitrogen-carbon single-atom catalysts (SACs) have recently emerged as selective electrocatalysts for the reduction of CO2 to CO, but their ability to further electroreduce CO is poor. Here, based on constant-potential density functional theory simulations, we predict that Co-N-M (M = Fe, Co) SACs with nonbonding metallic centers bridged by a common nitrogen atom can catalyze four-electron reduction of CO to methanol at an ultralow overpotential of 220-310 mV. We show that the metal atoms in the SACs are terminated by H species which prevent the formation of σ bonding between CO and the metal atoms. Thanks to the nonbonding electrostatic repulsion between Co and its adjacent M atom, the Co dxz band is broadened and shifted toward the Fermi level, leading to enhanced dxz - 2π* interaction that gives rise to stable CO adsorption and promotes its active and selective reduction. This work offers an alternative strategy to tackle the challenge of CO electroreduction on SACs and highlights the role of nonbonding metal-metal interactions in modulating adsorption properties of SACs.

Bimetallic Single-Atom Catalysts for Water Splitting

Green hydrogen from water splitting has emerged as a critical energy vector with the potential to spearhead the global transition to a fossil fuel-independent society. The field of catalysis has been revolutionized by single-atom catalysts (SACs), which exhibit unique and intricate interactions between atomically dispersed metal atoms and their supports. Recently, bimetallic SACs (bimSACs) have garnered significant attention for leveraging the synergistic functions of two metal ions coordinated on appropriately designed supports. BimSACs offer an avenue for rich metal-metal and metal-support cooperativity, potentially addressing current limitations of SACs in effectively furnishing transformations which involve synchronous proton-electron exchanges, substrate activation with reversible redox cycles, simultaneous multi-electron transfer, regulation of spin states, tuning of electronic properties, and cyclic transition states with low activation energies. This review aims to encapsulate the growing advancements in bimSACs, with an emphasis on their pivotal role in hydrogen generation via water splitting. We subsequently delve into advanced experimental methodologies for the elaborate characterization of SACs, elucidate their electronic properties, and discuss their local coordination environment. Overall, we present comprehensive discussion on the deployment of bimSACs in both hydrogen evolution reaction and oxygen evolution reaction, the two half-reactions of the water electrolysis process.

Novel Strategy for Efficient Recovery of CuO-Based Multiple-Metals from Copper Smelter Dust toward CO2 Electrocatalytic Reduction

Copper smelter dust, a typical hazardous waste that is abundant in valuable heavy metals, holds the potential to be regarded as a promising resource. This study introduces a new approach that integrates chlorination roasting and cascade condensation to efficiently recover heavy metals from copper smelter dust. The findings demonstrate the successful separation of heavy metals (Cu, Pb, and Zn) as chlorides at nearly 100% efficiency while also effectively converting trivalent arsenic (As(III)) into pentavalent arsenic (As(V)) and immobilizing it in the roasting residues, thereby reducing environmental risk. Through the utilization of thermogravimetric mass spectrum analysis and thermodynamic equilibrium calculations, the chlorination process for heavy metals was investigated, revealing both direct and indirect chlorination processes. Additionally, the study resulted in the development of a CuO-based multiple-metals electrocatalyst from the oxidized roasting-recovered heavy metal chlorides, exhibiting significantly enhanced catalytic activity and faradaic efficiency for the electroreduction of CO2 into CO and CH4 compared to pure CuO electrocatalyst under similar electrocatalytic conditions. Overall, this work presents a sustainable and scalable method and new insights for addressing environmental risks while repurposing copper smelter dust.

A General Metal Ion Recognition Strategy to Mediate Dual-Atomic-Site Catalysts

Heterogeneous dual-atomic-site catalysts (DACs) hold great potential for diverse applications. However, to date, the synthesis of DACs primarily relies on different atoms freely colliding on the support during synthesis, principally leading to low yields. Herein, we report a general metal ion recognition (MIR) strategy for constructing a series of DACs, including but not limited to Fe1Sn1, Fe1Co1, Fe1Ni1, Fe1Cu1, Fe1Mn1, Co1Ni1, Co1Cu1, Co2, and Cu2. This strategy is achieved by coupling target inorganometallic cations and anions as ion pairs, which are sequentially adsorbed onto a nitrogen-doped carbon substrate as the precursor. Taking the oxygen reduction reaction as an example, we demonstrated that the Fe1Sn1-DAC synthesized through this strategy delivers a record peak power density of 1.218 W cm-2 under 2.0 bar H2-O2 conditions and enhanced stability compared to the single-atom-site FeN4. Further study revealed that the superior performance arises from the synergistic effect of Fe1Sn1 dual vicinal sites, which effectively optimizes the adsorption of *OH and alleviates the troublesome Fenton-like reaction.

Surface Oxygen Defect Engineering of A2B2O7 Pyrochlore Semiconductors Boosts the Electrocatalytic Reduction of CO2-to-HCOOH

The electrocatalytic conversion of inert CO2 to value-added chemical fuels powered by renewable energy is one of the benchmark approaches to address excessive carbon emissions and achieve carbon-neutral energy restructuring. However, the adsorption/activation of supersymmetric CO2 is facing insurmountable challenges that constrain its industrial-scale applications. Here, this theory-guided study confronts these challenges by leveraging the synergies of bimetallic sites and defect engineering, where pyrochlore-type semiconductor A2B2O7 is employed as research platform and the conversion of CO2-to-HCOOH as the model reaction. Specifically, defect engineering intensified greatly the chemisorption-induced CO2 polarization via the bimetallic coordination, thermodynamically beneficial to the HCOOH production via the *HCO2 intermediate. The optimal V-BSO-430 electrocatalyst with abundant surface oxygen vacancies achieved a superior HCOOH yield of 116.7 mmol h-1 cm-2 at -1.2 VRHE, rivalling the incumbent similar reaction systems. Furthermore, the unique catalytic unit featured with a Bi1-Sn-Bi2 triangular structure, which is reconstructed by defect engineering, and altered the pathway of CO2 adsorption and activation to allow the preferential affinity of the suspended O atom in *HCO2 to H. As a result, V-BSO-430 gave an impressive FEHCOOH of 93% at -1.0 VRHE. This study held promises for inspiring the exploration of bimetallic materials from the massive semiconductor database.

