CO2RR Catalysts Research Articles

Nitrogen-Doped Bismuth Nanosheet as an Efficient Electrocatalyst to CO2 Reduction for Production of Formate.

Electrochemical CO2 reduction (CO2RR) to produce high value-added chemicals or fuels is a promising technology to address the greenhouse effect and energy challenges. Formate is a desirable product of CO2RR with great economic value. Here, nitrogen-doped bismuth nanosheets (N-BiNSs) were prepared by a facile one-step method. The N-BiNSs were used as efficient electrocatalysts for CO2RR with selective formate production. The N-BiNSs exhibited a high formate Faradic efficiency (FEformate) of 95.25% at -0.95 V (vs. RHE) with a stable current density of 33.63 mA cm-2 in 0.5 M KHCO3. Moreover, the N-BiNSs for CO2RR yielded a large current density (300 mA cm-2) for formate production in a flow-cell measurement, achieving the commercial requirement. The FEformate of 90% can maintain stability for 14 h of electrolysis. Nitrogen doping could induce charge transfer from the N atom to the Bi atom, thus modulating the electronic structure of N-Bi nanosheets. DFT results demonstrated the N-BiNSs reduced the adsorption energy of the *OCHO intermediate and promoted the mass transfer of charges, thereby improving the CO2RR with high FEformate. This study provides a valuable strategy to enhance the catalytic performance of bismuth-based catalysts for CO2RR by using a nitrogen-doping strategy.

Recent Progress in Surface and Interface Engineering for Electrocatalytic CO2 Reduction.

The conversion of CO2 through CO2 reduction reaction (CO2 RR) into valuable products has potential to lessen the greenhouse effect caused by uncontrolled CO2 emissions. Challenges of CO2 RR reaction lie in the stabilization of the reaction intermediate and the activation of the inert chemical bond of CO2 , but the application of CO2 RR at large scale is limited by the high cost and structural instability of traditional catalysts. By applying CO2 RR catalyst with delicate structure of stable CO2 intermediate to industrial production, the problems such as high cost of CO2 conversion, low catalytic selectivity and poor catalytic efficiency can be effectively solved, showing better application value and significance than traditional catalysts. This review focuses on the defects, and metal-support interaction (MSI) effect to modify the catalyst and other strategies to enhance the effectiveness of CO2 reduction. The challenges and prospects from the three perspectives are also discussed to provide suggestions for the designing of efficient CO2 RR catalysts in the future. This review offers new insights and research perspectives of reducing CO2 emission through recycling CO2 , and neutralizing the carbon cycle.

Bifunctional Nb-N-C atomic catalyst for aqueous Zn-air battery driving CO2 electrolysis

Designing efficient and cost-effective bifunctional catalysts is desirable for carbon dioxide and oxygen reduction reactions (CO2RR and ORR) to address carbon neutralization and energy conversion. Herein, a bifunctional CO2RR and ORR catalyst for aqueous Zn-air battery (ZAB) self-driving CO2RR electrolysis is developed using atomically dispersed niobium anchored onto N-doped ordered mesoporous carbon (Nb-N-C). The Nb-N-C atomic catalyst demonstrates aqueous CO2RR activity with CO Faradaic efficiency up to 90%, ORR activity with a half-wave potential of 0.84 V vs. reversible hydrogen electrode, and ZAB activity with a peak power density of 115.6 mW cm−2, owing to the high Nb atom-utilization efficiency and ordered mesoporous structure. Furthermore, two-unit ZABs in series, serving as the power source for the self-powered CO2 electrolysis system, continuously convert CO2 to CO with average productivity of 3.75 µmol h−1 mgcat−1 during the first 10 h. Moreover, theoretical calculations exhibit that atomic Nb anchored to N-doped carbon can form Nb-N coordination bonds, effectively reducing the energy barriers of potential-determining *COOH for CO2RR and *O formation for ORR.

