Electrocatalytic Membranes for Tunable Syngas Production and High-Efficiency Delivery to Biocompatible Electrolytes

The integration of electrochemical and biological CO2 reduction in artificial photosynthetic processes holds great promise to alleviate the current environmental stress of carbon-intensive industries and enable a circular carbon economy. The advancement of these devices hinges on the development of highly stable and selective CO2 reduction catalysts that can operate in an array of biocompatible conditions. Here, we fabricated a porous silver gas diffusion electrode (GDE) on the carbon nanotube (CNT)-supported hydrophobic membrane for tunable electrochemical syngas production. We then tested its performance under the direct gas delivery mode, different chamber thicknesses, and different microbial-electrolyte compositions. Distinct from traditional flow-by delivery, CO2 was directly flowed through the GDE and electrochemically converted to syngas and delivered into the electrolyte. The optimized reactor with the narrower chamber enabled higher CO faradic efficiencies (FEs) (∼92 vs ∼42%) and larger tunable CO/H2 ratios (35:65 to 91:9 vs 12:88 to 41:59). The impact of complex microbial growth media on electrocatalysis was also investigated, and it was found that the systems achieved consistent >90% FE for syngas production, but nutrient ingredients such as NH4Cl and yeast extract led to much higher H2 production due to the significant increase in proton availability from these species. The culmination of these findings helps address key limitations at the microbial-electrode interface that aid in the development of practical artificial photosynthetic technologies toward the sustainable production of green fuels and chemicals.