Catalyst For CO2 Reduction Reaction Research Articles

Backbone Engineering of Polymeric Catalysts for High‐Performance CO2 Reduction in Bipolar Membrane Zero‐Gap Electrolyzer

AbstractBipolar membranes (BPMs) have emerged as a promising solution for mitigating CO2 losses, salt precipitation and high maintenance costs associated with the commonly used anion‐exchange membrane electrode assembly for CO2 reduction reaction (CO2RR). However, the industrial implementation of BPM‐based zero‐gap electrolyzer is hampered by the poor CO2RR performance, largely attributed to the local acidic environment. Here, we report a backbone engineering strategy to improve the CO2RR performance of molecular catalysts in BPM‐based zero‐gap electrolyzers by covalently grafting cobalt tetraaminophthalocyanine onto a positively charged polyfluorene backbone (PF‐CoTAPc). PF‐CoTAPc shows a high acid tolerance in BPM electrode assembly (BPMEA), achieving a high FE of 82.6 % for CO at 100 mA/cm2 and a high CO2 utilization efficiency of 87.8 %. Notably, the CO2RR selectivity, carbon utilization efficiency and long‐term stability of PF‐CoTAPc in BPMEA outperform reported BPM systems. We attribute the enhancement to the stable cationic shield in the double layer and suppression of proton migration, ultimately inhibiting the undesired hydrogen evolution and improving the CO2RR selectivity. Techno‐economic analysis shows the least energy consumption (957 kJ/mol) for the PF‐CoTAPc catalyst in BPMEA. Our findings provide a viable strategy for designing efficient CO2RR catalysts in acidic environments.

Fe-C78, Fe-Si78, Fe-CNT (9, 0) and Fe-SiNT (9, 0) as Catalysts for CO2 Reduction Reaction

Fe-C78, Fe-Si78, Fe-CNT (9, 0) and Fe-SiNT (9, 0) as Catalysts for CO2 Reduction Reaction

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

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

Screening of Cu-Mn-Ni-Zn high-entropy alloy catalysts for CO2 reduction reaction by machine-learning-accelerated density functional theory

High-entropy-alloy (HEA) catalysts have been used in many challenging electrocatalytic reactions, e.g., CO2 reduction reaction (CO2RR) due to their promising properties. For CO2RR catalysts, tuning metal compositions in Cu-based catalysts is one of the techniques to control the desired products. Thus, this work investigated the optimal composition of Cu-Mn-Ni-Zn HEA catalysts using high-throughput screening (HTS) for CO2RR targeting on two competing routes toward CH4 and CH3OH products. The screening protocol evaluates catalytic activity through adsorption energy (Eads) of *CO2, *CO, *COOH, and *H. At the same time, the selectivity is represented by Eads of *COH, *CH4, *CHO, and *CH3OH, using density functional theory (DFT) accelerated by machine learning techniques. The screening result from 11,920 data revealed 259 candidates for CH4-selective and 4,214 for CH3OH-selective catalysts. Interestingly, the Cu-Mn-Ni-Zn excellently prevented competitive hydrogen evolution reaction by up to 90%. Optimal composition for each route are Cu0.1Mn0.4Ni0.2Zn0.3 and Cu0.2Mn0.4Ni0.1Zn0.3 in CH4-selective route and Cu0.3Mn0.3Ni0.2Zn0.2, Cu0.3Mn0.2Ni0.3Zn0.2, Cu0.3Mn0.2Ni0.2Zn0.3, and Cu0.2Mn0.3Ni0.3Zn0.2 in CH3OH-selective route. The optimal catalyst structure with high CO2RR activity in both routes was revealed to have the Mn atom as an active site, while Cu, Ni, and Zn as neighboring atoms. Hence, the Cu-Mn-Ni-Zn HEA catalyst is the promising electrocatalyst for CO2RR.

The meso-substituent electronic effect of Fe porphyrins on the electrocatalytic CO2 reduction reaction.

We report Fe porphyrins bearing different meso-substituents for the electrocatalytic CO2 reduction reaction (CO2RR). By replacing two and four meso-phenyl groups of Fe tetraphenylporphyrin (FeTPP) with strong electron-withdrawing pentafluorophenyl groups, we synthesized FeF10TPP and FeF20TPP, respectively. We showed that FeTPP and FeF10TPP are active and selective for CO2-to-CO conversion in dimethylformamide with the former being more active, but FeF20TPP catalyzes hydrogen evolution rather than the CO2RR under the same conditions. Experimental and theoretical studies revealed that with more electron-withdrawing meso-substituents, the Fe center becomes electron-deficient and it becomes difficult for it to bind a CO2 molecule in its formal Fe0 state. This work is significant to illustrate the electronic effects of catalysts on binding and activating CO2 molecules and provide fundamental knowledge for the design of new CO2RR catalysts.

