Performance For CO2 Reduction Reaction Research Articles

Pyrrolic N or pyridinic N: The active center of N-doped carbon for CO2 reduction

Pyridinic N is widely regarded as the active center while pyrrolic N has low-activity in metal-free N-doped carbon for electrocatalytic CO2 reduction reaction (CO2RR) to CO, but this viewpoint remains open to question. In this study, through density functional theoretical calculations, we first illustrate that the intrinsic activity of pyrrolic N is high enough for effectively catalyzing CO2RR, however, due to the interplay with the neighboring pyridinic N sites, the activity of pyrrolic N is dramatically suppressed. Then, experimentally, metal-free N-doped carbon spheres (NCS) electrocatalysts without significant pyridinic N content are prepared for CO2RR. The pyrrolic N in NCS shows a direct-positive correlation with the performance for CO2RR, representing the active center with high activity. The optimum NCS could produce syngas with a wide range of CO/H2 ratio (0.09 to 12) in CO2RR depending on the applied potential, meanwhile, the best selectivity of 71% for CO can be obtained. Intentionally adding a small amount of pyridinic N to the optimum NCS dramatically decreases the activity for CO2RR, further verifying the suppressed activity of pyrrolic N sites by the neighboring pyridinic N sites. This work reveals the interaction between a variety of N species in N-doped carbon, and the potential of pyrrolic N as the new type of active site for electrocatalysts, which can improve our understanding of the electrocatalysis mechanism and be helpful for the rational design of high-efficient electrocatalysts.

Design and screening of transition-metal doped chalcogenides as CO2-to-CO electrocatalysts

CO2 electroreduction is one of the most potential ways to realize CO2 recycle and energy regeneration. The key to promote this technology is the development of high-performance electrocatalysts. However, the rational design of electrocatalysts with highly catalytic activity and products selectivity toward CO2 reduction reaction (CO2RR) remains a challenging task. Herein, we developed a machine learning (ML) model to achieve efficient exploration of electrocatalysts for CO2RR by combining with density functional theory (DFT). The results show that the electron numbers of the d orbital is the most important descriptor and the support vector regression (SVR) has the best predictive performance. The coefficient of determination (R2) and mean squared error (MSE) are 0.9193 and 0.0162, respectively. Based on the well-trained model, the overpotential of Ni@MoS2 is successfully predicted to be 0.477 V and it shows the best electrocatalytic performance for CO2RR. DFT calculation results show that *COOH → *CO is the potential-limiting step of CO2-to-CO electroreduction for Ni@MoS2. The DFT-calculated overpotential is 0.481 V, which is consistent with the ML-predicted results. This work provides a convenient machine learning model for the effective theoretical design and screening of CO2-to-CO electrocatalysts.

Local Weak Hydrogen Bonds Significantly Enhance CO 2 Electroreduction Performances of a Metal–Organic Framework

Local Weak Hydrogen Bonds Significantly Enhance CO ₂ Electroreduction Performances of a Metal–Organic Framework

Data-Driven Investigation of Tellurium-Containing Semiconductors for CO2 Reduction: Trends in Adsorption and Scaling Relations.

Light-assisted conversion of CO2 into liquid fuels is one of several possible approaches to combating the rise of carbon dioxide emissions. Unfortunately, there are currently no known materials that are efficient, selective, or active enough to facilitate the photocatalytic CO2 reduction reaction (CO2RR) at an industrial scale. In this work, we employ density functional theory to explore potential tellurium-containing photocathodes for the CO2RR by observing trends in adsorption properties arising from over 350 *H, 200 *CO, and 110 *CHO surface–adsorbate structures spanning 39 surfaces of 11 materials. Our results reveal a scaling relationship between *CHO and *H chemisorption energies and charge transfer values, while the scaling relation (typically found in transition metals) between *CO and *CHO adsorption energies is absent. We hypothesize the scaling relation between *H and *CHO to be related to the lone electron located on the bonding carbon atom, while the lack of scaling relation in *CO we attribute to the ability of the lone pair on the C atom to form multiple bonding modes. We compute two predominant orbital-level interactions in the *CO-surface bonds (either using s or p orbitals) in addition to bonding modes involving both σ and π interactions using the Crystal Orbital Hamiltonian Population analysis. We demonstrate that bonds involving the C s orbital are more chemisorptive than the C p orbitals of CO. In general, chemisorption trends demonstrate decreased *H competition with respect to *CO adsorption and enhanced *CHO stability. Finally, we uncover simple element-specific design rules with Te, Se, and Ga sites showing increased competition and Zn, Yb, Rb, Br, and Cl sites showing decreased competition for hydrogen adsorption. We anticipate that these trends will help further screen these materials for potential CO2RR performance.