Anomalous Ru dissolution enabling efficient integrated CO2 electroreduction in strong acid

Recently, emerging acidic conditions CO2 electrolyzer overcomes the limitations of lower carbon utilization efficiency due to carbonate/bicarbonate formation in neutral/alkaline media, which offers a promising route to the realization of carbon cycle and environment optimization. Nevertheless, an integral CO2 conversion electrolyzer must consider the sluggish reaction kinetics of the oxygen evolution reaction (OER), especially in acid media. Herein, we demonstrate a significant improvement in anodic OER performance by tailoring the surface structure of RuO2 catalyst with potassium. The obtained K-RuO2 electrocatalyst can reach 10 mA/cm2 only with an overpotential of 170 mV and exhibits prolonged stability, showing overwhelming catalytic performance compared to RuO2. Advanced synchrotron radiation-based multi-techniques (SRMS) and theory calculations demonstrate the remarkable performance originating from the anomalous dissolution, which caused by consciously initiated K generating enhanced ratio of active RuCUS sites for K-RuO2. When K-RuO2 pairs with cathodic CO2RR catalyst of bismuth, it achieves the result of lower cell voltage and nearly 4-fold longer durability in strong acid compared to RuO2 catalyst. This work provides a deep insight into the true active structure of anode RuO2 catalyst, paves a new way to design high-performance noble metal-based catalysts for acidic OER, and finally contributes to the advancement of CO2 electrolysis.

Amorphization-Activated Copper Indium Core-Shell Nanoparticles for Stable Syngas Production from Electrochemical CO2 Reduction.

Electrochemical carbon dioxide reduction reaction (CO2 RR) refers to the conversion of carbon dioxide into compounds with added value through electrolysis. It is still a great challenge to design and manufacture efficient CO2 RR catalysts for desired products. Producing syngas via CO2 RR is an environmentally friendly way to reduce CO2 in the atmosphere and the dependence on fossil fuels. Herein, a new class of Cu/In2 O3 nanoparticles (NPs) with controlled phases and structures were successfully prepared as superior electrocatalysts for CO2 RR, where the CO/H2 ratios in syngas on Cu/In2 O3 NPs/C-H2 remained about 1 : 2 at a broad potential range and the total faradaic efficiency of H2 and CO always remained about 90 %. Electronic structural analysis revealed that the excellent performance was attributed to the electronic interaction between amorphous In2 O3 and Cu. This work broadens the horizons for designing and preparing fascinating electrocatalysts for CO2 RR.

A nitrogen-doped graphene-supported nickel-single-atom catalyst in the flow cell meets the industrial criteria of carbon dioxide reduction reaction to carbon monoxide

Carbon dioxide reduction reaction (CO2RR) is a promising approach to accomplishing net zero CO2 emissions. Among CO2RR catalysts, nitrogen-doped graphene-supported single-atom catalysts show a remarkable conversion rate from CO2 to CO; however, the low production amount has been limited using the conversion H cell, hindering its industrial development. In this work, we synthesize a nitrogen-doped graphene-supported nickel-single-atom catalyst and conduct CO2RR in a flow cell, exhibiting a CO2-to-CO Faradaic efficiency of 96% and a partial current density of 144 mA cm−2. It can also achieve the highest partial current density of 204 mA cm−2 with a turnover frequency of 7,852 h−1. According to the techno-economic analysis, these preeminent activities meet the industrial criteria (Faradaic efficiency >60% and partial current density >100 mA cm−2). This activity enhancement using a flow system can significantly accelerate net-zero CO2 emission realization.

Computational screening of TMN4 based graphene-like BC6N for CO2 electroreduction to C1 hydrocarbon products

Graphene-like BC6N monolayers supported with TMN4 (TM = Sc ∼ Zn) (TMN4@BC6N) centers, which can provide various coordination environment, was studied to explore its performance as efficient CO2RR catalysts through density functional theory (DFT). High-throughput screening based on structural stability and reaction pathways identified the most promising catalyst candidates. According to the optimal path and overpotential analysis, five TMN4@BC6N (TM = Cr, Mn, Fe, Co and Zn) systems with low limiting potentials exhibit high CO2RR activity towards C1 products. The potential origin of electrocatalytic performance shows the descriptors of Eb (*CO) and Eb (*OH) act as performance indicators. It is revealed that coordination environment with different charge near the TMN4 active center can modulate the catalytic activity of the catalyst. Overall, this work suggests the novel TMN4@BC6N SAC has potential application prospects in CO2RR and sheds light on designing of new two-dimensional materials with high stability and superior CO2RR activity.