Single-cluster anchored on PC6 monolayer as high-performance electrocatalyst for carbon dioxide reduction reaction: First principles study

Tremendous challenges remain to develop high-efficient catalysts for carbon dioxide reduction reaction (CO2RR) owing to the poor activity and low selectivity. However, the activity of catalyst with single active site is limited by the linear scaling relationship between the adsorption energy of intermediates. Motivated by the idea of multiple activity centers, triple metal clusters (M = Cr, Mn, Fe, Co, Ni, Cu, Pd, and Rh) doped PC6 monolayer (M3@PC6) were constructed in this study to investigate the CO2RR catalytic performance via density functional theory calculations. Results shows Mn3@PC6, Fe3@PC6, and Co3@PC6 exhibit high activity and selectivity for the reduction of CO2 to CH4 with limiting potentials of -0.32, -0.28, and -0.31 V, respectively. Analysis on the high-performance origin shows the more binding sites in M3@PC6 render the triple-atom anchored catalysts (TACs) high ability in regulating the binding strength with intermediates by self-adjusting the charges and conformation, leading to the improved performance of M3@PC6 than dual-atom doped PC6. This work manifests the huge application of PC6 based TACs in CO2RR, which hope to prove valuable guidance for the application of TACs in a broader range of electrochemical reactions.

Breaking the scaling relations of effective CO2 electrochemical reduction in diatomic catalysts by adjusting the flow direction of intermediate structures

The electrocatalytic carbon dioxide reduction reaction (CO2RR) is a promising approach to achieving a sustainable carbon cycle. Recently, diatomic catalysts (DACs) have demonstrated advantages in the CO2RR due to their complex and flexible active sites. However, our understanding of how DACs break the scaling relationship remains insufficient. Here, we investigate the CO2RR of 465 kinds of graphene-based DACs (M1M2-N6@Gra) formed from 30 metal atoms through high-throughput density functional theory (DFT) calculations. We find that the intermediates *COOH, *CO, and *CHO have multiple adsorption states, with 11 structural flow directions from *CO to *CHO. Four of these structural flow directions have catalysts that can break the linear scale relationship. Based on the adsorption energy relationship between *COOH, *CHO and *CO, we propose the concepts of linear scaling, moderate breaking, and severe deviation regions, leading to the establishment of new descriptors that identify 14 catalysts with potential superior performance. Among them, ZnRu-N6@Gra and CrNi-N6@Gra can reduce CO2 to CH4 at a low limiting potential. We also discovered that DACs have independent bidirectional electron transfer channels during the adsorption and activation of CO2, which can significantly improve the flexibility and efficiency of regulating the electronic structure. Furthermore, through machine learning (ML) analysis, we identify electronegativity, atomic number, and d electron count as key determinants of catalyst stability. This work provides new insights into the understanding of the DAC catalytic mechanism, as well as the design and screening of catalysts.

Computational screening of defective BC3-supported single-atom catalysts for electrochemical CO2 reduction

The electrochemical CO2 reduction reaction (eCO2RR) driven by renewable electricity offers a green and sustainable technology for synthesizing chemicals and managing global carbon balance. However, developing electrocatalysts with high activity and selectivity for producing C1 products (CO, HCOOH, CH3OH, and CH4) remains a daunting task. In this study, we conducted comprehensive first-principles calculations to investigate the eCO2RR mechanism using B-defective BC3-supported transition metal single-atom catalysts (TM@BC3 SACs). Initially, we evaluated the thermodynamic and electrochemical stability of the designed 26 TM@BC3 SACs by calculating the binding energy and dissolution potential of the anchored TM atoms. Subsequently, the selectivity of the eCO2RR and hydrogen evolution reaction (HER) on stable SACs was determined by comparing the free energy change (ΔG) for the first protonation of CO2 with the ΔG of *H formation. The stability and selectivity screening processes enabled us to narrow down the pool of SACs to the 14 promising ones. Finally, volcano plots for the eCO2RR towards different C1 products were established by using the adsorption energy descriptors of key intermediates, and three SACs were predicted to exhibit high activity and selectivity. The limiting potentials (UL) for HCOOH production on Pd@BC3 and Ag@BC3 are -0.11 V and -0.14 V. CH4 is a preferred product on Re@BC3 with UL of -0.22 V. Elaborate electronic structure calculations elucidate that the activity and selectivity originate from the sufficient activation of the C-O bond and the strong orbital hybridization between crucial intermediates and metal atoms. The proposed catalyst screening criteria, constructed volcano plots and predicted SACs may provide a theoretical foundation for the development of computationally guided catalyst designs for electrochemical CO2 conversion to C1 products.

Coordination Environment Engineering to Regulate the Adsorption Strength of Intermediates in Single Atom Catalysts for High-performance CO2 Reaction Reduction

The modulation of the coordination environment of single atom catalysts (SACs) plays a vital role in promoting CO2 reduction reaction (CO2RR). Herein, N or B doped Fe-embedded graphyne (Fe-GY), Fe-nXGYm (n = 1, 2, 3; X = N, B; m = 1, 2, 3), are employed as probes to reveal the effect of the coordination environment engineering on CO2RR performance via heteroatom doping in SACs. The results show that the doping position and number of N or B in Fe-GY significantly affects catalyst activity and CO2RR product selectivity. In comparison, Fe-1NGY exhibits high-performance CO2RR to CH4 with a low limiting potential of -0.17 V, and Fe-2NGY3 is demonstrated as an excellent CO2RR electrocatalyst for producing HCOOH with a low limiting potential of -0.16 V. With applied potential, Fe-GY, Fe-1NGY, and Fe-2NGY3 exhibit significant advantages in CO2RR to CH4 while hydrogen evolution reaction is inhibited. The intrinsic essence analysis illustrates that heteroatom doping modulates the electronic structure of active sites and regulates the adsorption strength of the intermediates, thereby rendering a favorable coordination environment for CO2RR. This work highlights Fe-nXGYm as outstanding SACs for CO2RR, and provides an in-depth insight into the intrinsic essence of the promotion effect from heteroatom doping.