Research Progress on Electrocatalysts for Electrocatalytic Carbon Dioxide Reduction

Electrochemical CO2 reduction reaction (CO2RR) is a vital strategy for achieving carbon neutrality by converting CO2 into high-energy-density, valuable chemical products, thereby facilitating carbon resource recycling and addressing environmental challenges. Herein, this paper emphasizes the role of CO2RR in diminishing the greenhouse effect through the transformation of CO2, with a particular focus on the latest advancements in Cu-based nanocatalysts, metal-organic framework (MOF)-based catalysts, and heteroatom-doped carbon materials, which are key innovations in achieving enhanced photoelectric conversion efficiency and steering CO2 conversion pathways. The paper also outlines the electrochemical principles of CO2RR, and the spectrum of potential reduction products, and navigates through the challenges of stability and production costs. The paper proposes strategies to surmount these hurdles, highlighting the critical role of industrial collaborations and breakthroughs in materials science. Future research should aim to pinpoint cost-effective, efficient catalysts for CO2RR, contributing significantly to mitigating the greenhouse effect and propelling forward sustainable energy solutions.

Theoretical study on electrocatalytic carbon dioxide reduction over copper with copper-based layered double hydroxides.

The conversion of CO2 into valuable fuels and multi-carbon chemical substances by electrical energy is an effective strategy to solve environmental problems by using renewable energy sources. In this work, the density functional theory (DFT) method is used to reveal the electrocatalytic mechanism of CO2 reduction reaction (CO2RR) over the surface of CuAl-Cl-layered double hydroxides (LDHs) with Cu monoatoms (Cu@CuAl-Cl-LDH), Cu2 diatoms (Cu2@CuAl-Cl-LDH), orthotetrahedral Cu4 clusters (Td-Cu4@CuAl-Cl-LDH) and planar Cu4 clusters (Pl-Cu4@CuAl-Cl-LDH). The active sites, density of states, adsorption energy, charge density difference and free energy are calculated. The results show that CO2RR over all the above five catalysts can generate C2 products. Pl-Cu4@CuAl-Cl-LDH tends to generate C2H5OH, while the remaining four structures all tend to produce C2H4. Cuδ+ favors CO2RR, and Td-Cu4@CuAl-Cl-LDH with a larger positively charged area at the active site has the better electrocatalytic performance among the calculated systems with a maximum step height of 0.78 eV. The selectivity of the products C2H4 and C2H5OH depends on the dehydration of the intermediate *C2H2O to *C2H3O or *CCH; if the dehydration produces *CCH intermediate, the final product is C2H4, and if no dehydration occurs, C2H5OH is produced. This work provides theoretical information and guidance for further rational design of efficient CO2RR catalysts for energy saving and emission reduction.

Electrochemical CO2 Reduction on Pd-Based Electrodes: From Mechanism Understanding to Rational Catalyst Design

Electrochemical CO2 reduction reaction (CO2RR) driven by clean electricity to valuable chemicals provides a feasible way to carbon neutrality and thus attracts increasing attention. Among different transition-metal based CO2RR catalysts,...

Micro-kinetic modelling of the CO reduction reaction on single atom catalysts accelerated by machine learning.

Electrochemical CO2 transformation to fuels and chemicals is an effective strategy for conversion of renewable electric energy into storable chemical energy in combination with reducing green-house gas emission. Metal-nitrogen-carbon (M-N-C) single atom catalysts (SAC) have shown great potential in the electrochemical CO2 reduction reaction (CO2RR). However, exploring advanced SACs with simultaneously high catalytic activity and high product selectivity remains a great challenge. In this study, density functional theory (DFT) calculations are combined with machine learning (ML) for rapid and high-throughput screening of high performance CO reduction catalysts. Firstly, the electrochemical properties of 99 M-N-C SACs were calculated by DFT and used as a database. By using different machine learning models with simple features, the investigated SACs were expanded from 99 to 297. Through several effective indicators of catalyst stability, inhibition of the hydrogen evolution reaction, and CO adsorption strength, 33 SACs were finally selected. The catalytic activity and selectivity of the remaining 33 SACs were explored by micro-kinetic simulation based on Marcus theory. Among all the studied SACs, Mn-NC2, Pt-NC2, and Au-NC2 deliver the best catalytic performance and can be used as potential catalysts for CO2/CO conversion to hydrocarbons with high energy density. This effective screening method using a machine learning algorithm can promote the exploration of CO2RR catalysts and significantly reduce the simulation cost.