Single-Atom Catalysts Supported on the Graphene/Graphdiyne Heterostructure for Effective CO2 Electroreduction

Electrochemical reduction of CO2 to high-energy chemicals is a promising strategy for achieving carbon-neutral energy circulation. However, designing high-performance electrocatalysts for the CO2 reduction reaction (CO2RR) remains a great challenge. In this work, by means of density functional theory calculations, we systematically investigate the transition metal (TM) anchored on the nitrogen-doped graphene/graphdiyne heterostructure (TM-N4@GRA/GDY) as a single-atom catalyst for CO2 electroreduction applications. The computational results show that Co-N4@GRA/GDY exhibits remarkable activity with a low limiting potential of -0.567 V for the reduction of CO2 to CH4. When the charged Co-N4@GRA/GDY system is immersed in a continuum solvent, the reaction barrier decreases to 0.366 eV, which is ascribed to stronger electron transfer between GDY and transition metal atoms in the GRA/GDY heterostructure. In addition, the GRA/GDY heterostructure system significantly weakens the linear scaling relationship between the adsorption free energy of key CO2 reduction intermediates, which leads to a catalytic activity that is higher than that of the single-GRA system and thus greatly accelerates the CO2RR. The electronic structure analysis reveals that the appropriate d-π interaction will affect the d orbital electron distribution, which is directly relevant to the selectivity and activity of catalysis. We hope these computational results not only provide a potential electrocatalyst candidate but also open up an avenue for improving the catalytic performance for efficient electrochemical CO2RR.

Benchmarking the Electrochemical CO2 Reduction on Polycrystalline Copper Foils: The Importance of Microstructure Versus Applied Potential

AbstractCopper is one of the most promising catalysts for the CO2 reduction reaction (CO2RR) due to its unique capability of producing multicarbon products in appreciable quantities. Most of the CO2RR research efforts have been directed towards the development of new electrocatalysts to either increase product selectivities or decrease overpotentials. In contrast, only a few studies have systematically tested or benchmarked CO2RR performances of electrocatalysts. In this paper, for the first time, the performances of five different polycrystalline copper foils purchased from different suppliers are benchmarked for their CO2RR performance. Their differences are characterized in terms of microstructural features and the effect that these microstructural properties have on the electrocatalytic behavior during potentiostatic CO2RR experiments are evaluated. It is shown that the potential applied is the dominant factor controlling CO2RR selectivities, leading to the conclusion that microstructural properties of polycrystalline copper electrodes have a negligible effect on the outcome of CO2RR experiments.

Boosting the Electrocatalytic CO2 Reduction Reaction by Nanostructured Metal Materials via Defects Engineering.

Electrocatalytic CO2 reduction reaction (CO2RR) is one of the most effective methods to convert CO2 into useful fuels. Introducing defects into metal nanostructures can effectively improve the catalytic activity and selectivity towards CO2RR. This review provides the recent progress on the use of metal nanomaterials with defects towards electrochemical CO2RR and defects engineering methods. Accompanying these ideas, we introduce the structure of defects characterized by electron microscopy techniques as the characterization and analysis of defects are relatively difficult. Subsequently, we present the intrinsic mechanism of how the defects affect CO2RR performance. Finally, to promote a wide and deep study in this field, the perspectives and challenges concerning defects engineering in metal nanomaterials towards CO2RR are put forward.