Selectivities of Stepped Cu-M (M = Pt, Ni, Pd, Zn, Ag, Au) Bimetallic Surface Environment for C1 and C2 Pathways

Copper (Cu) emerges as a highly efficient and cheap catalytic agent for the electrochemical reduction of carbon dioxide (CO2RR), promising a sustainable route toward carbon neutrality. Despite its utility, the Cu catalyst exhibits limitations in terms of product selectivity, highlighting the need for the development of a superior catalyst design. Herein, we present a density functional theory (DFT) investigation into the selectivities of Cu-M (M = Pt, Ni, Pd, Zn, Ag, Au) bimetallic catalysts (BMCs) for the carbon dioxide reduction reaction (CO2RR). The interaction between the metals of Cu-M makes the surface electrons reconstruct so that the d-band center shifts to the Fermi level. In terms of CO2 activation, the Cu-Ni catalyst exhibits superior performance. Additionally, the Cu-Pd catalyst favors the formation of *COH along the reaction pathway, favoring the generation of CH4. Conversely, the Cu-Ni catalyst preferentially produces *CHO, thereby favoring the production of CH3OH. For the Cu-Ag catalyst, the reaction intermediates along the C2 pathway are *CO-*CHO and *COH-*CHO. The Cu-Ni catalyst follows a reaction path that proceeds via *CO-*CO → *CO-*COH → *COH-CHO. On the other hand, the Cu-Pt catalyst exhibits a reaction sequence of *CO-*CO → *CO-*CHO → *OCH-*OCH. This study provides guiding significance for the design of Cu-based bimetallic catalysts aimed at improving the selectivities and efficiency of the CO2RR process.

Construction synergetic adsorption and activation surface via confined Cu/Cu2O and Ag nanoparticles on TiO2 for effective conversion of CO2 to CH4

High-performance photocatalysts for catalytic reduction of CO2 are largely impeded by inefficient charge separation and surface activity. Reasonable design and efficient collaboration of multiple active sites are important for attaining high reactivity and product selectivity. Herein, Cu-Cu2O and Ag nanoparticles are confined as dual sites for assisting CO2 photoreduction to CH4 on TiO2. The introduction of Cu-Cu2O leads to an all-solid-state Z-scheme heterostructure on the TiO2 surface, which achieves efficient electron transfer to Cu2O and adsorption and activation of CO2. The confined nanometallic Ag further enhances the carrier's separation efficiency, promoting the conversion of activated CO2 molecules to •COOH and further conversion to CH4. Particularly, this strategy is highlighted on the TiO2 system for a photocatalytic reduction reaction of CO2 and H2O with a CH4 generation rate of 62.5 μmol∙g-1∙h-1 and an impressive selectivity of 97.49 %. This work provides new insights into developing robust catalysts through the artful design of synergistic catalytic sites for efficient photocatalytic CO2 conversion.

Influence factors of CO adsorption on C2N-supported dual-atom catalysts unveiled by machine learning and twofold feature engineering

Dual-atom catalysts (DACs) have emerged as a compelling frontier in the realm of the electrochemical carbon dioxide reduction reaction (CO2RR). However, elucidating the intrinsic properties of dual-atom pairs and their direct correlation with catalytic activity poses significant challenges. Herein, we investigate CO adsorption on 248 kinds of C2N-supported DACs and analyze the underlying structure-activity relationships of dual transition metal (TM) atoms based on density functional theory (DFT) calculations and machine learning (ML) models. Compared to the direct input of atomic features in the decision tree model of ML, we confirm that extra feature engineering with the introduction of the arithmetic combination of atomic features can better reflect the correlation of dual TM atoms on C2N-based DACs. Further feature importance analysis reveals a strong relationship between the last one occupied orbital radius (rv), group number (G) for dual TM atoms and the CO binding strength, as well as a potential connection with the d band centre (εd). Our work provides deeper insights into the design of DACs and highlights the significance of twofold feature engineering for the synergistic effects between dual TM atoms.

ClAg14 (C≡Ct Bu)12 Nanoclusters as Efficient and Selective Electrocatalysts Toward Industrially Relevant CO2 Conversion

Atomically precise metal nanoclusters (NCs) have emerged as a promising frontier in the field of electrochemical CO2 reduction reactions (CO2 RR) because of their distinctive catalytic properties. Although numerous metal NCs are developed for CO2 RR, their use in practical applications has suffered from their low-yield synthesis and insufficient catalytic activity. In this study, the large-scale synthesis and electrocatalytic performance of ClAg14 (C≡Ct Bu)12 + NCs, which exhibit remarkable efficiency in catalyzing CO2 -to-CO electroreduction with a CO selectivity of over 99% are reported. The underlying mechanisms behind this extraordinary CO2 RR activity of ClAg14 (C≡Ct Bu)12 + NCs are investigated by a combination of electrokinetic and theoretical studies. These analyses reveal that different active sites, generated through electrochemical activation, have unique adsorption properties for the reaction intermediates, leading to enhanced CO2 RR and suppressed hydrogen production. Furthermore, industrially relevant CO2 -to-CO electroreduction using ClAg14 (C≡Ct Bu)12 + NCs in a zero-gap CO2 electrolyzer, achieving high energy efficiency of 51% and catalyst activity of over 1400 A g-1 at a current density of 400 mA cm-2 is demonstrated.

Current Status and Perspectives of Dual-Atom Catalysts Towards Sustainable Energy Utilization

The exploration of sustainable energy utilization requires the implementation of advanced electrochemical devices for efficient energy conversion and storage, which are enabled by the usage of cost-effective, high-performance electrocatalysts. Currently, heterogeneous atomically dispersed catalysts are considered as potential candidates for a wide range of applications. Compared to conventional catalysts, atomically dispersed metal atoms in carbon-based catalysts have more unsaturated coordination sites, quantum size effect, and strong metal-support interactions, resulting in exceptional catalytic activity. Of these, dual-atomic catalysts (DACs) have attracted extensive attention due to the additional synergistic effect between two adjacent metal atoms. DACs have the advantages of full active site exposure, high selectivity, theoretical 100% atom utilization, and the ability to break the scaling relationship of adsorption free energy on active sites. In this review, we summarize recent research advancement of DACs, which includes (1) the comprehensive understanding of the synergy between atomic pairs; (2) the synthesis of DACs; (3) characterization methods, especially aberration-corrected scanning transmission electron microscopy and synchrotron spectroscopy; and (4) electrochemical energy-related applications. The last part focuses on great potential for the electrochemical catalysis of energy-related small molecules, such as oxygen reduction reaction, CO2 reduction reaction, hydrogen evolution reaction, and N2 reduction reaction. The future research challenges and opportunities are also raised in prospective section.