Benchmarking the two-dimensional conductive Y3(C6X6)2 (Y = Co, Cu, Pd, Pt; X = NH, NHS, S) metal-organic framework nanosheets for CO2 reduction reaction with tunable performance

Scrutinizing competent and economical electrocatalysts for carbon-di-oxide reduction reactions (CO2RR) is essential for wide-range commercialization of livestock feed. Therefore, via density functional theory (DFT), we broadly explored the electrocatalytic performance of two-dimensional (2D) metal−organic frameworks (Y3(C6X6)2), where Y indicates Co, Cu, Pd, Pt; and X indicates organic ligands; (NH, NHS, S) for CO2RR. The 2D Y3(C6X6)2 monolayers unveiled metallic behavior due to the suitable π electron conjugation network and the productive interaction among the metal atom, organic ligands, and benzene rings, except for Co3(C6S6)2, which revealed semiconducting behavior. Significantly, the catalytic performance of Y3(C6X6)2 is influenced by the strength of interaction between the CO2RR intermediates and the metal complex (Y-X4), which may be altered by varying the central metal atom with different d-electron orbitals or by organic ligands. Surprisingly, Co3(C6(NH)3S3)2, Co3(C6(NH)3)2, and Cu3(C6S6)2 have excellent CO2RR to formic acid activity. Whereas, Pt3(C6(NH)3)2 and Pd3(C6(NH)3)2 shows good CO2RR to carbon mono-oxide activity. Our research provides imperative insights for designing and screening efficient CO2RR catalysts. This research put forward the idea of developing metal-organic frameworks with beneficial properties to meet the specific requirements of diverse research areas, such as catalysis, energy storage, and molecular sensing.

Two–dimensional metal organic nanosheet as promising electrocatalysts for carbon dioxide reduction: A computational study

Designing high–selectivity and low-cost electrocatalysts are highly desirable for the carbon dioxide reduction reaction (CO2RR). Herein, the promising CO2RR electrocatalysts were screened out from several two–dimensional metal organic frameworks (2D–MOFs) nanosheets by means of density functional theory (DFT) calculations. According to the computational results, we identified three promising CO2RR catalysts for different products. The main products of CO2RR by Fe3(HHTP)2, Co3(HHTP)2 and Ir3(HHTP)2 are HCOOH, CH3OH and CH4, respectively. Particularly, the Ir3(HHTP)2 shows remarkable high catalytic activity with lowest limiting potential (UL = –0.22 V) for CH4 production. Therefore, the rational controlled chemical modifications of 2D–MOFs materials provide a new scenario for the design of promising novel CO2RR electrocatalyst.

Characterizing CO2 Reduction Catalysts on Gas Diffusion Electrodes: Comparing Activity, Selectivity, and Stability of Transition Metal Catalysts.

Continued advancements in the electrochemical reduction of CO2 (CO2RR) have emphasized that reactivity, selectivity, and stability are not explicit material properties but combined effects of the catalyst, double-layer, reaction environment, and system configuration. These realizations have steadily built upon the foundational work performed for a broad array of transition metals performed at 5 mA cm–2, which historically guided the research field. To encompass the changing advancements and mindset within the research field, an updated baseline at elevated current densities could then be of value. Here we seek to re-characterize the activity, selectivity, and stability of the five most utilized transition metal catalysts for CO2RR (Ag, Au, Pd, Sn, and Cu) at elevated reaction rates through electrochemical operation, physical characterization, and varied operating parameters to provide a renewed resource and point of comparison. As a basis, we have employed a common cell architecture, highly controlled catalyst layer morphologies and thicknesses, and fixed current densities. Through a dataset of 88 separate experiments, we provide comparisons between CO-producing catalysts (Ag, Au, and Pd), highlighting CO-limiting current densities on Au and Pd at 72 and 50 mA cm–2, respectively. We further show the instability of Sn in highly alkaline environments, and the convergence of product selectivity at elevated current densities for a Cu catalyst in neutral and alkaline media. Lastly, we reflect upon the use and limits of reaction rates as a baseline metric by comparing catalytic selectivity at 10 versus 200 mA cm–2. We hope the collective work provides a resource for researchers setting up CO2RR experiments for the first time.

Seeded Growth of Gold-Copper Janus Nanostructures as a Tandem Catalyst for Efficient Electroreduction of CO2 to C2+ Products.

Gold-copper (Au-Cu) Janus nanostructures (Au-Cu Janus NSs) are successfully prepared using N-oleyl-1,3-propanediamine as capping agent and Cu(acac)2 as the precursor in a typical seeded growth strategy. By preferably depositing Cu atoms on one side of concave cubic Au seeds, the Cu part gradually grows larger as more Cu precursors are added, making the size tuning feasible in the range of 74-156nm. When employed as an electrocatalyst for electrochemical CO2 reduction (CO2 RR), the Au-Cu Janus NSs display superior performance to Au@Cu core-shell NSs and Cu NPs in terms of C2+ products selectivity (67%) and C2+ partial current density (-0.29Acm-2 ). Combined experimental verification and theoretical simulations reveal that CO spillover from Au sites to the nearby Cu counterparts would enhance CO coverage and thus promote C-C coupling, highlighting the unique structural advantages of the Au-Cu Janus NSs toward deep reduction of CO2 . The current work provides a facile strategy to fabricate tandem catalyst with a Janus structure and validates its structural advantages toward CO2 RR, which are of critical importance for the rational design of efficient CO2 RR catalyst.