Electrospun Polymer Supported Cux O Nanostructures for CO2 Reduction Reaction

The reduction of carbon dioxide (CO2) to value-added products is a promising approach for mitigating the impact of CO2 emissions on the environment [1]. Copper oxide (CuO) and copper oxide (Cu2O) have been identified as effective catalysts for CO2 reduction reaction (CO2RR) due to their unique electronic properties [2]. Electrospinning is a versatile and efficient technique for the fabrication of high surface area polymer (P) nanofibers which enables a promising range of applications in energy storage and conversion [3].In this study, we investigate the synthesis of CuxO-incorporated polyacrylonitrile (PAN) and PAN/polyaniline (PANI) nanofibers via electrospinning and evaluate their performance as a catalyst for CO2RR. The CuxO/P nanofibers were characterized by various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy.The results revealed that CuxO nanoparticles were dispersed on the surface of the polymer nanofibers. The XRD analysis confirmed the presence of crystalline CuxO nanoparticles in the nanofibers. The FTIR spectra indicated that CuxO was successfully incorporated into the polymer nanofibers without new chemical bond formation between CuxO and PAN.The catalytic performance of CuxO/P nanofibers was evaluated for CO2RR in a three-electrode electrochemical cell. The CuxO/P nanofibers showed a significantly enhanced catalytic activity for CO2RR. Moreover, the CuxO/P nanofibers showed good stability during the electrochemical CO2RR.The enhanced catalytic performance of CuxO/P nanofibers can be attributed to the unique electronic properties of CuxO nanoparticles, which can facilitate the adsorption and activation of CO2 molecules. Furthermore, the high surface area and porous structure of the polymer nanofibers provide abundant active sites for the CO2RR. The dispersion of CuxO nanoparticles on the surface of the polymer nanofibers can also enhance electron transfer and reduce charge transfer resistance during the CO2RR.In conclusion, CuxO-incorporated polymer nanofibers were successfully synthesized by electrospinning and showed excellent catalytic activity for CO2RR. The CuxO/P nanofibers exhibited high selectivity and stability for the electrochemical reduction of CO2 to useful chemicals. These findings suggest that CuxO/P nanofibers have great potential as an efficient catalyst for CO2RR and could contribute to the development of sustainable energy conversion and storage systems.[1] A. Aljabour, D. H. Apaydin, H. Coskun, F. Ozel, M. Ersoz, P. Stadler, N. S. Sariciftci, and M. Kus, ACS Applied Materials & Interfaces, 8 (46), 31695-31701 (2016).[2] R. W. Abebe, H. Zanling, Z. Pengxiang, H. Liangsheng, A. Didier, Coordination Chemistry Reviews, 454, 214340 (2022).[3] A. Aljabour, ChemistrySelect 5, 7482 (2020). Figure 1

Non-Noble Metal Incorporated Transition Metal Dichalcogenide Monolayers for Electrochemical CO2 Reduction: A First-Principles Study.

Using non-noble metal atoms as catalysts is attractive for decreasing the cost of the CO2 reduction reaction (CO2RR). By screening first-row transition metals and noble metals through extensive first-principles calculations, non-noble Sc and Ti single atoms binding on vacancy-defected transition metal dichalcogenide (TMD) monolayers exhibit better catalytic performance and selectivity for electrochemical CO2RR than noble metal single atoms. The overpotentials of Sc and Ti atoms for the CO2RR can be reduced lower than 0.09 V after applying suitable biaxial tensile strains on vacancy-defected TMDs, which are approximately 1 order of magnitude lower than that of most reported metal atom catalysts. The vacancy defects of TMDs and charge transfer to metal atoms induced by tensile strain play a key role in improving the catalytic activity of non-noble metal single atoms. These results highlight a possible way to design new single atom catalysts for electrochemical CO2RR by utilizing the combination of non-noble metal atoms, defected TMDs, and strain engineering.

Enhancing effect of cobalt phthalocyanine dispersion on electrocatalytic reduction of CO2 towards methanol.

