Can N, S Cocoordination Promote Single Atom Catalyst Performance in CO2 RR? Fe-N2 S2 Porphyrin versus Fe-N4 Porphyrin

The spin polarization strategy regulates heterogeneous catalytic activity performance: from fundamentals to applications

In recent years, there has been significant attention towards the development of catalysts that exhibit superior performance and environmentally friendly attributes. This surge in interest is driven by the growing demands for energy utilization and storage as well as environmental preservation. Spin polarization plays a crucial role in catalyst design, comprehension of catalytic mechanisms, and reaction control, offering novel insights for the design of highly efficient catalysts. However, there are still some significant research gaps in the current study of spin catalysis. Therefore, it is urgent to understand how spin polarization impacts catalytic reactions to develop superior performance catalysts. Herein, we present a comprehensive summary of the application of spin polarization in catalysis. Firstly, we summarize the fundamental mechanism of spin polarization in catalytic reactions from two aspects of kinetics and thermodynamics. Additionally, we review the regulation mechanism of spin polarization in various catalytic applications and several approaches to modulate spin polarization. Moreover, we discuss the future development of spin polarization in catalysis and propose several potential avenues for further progress. We aim to improve current catalytic systems through implementing a novel and distinctive spin engineering strategy.

High energy-efficiency decomplexation of metal-complexes by H*-mediated electro-reduction on hydroxyphenyl Co-porphyrin catalysts

Electrochemical reduction of metal-organic complex pollutants has been recognized as an environmental benign method that operates at mild condition. However, the selective reduction of metal complexes and energy consumption in cathodic process are still a big challenge. Herein, we found that hydroxyphenyl Co-porphyrin catalyst (CoTH@NG) realizes the highly selective decomplexation of metal-organic complexes by H* -mediated reduction, and simultaneously the impressive recovery efficiency of metal ions. Density functional theory (DFT) confirms the generation and capturing ability of H* on CoTH@NG, verifying the dominant role of H* -mediated reduction in the selective decomplexation of Cu-EDTA. CoTH@NG realizes the superior energy efficiency for Cu-EDTA removal (279.3 g kWh-1 of EEOCu-EDTA) and Cu recovery (48.6 g kWh-1 of EEOCu), which are remarkably 3.3 × 102 and 9.7 × 102 times higher than traditional carbon cloth electrode. Moreover, the recovered Cu0(s) nanowires on the electrode surface can be efficiently regenerated in HCOOH by a galvanic reaction through the electron channel of CoTH@NG, regenerating catalytic electrode. This is one of the pioneer studies on H* -mediated electro-reduction decomplexation of metal-complexes, metal recovery, and electrode regeneration on CoTH@NG, which providing a technical strategy for developing efficient electrocatalytic system for pollution control. Environmental Implication Metal complexes is a dramatic increase in the electroplating and mining industries, and seriously affect both public health and environmental sustainability. Our work reported a new hydroxyphenyl Co-porphyrin catalyst (CoTH@NG) which achieves the selective decomplexation of metal-organic complexes, and simultaneously the recovery of metal ions. CoTH@NG realizes the superior energy efficiency for Cu-EDTA removal (279.3 g kWh-1) and Cu0(s) recovery (48.6 g kWh-1), which are remarkably 3.3 × 102 and 9.7 × 102 times higher than traditional carbon cloth electrode. Moreover, the recovered Cu0(s) can be efficiently regenerated in HCOOH by a galvanic reaction through the electron channel of CoTH@NG, regenerating catalytic electrode.

Advances and challenges in the electrochemical reduction of carbon dioxide

The electrocatalytic carbon dioxide reduction reaction (ECO2RR) is a promising way to realize the transformation of waste into valuable material, which can not only meet the environmental goal of reducing carbon emissions, but also obtain clean energy and valuable industrial products simultaneously. Herein, we first introduce the complex CO2RR mechanisms based on the number of carbons in the product. Since the coupling of C-C bonds is unanimously recognized as the key mechanism step in the ECO2RR for the generation of high-value products, the structural-activity relationship of electrocatalysts is systematically reviewed. Next, we comprehensively classify the latest developments, both experimental and theoretical, in different categories of cutting-edge electrocatalysts and provide theoretical insights on various aspects. Finally, challenges are discussed from the perspectives of both materials and devices to inspire researchers to promote the industrial application of the ECO2RR at the earliest.