Complementary Operando Spectroscopy identification of in-situ generated metastable charge-asymmetry Cu2-CuN3 clusters for CO2 reduction to ethanol

Copper-based materials can reliably convert carbon dioxide into multi-carbon products but they suffer from poor activity and product selectivity. The atomic structure-activity relationship of electrocatalysts for the selectivity is controversial due to the lacking of systemic multiple dimensions for operando condition study. Herein, we synthesized high-performance CO2RR catalyst comprising of CuO clusters supported on N-doped carbon nanosheets, which exhibited high C2+ products Faradaic efficiency of 73% including decent ethanol selectivity of 51% with a partial current density of 14.4 mA/cm−2 at −1.1 V vs. RHE. We evidenced catalyst restructuring and tracked the variation of the active states under reaction conditions, presenting the atomic structure-activity relationship of this catalyst. Operando XAS, XANES simulations and Quasi-in-situ XPS analyses identified a reversible potential-dependent transformation from dispersed CuO clusters to Cu2-CuN3 clusters which are the optimal sites. This cluster can’t exist without the applied potential. The N-doping dispersed the reduced Cun clusters uniformly and maintained excellent stability and high activity with adjusting the charge distribution between the Cu atoms and N-doped carbon interface. By combining Operando FTIR and DFT calculations, it was recognized that the Cu2-CuN3 clusters displayed charge-asymmetric sites which were intensified by CH3* adsorbing, beneficial to the formation of the high-efficiency asymmetric ethanol.

General Synthetic Strategy to Ordered Mesoporous Carbon Catalysts with Single-Atom Metal Sites for Electrochemical CO2 Reduction.

The electrochemical carbon dioxide reduction reaction (CO2 RR) is a transformative technology to reduce the carbon footprint of modern society. Single-site catalysts have been demonstrated as promising catalysts for CO2 RR, but general synthetic methods for catalysts with high surface area and tunable single-site metal composition still need to be developed to unambiguously investigate the structure-activity relationship crossing various metal sites. Here, a generalized coordination-condensation strategy is reported to prepare single-atom metal sites on ordered mesoporous carbon (OMC) with high surface areas (average 800m2 g-1 ). This method is applicable to a broad range of metal sites (Fe, Co, Ni, Cu, Pt, Pd, Ru, and Rh) with loadings up to 4wt.%. In particular, the CO2 RR to carbon monoxide (CO) Faradaic efficiency (FE) with Ni single-site OMC catalyst reaches 95%. This high FE is maintained even under large current density (>140mAcm-2 ) and in a long-term study (14h), which suits the urgently needed large-scale applications. Theoretical calculations suggest that the enhanced activity on single-atom Ni sites results from balanced binding energies between key intermediates, COOH and CO, for CO2 RR, as mediated by the coordination sphere.

Organic frameworks confined Cu single atoms and nanoclusters for tandem electrocatalytic CO2 reduction to methane

AbstractThe electrochemical reduction reaction of carbon dioxide (CO2RR) is considered to be an effective way to realize carbon neutrality. As a type of intensively studied materials, covalent organic frameworks (COFs) with a tunable pore structure and various functional groups are promising catalysts for CO2RR. Herein, COF synthesized by 2,6‐diaminoanthraquinone and 2,4,6‐triformylphloroglucinol is employed to assist the synthesis of electrocatalysts from Cu single atoms (SAs) to nanoclusters by controlling the electrodeposition. A tandem catalyst for CO2‐to‐CH4 conversion is thus achieved by the Cu nanoclusters dispersed among the isolated Cu SAs in the COF network. It is proposed that CO2 is first reduced to CO over the atomically isolated Cu SAs, followed by diffusion onto the neighboring Cu nanoclusters for further reduction into CH4. In addition, mechanistic analysis suggests that the coordinated K+ ions on the COF network promote the activation of CO2 and the adsorption of reaction intermediates, thus realizing the suppressed hydrogen evolution reaction and selective production of CH4. This study presents a new insight of COFs for the confined synthesis of a tunable SA to nanocluster electrocatalysts, disclosing the great potential of COFs in electrocatalysis.