This paper focuses on enhancing the performance of electrocatalytic CO2 reduction reaction (CO2RR) by improving the dispersion of cobalt phthalocyanine (CoPc), especially for the methanol formation with multi-walled carbon nanotubes (CNTs) as a support. The promising CNTs-supported CoPc hybrid was prepared based on ball milling technique, and the surface morphology was characterized by means of those methods such as scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectra (XPS). Then, the synergistic effect of CNTs and ball milling on CO2RR performance was analyzed by those methods of cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), gas chromatography (GC), and proton nuclear magnetic resonance spectroscopy (1HNMR). Subsequently, the reduction mechanism of CO2 on ball-milled CoPc/CNTs was revealed based on the DFT calculations. The results showed that the electrocatalyst CoPc/CNTs hybrid prepared with sonication exhibited a conversion efficiency of CO2 above 60% at -1.0V vs. RHE, accompanied by the Faradaic efficiencies of nearly 50% for CO and 10% for methanol, respectively. The addition of CNTs as the support improved the utilization efficiency of CoPc and reduced the transfer resistance of species and electrons. Then the ball-milling method further improved the dispersion of CoPc on CNTs, which resulted in the fact that the methanol efficiency was raised by 6% and partial current density was increased by nearly 433%. The better dispersion of CoPc on CNTs adjusted the reduction pathway of CO2 and resulted in the enhancement of methanol selectivity and catalytic activity of CO2. The probable pathway for methanol production was proposed as CO2 → *CO2- → *COOH → *CO → *CHO → *CH2O → *OCH3 → CH3OH. This suggests the significance of the ball-milling method during the preparation of better supported catalysts for CO2RR towards those high-valued products.

Tailoring grain boundaries and doping on Cu-based electrocatalyst for efficient CO2 reduction reaction

Electrochemical conversion of CO2 on Cu-based catalysts offers an auspicious strategy for addressing the increasingly serious environmental issues. However, there is still a challenge in the regulation of selectivity for an efficient CO2 conversion process on Cu-based catalysts due to the complexity of the internal structure of catalysts. Herein, we step wisely control the intrinsic grain boundaries (GBs) and Sn doping in Cu substrate to optimize the CO2 reduction reaction (CO2RR) performance of catalyst, which also clearly clarify the contribution of above two factors towards CO2RR performance. As a result, the as-synthesized R-SnCu catalyst with both GBs and Sn doing exhibits the highest CO selectivity of 99 % at −0.8 V versus hydrogen electrode (vs. RHE). In-situ Raman spectroscopy was further used to provide critical evidence of the key intermediates during CO2RR. We find that compared to the catalysts containing only GBs or Sn doping, the R-SnCu catalyst controlled by both GBs and Sn doping exhibits a more pronounced adsorption preference for C-bound *COOH intermediate peaks related to CO generation. These findings provide new ideas for the effective design of high-performance Cu-based CO2RR catalysts.

Copper‐Sulfur‐Nitrogen Cluster Providing a Local Proton for Efficient Carbon Dioxide Photoreduction

AbstractAtomically precise Cu clusters are highly desirable as catalysts for CO2 reduction reaction (CO2RR), and they provide an appropriate model platform for elaborating their structure–activity relationship. However, an efficient overall photocatalytic CO2RR with H2O using assembled Cu‐cluster aggregates as single component photocatalyst has not been reported. Herein, we report a stable crystalline Cu−S−N cluster photocatalyst with local protonated N−H groups (denoted as Cu6−NH). The catalyst exhibits suitable photocatalytic redox potentials, high structural stability, active catalytic species, and a narrow band gap, which account for its outstanding photocatalytic CO2RR performance under visible light, with ≈100 % selectivity for CO evolution. Remarkably, systematic isostructural Cu‐cluster control experiments, in situ infrared spectroscopy, and density functional theory calculations revealed that the protonated pyrimidine N atoms in the Cu6−NH cluster act as a proton relay station, providing a local proton during the photocatalytic CO2RR. This efficiently lowers the energy barrier for the formation of the *COOH intermediate, which is the rate‐limiting step, efficiently enhancing the photocatalytic performance. This work lays the foundation for the development of atomically precise metal‐cluster‐based photocatalysts.

Copper-Sulfur-Nitrogen Cluster Providing a Local Proton for Efficient Carbon Dioxide Photoreduction.

