Hybrid solar-to-methane conversion system with a Faradaic efficiency of up to 96%

Solar-driven electrochemical CO2 reduction to fuels has considerable potential to satisfy future renewable energy needs and mitigate CO2 emissions, but current approaches face significant challenges, such as poor selectivity and large overpotential for the catalytic reactions. Here we present a hybrid microbial-photoelectrochemical system that selectively converts CO2 into methane in a single step without any by-products. The hybrid system employs a biocathode that was capable of reducing CO2 into CH4 with an unprecedentedly low overpotential (< 50 mV) and a TiO2 nanowire array photoanode for light harvesting and water oxidation. Using sunlight as the sole energy input, we demonstrate highly selective CO2 reduction to CH4 with an overall Faradaic efficiency of up to 96%. With a continuous supply of CO2, the hybrid system generates a stable current over 90 h, demonstrating its long-term stability.