Optimizing the Electrocatalytic Selectivity of Carbon Dioxide Reduction Reaction by Regulating the Electronic Structure of Single‐Atom M‐N‐C Materials

AbstractElectrochemical carbon dioxide reduction reaction (CO2RR) is an efficient strategy to relieve global environmental and energy issues by converting excess CO2 from the atmosphere to value‐added products. Atomically dispersed metal‐nitrogen‐doped carbon (M‐N‐C) materials are superior catalysts for electrocatalytic CO2RR because of the 100% atomic utilization, unsaturated coordination configuration, relatively uniform active sites, and well‐defined and adjustable structure of active centers. However, the electrochemical CO2RR is a great challenge due to the process involving proton‐coupled multi‐electron transfer with a high energy barrier, which leads to unsatisfactory selectivity to the targeted product, especially for C2 products (e.g., C2H4 and C2H5OH). Here, the authors systematically summarize effective means, including reasonable selection of isolated metal sites, regulation of the coordination environment of isolated metal atoms, and fabrication of dimetallic single‐atom sites for attaining optimal geometric and electronic structures of M‐N‐C materials and further correlate these structures with catalytic selectivity to various C1 (e.g., CO and CH4) and C2 products in the CO2RR. Moreover, constructive strategies to further optimize M‐N‐C materials for electrocatalytic CO2RR are provided. Finally, the challenges and future research directions of the application of M‐N‐C materials for electrocatalytic CO2RR are proposed.

CO2 reduction on single-atom Ir catalysts with chemical functionalization

As promising catalytic systems, single-atom catalysts (SACs) demonstrate improved catalytic performance for electrochemical reactions. However, the pinning of metal atoms on surfaces usually depends on the adsorption on defects. In this study, defect-free functionalization by attaching IrX3 (X = F or Cl) complexes on the MoS2 monolayer is theoretically demonstrated. The ligand-based method offers a damage-free route for stabilizing SACs on 2D materials. We demonstrate the CO2 reduction process on MoS2-IrX3 with a small change in free energy and a low onset potential. The d6 shell of Ir acts as a molecular joint with universal orbital orientations, which benefits the adsorption of different reaction intermediates. This study shows the superiority of defect-free functionalization of 2D materials using SAC-ligand complexes.

A metallic Cu2N monolayer with planar tetracoordinated nitrogen as a promising catalyst for CO2 electroreduction

By means of a particle swarm optimization search and density functional theory computations, we predicted a hitherto unknown Cu2N monolayer with planar hexacoordinate Cu and tetracoordinate N atoms as a CO2RR catalyst.

Mechanistic understanding and design of non-noble metal-based single-atom catalysts supported on two-dimensional materials for CO2 electroreduction

This review delivers an overview of non-noble metal-based single-atom catalysts (SACs) for CO2RR and provides insights into mechanistic understanding from different aspects.

Why heterogeneous single-atom catalysts preferentially produce CO in the electrochemical CO2 reduction reaction.

Formate and CO are competing products in the two-electron CO2 reduction reaction (2e CO2RR), and they are produced via *OCHO and *COOH intermediates, respectively. However, the factors governing CO/formate selectivity remain elusive, especially for metal–carbon–nitrogen (M–N–C) single-atom catalysts (SACs), most of which produce CO as their main product. Herein, we show computationally that the selectivity of M–N–C SACs is intrinsically associated with the CO2 adsorption mode by using bismuth (Bi) nanosheets and the Bi–N–C SAC as model catalysts. According to our results, the Bi–N–C SAC exhibits a strong thermodynamic preference toward *OCHO, but under working potentials, CO2 is preferentially chemisorbed first due to a charge accumulation effect, and subsequent protonation of chemisorbed CO2 to *COOH is kinetically much more favorable than formation of *OCHO. Consequently, the Bi–N–C SAC preferentially produces CO rather than formate. In contrast, the physisorption preference of CO2 on Bi nanosheets contributes to high formate selectivity. Remarkably, this CO2 adsorption-based mechanism also applies to other typical M–N–C SACs. This work not only resolves a long-standing puzzle in M–N–C SACs, but also presents simple, solid criteria (i.e., CO2 adsorption modes) for indicating CO/formate selectivity, which help strategic development of high-performance CO2RR catalysts.

NiFe-CN catalysts derived from the solid-phase exfoliation of NiFe-layered double hydroxide for CO2 electroreduction

The strategy of preparing a CO2RR catalyst on the basis of solid-phase exfoliation helps to fully expose the catalytic centers of Ni and Fe, and provides a channel for proton transfer, so that the catalyst exhibits excellent performance.