Ambient CO₂ Capture and Valorization Enabled by Tandem Electrolysis Using Solid-State Electrolyte Reactor

Electrocatalytic carbon dioxide reduction is a promising technology for addressing global energy and environmental crises. However, its practical application faces two critical challenges: the complex and energy-intensive process of separating mixed reduction products and the economic viability of the carbon sources (reactants) used. To tackle these challenges simultaneously, solid-state electrolyte (SSE) reactors are emerging as a promising solution. In this review, we focus on the feasibility of applying SSE for tandem electrochemical CO₂ capture and conversion. The configurations and fundamental principles of SSE reactors are first discussed, followed by an introduction to its applications in these two specific areas, along with case studies on the implementation of tandem electrolysis. In comparison to conventional H-type cell, flow cell and membrane electrode assembly cell reactors, SSE reactors incorporate gas diffusion electrodes and utilize a solid electrolyte layer positioned between an anion exchange membrane (AEM) and a cation exchange membrane (CEM). A key innovation of this design is the sandwiched SSE layer, which enhances efficient ion transport and facilitates continuous product extraction through a stream of deionized water or humidified nitrogen, effectively separating ion conduction from product collection. During electrolysis, driven by an electric field and concentration gradient, electrochemically generated ions (e.g., HCOO^– and CH₃COO^–) migrate through the AEM into the SSE layer, while protons produced from water oxidation at the anode traverse the CEM into the central chamber to maintain charge balance. Targeted products like HCOOH can form in the middle layer through ionic recombination and are efficiently carried away by the flowing medium through the porous SSE layer, in the absence of electrolyte salt impurities. As CO₂RR can generate a series of liquid products, advancements in catalyst discovery over the past several years have facilitated the industrial application of SSE for more efficient chemicals production. Also noteworthy, the cathode reduction reaction can readily consume protons from water, creating a highly alkaline local environment. SSE reactors are thereby employed to capture acidic CO₂, forming CO₃^2– from various gas sources including flue gases. Driven by the electric field, the formed CO₃^2– can traverse through the AEM and react with protons originating from the anode, thereby regenerating CO₂. This CO₂ can then be collected and utilized as a low-cost feedstock for downstream CO₂ electrolysis. Based on this principle, several cell configurations have been proposed to enhance CO₂ capture from diverse gas sources. Through the collaboration of two SSE units, tandem electrochemical CO₂ capture and conversion has been successfully implemented. Finally, we offer insights into the future development of SSE reactors for practical applications aimed at achieving carbon neutrality. We recommend that greater attention be focused on specific aspects, including the fundamental physicochemical properties of the SSE layer, the electrochemical engineering perspective related to ion and species fluxes and selectivity, and the systematic pairing of consecutive CO₂ capture and conversion units. These efforts aim to further enhance the practical application of SSE reactors within the broader electrochemistry community.