CO2 capture and electrocatalytic reduction to formate: A comprehensive review

Given that CO2 is the predominant greenhouse gas, its excessive emission has resulted in unprecedented climate change, necessitating the implementation of specific measures to mitigate atmospheric CO2 levels. CO2 capture and CO2 electroreduction represent two pivotal approaches for reducing carbon emissions and improving the sustainable utilization of carbon resources. These two technologies exist independently, but can also be synergistically integrated as the upper and lower components of the carbon cycle. Initially, CO2 in the mixture is captured and purified, followed by carrying out an electrocatalytic reduction reaction on the collected high-purity CO2 to further transform it into more useful chemicals. This review comprises three sections: (1) The review provides a comprehensive overview of the current research advancements in CO2 capture technology, which plays a pivotal role in the development of carbon capture, utilization, and storage (CCUS) technology. The CO2 capture technology can be categorized into absorption, adsorption, membrane separation and low-temperature methods. The chemical absorption method stands out as one of the most extensively employed and commercially viable technologies. The underlying principle involves the utilization of alkaline chemical absorbents to initiate a reaction with CO2, resulting in the formation of unstable salt products (such as carbonate, carbamate, etc.) in either liquid or solid phases. These generated salts can subsequently undergo decomposition under specific conditions, which can realize the separation and enrichment of CO2 and the regeneration of the absorbent. In addition, the pressure swing adsorption method is widely used in industrial CO2 separation, leveraging the reversible adsorption phenomenon of CO2 by an adsorbent, i.e., adsorption at a higher pressure, desorption at a lower pressure or vacuum, to effectively isolate it from other components. This method is a more suitable physical adsorption technology for carbon capture in power plants, and it also stands as a well-established post-combustion carbon capture technology. (2) Considering that formate is the most economically and technologically reduction product, this paper summarizes the development in the field of CO2 electroreduction to formate in recent years. The optimization of the electrocatalyst and the design of the reactor are the central of this research direction. The catalysts are usually optimized through the morphology control, crystal surface, and composition. The design of the reactor primarily relies on constructing three-phase interfaces, while ensuring low ohmic resistance and sufficient mass transfer capacity in the electrolytic reactor to achieve efficient CO2 electroreduction performance. (3) In view of the current research status of the two technologies, this review suggests that the further development should focus on the acceleration and development of new CCUS technologies, the exploitation of low-cost, efficient, and stable electrocatalysts, as well as the design of reactors with low ohmic resistance and high conversion energy efficiency.