Microenvironmental Engineering of a Solid-State Electrolyte Reactor for Efficient Microbial Electrosynthesis of Acetate from CO2

Tandem systems coupling electrochemical CO2 reduction (CO2RR) with microbial conversion offer a promising strategy to overcome the limitations of conventional microbial electrosynthesis (MES), which typically suffers from low reaction rates due to its reliance on electrode–biofilm architectures. In this study, we develop a solid-state electrolyte (SSE) reactor through microenvironmental engineering, eliminating the need for prefabricated anion exchange membranes (AEMs) and advanced electrocatalysts—both of which have constrained the practical deployment of SSE systems. A potassium-infused, sandwich-structured gas diffusion electrode (GDE) is fabricated via a three-layer, layer-by-layer assembly, an approach shown to be superior to the physical mixing of any two of the constituent layers. Furthermore, a simple filter paper separator is employed in place of pristine or porous AEMs to mitigate hydrogen accumulation and maintain a pH gradient at the GDE–SSE interface. Using commercial bismuth nanoparticles as the electrocatalyst, this configuration enables stable operation for over 130 h, yielding more than 3 litres of pure formic acid solution at concentrations exceeding 0.1 M. For microbial conversion, the integrated system achieves a near-theoretical formate-to-acetate molar ratio of 4.1:1 with a pure acetogenic culture, while a mixed consortium yields a slightly higher ratio of 5.0:1. This work underscores the potential of microenvironmental engineering in advancing cost-effective tandem systems for CO2 valorization.