Nano zero-valent iron functioned 3D printing graphene aerogel electrode for efficient solar-driven biocatalytic methane production

To address the urgent need for developing carbon-neutral technologies, microbial electrosynthesis (MES), as an important contributor to the renewable energy field, can convert carbon dioxide to multi-carbon chemicals using microbes serving as living catalysts at the cathode. However, the performance of the cathode is restricted by the weak electrochemical reaction kinetics of the organisms, the specific area of the electrode, and the mass transfer under high current. Herein, we report a facile 3D-printed graphene aerogel (GA) electrode built with a nanozero-valent iron (NZVI)-functionalized graphene ink. The 3D-printed GA electrode was designed to possess hierarchical pores with an enhanced high specific surface area for microbial colonization while ensuring mass transfer. NZVI can assist in-situ hydrogen generation, facilitating biofilm formation and methane (CH4) production in the indirect electron transfer pathway. Consequently, the optimized 3D-printed electrode achieved a maximum CH4 production rate of 6993 ± 832 mmol/m2/d with a faradaic efficiency of 83.7%, which increased by 3.24-fold to the carbon felt electrode. In addition, integrating the proposed cathode into a PV-electrolyzer cell yielded a solar-to-CH4 efficiency of 4.70%. This study provides a unique method for the development of advanced cathodes and underscores the potential of integrating MES with renewable energy technologies.