Atomically precise Cu clusters are highly desirable as catalysts for CO2 reduction reaction (CO2 RR), and they provide an appropriate model platform for elaborating their structure-activity relationship. However, an efficient overall photocatalytic CO2 RR with H2 O using assembled Cu-cluster aggregates as single component photocatalyst has not been reported. Herein, we report a stable crystalline Cu-S-N cluster photocatalyst with local protonated N-H groups (denoted as Cu6 -NH). The catalyst exhibits suitable photocatalytic redox potentials, high structural stability, active catalytic species, and a narrow band gap, which account for its outstanding photocatalytic CO2 RR performance under visible light, with ≈100 % selectivity for CO evolution. Remarkably, systematic isostructural Cu-cluster control experiments, in situ infrared spectroscopy, and density functional theory calculations revealed that the protonated pyrimidine N atoms in the Cu6 -NH cluster act as a proton relay station, providing a local proton during the photocatalytic CO2 RR. This efficiently lowers the energy barrier for the formation of the *COOH intermediate, which is the rate-limiting step, efficiently enhancing the photocatalytic performance. This work lays the foundation for the development of atomically precise metal-cluster-based photocatalysts.

Insight into coupled Ni-Co dual-metal atom catalysts for efficient synergistic electrochemical CO2 reduction

The development of highly active, selective, and stable electrocatalysts can facilitate the effective implementation of electrocatalytic CO2 conversion into fuels or chemicals for mitigating the energy crisis and climate problems. Therefore, it is necessary to achieve the goal through reasonable material design based on the actuality of the operational active site at the molecular scale. Inspired by the stimulating synergistic effect of coupled heteronuclear metal atoms, a novel Ni-Co atomic pairs configuration (denoted as NiN3©CoN3-NC) active site was theoretically screened out for improving electrochemical CO2 reduction reaction (CO2RR). The structure of NiN3©CoN3-NC was finely regulated by adjusting Zn content in the precursors Zn/Co/Ni-zeolite imidazolate frameworks (Zn/Co/Ni-ZIFs) and pyrolysis temperature. The structural features of NiN3©CoN3-NC were systematically confirmed by aberration-corrected HAADF-STEM coupled with 3D atom-overlapping Gaussian-function fitting mapping, XAFS, and XRD. The results of theoretical calculations reveal that the synergistic effect of Ni-Co atomic pairs can effectively promote the *COOH intermediate formation and thus the overall CO2RR kinetic was improved, and also restrained the competitive hydrogen evolution reaction. Due to the attributes of Ni-Co atomic pairs configuration, the developed NiN3©CoN3-NC with superior catalytic activity, selectivity, and durability, with a high turnover frequency of 2265 h−1 at −1.1 V (vs. RHE) and maximum Faradaic efficiency of 97.7% for CO production. This work demonstrates the great potential of DACs as highly efficient catalysts for CO2RR, provides a useful strategy to design heteronuclear DACs, exploits the synergistic effect of multiple metal sites to facilitate complex CO2RR catalytic reactions, and inspires more efforts to develop the potential of DACs in various fields.

Rational Design of Advanced Metal Organic Framework‐Based Nanostructured Catalysts toward Electrocatalytic CO2 Conversion: A Mini Review

Carbon dioxide emission into the atmosphere, which originates from fossil fuels consumption, has led to a serious environmental and energy crisis. Electrochemical CO2 reduction reaction (CO2RR) into valuable chemicals such as carbon monoxide, ethanol, ethylene, and methane not only help lower the CO2 concentration in the atmosphere but is also beneficial for sustainable energy production. Therefore, numerous works are assigned to improving efficient electrocatalytic materials for the selective CO2RR. Metal–organic framework (MOF)‐derived catalytic materials mostly based on transition metals demonstrate permissible CO2RR owing to their specific composition, tunable surface nanostructure and texture, and affordable market prices. In this work, the best effort is put to describe the most basic concept of electrochemical CO2RR to provide a consensus. The effect of MOF structure and surface analysis are discussed. This is reason that MOFs as catalysts for electrochemical CO2RR offers several advantages over traditional catalysts, such as tunable surface structure, multifunctionality, selectivity control, and stability under CO2RR operation. And then, some of the most recent reported works on MOF‐based catalysts are summarized, to provide and inspire further investigations and ideas in this research field. However, despite these advantages, there are still research gaps that need to be addressed. Some of these gaps include being cost‐effective and economical process for preparing MOF‐based catalysts, long‐term stability for industrial usage, and scalability of the catalyst. Thereby, further studies are essential to fully exploit the potential of MOFs in advancing CO2RR technologies.