Selective Electrochemical CO2 Reduction to Formate over Bismuth Nanosheets Derived By in-Situ Morphology Transformation of Bismuth Oxides

The electrochemical CO2 reduction reaction (CO2RR) has attracted enormous attention as a promising technology not only to mitigate CO2 accumulation, but also to convert CO2 into valuable chemicals and fuels.Formate/formic acid is a value-added product from CO2RR that is an important intermediate for chemical industries such as medicines, rubbers, leather and deicing materials. Moreover, it can be used as a source for hydrogen storage, transportation, as well as a fuel for direct formic acid fuel cells. Bismuth nanosheets (BiNSs) have been recognized as a promising catalyst for electrochemical CO2 reduction (CO2RR) to formate, but its preparation typically involves an elaborate synthesis of Bi-precursors under elevated temperature and pressure. Here, we have demonstrated a simple, low-cost preparation method for BiNSs by in-situ morphology transformation of Bi2O3 particles by simple electrochemical processing. SEM analysis showed that such transformation is exceedingly facile on the precipitated Bi2O3 particles compared to BiNPs and Oxi-BiNPs, revealing the crucial roles of oxygen and the initial morphology of Bi precursor in the exfoliation of BiNSs. The OD-BiNS exhibited superior CO2RR performance compared to the BiNPs and Oxi-BiNPs. 93% of FE was achieved with the current density of 62 mA cm−2 at −0.95 VRHE in the H-type cell. The enhanced CO2RR performance of OD-BiNSs can be attributed to its higher intrinsic activity and increased ECSA. 94% of FE with a high current density of 200 mA cm−2 was achieved in the flow cell, suggesting OD-BiNSs as a promising catalyst for practical applications of CO2RR. Our recent research on flow electrolytic cells for CO2 reduction will also be presented.

(Invited) Effect of Nanostructure and Surface Chemistry on Activity and Selectivity of Cu-Based Electrocatalysts for Carbon Dioxide Reduction

Electrochemical conversion of carbon dioxide (CO2) to value-added chemicals using electricity from renewable sources represents a promising path to carbon-neutral fuel cycle and enhanced economic benefits.1 To date, copper (Cu) has been the leading metal electrocatalyst for the electroreduction of CO2 to high-value chemicals: fuels and chemical feedstocks. Although there has been a significant progress in CO2 reduction reaction (CO2RR), the overall CO2RR performance of Cu-based electrocatalysts is still limited by poor selectivity, resulting in a variety of products, such as hydrogen, carbon monoxide, formic acid, methane, and ethylene.2 Enhancing the CO2RR rate relative to the competing hydrogen evolution reaction (HER) and achieving high selectivity for multi-carbon products thus represent the major scientific challenges.In this presentation, we will summarize our study of innovative Cu-based catalysts aimed at producing high energy-density chemicals, enhancing the understanding of reaction mechanism, and bringing CO2RR closer to practical application. The study has focused on the relationship between the composition and structure of Cu-based electrocatalysts, especially the nanostructure and oxidation states (Cu0, Cu+, and Cu2+), on CO2RR activity. By using a novel approach in the catalyst synthesis we have been able to obtain Cu-based materials with controlled nanostructure, e.g., pore-size distribution, higher surface area, and correlate the catalyst morphology with the selectivity for multi-carbon products. We have associated the formation of CO2RR products with the presence of different active sites on the catalyst surface, a necessary step towards achieving desirable selectivity.We will also recap the results of a study on the effect of adding a secondary transition metal, e.g., Zn, Ni, and Ag, on electrocatalytic properties of Cu-based catalysts. The rationale behind this approach has been to tune electrocatalytic activity and selectivity via changing the binding strength of the key intermediates, such as *OCHO, *CO, *COOH, *CHO, and *COH. References G. Kibria, J. P. Edwards, C. M. Gabardo, C.-T. Dinh, A. Seifitokaldani, D. Sinton, and E. H. Sargent, Adv. Mater. 2019, 31, 1807166.S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramillo, and I. Chorkendorff, Chem. Rev. 2019, 119, 7610−7672.