Structural engineering of atomic catalysts for electrocatalysis

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

Single-Atom Catalysts on Covalent Organic Frameworks for Energy Applications

Single-atom catalysts (SACs) have been investigated and applied to energy conversion devices. However, issues of metal agglomeration, low metal loading, and substrate stability have hindered realization of the SACs' full potential. Recently, covalent organic framework (COF)-based SACs have emerged as promising materials to enable highly efficient catalytic reactions. Here, we summarize the representative COF-based SACs and their wide application in clean energy devices and conversion reactions, such as hydrogen evolution reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, and oxygen evolution reaction. Based on their catalysis conditions, these reactions are categorized into photocatalyzed and electrocatalyzed reactions. We also summarize their design strategies, including heteroatom inclusion, donor-acceptor pairs, pore engineering, interface engineering, etc. Although COF-based SACs are promising, more efforts, such as linkage engineering, functional groups, ionization, multifunctional sites for cocatalyzed systems, etc., could improve them to be the ideal SAC materials. At the end, we provide our perspectives on where the field will proceed in the next 5 years.

Electronic Modulation in Homonuclear Dual-Atomic Catalysts for Enhanced CO2 Electroreduction

Homonuclear dual-atomic catalysts showcase unique electronic modulation due to their dual metal centres, providing new direction in development of efficient catalysts for CO2 electroreduction. This article highlights a few cutting-edge homonuclear dual-atomic catalysts, focusing on their inherent advantages in efficient and selective CO2 electroreduction, to spotlight the potential application of dual-atomic catalysts in CO2 electroreduction.

Enhancing CO2 electroreduction performance through transition metal atom doping and strain engineering in γ-GeSe: a first-principles study

The development of electrocatalysts that exhibit stability, high activity, and selectivity for CO2 reduction reactions (CO2RR) remains a significant challenge. Single-atom catalysts (SACs) hold promise in addressing this challenge due to their high atomic utilization efficiency. In this study, we explore the potential of monolayer γ-GeSe doped with transition metals, referred to as TM@γ-GeSe, for facilitating electrocatalytic CO2RR. Among the 26 TM@γ-GeSe SACs systematically designed, we have identified four stable transition metal catalysts (TM = Rh, Pd, Pt, and Au). Mechanistic investigations into the CO2RR pathways reveal exceptional electrocatalytic activity for Rh@γ-GeSe and Pd@γ-GeSe, with limiting potentials of -0.26 and -0.35 V, respectively. Particularly, Pd@γ-GeSe exhibits outstanding product selectivity toward formic acid. The introduction of strain engineering induces modifications in the catalytic activity and selectivity of Rh@γ-GeSe. Notably, a 1% tensile strain promotes formic acid as the preferred product, thereby improving the specific product selectivity of Rh@γ-GeSe. Conversely, compressive strain reduces CO2RR activity while enhancing the hydrogen evolution reaction, leading to a decrease in CO2RR selectivity. Furthermore, we use the work function as a descriptor to elucidate the underlying mechanism of strain tunability. We hope that our theoretical study will offer valuable insights for the design of catalysts based on γ-GeSe for electrocatalytic CO2RR.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.

N,S coordination in Ni single-atom catalyst promoting CO2RR towards HCOOH

Carbon-based single atom catalysts (SACs) are attracting extensive attention in the CO2 reduction reaction (CO2RR) due to their maximal atomic utilization, easily regulated active center and high catalytic activity, in which the coordination environment plays a crucial role in the intrinsic catalytic activity. Taking NiN4 as an example, this study reveals that the introduction of different numbers of S atoms into N coordination (Ni-NxS4-x (x = 1-4)) results in outstanding structural stability and catalytic activity. Owing to the additional orbitals around -1.60 eV and abundant Ni dxz, dyz, dx2, and dz2 orbital occupation after S substitution, N,S coordination can effectively facilitate the protonation of adsorbed intermediates and thus accelerate the overall CO2RR. The CO2RR mechanisms for CO and HCOOH generation via two-electron pathways are systematically elucidated on NiN4, NiN3S1 and NiN2S2. NiN2S2 yields HCOOH as the most favorable product with a limiting potential of -0.24 V, surpassing NiN4 (-1.14 V) and NiN3S1 (-0.50 V), which indicates that the different S-atom substitution of NiN4 has considerable influence on the CO2RR performance. This work highlights NiN2S2 as a high-performance CO2RR catalyst to produce HCOOH, and demonstrates that N,S coordination is an effective strategy to regulate the performance of atomically dispersed electrocatalysts.