Unravelling the Structure Change and Its Catalytic Consequence of CuO Nanowires Towards CO2 Reduction Reaction

The CO2 reduction reaction (CO2RR) is a complex process with many possible products, and maintaining high selectivity for multi-carbon products remains a challenge. Currently, Cu-based catalysts are the only transition metal catalysts that can produce C2 products, and one of the popular Cu-based catalysts is CuO nanowires (NWs). We studied a series of CuO nanowires ranging from 50 to 200 nm for CO2RR using multiple characterization techniques including transmission electron microscopy(TEM), small angle X-ray scattering (SAXS) and in situ X-ray adsorption spectroscopy. We found that there could be an activation process required for such CuO NWs to serve as efficient CO2RR catalysts. The CuO can go through multiple steps resulting in the severe morphology changes during the activation process, confirmed by TEM and SAXS. In situ XAS results showed that the CuO NWs will be reduced from Cu(II) to Cu(0) during the reaction, consistent with our previous work(1). H-cell testing results also indicated the C2 production can be boosted after specific activation pathway, which highlights the importance of catalyst pre-treatment. These findings not only deepen our understanding of CO2RR mechanism but also provide fundamental insights for CO2RR catalysts synthesis. References (1) Soo Hong Lee, Ian Sullivan, David M. Larson, Guiji Liu, Francesca M. Toma, Chengxiang Xiang, and Walter S. Drisdell. ACS Catalysis, 2020, 10(14), 8000-8011 Acknowledgement The authors acknowledge the funding support from the Laboratory Directed Research and Development Program of the Lawrence Berkeley National Laboratory under the U.S. Department of Energy Contract (No. DE-AC02-05CH11231).

Design principles for selective and economical CO2 electrolysis in acids

The electrochemical CO2 reduction reaction (CO2RR) is a promising pathway for converting CO2 into valuable products such as carbon monoxide (CO). Here we show that a remarkably high CO selectivity can be achieved in a gas diffusion electrode-based CO2RR flow cell by using different characteristics of the proton and CO2 reduction reactions over a wide range of pHs, while H2 evolution from H2O reduction can be effectively avoided. The potential window of a high-performance Ni single-atom catalyst for CO2RR does not overlap with that for H2O reduction; this allows CO selectivity to exceed 90% in a pH 2 electrolyte, thereby attaining a CO2-to-CO conversion rate of approximately 77%. Effects of electrolyte compositions on CO2RR are also evaluated. Techno-economic and life cycle assessments establish that CO2RR is more favorable in acidic conditions, which can minimize the additional CO2 recycling and electrolyte regeneration processes, if surplus or cheap renewable electricity is available.

Unraveling the Electronic Structure and Dynamics of the Atomically Dispersed Iron Sites in Electrochemical CO2 Reduction.

Single-atom catalysts with a well-defined metal center open unique opportunities for exploring the catalytically active site and reaction mechanism of chemical reactions. However, understanding of the electronic and structural dynamics of single-atom catalytic centers under reaction conditions is still limited due to the challenge of combining operando techniques that are sensitive to such sites and model single-atom systems. Herein, supported by state-of-the-art operando techniques, we provide an in-depth study of the dynamic structural and electronic evolution during the electrochemical CO2 reduction reaction (CO2RR) of a model catalyst comprising iron only as a high-spin (HS) Fe(III)N4 center in its resting state. Operando 57Fe Mössbauer and X-ray absorption spectroscopies clearly evidence the change from a HS Fe(III)N4 to a HS Fe(II)N4 center with decreasing potential, CO2- or Ar-saturation of the electrolyte, leading to different adsorbates and stability of the HS Fe(II)N4 center. With operando Raman spectroscopy and cyclic voltammetry, we identify that the phthalocyanine (Pc) ligand coordinating the iron cation center undergoes a redox process from Fe(II)Pc to Fe(II)Pc-. Altogether, the HS Fe(II)Pc- species is identified as the catalytic intermediate for CO2RR. Furthermore, theoretical calculations reveal that the electroreduction of the Pc ligand modifies the d-band center of the in situ generated HS Fe(II)Pc- species, resulting in an optimal binding strength to CO2 and thus boosting the catalytic performance of CO2RR. This work provides both experimental and theoretical evidence toward the electronic structural and dynamics of reactive sites in single-Fe-atom materials and shall guide the design of novel efficient catalysts for CO2RR.