Perspectives and Challenges of Electrochemical, Photochemical, and Photoelectrochemical Conversion of CO2 into Valuable Fuels Using Metal and Metal Oxide-Based Catalysts

Abstract

The rise in atmospheric carbon dioxide due to burning fossil fuels, industrial activities, and change in land use, is the primary cause of global climate change with concomitant decline in environmental quality. To address this problem new and scalable solutions are required for carbon capture and utilization. In this context, promising and sustainable approaches to minimize energy shortages and greenhouse gas emissions include reduction of CO2 via electrochemical eCO2RR, photochemical, and photoelectrochemical (PEC) pathways to valuable fuels. This review summarizes the current developments in metal- and metal oxide-based catalysts for CO2 reduction, focusing on their mechanisms, catalytic activities, and structural designs. The fundamentals of electrocatalysis, reaction routes, thermodynamic and kinetic limitations, product specificity, Faradaic efficiency, and current density are highlighted. The structure-function relationship regarding CO2RR performance of the transition metals, single-atom catalysts (SACs), and dual-atom catalysts (DACs) are compared with noble metals. Particular focus is on oxide-based catalysts, in which defect generation and control of oxygen vacancies can promote activation of CO2 and its conversion to value added products. The photocatalytic CO2 reduction has been discussed in the context of artificial photosynthesis where photo reaction efficiency is dependent upon semiconductor band alignment, separation of charges, and charge carrier dynamics at the reaction surface. Hybrid light-harvesting nanostructures combined with redox-active centers have been highlighted as an active area of research in PEC systems. It exhibits a synergistic effect by exploiting light-absorption process and electrochemical reactions to achieve separation of charges, thereby maximizing overall efficiency. This document also outlines the main limitations, including catalyst stability, C-C coupling efficiency, and competing hydrogen evolution reactions, and recommend follow-up research directions based on operando studies, application of machine learning-informed catalyst design, and integration of renewable energy to make CO2 valorization possible on an industrial scale. The present article is unique as it presents a comprehensive framework that integrates photochemical and electrochemical methods to develop next-generation catalytic systems to meet environmental and industrial needs.