3D Hollow Hierarchical Porous Carbon with Fe-N4 -OH Single-Atom Sites for High-Performance Zn-Air Batteries

The development of innovative and efficient Fe-N-C catalysts is crucial for the widespread application of zinc-air batteries (ZABs), where the inherent oxygen reduction reaction (ORR) activity of Fe single-atom sites needs to be optimized to meet the practical application. Herein, a three-dimensional (3D) hollow hierarchical porous electrocatalyst (ZIF8@FePMPDA-920) rich in asymmetric Fe-N4 -OH moieties as the single atomic sites is reported. The Fe center is in a penta-coordinated geometry with four N atoms and one O atom to form Fe-N4 -OH configuration. Compared to conventional Fe-N4 configuration, this unique structure can weaken the adsorption of intermediates by reducing the electron density of the Fe center for oxygen binding, which decreases the energy barrier of the rate-determining steps (RDS) to accelerate the ORR and oxygen evolution reaction (OER) processes for ZABs. The rechargeable liquid ZABs (LZABs) equipped with ZIF8@FePMPDA-920 display a high power density of 123.11 mW cm-2 and a long cycle life (300 h). The relevant flexible all-solid-state ZABs (FASSZABs) also display outstanding foldability and cyclical stability. This work provides a new perspective for the structural design of single-atom catalysts in the energy conversion and storage areas.

Regulating Efficient and Selective Single-atom Catalysts for Electrocatalytic CO2 Reduction

Anchoring transition metal (TM) atoms on suitable substrates to form single-atom catalysts (SACs) is a novel approach to constructing electrocatalysts. Graphdiyne with sp-sp2 hybridized carbon atoms and uniformly distributed pores have been considered as a potential carbon material for supporting metal atoms in a variety of catalytic processes. Herein, density functional theory (DFT) calculations were performed to study the single TM atom anchoring on graphdiyne (TM1 -GDY, TM=Sc, Ti, V, Cr, Mn, Co and Cu) as the catalysts for CO2 reduction. After anchoring metal atoms on GDY, the catalytic activity of TM1 -GDY (TM=Mn, Co and Cu) for CO2 reduction reaction (CO2 RR) are significantly improved comparing with the pristine GDY. Among the studied TM1 -GDY, Cu1 -GDY shows excellent electrocatalytic activity for CO2 reduction for which the product is HCOOH and the limiting potential (UL ) is -0.16 V. Mn1 -GDY and Co1 -GDY exhibit superior catalytic selectivity for CO2 reduction to CH4 with UL of -0.62 and -0.34 V, respectively. The hydrogen evolution reaction (HER) by TM1 -GDY (TM=Mn, Co and Cu) occurs on carbon atoms, while the active sites of CO2 RR are the transition metal atoms . The present work is expected to provide a solid theoretical basis for CO2 conversion into valuable hydrocarbons.

Constructing N,S and N,P Co-Coordination in Fe Single-Atom Catalyst for High-Performance Oxygen Redox Reaction

Single-atom catalysts (SACs) are promising electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), in which the coordination environment plays a crucial role in activating the intrinsic activity of the central metal. Taking the FeN4 SAC as a probe, this work investigates the effect of introducing S or P atoms into N coordination (FeSx N4-x and FePx N4-x (x=1-4)) on the electronic structure optimization of Fe center and its catalytic performance. Attributing to the optimal Fe 3d orbitals, FePN3 can effectively activate O2 and promote ORR with a low overpotential of 0.29 V, surpassing FeN4 and most reported catalysts. FeSN3 is beneficial to H2 O activation and OER, proceeding with an overpotential of 0.68 V, which is superior to FeN4 . Both FePN3 and FeSN3 exhibit outstanding thermodynamic and electrochemical stability with negative formation energies and positive dissolution potentials. Hence, the N,P and N,S co-coordination might provide better catalytic environment than regular N coordination for SACs in ORR and OER. This work demonstrates FePN3 /FeSN3 as high-performance ORR/OER catalysts and highlights N,P and N,S co-coordination regulation as an effective approach to fine tune high atomically dispersed electrocatalysts.