Atomically dispersed dual-atom catalysts: A new rising star in environmental remediation

Single-atom catalysts, characterized by individual metal atoms as active centers, have emerged as promising candidates owing to their remarkable catalytic efficiency, maximum atomic utilization efficiency, and robust stability. However, the limitation of single-atom catalysts lies in their inability to cater to multistep reactions using a solitary active site. Introducing an additional metal atom can amplify the number of active sites, modulate the electronic structure, bolster adsorption ability, and enable a gamut of core reactions, thus augmenting their catalytic prowess. As such, dual-atom catalysts have risen to prominence. However, a comprehensive review elucidating the realm of dual-atom catalysts in environmental remediation is currently lacking. This review endeavors to bridge this gap, starting with a discourse on immobilization techniques for dual-atom catalysts, which includes configurations such as adjacent atoms, bridged atoms, and co-facially separated atoms. The review then delves into the intrinsic activity mechanisms of these catalysts, elucidating aspects like adsorption dynamics, electronic regulation, and synergistic effects. Following this, a comprehensive summarization of dual-atom catalysts for environmental applications is provided, spanning electrocatalysis, photocatalysis, and Fenton-like reactions. Finally, the existing challenges and opportunities in the field of dual-atom catalysts are extensively discussed. This work aims to be a beacon, illuminating the path towards the evolution and adoption of dual-atom catalysts in environmental remediation.

Dual-Atom Co/Ni Electrocatalyst Anchored at the Surface-Modified Ti3C2Tx MXene Enables Efficient Hydrogen and Oxygen Evolution Reactions

Dual-atom catalytic sites on conductive substrates offer a promising opportunity for accelerating the kinetics of multistep hydrogen and oxygen evolution reactions (HER and OER, respectively). Using MXenes as substrates is a promising strategy for depositing those dual-atom electrocatalysts, if the efficient surface anchoring strategy ensuring metal-substrate interactions and sufficient mass loading is established. We introduce a surface-modification strategy of MXene substrates by preadsorbing L-tryptophan molecules, which enabled attachment of dual-atom Co/Ni electrocatalyst at the surface of Ti3C2Tx by forming N-Co/Ni-O bonds, with mass loading reaching as high as 5.6 wt %. The electron delocalization resulting from terminated O atoms on MXene substrates, N atoms in L-tryptophan anchoring moieties, and catalytic metal atoms Co and Ni provides an optimal adsorption strength of intermediates and boosts the HER and OER kinetics, thereby notably promoting the intrinsic activity of the electrocatalyst. CoNi-Ti3C2Tx electrocatalyst displayed HER and OER overpotentials of 31 and 241 mV at 10 mA cm-2, respectively. Importantly, the CoNi-Ti3C2Tx electrocatalyst also exhibited high operational stability for both OER and HER over 100 h at an industrially relevant current density of 500 mA cm-2. Our study provided guidance for constructing dual-atom active metal sites on MXene substrates to synergistically enhance the electrochemical efficiency and stability of the energy conversion and storage systems.

Screening of transition metal and boron atoms co-doped graphdiyne catalysts for electrocatalytic urea synthesis

Electrocatalytic CN coupling using nitrogen (N2) and carbon dioxide (CO2) as precursors offers a promising alternative for urea production under mild conditions, compared to traditional synthesis approaches. However, the design and screening of extremely efficient electrocatalysts remains a significant challenge in this field. Hence, we propose a systematic approach to screen efficient double-atom catalysts (DACs) with both metal and boron active sites, employing density functional theory (DFT). A comprehensive evaluation of 27 potential catalysts were performed, taking into account their stability, co-adsorption of N2 and CO2, as well as the potential-determining step (PDS) involved urea formation. The calculated results show that co-doped graphdiyne with CrB and MnB double atoms (CrB@GDY and MnB@GDY) emerge as potential electrocatalysts for urea production, displaying thermodynamic energy barriers of 0.41 eV and 0.66 eV, respectively. More importantly, these two DACs can significantly suppress the ammonia (NH3) and C1 products formation. Furthermore, a catalytic activity relationship between the d-band centers of the DACs and urea production performance were established. This study not only forecasts two promising DACs for subsequent experimental work but also establishes a theoretical framework for the evaluation of DACs in electrocatalytic urea synthesis.

Coordination Engineering of Heteronuclear Fe-Mo Dual-Atom Catalyst for Promoted Electrocatalytic Nitrogen Fixation: A DFT Study

Developing efficient nanostructured electrocatalysts for N2 reduction to NH3 under mild conditions remains a major challenge. The Fe-Mo cofactor serves as the archetypal active site in nitrogenase. Inspired by nitrogenase, we designed a series of heteronuclear dual-atom catalysts (DACs) labeled as FeMoN6-a Xa (a=1, 2, 3; X=B, C, O, S) anchored on the pore of g-C3 N4 to probe the impact of coordination on FeMo-catalyzed nitrogen fixation. The stability, reaction paths, activity, and selectivity of 12 different FeMoN6-a Xa DACs have been systematically studied using density functional theory. Of these, four DACs (FeMoN5 B1 , FeMoN5 O1 , FeMoN4 O2 , and FeMoN3 C3 ) displayed promising nitrogen reduction reaction (NRR) performance. Notably, FeMoN5 O1 stands out with an ultralow limiting potential of -0.11 V and high selectivity. Analysis of the density of states and charge/spin changes shows FeMoN5 O1 's high activity arises from optimal N2 binding on Fe initially and synergy of the FeMo dimer enabling protonation in NRR. This work contributes to the advancement of rational design for efficient NRR catalysts by regulating atomic coordination environments.

C2 Product Formation over the C1 Product and HER on the 111 Plane of Specific Cu Alloy Nanoparticles Identified through Multiparameter Optimization

C2 products are more desirable than C1 products during CO2 electroreduction (CO2ER) because the former possess higher energy density and greater industrial value. For CO2ER, Cu is a well-known catalyst, but the selectivity toward C2 products is still a big challenge for researchers due to complex intermediates, different final products, and large space of the catalyst due to its morphology, plane, size, host surface etc. Using density functional theory (DFT) calculations, we find that alloying of Cu nanoparticles can help to enhance the selectivity toward C2 products during CO2ER with a low overpotential. By a systematic investigation of 111 planes (which prefer the C1 product in the case of bulk Cu), the alloys show the generation of C2 products via *CO-*CO dimerization (* indicates adsorbed state). It also suppresses the counter-pathway of hydrogenation of *CO to *CHO, which leads to C1 products. Further, we find that *CH2CHO is the bifurcating intermediate to distinguish between ethanol and ethylene as the final product. We have used simple graphical construction to identify the catalyst for CO2ER over HER, and vice versa. We have also defined the case of hydrogen poisoning and projected a parity plot to recognize the catalyst for C2 product evolution over the C1 product. Our study reveals that Cu-Ag and Cu-Zn catalysts selectively promote ethanol production on 111 planes. Moreover, an edge-doped 2SO2 graphene nanoribbon as the host layer further lowers the barrier and selectively promotes ethanol on Cu38- and Cu79-based alloys. This work provides new theoretical insights into designing Cu-based nanoalloy catalysts for C2 product formation on the 111 plane.

