Solid-state electrolytes for CO2 electroreduction: From mechanisms to applications

Conventional liquid CO 2 electroreduction faces carbonate loss, flooding, and product dilution. Separation energy and stability costs remain high. Solid-state electrolytes (SSEs) offer an alternative. They separate ionic transport from bulk liquid, suppress carbonate formation and flooding, which enables high-purity and high-concentration products at relevant current densities. This review links microenvironment mechanisms factors—pH, water activity, ion speciation, and electric fields—to ionic conductivity, stability and high-frequency resistance. Moreover, this review maps the evolution and taxonomy of SSEs, including dense ionomers, inorganic solids, and porous composites. Then, this review analyzes key challenges: humidity and salt management, mechanical integrity, chemical compatibility, thermal effects, and structural changes in porous media. Next, this review summarizes device-level strategies: electrode–electrolyte interface design, thin SSEs with buffer layers, multi-chamber reactors, and tandem reactor design. Finally, it points out three potential ways to develop solid-state electrolyte systems. Overall, SSE-based CO 2 reduction reaction converts long-standing bottlenecks into engineered variables and enables efficient, stable, and scalable product streams. • Liquid CO 2 RR is limited to poor stability, low energy and reactant efficiency. • SSE can suppress carbonate generation and flooding. • SSE can achieve the continuous production of high-purity, concentrated products. • SSE faces challenges of humidity & salt, thermal, chemical, structure and mechanical factors. • Optimization is achieved by electrode interface and reactor design.