A MoS₂ catalyzed bioelectrochemical system is successfully constructed, in which microbial protein can be produced from the simplest small molecule substances (CO₂, N₂, and H₂O) and Xanthobacter-dominanted hydrogen oxidizing bacteria can be enriched. Additionally, MoS₂ can improve biofilm extracellular electron transfer (EET) and enhance proline production.

Abstract

Carbon dioxide can be relatively easily reduced to organic matter in a bioelectrochemical system (BES). However, due to insufficient reduction force from in-situ hydrogen evolution, it is difficult for nitrogen reduction. In this study, MoS₂ was firstly used as an electrocatalyst for the simultaneous reduction of CO₂ and N₂ to produce microbial protein (MP) in a BES. Cell dry weight (CDW) could reach 0.81±0.04 g/L after 14 d operation at −0.7 V (vs. RHE), which was 108±3 % higher than that from non-catalyst control group (0.39±0.01 g/L). The produced protein had a better amino acid profile in the BES than that in a direct hydrogen system (DHS), particularly for proline (Pro). Besides, MoS₂ promoted the growth of bacterial cell on an electrode and improved the biofilm extracellular electron transfer (EET) by microscopic observation and electrochemical characterization of MoS₂ biocathode. The composition of the microbial community and the relative abundance of functional enzymes revealed that MoS₂ as an electrocatalyst was beneficial for enriching Xanthobacter and enhancing CO₂ and N₂ reduction by electrical energy. These results demonstrated that an efficient strategy to improve MP production of BES is to use MoS₂ as an electrocatalyst to shift amino acid profile and microbial community.