Mechanism-Guided Design of Photocatalysts for CO2 Reduction toward Multicarbon Products

Photocatalytic reduction of CO2 to high value-added multicarbon (C2+) products is an important way to achieve sustainable production of green energy but limited by the low efficiency of catalysts. One fundamental issue lies in the high complexity of catalyst structure and reaction process, making the rational catalyst design and targeted performance optimization a grand challenge. Herein, we performed a mechanism-guided design of photocatalysts for CO2 reduction by using the experimentally reported Cu doped TiO2 (Cu-TiO2) with high C3H8 selectivity and well-defined structure as the prototype. Our mechanistic study highlights three key factors for C3H8 formation, i.e., formation of double O vacancies (Vdi-O) for selectivity, C-C coupling for activity, and Vdi-O recovery for durability. More importantly, Vdi-O formation/recovery and C-C coupling are negatively correlated, indicating that ideal candidates should achieve a balance between oxygen vacancy (VO) formation and C-C coupling. On this basis, TiO2 with the doping of two adjacent Cu atoms (Cu-Cu-TiO2) was designed with enhanced performance for CO2 photoreduction toward C3H8. Furthermore, a simple descriptor (Nμ, "effective d electron number") based on inherent atomic properties was constructed to uncover the underlying causes of the performance variation of different systems. These results provide new insights into the "structure-performance" relation of metal oxide-based photocatalysts, thus offering useful strategies for the rational design of excellent catalysts for CO2 photoreduction.

CO2 reduction reaction on Sc-doped nanocages as catalysts

CONTEXT

The catalytic ability of Sc-doped C46 and Sc-doped Al23P23 as catalysts of CO2-RR to create the CH4 and CH3OH is investigated. The mechanisms of CO2-RR are examined by theoretical methods and ΔGreaction of reaction steps of CO2-RR mechanisms are calculated. The overpotential of CH4 and CH3OH production on Sc-doped C46 and Sc-doped Al23P23 is calculated. The Sc atoms of Sc-doped C46 and Sc-doped Al23P23 can adsorb the CO2 molecule as the first step of CO2-RR. The CH4 is produced from hydrogenation of *CH3O and the *CO → *CHO reaction step is the rate limiting step for CH4 production. The CH3OH can be formed on Sc-doped C46 and Sc-doped Al23P23 by *CO → *CHO → *CH2O → *CH3O → CH3OH mechanism and HCOOH → *CHO → *CH2O → *CH3O → CH3OH mechanism. The Sc-C46 and Sc-Al23P23 can catalyze the CO2-RR to produce the CH4 and CH3OH by acceptable mechanisms.

METHODS

Here, the structures are optimized by PW91PW91/6-311+G (2d, 2p) and M06-2X/cc-pVQZ methods in GAMESS software. The frequencies of nanocages and their complexes with species of CO2-RR are investigated by mentioned methods. The transition state of each reaction step of CO2-RR is searched by Berny method to find the CO2-RR intermediates. The ∆Eadsorption of intermediates of CO2-RR on surfaces of nanocages is calculated and the ∆Greaction of reaction steps of CO2-RR is calculated.

Modeling Single-Atom Catalysis

Electronic structure calculations represent an essential complement of experiments to characterize single-atom catalysts (SACs), consisting of isolated metal atoms stabilized on a support, but also to predict new catalysts. However, simulating SACs with quantum chemistry approaches is not as simple as often assumed. In this work, the essential factors that characterize a reliable simulation of SACs activity are examined. The Perspective focuses on the importance of precise atomistic characterization of the active site, since even small changes in the metal atom's surroundings can result in large changes in reactivity. The dynamical behavior and stability of SACs under working conditions, as well as the importance of adopting appropriate methods to solve the Schrödinger equation for a quantitative evaluation of reaction energies are addressed. The Perspective also focuses on the relevance of the model adopted. For electrocatalysis this must include the effects of the solvent, the presence of electrolytes, the pH, and the external potential. Finally, it is discussed how the similarities between SACs and coordination compounds may result in reaction intermediates that usually are not observed on metal electrodes. When these aspects are not adequately considered, the predictive power of electronic structure calculations is quite limited.

Boosting the Proton-coupled Electron Transfer via Fe-P Atomic Pair for Enhanced Electrochemical CO2 Reduction

Single-atom catalysts exhibit superior CO2 -to-CO catalytic activity, but poor kinetics of proton-coupled electron transfer (PCET) steps still limit the overall performance toward the industrial scale. Here, we constructed a Fe-P atom paired catalyst onto nitrogen doped graphitic layer (Fe1 /PNG) to accelerate PCET step. Fe1 /PNG delivers an industrial CO current of 1 A with FECO over 90 % at 2.5 V in a membrane-electrode assembly, overperforming the CO current of Fe1 /NG by more than 300 %. We also decrypted the synergistic effects of the P atom in the Fe-P atom pair using operando techniques and density functional theory, revealing that the P atom provides additional adsorption sites for accelerating water dissociation, boosting the hydrogenation of CO2 , and enhancing the activity of CO2 reduction. This atom-pair catalytic strategy can modulate multiple reactants and intermediates to break through the inherent limitations of single-atom catalysts.

Inter-Metal Interaction of Dual-Atom Catalysts in Heterogeneous Catalysis

Dual-atom catalysts (DACs) have been a new frontier in heterogeneous catalysis due to their unique intrinsic properties. The synergy between dual atoms provides flexible active sites, promising to enhance performance and even catalyze more complex reactions. However, precisely regulating active site structure and uncovering dual-atom metal interaction remain grand challenges. In this review, we clarify the significance of the inter-metal interaction of DACs based on the understanding of active center structures. Three diatomic configurations are elaborated, including isolated dual single-atom, N/O-bridged dual-atom, and direct dual-metal bonding interaction. Subsequently, the up-to-date progress in heterogeneous oxidation reactions, hydrogenation/dehydrogenation reactions, electrocatalytic reactions, and photocatalytic reactions are summarized. The structure-activity relationship between DACs and catalytic performance is then discussed at an atomic level. Finally, the challenges and future directions to engineer the structure of DACs are discussed. This review will offer new prospects for the rational design of efficient DACs toward heterogeneous catalysis.

