Surface display engineering of specific proteins enhanced oxygen reduction at biocathodes

Microbial fuel cells (MFCs) represent a green and promising technology for interconverting electrical and chemical energy. However, the efficiency of microbial catalysts is often fundamentally limited by inherent catalytic constrains of natural enzymes and insulating barrier of the cell membrane. In this study, we heterologously expressed leghemoglobin 4 (LB4) in Escherichia coli (E. coli) and displayed it on the cell surface using an ice nucleation protein (INP). LB4 serves as an efficient electrocatalyst for the oxygen reduction reactions (ORR), exhibiting high intrinsic activity. The surface-display strategy not only increased the protein level of active LB4 but also effectively circumvented the insulating cell membrane barrier. As a result, the engineered strain INP-Soya achieved an ORR current density of 3.46 mA cm^-2 (vs. RHE) and an onset potential of 0.78 V. The MFC constructed with INP-Soya generated a maximum power density of 300 μW cm^-2. This work demonstrates that the surface display of catalytically active proteins provides a viable strategy for achieving efficient bioelectrocatalysis.