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.

Designing N-Confused Metalloporphyrin-Based Covalent Organic Frameworks for Enhanced Electrocatalytic Carbon Dioxide Reduction

Electrochemical conversion of carbon dioxide (CO2 ) into value-added products is promising to alleviate greenhouse gas emission and energy demands. Metalloporphyrin-based covalent organic frameworks (MN4 -Por-COFs) provide a platform for rational design of electrocatalyst for CO2 reduction reaction (CO2 RR). Herein, through systematic quantum-chemical studies, the N-confused metallo-Por-COFs are reported as novel catalysts for CO2 RR. For MN4 -Por-COFs, among the ten 3d metals, M = Co/Cr stands out in catalyzing CO2 RR to CO or HCOOH; hence, N-confused Por-COFs with Co/CrN3 C1 and Co/CrN2 C2 centers are designed. Calculations indicate CoNx Cy -Por-COFs exhibit lower limiting potential (-0.76 and -0.60 V) for CO2 -to-CO reduction than its parent CoN4 -Por-COFs (-0.89 V) and make it feasible to yield deep-reduction degree C1 products CH3 OH and CH4 . Electronic structure analysis reveals that substituting CoN4 to CoN3 C1 /CoN2 C2 increases the electron density on Co-atom and raises the d-band center, thus stabilizing the key intermediates of the potential determining step and lowering the limiting potential. For similar reason, changing the core from CrN4 to CrN3 C1 /CrN2 C2 lowers the limiting potential for CO2 -to-HCOOH reduction. This work predicts N-confused Co/CrNx Cy -Por-COFs to be high-performance CO2 RR catalyst candidates. Inspiringly, as a proof-of-concept study, it provides an alternative strategy for coordination regulation and theoretical guidelines for rational design of catalysts.

Grand Canonical Ensemble Modeling of Electrochemical Interfaces Made Simple

Grand canonical ensemble (GCE) modeling of electrochemical interfaces, in which the electrochemical potential is converged to a preset constant, is essential for understanding electrochemistry and electrocatalysis at the electrodes. However, it requires developing efficient and robust algorithms to perform practical and effective GCE modeling with density functional theory (DFT) calculations. Herein, we developed an efficient and robust fully converged constant-potential (FCP) algorithm based on Newton's method and a polynomial fitting to calculate the necessary derivative for DFT calculations. We demonstrated with the constant-potential geometry optimization and Born-Oppenheimer molecular dynamics (BOMD) calculations that our FCP algorithm is resistant to the numerical instability that plagues other algorithms, and it delivers efficient convergence to the preset electrochemical potential and renders accurate forces for updating the nuclear positions of an electronically open system, outperforming other algorithms. The implementation of our FCP algorithm enables flexibility in using various computational codes and versatility in performing advanced tasks including the constant-potential enhanced-sampling BOMD simulations that we showcased with the modeling of the electrochemical hydrogenation of CO, and it is thus expected to find a wide spectrum of applications in the modeling of chemistry at electrochemical interfaces.

