Mechanistic Understanding of CO2 Reduction Reaction (CO2RR) Toward Multicarbon Products by Heterogeneous Copper-Based Catalysts

Defect Engineering on Carbon-Based Catalysts for Electrocatalytic CO2 Reduction

Electrocatalytic carbon dioxide (CO₂) reduction (ECR) has become one of the main methods to close the broken carbon cycle and temporarily store renewable energy, but there are still some problems such as poor stability, low activity, and selectivity. While the most promising strategy to improve ECR activity is to develop electrocatalysts with low cost, high activity, and long-term stability. Recently, defective carbon-based nanomaterials have attracted extensive attention due to the unbalanced electron distribution and electronic structural distortion caused by the defects on the carbon materials. Here, the present review mainly summarizes the latest research progress of the construction of the diverse types of defects (intrinsic carbon defects, heteroatom doping defects, metal atomic sites, and edges detects) for carbon materials in ECR, and unveil the structure-activity relationship and its catalytic mechanism. The current challenges and opportunities faced by high-performance carbon materials in ECR are discussed, as well as possible future solutions. It can be believed that this review can provide some inspiration for the future of development of high-performance ECR catalysts.

CO2 and H2O Coadsorption and Reaction on the Low-Index Surfaces of Tantalum Nitride: A First-Principles DFT-D3 Investigation

A comprehensive mechanistic insight into the photocatalytic reduction of CO2 by H2O is indispensable for the development of highly efficient and robust photocatalysts for artificial photosynthesis. This work presents first-principles mechanistic insights into the adsorption and activation of CO2 in the absence and presence of H2O on the (001), (010), and (110) surfaces of tantalum nitride (Ta3N5), a photocatalysts of significant technological interest. The stability of the different Ta3N surfaces is shown to dictate the strength of adsorption and the extent of activation of CO2 and H2O species, which bind strongest to the least stable Ta3N5(001) surface and weakest to the most stable Ta3N5(110) surface. The adsorption of the CO2 on the Ta3N5(001), (010), and (110) surfaces is demonstrated to be characterized by charge transfer from surface species to the CO2 molecule, resulting in its activation (i.e., forming negatively charged bent CO2−δ species, with elongated C–O bonds confirmed via vibrational frequency analyses). Compared to direct CO2 dissociation, H2O dissociates spontaneously on the Ta3N5 surfaces, providing the necessary hydrogen source for CO2 reduction reactions. The coadsorption reactions of CO2 and H2O are demonstrated to exhibit the strongest attractive interactions on the (010) surface, giving rise to proton transfer to the CO2 molecule, which causes its spontaneous dissociation to form CO and 2OH− species. These results demonstrate that Ta3N5, a narrow bandgap photocatalyst able to absorb visible light, can efficiently activate the CO2 molecule and photocatalytically reduce it with water to produce value-added fuels.

Fundamentals of Gas Diffusion Electrodes and Electrolysers for Carbon Dioxide Utilisation: Challenges and Opportunities

Electrocatalysis plays a prominent role in the development of carbon dioxide utilisation technologies. Many new and improved CO2 conversion catalysts have been developed in recent years, progressively achieving better performance. However, within this flourishing field, a disconnect in catalyst performance evaluation has emerged as the Achilles heel of CO2 electrolysis. Too often, catalysts are assessed in electrochemical settings that are far removed from industrially relevant operational conditions, where CO2 mass transport limitations should be minimised. To overcome this issue, gas diffusion electrodes and gas-fed electrolysers need to be developed and applied, presenting new challenges and opportunities to the CO2 electrolysis community. In this review, we introduce the reader to the fundamentals of gas diffusion electrodes and gas-fed electrolysers, highlighting their advantages and disadvantages. We discuss in detail the design of gas diffusion electrodes and their operation within gas-fed electrolysers in both flow-through and flow-by configurations. Then, we correlate the structure and composition of gas diffusion electrodes to the operational performance of electrolysers, indicating options and prospects for improvement. Overall, this study will equip the reader with the fundamental understanding required to enhance and optimise CO2 catalysis beyond the laboratory scale.

Optical Excitation of a Nanoparticle Cu/p-NiO Photocathode Improves Reaction Selectivity for CO2 Reduction in Aqueous Electrolytes

We report the light-induced modification of catalytic selectivity for photoelectrochemical CO₂ reduction in aqueous media using copper (Cu) nanoparticles dispersed onto p-type nickel oxide (p-NiO) photocathodes. Optical excitation of Cu nanoparticles generates hot electrons available for driving CO₂ reduction on the Cu surface, while charge separation is accomplished by hot-hole injection from the Cu nanoparticles into the underlying p-NiO support. Photoelectrochemical studies demonstrate that optical excitation of plasmonic Cu/p-NiO photocathodes imparts increased selectivity for CO₂ reduction over hydrogen evolution in aqueous electrolytes. Specifically, we observed that plasmon-driven CO₂ reduction increased the production of carbon monoxide and formate, while simultaneously reducing the evolution of hydrogen. Our results demonstrate an optical route toward steering the selectivity of artificial photosynthetic systems with plasmon-driven photocathodes for photoelectrochemical CO₂ reduction in aqueous media.

Integrated design for electrocatalytic carbon dioxide reduction

We have summarized three novel strategies for electrocatalytic carbon dioxide reduction, including concurrent CO₂ electroreduction, tandem CO₂ electroreduction and hybrid CO₂ electroreduction.