Fabrication of ZnO/CuO nanoforests and their applicability to microbial photoelectrochemical cells

Three-dimensional ZnO/CuO nanoforests (NFRs) were fabricated via the galvanic submerged photosynthesis of crystallites in water at ambient temperature and pressure, and their photoelectrochemical (PEC) properties and applicability to microbial PEC (MPEC) cells were evaluated. ZnO/CuO NFRs irradiated with UV light for 48 h showed a high PEC current of −2.9 ± 1.3 mA/cm2 and hydrogen (H2) generation rate of 0.63 ± 0.29 µmol/cm2/min at 0 V vs. RHE owing to their superior light absorption, large BET specific surface area, and low charge recombination. The biocompatibility of the ZnO/CuO NFRs was evaluated by assessing their influence on Escherichia coli MG1655 growth. The ZnO/CuO NFRs leached Cu2+ and inhibited bacterial growth after immersion in the medium. Cu elution could be prevented by maintaining the potential at 0.01 V vs. RHE. The ZnO/CuO NFRs can be used as photocathodes for PEC H2 generation and the MPEC-based synthesis of valuable CO2-reduction products.