Insight on Atomically Dispersed Cu Catalysts for Electrochemical CO2 Reduction

Electrochemical CO2 reduction (ECO2R) with renewable electricity is an advanced carbon conversion technology. At present, copper is the only metal to selectively convert CO2 into multicarbon (C2+) products. Among them, atomically dispersed (AD) Cu catalysts have received great attention due to the relatively single chemical environment, which are able to minimize the negative impact of morphology, valence state, and crystallographic properties, etc. on product selectivity. Furthermore, the completely exposed atomic Cu sites not only provide space and bonding electrons for the adsorption of reactants in favor of better catalytic activity but also provide an ideal platform for studying its reaction mechanism. This review summarizes the recent progress of AD Cu catalysts as a chemically tunable platform for ECO2R, including the atomic Cu sites dynamic evolution, the catalytic performance, and mechanism. Furthermore, the prospects and challenges of AD Cu catalysts for ECO2R are carefully discussed. We sincerely hope that this review can contribute to the rational design of AD Cu catalysts with enhanced performance for ECO2R.

Charge-orbital synergistic engineering of TM@Ti3C2O1-xBx for highly selective CO2 electrochemical reduction

Inspired by MXene nanosheets and their regulation of surface functional groups, a series of Ti3C2-MXene-based single TM atom electrocatalysts with a doped boron (B) atom (TM@Ti3C2O2-xBx, TM is V, Cr, Mn, Fe, Co or Ni, x = 0.11) are proposed for achieving a high performance catalytic CO2 reduction reaction (CO2RR). The results reveal that the doped B atom involves in the adsorption reaction of CO2 molecules and CO intermediates in the CO2RR. The TM-to-C and B-to-C π-back bonding contribute to the activation of the CO2 molecules and CO intermediates in the CO2RR. Enough electrons from the single TM atom and B atom occupied orbitals can be injected into the CO2 molecules and *CO intermediates through direct bonding interactions, which effectively alleviates the difficulty of the first hydrogenation reaction step and further helps CO reduction towards CH4. The calculated values of ΔG for the first hydrogenation reaction and the formation of *CHO on Ti3C2O2-xBx are significantly smaller than those of other single-atom catalysts (SACs). Fe@Ti3C2O2-xBx is found to have the highest electrocatalytic activity with a limiting potential of ∼0.40 V and exhibits a high selectivity for obtaining CH4 through the CO2RR compared with the hydrogen evolution reaction. This work is expected to open a research path for engineering the charge-orbital state of the innate atoms of a substrate based on mechanistic insights, which guides the rational design of highly selective MXene-based CO2RR electrocatalysts.

Theoretical exploration on the performance of single and dual-atom Cu catalysts on the CO2 electroreduction process: a DFT study

Carbon dioxide (CO2) electroreduction by metal-nitrogen-doped carbon (MNC) catalysts is a promising and efficient method to mitigate global warming by converting CO2 molecules to value-added chemicals. In this research, we systematically studied the behaviours of single and dual-atom Cu catalysts during the CO2 electroreduction process using density functional theory (DFT) calculations. Two structures, i.e., CuNC-4-pyridine and CuCuNC-4a, were found to be beneficial for C2 chemical generation with relatively high stabilities. Subsequently, we explored the detailed pathways of key products (CO, HCOOH, CH3OH, CH4, C2H6O, C2H4 and C2H6) during CO2 electroreduction on CuNC-4-pyridine and CuCuNC-4a. This research reveals the mechanisms of key product formation during CO2 electroreduction on CuNC-4-pyridine and CuCuNC-4a, which would provide important insights to guide the design of MNC catalysts with low limiting potentials and high product selectivity.

Dual-Site Metal Catalysts for Electrocatalytic CO2 Reduction Reaction

Electrocatalytic CO2 reduction reaction (CO2 RR) is a promising and green approach for reducing atmospheric CO2 concentration and achieving high-valued conversion of CO2 under the carbon-neutral policy. In CO2 RR, the dual-site metal catalysts (DSMCs) have received wide attention for their ingenious design strategies, abundant active sites, and excellent catalytic performance attributed to the synergistic effect between dual-site in terms of activity, selectivity and stability, which plays a key role in catalytic reactions. This review provides a systematic summary and detailed classification of DSMCs for CO2 RR, describes the mechanism of synergistic effects in catalytic reactions, and also introduces in situ characterization techniques commonly used in CO2 RR. Finally, the main challenges and prospects of dual-site metal catalysts and even multi-site catalysts for CO2 recycling are analyzed. It is believed that based on the understanding of bimetallic site catalysts and synergistic effects in CO2 RR, well-designed high-performance, low-cost electrocatalysts are promising for achieving CO2 conversion, electrochemical energy conversion and storage in the future.

Synergy of dual-atom catalysts deviated from the scaling relationship for oxygen evolution reaction

Dual-atom catalysts, particularly those with heteronuclear active sites, have the potential to outperform the well-established single-atom catalysts for oxygen evolution reaction, but the underlying mechanistic understanding is still lacking. Herein, a large-scale density functional theory is employed to explore the feasibility of *O-*O coupling mechanism, which can circumvent the scaling relationship with improving the catalytic performance of N-doped graphene supported Fe-, Co-, Ni-, and Cu-containing heteronuclear dual-atom catalysts, namely, M'M@NC. Based on the constructed activity maps, a rationally designed descriptor can be obtained to predict homonuclear catalysts. Seven heteronuclear and four homonuclear dual-atom catalysts possess high activities that outperform the minimum theoretical overpotential. The chemical and structural origin in favor of *O-*O coupling mechanism thus leading to enhanced reaction activity have been revealed. This work not only provides additional insights into the fundamental understanding of reaction mechanisms, but also offers a guideline for the accelerated discovery of efficient catalysts.

