Efficient CO₂ conversion to formic acid in a novel microbial photoelectrochemical cell using a visible-light responsive Co₃O₄ nanorod-arrayed photocathode

A microbial photoelectrochemical cell (MPEC) is a self-biased, solar-driven device combining bioenergy with solar energy to produce sustainable electricity and chemicals. Here, an MPEC with a p-type Co₃O₄ nanorod-arrayed photocathode and bio-anode was constructed that matched well the redox potentials of anode microorganisms with the band gap of the Co₃O₄. The yield of formic acid produced by this MPEC under visible light irradiation with an external resistance of 300 Ω was 239 ± 10 μmol in 10 h, which was 1.8 times that produced by a bare Co₃O₄ photocathode under visible light, and 4.9 times that produced by the MPEC operated in dark. The maximum power density was 331 ± 4 mW m^–2 under visible light, compared to 175 ± 25 mW m^–2 in the dark. This study of MPEC with the synergistic effect of light energy and bioenergy opens up new opportunities for applications in environmental treatment of wastewaters and chemicals production.