Sludge reduction and hydrogen production in a microbial photoelectrochemical cell with a g-C3N4/CQDs/BiOBr composite photocathode.

Hydrogen (H₂) remains a pivotal clean energy source, and the emergence of Solar-powered Microbial Photoelectrochemical Cells (MPECs) presents promising avenues for H₂ production while concurrently aiding organic matter degradation. This study introduces an MPEC system employing a g-C₃N₄/CQDs/BiOBr photocathode and a bioanode, successfully achieving simultaneous H₂ production and sludge reduction. The research highlights the effective formation of a Z-type heterojunction in the g-C₃N₄/CQDs/BiOBr photocathode, substantially enhancing the photocurrent response under light conditions. Operating at - 0.4 V versus RHE, it demonstrated a current density of - 3.25 mA·cm^-2, surpassing that of g-C₃N₄/BiOBr (-2.25 mA·cm^-2) by 1.4 times and g-C₃N₄ (-2.04 mA·cm^-2) by 1.6 times. When subjected to visible light irradiation and a 0.8 V applied bias voltage, the MPEC system achieved a current density of 1.0 mA·cm^-2. The cumulative H₂ production of the MPEC system reached 8.9 mL, averaging a production rate of 0.13 mL·h^-1. In the anode chamber, the degradation rates of total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total suspended solids (TSS), volatile suspended solids (VSS), proteins, polysaccharides, and volatile fatty acids (VFA) in the sludge were recorded at 57.18%, 82.64%, 64.98%, 86.39%, 42.81%, 67.34%, and 29.01%, respectively.