Electrochemical Reduction of CO2: A Review of Cobalt Based Catalysts for Carbon Dioxide Conversion to Fuels

Electrochemical CO2 reduction reaction (CO2RR) provides a promising approach to curbing harmful emissions contributing to global warming. However, several challenges hinder the commercialization of this technology, including high overpotentials, electrode instability, and low Faradic efficiencies of desirable products. Several materials have been developed to overcome these challenges. This mini-review discusses the recent performance of various cobalt (Co) electrocatalysts, including Co-single atom, Co-multi metals, Co-complexes, Co-based metal–organic frameworks (MOFs), Co-based covalent organic frameworks (COFs), Co-nitrides, and Co-oxides. These materials are reviewed with respect to their stability of facilitating CO2 conversion to valuable products, and a summary of the current literature is highlighted, along with future perspectives for the development of efficient CO2RR.

REACTION OF OXYGEN REDUCTION ON THE SURFACE OF AU ON TI WITH OXIDEFORMED POTENTIODYNAMICALLY BEFORE AND AFTER THE DEPOSITION OF AU

One of the most important reactions for electrochemical science and technology is the electrocatalytic reduction ofoxygen. It is particularly relevant in fuel cells because it is slow to react and requires high overpotentials. This workaims to study electrodes with deposits of Au on Ti obtained by electrodeposition. The substrates have undergone po-tentiodynamic growths of oxides before deposition for some electrodes and after deposition for other electrodes understudy, at different final potentials. Both procedures resulted in the formation of a composite Au layer on the Ti surface.The electrochemical behavior of these composite layers was examined in a 0.01 M HClO4solution, both oxygen-freeand oxygen-saturated, and compared with the behavior of Ti as a target, using the cyclic voltammetry technique. In thepotential region of the oxygen reduction reaction (RRO), the Au layer on the Ti obtained by first performing the Audeposition and then the growth of the anode oxide showed a better response, not only in the onset potential of the RRO,but also in the current densities. In all cases the voltammetry curves of the Au and TiO2 composite layers were similarto those shown by the Au polycrystalline.

Self-supported Ni3S2@Ni2P/MoS2 heterostructure on nickel foam for outstanding oxygen evolution reaction and efficient overall water splitting

Hydrogen production by electrocatalytic water splitting is a pollution-free, energy-saving, efficient method. The low efficiency of hydrogen production, high overpotentials and expensive noble-metal catalysts have limited the development of hydrogen...

Controllable synthesis of multidimensional carboxylic acid-based NiFe MOFs as efficient electrocatalysts for oxygen evolution

Oxygen evolution reaction (OER), as an essential half reaction of water splitting that producing green hydrogen, has been subject to high overpotentials and restrictions on the use of noble metal...

Industrially promising NiCoP nanorod arrays tailored with trace W and Mo atoms for boosting large-current-density overall water splitting

Nanoarray catalysts supported on the substrates provide an opportunity for industrially promising overall water splitting at large-current-densities. However, most of the present electrocatalysts show high overpotentials at a large current...

Electron Transfer Limitation in Carbon Dioxide Reduction Revealed by Data-Driven Tafel Analysis

Carbon dioxide (CO₂) recycling holds promise to mitigate anthropogenic emissions and to increase the sustainability of many chemical and fuel production processes. Despite marked advances in catalyst activity and selectivity at laboratory scale, fundamental understanding of the electrocatalytic reduction of CO₂ remains limited, resulting in great uncertainty when extrapolating data to industrially relevant reaction rates. Importantly, the predominant models apply linear Tafel extrapolation, which drastically overpredicts the current density at large overpotentials. Researchers have posited several models to explain the curvature in Tafel behavior for CO₂ reduction catalysis. Here we compare the ability of select models using Bayesian inference to explain curvature in Tafel behavior within the context of CO₂ reduction to CO catalyzed by gold surfaces. By harvesting Tafel data on gold surfaces from multiple literature sources in a variety of reactor configurations, we identify three important features common to the aggregate data on Au-mediated CO₂ reduction: (1) curvature in the Tafel plot at high overpotentials is only partly caused by mass transfer limitations; (2) the Marcus-Hush-Chidsey model for rate-limiting single-electron transfer kinetics provides the best fit to the data of the models tested; and finally, (3) the highly varied data collapse onto a single curve governed by the maximum predicted current in the electron-transfer-limited model. This analysis sets a foundation for determining more accurate activity-driving force relationships for CO₂ reduction on electrocatalytic surfaces, both improving the quality of system-level analyses and motivating further research into the underlying mechanisms of CO₂ reduction catalysis.