Revealing electrocatalytic C N coupling for urea synthesis with metal–free electrocatalyst

Urea is ubiquitous in agriculture and industry, but its production consumes a lot of energy. The conversion of nitrogen (N₂) and carbon dioxide (CO₂) into urea via an electrocatalytic CN coupling reaction under ambient conditions would be a major boon to sustainable development. However, designing a metal - free catalyst with high activity and selectivity for urea remains a major challenge. Herein, by means of density functional theory (DFT) and ab - initio molecular dynamics (AIMD) computations, the B₁₂ cluster doped on nitrogenated graphene (C₂N) substrate catalyst (B₁₂@C₂N) with superior stability was designed for electrocatalytic urea synthesis starting from the CO₂ and N₂ through four reaction mechanisms. The nature of the co-adsorption activation of CO₂ and N₂ on the B₁₂@C₂N catalyst was investigated, the electrochemical proton - electron transfer steps and the CN thermochemical coupling led to the synthesis of urea. The study showed that the B₁₂@C₂N catalyst exhibited high catalytic activity for urea synthesis with the lowest limiting potential of - 1.01 V following the *HNNH mechanism compared with other mechanisms. The potential - determining step (PDS) is the formation of the *CO+*NH₂NH₂ species. However, the two - step CN coupling barriers of *NCON species are 0.13 eV and 0.60 eV using AIMD and a "slow - growth" sampling approach in an explicit water molecules model. Calculations also showed that the byproducts of carbon monoxide (CO), methane (CH₄), methanol (CH₃OH), ammonia (NH₃), and hydrogen (H₂) can be inhibited on the B₁₂@C₂N catalyst. Therefore, the metal - free catalyst not only has a good performance for the hydrogenation of CO₂ and N₂ promoting the electrochemical reaction, but also facilitates CN thermochemical coupling for urea synthesis. This work provides new insights into the synthesis of urea via the CN coupling reaction on a metal - free electrocatalyst, a process that could contribute to greenhouse gas mitigation to help meet carbon neutrality targets.

Electrochemical Reduction of CO2 via Single-Atom Catalysts Supported on α-In2Se3

In this work, the electrochemical CO₂ reduction reaction (CO₂RR) over transition metal and α-In₂Se₃ monolayer catalysts was investigated by density functional theory (DFT) and an effective screening medium method-reference interaction site model (ESM-RISM). On the basis of the scaling relationship between the adsorption free energies of intermediates, we constructed the relationships between oxygen-bound intermediates with *O and carbon-bound intermediates with *CHO. The calculation results indicate that *OCHO intermediates are more favorable for the first hydrogenation of CO₂ on M@In₂Se₃ catalysts; thus, the adsorption energy of oxygen-bound species determines the catalytic performance of M@In₂Se₃. The Co@In₂Se₃↓-C was predicted to be the most promising catalyst with a low limiting potential of -0.385 V as determined by the computational hydrogen electrode method. Constant potential calculations also demonstrate that the M@In₂Se₃ catalysts hold great potential for highly efficient CO₂RR. This work provides a fundamental understanding for the rational design of ferroelectric single-atom catalysts for the purpose of highly efficient electrocatalytic CO₂ reduction.

Efficient asymmetrical silicon-metal dimer electrocatalysts for the nitrogen reduction reaction

The electrocatalytic nitrogen reduction reaction (ENRR) has been regarded as an eco-friendly and feasible substitute for the Haber-Bosch method. Identifying the effective catalysts for the ENRR is an extremely important prerequisite but challenging. Herein, asymmetrical silicon-metal dimer catalysts doped into g-C₃N₄ nanosheets with nitrogen vacancies (SiM@C₃N₄) were designed to address nitrogen activation and reduction. The concept catalysts of SiM@C₃N₄ can combine the advantages of silicon-based and metal-based catalysts during the ENRR. Among the catalysts investigated, SiMo@C₃N₄ and SiRu@C₃N₄ exhibited the highest activities towards the ENRR with ultra-low onset potentials of -0.20 and -0.39 V; meanwhile, they suppressed the competing hydrogen evolution reaction (HER) due to the relative difficulty in releasing hydrogen. Additionally, SiRu@C₃N₄ is demonstrated to possess strong hydrophobicity, which is greatly beneficial to the production of ammonia. This research provides insights into asymmetrical silicon-metal dimer catalysts and reveals a new method for developing dual-atom electrocatalysts. This asymmetrical dimer strategy can be applied in other electrocatalytic reactions for energy conversion.

Adaptive Design of Alloys for CO2 Activation and Methanation via Reinforcement Learning Monte Carlo Tree Search Algorithm

Data-driven machine learning (ML) has earned remarkable achievements in accelerating materials design, while it heavily relies on high-quality data acquisition. In this work, we develop an adaptive design framework for searching for optimal materials starting from zero data and with as few DFT calculations as possible. This framework integrates automatic density functional theory (DFT) calculations with an improved Monte Carlo tree search via reinforcement learning algorithm (MCTS-PG). As a successful example, we apply it to rapidly identify the desired alloy catalysts for CO₂ activation and methanation within 200 MCTS-PG steps. To this end, seven alloy surfaces with high theoretical activity and selectivity for CO₂ methanation are screened out and further validated by comprehensive free energy calculations. Our adaptive design framework enables the fast computational exploration of materials with desired properties via minimal DFT calculations.

TM2 -B2 Quadruple Active Sites Supported on a Defective C3 N Monolayer as Catalyst for the Electrochemical CO2 Reduction: A Theoretical Perspective

Developing high-performance electrocatalysts for the CO₂ reduction reaction (CO₂ RR) holds great potential to mitigate the depletion of fossil feedstocks and abate the emission of CO₂ . In this contribution, using density functional theory calculations, we systematically investigated the CO₂ RR performance catalyzed by TM₂ -B₂ (TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) supported on a defective C₃ N monolayer (V-C₃ N). Through the screening in terms of stability of catalyst, activity towards CO₂ adsorption, and selectivity against hydrogen evolution reaction, Mn₂ -, Fe₂ -, Co₂ -, and Ni₂ -B₂ @V-C₃ N were demonstrated to be a highly promising CO₂ RR electrocatalyst. Due to quadruple active sites, these candidates can adsorb two or three CO₂ molecules. Strikingly, different products, distributing from C₁ to C₂₊ , can be generated. The high activity originates from the synergistic effect of TM and B atoms, in which they serve as adsorption sites for the C- and O-species, respectively. The high selectivity towards C₂₊ products at the Fe₂ -, and Ni₂ -B₂ sites stems from moderate C adsorption strength but relatively weak O adsorption strength, in which a universal descriptor, that is, 0.6 ΔE_C -0.4 ΔE_O =-1.77 eV (ΔE_C /ΔE_O is the adsorption energy of C/O), was proposed. This work would offer a novel perspective for the design of high active electrocatalysts towards CO₂ RR and for the synthesis of C₂₊ compounds.

