Efficient H₂ production in a microbial photoelectrochemical cell with a composite Cu₂O/NiO_x photocathode under visible light

Microbial photoelectrochemical cells (MPEC) is a state-of-the-art and self-sustained 'waste-to-energy' solution through coupling a synergistic microbial conversion of waste organics into electron and proton in a bioanode and photoelectrochemical catalysis of proton reduction for hydrogen evolution in a photocathode. With the advantage of visible light adsorption, p-type semiconductor Cu₂O has exhibited superior photocatalytic potential for hydrogen evolution reaction (HER), but the instability of p-type Cu₂O hinders its further practical application. Here, we fabricated a Cu₂O/NiO_x composite photocathode by spin coating a thin film of NiO_x on Cu₂O photocathode to improve its stability and photocurrent. Results showed that NiO_x layer on Cu₂O had a trade-off effect on photocathode performance. The thicker of NiO_x film on Cu₂O, the lower of the photocurrent, but more stable of the Cu₂O electrode. With an optimal 240 nm thickness of NiO_x layer, the Cu₂O/NiO_x composite photocathode extracted excited electrons effectively, and a H₂ production rate of 5.09 μL h^-1 cm^-2 was obtained from a MPEC under continuous light illumination with 0.2 V external bias. By tuning the synergistic effect of bioanode and photocathode, MPEC could provide a feasible solution on simultaneously organic conversion and energy restoration from wastewater and solar light.