Unveiling the Proton‐Feeding Effect in Sulfur‐Doped Fe−N−C Single‐Atom Catalyst for Enhanced CO2 Electroreduction

AbstractHeteroatom‐doping in metal‐nitrogen‐carbon single‐atom catalysts (SACs) is considered a powerful strategy to promote the electrocatalytic CO2 reduction reaction (CO2RR), but the origin of enhanced catalytic activity is still elusive. Here, we disclose that sulfur doping induces an obvious proton‐feeding effect for CO2RR. The model SAC catalyst with sulfur doping in the second‐shell of FeN4 (Fe1−NSC) was verified by X‐ray absorption spectroscopy and aberration‐corrected scanning transmission electron microscopy. Fe1−NSC exhibits superior CO2RR performance compared to sulfur‐free FeN4 and most reported Fe‐based SACs, with a maximum CO Faradaic efficiency of 98.6 % and turnover frequency of 1197 h−1. Kinetic analysis and in situ characterizations confirm that sulfur doping accelerates H2O activation and feeds sufficient protons for promoting CO2 conversion to *COOH, which is also corroborated by the theoretical results. This work deepens the understanding of the CO2RR mechanism based on SAC catalysts.

Boosting Electrocatalytic CO 2 Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Boosting Electrocatalytic CO ₂ Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Carbon Dioxide Valorization via Formate Electrosynthesis in a Wide Potential Window

AbstractThe electrochemical CO2 reduction reaction (CO2RR) is a promising strategy to convert CO2 to carbon‐based fuels and to simultaneously reduce the emission of greenhouse gases into the atmosphere. In this work, the bismuth subcarbonate nanoflowers (BOC NFs) are facilely prepared through a one‐pot synthesis method for efficient formate electrosynthesis through CO2RR. Benefiting from the crystal structure and sheet‐stacked morphology, the in situ measurements and theoretical calculation results reveal the self‐reinforced CO2 adsorption properties and rapid CO2 adsorption–desorption kinetics on the catalyst surface, which significantly facilitate the CO2RR process. As a result, the desirable Faradaic efficiencies of over 90%, with a maximum value of 98.9%, toward formate formation, are achieved in a wide potential window from −0.8 to −1.4 V in an H‐type cell. Moreover, in a flow cell, the superior intrinsic activity of BOC NFs guarantees the high throughput electrocatalytic performance of CO2RR and the FEformate of over 90% with high current density is achieved in a potential range as wide as 1200 mV, demonstrating the great potential of BOC NFs for practical CO2RR applications. These results underscore the effectiveness of designing electrocatalysts with self‐reinforced CO2 adsorption properties to improve electrocatalytic performance for efficient CO2RR.

Cu cluster embedded porous nanofibers for high-performance CO2 electroreduction

Metal-doped carbon materials, as one of the most important electrocatalytic catalysts for CO2 reduction reaction (CO2RR), have attracted increasing attention. Herein, a series of Cu cluster embedded highly porous nanofibers have been prepared through the carbonization of electro-spun MOF/PAN nanofibers. The obtained Cu cluster doped porous nanofibers possessed fibrous morphology, high porosity, conductivity, and uniformly dispersed Cu clusters, which could be applied as promising CO2RR catalysts. Specifically, best of them, MCP-500 exhibited high catalytic performance for CO2RR, in which the Faradaic efficiency of CO (FECO) was as high as 98% at −0.8 V and maintained above 95% after 10 h continuous electrocatalysis. The high performance might be attributed to the synergistic effect of tremendously layered graphene skeleton and uniformly dispersed Cu clusters that could largely promote the electron conductivity, mass transfer and catalytic activity during the electrocatalytic CO2RR process. This attempt will provide a new idea to design highly active CO2RR electrocatalyst.

Investigation of Electrochemical Parameters on Cost-Effective Zn/Ni-Based Electrocatalysts for Electrochemical CO2 Reduction Reaction to SYNGAS(H2+CO)