Recent advances in the theoretical studies on the electrocatalytic CO2 reduction based on single and double atoms

Excess of carbon dioxide (CO2) in the atmosphere poses a significant threat to the global climate. Therefore, the electrocatalytic carbon dioxide reduction reaction (CO2RR) is important to reduce the burden on the environment and provide possibilities for developing new energy sources. However, highly active and selective catalysts are needed to effectively catalyze product synthesis with high adhesion value. Single-atom catalysts (SACs) and double-atom catalysts (DACs) have attracted much attention in the field of electrocatalysis due to their high activity, strong selectivity, and high atomic utilization. This review summarized the research progress of electrocatalytic CO2RR related to different types of SACs and DACs. The emphasis was laid on the catalytic reaction mechanism of SACs and DACs using the theoretical calculation method. Furthermore, the influences of solvation and electrode potential were studied to simulate the real electrochemical environment to bridge the gap between experiments and computations. Finally, the current challenges and future development prospects were summarized and prospected for CO2RR to lay the foundation for the theoretical research of SACs and DACs in other aspects.

Active Learning Accelerating to Screen Dual-Metal-Site Catalysts for Electrochemical Carbon Dioxide Reduction Reaction

Dual-metal-site catalysts (DMSCs) are increasingly important catalysts in the field of electrochemical carbon dioxide reduction reaction (CO₂RR) in recent years. However, rapid screening of suitable metal combinations of DMSCs remains a huge challenge. Herein, we constructed an active learning (AL) framework to study CO₂RR to HCOOH. This AL framework turned out a success in the accurate prediction of 282 DMSCs for CO₂RR through interactive learning between users and machine learning (ML) models. Among the 42 DMSCs calculated in three iteration loops of AL, 29 DMSCs were obtained, where the screening success rate was as high as 70%. Furthermore, we found five experimentally unexplored DMSCs that exhibited better CO₂RR activity and selectivity than pure Bi. Low prediction errors on other DMSCs show that the AL model possessed outstanding universality. The results prove the excellent potential of the AL method and provide guidance on the design of high-performance electrocatalysts for CO₂RR.

Bioinspired and Bioderived Aqueous Electrocatalysis

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO2 reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices.

Copper-based catalysts for the electrochemical reduction of carbon dioxide: progress and future prospects

There is an urgent need for the development of high performance electrocatalysts for the CO₂ reduction reaction (CO₂RR) to address environmental issues such as global warming and achieve carbon neutral energy systems. In recent years, Cu-based electrocatalysts have attracted significant attention in this regard. The present review introduces fundamental aspects of the electrocatalytic CO₂RR process together with a systematic examination of recent developments in Cu-based electrocatalysts for the electroreduction of CO₂ to various high-value multicarbon products. Current challenges and future trends in the development of advanced Cu-based CO₂RR electrocatalysts providing high activity and selectivity are also discussed.

Proton Transfer Dynamics-Mediated CO2 Electroreduction

Electrochemical CO₂ reduction reaction (CO₂ RR) is crucial to addressing environmental crises and producing chemicals. Proton activation and transfer are essential in CO₂ RR. To date, few research reviews have focused on this process and its effect on catalytic performance. Recent studies have demonstrated ways to improve CO₂ RR by regulating proton transfer dynamics. This Concept highlights the use of regulating proton transfer dynamics to enhance CO₂ RR for the target product and discusses modulation strategies for proton transfer dynamics and operative mechanisms in typical systems, including single-atom catalysts, molecular catalysts, metal heterointerfaces, and organic-ligand modified metal catalysts. Characterization methods for proton transfer dynamics during CO₂ RR are also discussed, providing powerful tools for the hydrogen-involving electrochemical study. This Concept offers new insights into the CO₂ RR mechanism and guides the design of efficient CO₂ RR systems.

Highly Efficient Hydroxyl Radicals Production Boosted by the Atomically Dispersed Fe and Co Sites for Heterogeneous Electro-Fenton Oxidation

The heterogeneous electro-Fenton (hetero-e-Fenton)-coupled electrocatalytic oxygen reduction reaction (ORR) is regarded as a promising strategy for ^·OH production by simultaneously driving two-electron ORR toward H₂O₂ and stepped activating the as-generated H₂O₂ to ^·OH. However, the high-efficiency electrogeneration of ^·OH remains challengeable, as it is difficult to synchronously obtain efficient catalysis of both reaction steps above on one catalytic site. In this work, we propose a dual-atomic-site catalyst (CoFe DAC) to cooperatively catalyze ^·OH electrogeneration, where the atomically dispersed Co sites are assigned to enhance O₂ reduction to H₂O₂ intermediates and Fe sites are responsible for activation of the as-generated H₂O₂ to ^·OH. The CoFe DAC delivers a higher ^·OH production rate of 2.4 mmol L^-1 min^-1 g_cat^-1 than the single-site catalyst Co-NC (0.8 mmol L^-1 min^-1 g_cat^-1) and Fe-NC (1.0 mmol L^-1 min^-1 g_cat^-1). Significantly, the CoFe DAC hetero-e-Fenton process is demonstrated to be more energy-efficient for actual coking wastewater treatment with an energy consumption of 19.0 kWh kg^-1 COD^-1 than other electrochemical technologies that reported values of 29.7∼68.0 kW h kg^-1 COD^-1. This study shows the attractive advantages of efficiency and sustainability for ^·OH electrogeneration, which should have fresh inspiration for the development of new-generation wastewater treatment technology.

Tuning reactivity in trimetallic dual-atom alloys: molecular-like electronic states and ensemble effects

Single-atom alloys (SAAs) have drawn significant attention in recent years due to their excellent catalytic properties. Controlling the geometry and electronic structure of this type of localized catalytic active site is of fundamental and technological importance. Dual-atom alloys (DAAs) consisting of a heterometallic dimer embedded in the surface layer of a metal host would bring increased tunability and a larger active site, as compared to SAAs. Here, we use computational studies to show that DAAs allow tuning of the active site electronic structure and reactivity. Interestingly, combining two SAAs into a dual-atom site can result in molecular-like hybridization by virtue of the free-atom-like electronic d states exhibited by many SAAs. DAAs can inherit the weak d-d interaction between dopants and hosts from the constituent SAAs, but exhibit new electronic and reactive properties due to dopant-dopant interactions in the DAA. We identify many heterometallic DAAs that we predict to be more stable than either the constituent SAAs or homometallic dual-atom sites of each dopant. We also show how both electronic and ensemble effects can modify the strength of CO adsorption. Because of the molecular-like interactions that can occur, DAAs require a different approach for tuning chemical properties compared to what is used for previous classes of alloys. This work provides insights into the unique catalytic properties of DAAs, and opens up new possibilities for tailoring localized and well-defined catalytic active sites for optimal reaction pathways.