Solar-driven methanogenesis with ultrahigh selectivity by turning down H2 production at biotic-abiotic interface

Integration of methanogens with semiconductors is an effective approach to sustainable solar-driven methanogenesis. However, the H-2 production rate by semiconductors largely exceeds that of methanogen metabolism, resulting in abundant H-2 as side product. Here, we report that binary metallic active sites (namely, NiCu alloys) are incorporated into the interface between CdS semiconductors and Methanosarcina barkeri. The self-assembled Methanosarcina barkeri-NiCu@CdS exhibits nearly 100% CH4 selectivity with a quantum yield of 12.41 +/- 0.16% under light illumination, which not only exceeds the reported biotic-abiotic hybrid systems but also is superior to most photocatalytic systems. Further investigation reveal that the Ni-Cu-Cu hollow sites in NiCu alloys can directly supply hydrogen atoms and electrons through photocatalysis to the Methanosarcina barkeri for methanogenesis via both extracellular and intracellular hydrogen cycles, effectively turning down the H-2 production. This work provides important insights into the biotic-abiotic hybrid interface, and offers an avenue for engineering the methanogenesis process. While the combination of synthetic and biological systems offers an appealing strategy for solar-to-fuel conversion, such hybrid systems typically suffer from low selectivity. Here, authors integrate a bimetallic alloy with a CdS-containing methanogen for selective CO2 reduction to methane.