Electrochemical CO2 reduction reaction (CO2RR) has been studied in 0.1 M of KCl (pH of 6.96), NaHCO3 (pH of 8.3) and K2CO3 (pH of 11.36) cathodic solutions with various counter electrodes including graphite rod, SS316 rod and Pt mesh at different potential ranges on the Znx–Ni1-x bimetallic electrocatalysts. Among the Znx–Ni1-x electrocatalysts, the Zn–Ni electrode with a composition of 65 wt% Zn and 35 wt% Ni and cluster-like microstructure has the best performance for CO2RR by according to minimum coke formation and optimum CO and H2 faradaic efficiencies (CO FE% = 55% and H2 FE% = 45%). The cyclic voltammetry (CV) measurements and gas chromatography (GC) analysis for the CO2RR showed that KCl solution as the cathodic electrolyte with pH of 7 has the best performance and appropriate faradaic efficiency for H2(40%) and CO(30%) products in low potential value (−0.6 v) in this study. The best potential range for the CO2RR on the Zn-Ni bimetallic electrocatalyst in KCl solution with the scan rate (SR) 0.05 V. s−1 is between −0.3 V to −1 V vs Ag/AgCl. The use of stainless-steel electrode (SS316) as a counter electrode for electrochemical CO2RR is cost-effective and performs better than graphite electrode, but at high applied potential it oxidizes and dissolves in the electrolyte and then ions transfer to the Nafion membrane and poisons it.

Effect of Bimetallic Dimer-Embedded TiO2(101) Surface on CO2 Reduction: The First-Principles Calculation.

The first-principles calculation was used to explore the effect of a bimetallic dimer-embedded anatase TiO2(101) surface on CO2 reduction behaviors. For the dimer-embedded anatase TiO2(101) surface, Zn-Cu, Zn-Pt, and Zn-Pd dimer interstitials could stably stay on the TiO2(101) surface with a binding energy of about −2.36 eV, as well as the electronic states’ results. Meanwhile, the results of adsorption energy, structure parameters, and electronic states indicated that CO2 was first physically and then chemically adsorbed much more stably on these three kinds of dimer-embedded TiO2(101) substrate with a small barrier energy of 0.03 eV, 0.23 eV, and 0.12 eV. Regarding the reduction process, the highest-energy barriers of the CO2 molecule on the Zn-Cu dimer-embedded TiO2(101) substrate was 0.31 eV, which largely benefited the CO2-reduction reaction (CO2RR) activity and was much lower than that of the other two kinds of Zn-Pt and Cu-Pt dimer-TiO2 systems. Simultaneously, the products CO* and *O* of CO2 reduction were firmly adsorbed on the dimer-embedded TiO2(101) surface. Our results indicated that a non-noble Zn-Cu dimer might be a more suitable and economical choice, which might theoretically promote the designation of high CO2RR performance on TiO2 catalysts.

Controllable fabrication of atomic dispersed low-coordination nickel-nitrogen sites for highly efficient electrocatalytic CO2 reduction

Single-atom catalysis has been considered as a powerful approach for CO2 reduction reaction (CO2RR) to achieve efficient resource conversion and carbon neutrality. The electrocatalytic activity of single-atom catalysts (SACs) is closely related to the local coordination environment. Herein, Ni SACs with well-defined low-coordination nickel-nitrogen sites (denoted as NiSA@N3-C) have been successfully developed via a facile sacrificial template method. XAS results reveal that the coordination environment of the atomically dispersed Ni active sites can be controlled by the pyrolysis temperature. Significantly, NiSA@N3-C displays remarkably excellent activity toward electrocatalytic CO2RR with CO Faradaic efficiency (FECO) of 96.0% at −0.83 V vs. RHE and remains high FECO exceeding 90% over a broad potential range from −0.63 to −0.93 V vs. RHE, outperforming those of NiSA@N4-C and NiNP@NC. More importantly, NiSA@N3-C exhibits an excellent CO selectivity of 99.2% with a considerable current density of −160 mA cm−2 in the flow cell reactor. Density functional theory (DFT) calculations further suggest that the Ni single atoms coordinated by three N atoms possesses a suitable free energy barrier for *COOH formation and *CO desorption, thereby exhibiting the most excellent CO2RR performance. This study sheds a new light on the design of SACs with controllable coordination structures for CO2RR.

