Photoelectrocatalytic-Microbial Biohybrid for Nitrogen Reduction.

Nitrogen (N 2 ) conversion to ammonia (NH 3 ) in a mild condition is a big chemical challenge. The whole-cell diazotrophs based biological NH 3 synthesis is one of the most promising strategies. Herein, the first attempt of photoelectrochemical-microbial (PEC-MB) biohybrid is contributed for artificial N 2 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 NH 3 production yield of 1.85   µmol h -1 /10 8 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 NH 3 synthesis. The enhancement mechanism of NH 3 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.