Precise electronic structure modulation on MXene-based single atom catalysts for high-performance electrocatalytic CO2 reduction reaction: A first-principle study

Electrocatalytic CO₂ reduction reaction (CO₂RR) to CO is a logical approach to achieve a carbon-neutral cycle. In this work, a series of Ti₂CO₂ and O vacancy containing Ti₂CO₂ MXene-based transition metal (TM) single atom catalysts (SACs), including TM-Ti₂CO₂ and TM-O_v-Ti₂CO₂, are explored for high-performance CO₂RR. Sc/Ti/V/Cr-Ti₂CO₂ and Ni-O_v-Ti₂CO₂ are screened out with limiting potential (U_L) more positive than -0.50 V. Ni-O_v-Ti₂CO₂ is a candidate catalyst for CO₂RR to CO, considering its activity with U_L of -0.27 eV, and the selectivity relevant to hydrogen evolution reaction and HCOOH production. Meanwhile, a novel activity descriptor of TM-Ti-O group valence state is proposed according to that TMs work in synergy with coordinated Ti and O atoms and a level of around 0.64 e^- benefits to CO₂RR. This work highlights oxygen vacancy containing Ti₂CO₂-based Ni SAC as a promising catalyst for CO₂RR, and provides a feasible electronic structure design principle for guiding the design of MXene-based SACs for CO₂RR.

Design of a Four-Atom Cluster Embedded in Carbon Nitride for Electrocatalytic Generation of Multi-Carbon Products

The development of efficient and stable catalysts for the electrocatalytic CO₂ and CO reduction reactions (CORR) is under active investigation, but the problems of poor selectivity and low efficiency for C₂ products still exist. We design a two-dimensional carbon nitride material (C₅N₂H₂) that contains an eight N-atom structure capable of coordinating four-metal atom clusters and supporting simultaneously two carbon oxide molecules needed for the C₂ coupling. The designed material has excellent electrical conductivity and stability. After high-throughput screening of catalytic performance of multiple four-metal clusters embedded into the framework, we systematically investigate the CORR process of 11 candidates. We find that Cu₄-C₅N₂H₂ has superior selectivity and low limiting potential for generating ethylene, while Cu₂Zn₂-C₅N₂H₂ is selective and efficient to synthesize ethanol. Further, we discover a novel type of descriptor related to 2D material flexibility to evaluate the potential-determining step for generating ethylene. Our report both broadens the possibilities for few-atom CO reduction and demonstrates a novel substrate flexibility-related descriptor to predict the catalytic performance of materials.

Emerging materials for electrochemical CO2 reduction: progress and optimization strategies of carbon-based single-atom catalysts

The electrochemical CO₂ reduction reaction can effectively convert CO₂ into promising fuels and chemicals, which is helpful in establishing a low-carbon emission economy. Compared with other types of electrocatalysts, single-atom catalysts (SACs) immobilized on carbon substrates are considered to be promising candidate catalysts. Atomically dispersed SACs exhibit excellent catalytic performance in CO₂RR due to their maximum atomic utilization, unique electronic structure, and coordination environment. In this paper, we first briefly introduce the synthetic strategies and characterization techniques of SACs. Then, we focus on the optimization strategies of the atomic structure of carbon-based SACs, including adjusting the coordination atoms and coordination numbers, constructing the axial chemical environment, and regulating the carbon substrate, focusing on exploring the structure-performance relationship of SACs in the CO₂RR process. In addition, this paper also briefly introduces the diatomic catalysts (DACs) as an extension of SACs. At the end of the paper, we summarize the article with an exciting outlook discussing the current challenges and prospects for research on the application of SACs in CO₂RR.

Electrocatalytic Hydrogen Evolution of Bent Bis(dipyrrin) Ni(II) Complexes

Planar Ni(II) porphyrinoid complexes have been widely used in electrochemical carbon dioxide reduction reaction and oxygen reduction reaction as well as hydrogen evolution reaction (HER). However, nonplanar Ni(II) tetra-pyrrolic complexes have not been thoroughly investigated thus far. In this study, three highly bent bis(dipyrrin) Ni(II) complexes have been synthesized to investigate their structure, electronic property, and electrocatalytic HER activities. Cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry studies revealed four redox processes, yielding two reduced species as the final products. The i_c/i_p values of phenyl- and pentafluorophenyl-bearing bis(dipyrrin) Ni(II) complexes were >30 when trifluoroacetic acid was used as the proton source, and their Faradaic efficiencies for H₂ generation were >93%. Density functional theory calculations of the HERs revealed low endothermic energies of bent bis(dipyrrin) Ni(II) complexes.