Evolution of Triple-Phase interface for enhanced electrochemical CO2 reduction

Selective electrochemical CO2 reduction reaction (CO2RR) requires efficient triple-phase contact of CO2 molecules, electrolyte and active sites of electrocatalyst. To achieve this, studies have sought to use surface modifications to electrodes. However, the stability of these modifications and their effects on the intrinsic properties of electrodes are rarely discussed. Here, hydrophobic treatment of 1-octadecanethiol modification to a copper dendrite electrode was taken as a benchmark to investigate the evolution of the electrode surface and corresponding CO2RR performance after modifications. We show that the initial hydrophobic surface (HB-Cu) eventually transformed into a stable triple-phase interface (TP-Cu), ascribed to the formation of stable copper thiolate and the generation of crevices from alkane sulfonate dissolution. Surprisingly, this structural evolution leads to lower resistance of charge transfer and more sufficient exposure of active sites, enabling efficient triple-phase contact. As a result, TP-Cu achieved a near 4-fold enhancement of current density and a more than 2-fold reduction of H2 production compared to HB-Cu. Compared to previous studies, we have demonstrated extra power of the surface modification strategy to design triple-phase electrode interface, facilitating selective and efficient electrochemical CO2 reduction.

MOF‐Derived Cu/Bi Bi‐metallic Catalyst to Enhance Selectivity Toward Formate for CO2 Electroreduction

AbstractConverting CO2 into high‐value liquid products is a promising strategy to alleviate energy crisis. Herein, a novel Cu/Bi bi‐metal catalyst derived from MOFs has been prepared by a hydrothermal synthesis combining with high temperature calcination under N2 atmosphere, which shows cylindrical morphology composed of bi‐metallic nanoparticles. It is found that Cu/Bi bi‐metallic system is beneficial to lower the activate energy barrier of CO2 and shows a stronger adsorption capability for the CO2 ⋅ − intermediate than that of reference Bi/Bi2O3@C without Cu species. XPS analysis indicates the boosted performance for CO2 reduction reaction, which could be ascribed to synergistic coordination of Bi0 and Bi3+ in the catalyst. The optimized Cu1−Bi/Bi2O3@C exhibits excellent selectivity toward HCOOH with faradaic efficiency (FE) exceeding 84 % between −0.84 and −1.14 V vs. RHE, and even reaching 93 % at −0.94 V vs. RHE. The obtained Cu/Bi bi‐metal catalyst shows a promising application prospect in the CO2 reduction.

Rare earth praseodymium-based single atom catalyst for high performance CO2 reduction reaction

Rare earth single-atom catalysts (SACs) can be used to obtain atomically dispersed species on supports to provide the maximum number of well-defined active sites, which would subsequently maximize the utilizationof rare earth metals. However, the design and synthesis of SACs are mostly based on transition metals, and rare earth SACs have been rarely explored. Herein, we report a rare earth praseodymium SAC dispersed on a porous carbon substrate by utilizing the cascade anchoring strategy, with a metal loading of up to 5.07 wt%. This praseodymium SAC exhibits excellent catalytic performance for the electrochemical CO2 reduction reaction (CO2RR) and achieves high selectivity for CO, with a faradaic efficiency (FECO) of up to 93% at a low potential of −0.43 V vs RHE. Experiments and theoretical calculations confirm that the isolated praseodymium atoms on the substrate are critical for improving the CO2RR performance of the material.

Surface and interface chemistry in metal‐free electrocatalysts for electrochemical CO2 reduction

AbstractThe electrochemical reduction of carbon dioxide (CO2) into value‐added fuels and chemicals presents a sustainable route to alleviate CO2 emissions, promote carbon‐neutral cycles and reduce the dependence on fossil fuels. Considering the thermodynamic stability of the CO2 molecule and sluggish reaction kinetics, it is still a challenge to design highly efficient electrocatalysts for the CO2 reduction reaction (CO2RR). It has been found that the surface and interface chemistry of electrocatalysts can modulate the electronic structure and increase the active sites, which is favorable for CO2 adsorption, electron transfer, mass transport, and optimizing adsorption strength of reaction intermediates. However, the effect of surface and interface chemistry on metal‐free electrocatalysts (MFEs) for CO2RR has not been comprehensively reviewed. Herein, we discuss the importance of the surface and interface chemistry on MFEs for improving the electrochemical CO2RR performance based on thermodynamic and kinetic views. The fundamentals and challenges of CO2RR are firstly presented. Then, the recent advances of the surface and interface chemistry in improving reaction rate and overcoming reaction constraints are reviewed from regulating electronic structure, active sites, electron transfer, mass transport, and intermediate binding energy. Finally, the research challenges and prospects are proposed to suggest the future designs of advanced MFEs in CO2RR.