Photoelectrocatalytic-Microbial Biohybrid for Nitrogen Reduction

Nitrogen (N₂) conversion to ammonia (NH₃) in a mild condition is a big chemical challenge. The whole-cell diazotrophs based biological NH₃ synthesis is one of the most promising strategies. Herein, the first attempt of photoelectrochemical-microbial (PEC-MB) biohybrid is contributed for artificial N₂ fixation, where Azotobacter vinelandii (A. vinelandii) is interfaced directly with polydopamine encapsulated nickel oxide (NiO) nanosheets (NiO@PDA). By virtue of excellent bio-adhesive activity, high conductivity, and good biocompatibility of PDA layer, abundant A. vinelandii are effectively adsorbed on NiO@PDA to form NiO@PDA/A. vinelandii biohybrid, and the rationally designed biohybrid achieved a record-high NH₃ production yield of 1.85µmol h⁻¹/10⁸ cells (4.14 µmol h⁻¹ cm⁻²). In addition, this biohybrid can operate both under illumination with a PEC model or in dark with an electrocatalytic (EC) model to implement long-term and successional NH₃ synthesis. The enhancement mechanism of NH₃ synthesis in NiO@PDA/A. vinelandii biohybrid can be ascribed to the increase of nicotinamide adenine dinucleotide-hydrogen (NADH) and adenosine 5-triphosphate (ATP) concentrations and over expression of nitrogen-fixing genes of nifH, nifD and nifK in nitrogenase. This innovative PEC-MB biohybrid strategy sheds light on the fundamental mechanism and establishes proof of concept of biotic-abiotic photosynthetic systems for sustainable chemical production.