Isopropanol production from carbon dioxide by Cupriavidus necator using a zero-gap cell with culture broth as catholyte

Microbial CO₂ fixation is a promising route for sustainable chemical production. The facultative chemolithoautotroph <i>Cupriavidus necator</i> can convert CO₂ into value-added compounds using H₂ and O₂. Here, we developed a bioelectrochemical system (BES) for isopropanol production that integrates CO₂ fixation with <i>in situ</i> H₂ generation via a zero-gap proton exchange membrane electrolyzer. Using the culture broth as catholyte, a pentlandite-based cathode supplied dissolved H₂ directly to engineered <i>C. necator</i>, eliminating the need for pressurized gas. Real-time monitoring of dissolved and off-gas compositions guided system operation, yielding an isopropanol titer of 1.1 g L^-1. The pentlandite electrode remained stable with negligible leaching. This platform demonstrates a scalable approach for coupling electrolysis and microbial synthesis and can be extended to other H₂-utilizing microbes.