Abstract Photofermentative biohydrogen production (PFHP) is a promising route for sustainable biohydrogen production, but its efficiency is constrained by inefficient intra/extracellular electron transfer (IET/EET). Biochar (BC) provides unique characteristics to enhance IET/EET in biochemical systems; however, non-conductive polymer groups hinder its charge transfer efficiency. The present study proposes the engineering of the microbial-electrochemical interface through dual metal (Co and Fe) functionalization of BC to improve charge transfer within the fermentative medium, thus leading to an increase in hydrogen production. SEM, BET, XPS, and Raman spectroscopy demonstrated that Co-Fe/BC functionalization results in 22.83% higher porosity and surface area compared to pristine biochar (PBC) and single metal functionalization, suggesting increased electrons from surface defects like oxygen vacancies (OVs). The optimal loading concentration (20 mg/L) of Co-Fe/BC enhanced the biohydrogen production rate and yield by 101.61% and 103.11%, respectively, exceeding the control group (CG). Electrochemical studies showed that the lowest interfacial charge transfer resistance (1.74 Ω, 1.22 mA redox current) in Co-Fe/BC increases charge transfer capabilities by 106.77% compared to PBC (4.66 Ω, 0.59 mA redox current) thus serving as an electron shuttle to increase redox sites through flavin and c-cytochrome. IET/EET enhancement in a bioreactor loaded with Co-Fe/BC regulates butyric acid to acetic acid metabolism, as revealed by microbial community analysis, where Clostridium was 86.72% more prevalent than CG (79.77%). This work demonstrates that Co-Fe functionalized BC not only bridges electron transfer bottlenecks but also provides a conductive interface for sustained microbial-electrochemical interactions, offering a scalable strategy for optimizing renewable biohydrogen production. Graphical Abstract
Tahir et al. (Sun,) studied this question.