Significance of density functional theory (DFT) calculations for electrocatalysis of N2 and CO2 reduction reactions

Density functional theory (DFT) based computational methods have shown great significance in developing high-performance electrocatalysts. In this perspective, we briefly summarized the state-of-the-art research progress of electrocatalysts for the nitrogen reduction reaction (NRR) and CO₂ reduction reaction (CO₂RR), which are important processes for the conversion of common molecules into value-added products. With the help of DFT calculations, various modulation strategies are employed to improve the catalytic activity and performance of NRR and CO₂RR electrocatalysts. DFT calculations are performed to confirm the surface catalytic sites, evaluate the catalytic activity, reveal the possible reaction mechanisms, and design novel structures with high catalytic performance. By discussing the currently applied computational methods and conditions during the calculations, we outlined our concerns on the prospects and future challenges of DFT calculations in electrocatalysis studies.

Modulating intramolecular electron and proton transfer kinetics for promoting carbon dioxide conversion

A novel pentagon-heptagon paired azulene group that possesses a large dipole moment is immobilized onto a porphyrin. The as-prepared azulene iron porphyrin exhibits a narrower bandgap and higher electrocatalytic CO₂ reduction activity than the pristine iron porphyrin. The maximum CO faradaic efficiency reaches 99.9%, which is the state-of-the-art value among molecular catalysts.

CO2 Capture, Separation and Reduction on Boron-Doped MoS2 , MoSe2 and Heterostructures with Different Doping Densities: A Theoretical Study

Designing high-performance materials for CO₂ capture and conversion is of great significance to reduce the greenhouse effect and alleviate the energy crisis. The strategy of doping is widely used to improve activity and selectivity of the materials. However, it is unclear how the doping densities influence the materials' properties. Herein, we investigated the mechanism of CO₂ capture, separation and conversion on MoS₂ , MoSe₂ and Janus MoSSe monolayers with different boron doping levels using density functional theory (DFT) simulations. The results indicate that CO₂ , H₂ and CH₄ bind weakly to the monolayers without and with single-atom boron doping, rendering these materials unsuitable for CO₂ capture from gas mixtures. In contrast, CO₂ binds strongly to monolayers doped with diatomic boron, whereas H₂ and CH₄ can only form weak interactions with these surfaces. Thus, the monolayers doped with diatomic boron can efficiently capture and separate CO₂ from such gas mixtures. The electronic structure analysis demonstrates that monolayers doped with diatomic doped are more prone to donating electrons to CO₂ than those with single-atom boron doped, leading to activation of CO₂ . The results further indicate that CO₂ can be converted to CH₄ on diatomic boron doped catalysts, and MoSSe is the most efficient of the surfaces studied for CO₂ capture, separation and conversion. In summary, the study provides evidence for the doping density is vital to design materials with particular functions.

Hybrid Metal-Boron Diatomic Site Embedded in C2 N Monolayer Promotes C-C Coupling in CO2 Electroreduction

Double-atom catalyst (DAC) has gained much interest for its versatile tuning and synergistic effect of dual-atom active sites. Metal (M)-metal (M) diatomic sites, either homo- or heteronuclear, are typically researched. Hybrid metal-non-metal combined sites have rarely been studied and even the viability of such active sites are unknown. Herein, CO₂ electroreduction (CO₂ RR) is explored on M@X-C₂ N (M = Fe, Co, Ni, and Cu; X = S, P, and B) which renders naturally generated M-X diatomic site. Using spin-polarized density functional theory coupled with computational hydrogen electrode model, it is demonstrated that the functionality of hybrid M-B dual-atom center is superior over that of a single- or double-M center in driving CO₂ RR especially C-C coupling. Among metal-boron DACs studies, Fe@B-C₂ N (μ = 2μ_B ) exhibits the lowest free energy barrier of 0.17 eV in C-C coupling whereas Ni@B-C₂ N (μ = 0μ_B ) mainly produces CH₄ with the lowest barrier of 0.42 eV. Hence, the electronic spin state of M can be particularly important in modulating selectivity and C-C coupling barrier in CO₂ RR. Fe@B-C₂ N is predicted as the promising catalyst for CO₂ RR towards C₂₊ products owing partially to its enhanced spin state. The findings can enrich the design strategy of electrocatalysts normally running at ambient conditions.