Electron Transfer Limitation in Carbon Dioxide Reduction Revealed by Data-Driven Tafel Analysis

Carbon dioxide (CO₂) recycling holds promise to mitigate anthropogenic emissions and to increase the sustainability of many chemical and fuel production processes. Despite marked advances in catalyst activity and selectivity at laboratory scale, fundamental understanding of the electrocatalytic reduction of CO₂ remains limited, resulting in great uncertainty when extrapolating data to industrially relevant reaction rates. Importantly, the predominant models apply linear Tafel extrapolation, which drastically overpredicts the current density at large overpotentials. Researchers have posited several models to explain the curvature in Tafel behavior for CO₂ reduction catalysis. Here we compare the ability of select models using Bayesian inference to explain curvature in Tafel behavior within the context of CO₂ reduction to CO catalyzed by gold surfaces. By harvesting Tafel data on gold surfaces from multiple literature sources in a variety of reactor configurations, we identify three important features common to the aggregate data on Au-mediated CO₂ reduction: (1) curvature in the Tafel plot at high overpotentials is only partly caused by mass transfer limitations; (2) the Marcus-Hush-Chidsey model for rate-limiting single-electron transfer kinetics provides the best fit to the data of the models tested; and finally, (3) the highly varied data collapse onto a single curve governed by the maximum predicted current in the electron-transfer-limited model. This analysis sets a foundation for determining more accurate activity-driving force relationships for CO₂ reduction on electrocatalytic surfaces, both improving the quality of system-level analyses and motivating further research into the underlying mechanisms of CO₂ reduction catalysis.

Circumventing Scaling Relations in Oxygen Electrochemistry using Metal-Organic Frameworks

It has been well-established that unfavorable scaling relationships between *OOH, *OH, and *O are responsible for the high overpotentials associated with oxygen electrochemistry. A number of strategies have been proposed for breaking these linear constraints for traditional electrocatalysts (e.g. metals, alloys, metal-doped carbons); such approaches have not yet been validated experimentally for heterogenous catalysts. Development of a new class of catalysts capable of circumventing such scaling relations remains an ongoing challenge in the field. In this work, we use density functional theory (DFT) calculations to demonstrate that bimetallic porphyrin-based MOFs (PMOFs) are an ideal materials platform for rationally-designing the 3D active site environments for oxygen reduction reaction (ORR). Specifically, we show that the *OOH binding energy and the theoretical limiting potential can be optimized by appropriately tuning the transition metal active site, the oxophilic spectator, and the MOF topology. Our calculations predict theoretical limiting potentials as high as 1.07 V for Fe/Cr-PMOF-Al, which exceeds the Pt/C benchmark for 4e ORR. More broadly, by highlighting their unique characteristics, this works aims to establish bimetallic porphyrin-based MOFs as a viable materials platform for future experimental and theoretical ORR studies.

Circumventing Scaling Relations in Oxygen Electrochemistry using Metal-Organic Frameworks

It has been well-established that unfavorable scaling relationships between *OOH, *OH, and *O are responsible for the high overpotentials associated with oxygen electrochemistry. A number of strategies have been proposed for breaking these linear constraints for traditional electrocatalysts (e.g. metals, alloys, metal-doped carbons); such approaches have not yet been validated experimentally for heterogenous catalysts. Development of a new class of catalysts capable of circumventing such scaling relations remains an ongoing challenge in the field. In this work, we use density functional theory (DFT) calculations to demonstrate that bimetallic porphyrin-based MOFs (PMOFs) are an ideal materials platform for rationally-designing the 3D active site environments for oxygen reduction reaction (ORR). Specifically, we show that the *OOH binding energy and the theoretical limiting potential can be optimized by appropriately tuning the transition metal active site, the oxophilic spectator, and the MOF topology. Our calculations predict theoretical limiting potentials as high as 1.07 V for Fe/Cr-PMOF-Al, which exceeds the Pt/C benchmark for 4e ORR. More broadly, by highlighting their unique characteristics, this works aims to establish bimetallic porphyrin-based MOFs as a viable materials platform for future experimental and theoretical ORR studies.