A photoelectrochemical-thermoelectric device for semi-artificial CO2 fixation employing full solar spectrum utilization

The bigger pictureThe utilization of the full solar spectrum, from ultraviolet to infrared, is crucial for efficient solar fuel and chemical production. Low-energy photons are often lost as waste heat in conventional photoelectrochemical cells, reducing performance and stability. We demonstrate a proof-of-concept device that synergistically uses high-energy photons via photoexcitation of a semiconductor photoanode and low-energy photons via waste heat utilization with a thermoelectric generator to drive solar CO2 fixation. Enzymatic catalysis complements the process, producing formate with high selectivity and rate, enhanced by heat from concentrated solar irradiation. This concept drives the artificial photosynthetic reaction of CO2 reduction coupled with water oxidation to O2, employing a thermoelectric generator to fully utilize the solar spectrum.Highlights•Photoelectrochemical CO2 reduction has been enhanced through waste heat utilization•Heat enhances kinetics and thermodynamics in the device, powered by concentrated sunlight•A thermoelectric generator has been coupled to enzyme catalysis•The photoelectrochemical-thermoelectric device produces formate and oxygen at a 2:1 ratioSummaryNatural and most artificial photosynthesis systems utilize a pair of light absorbers to convert CO2 into sugar and fuels. However, much of the solar energy is lost as unabsorbed (mainly infrared [IR]) irradiation and thermalization heat, limiting efficiency. Here, we show that a thermoelectric (TE) generator can harvest this waste heat toward unassisted CO2 reduction with a water-oxidizing BiVO4 photoanode upon irradiation by concentrated sunlight. We employ the enzyme formate dehydrogenase (FDh) as a model catalyst to achieve selective CO2-to-formate conversion with minimal overpotential. The catalytic activity of the FDh cathode and BiVO4 photoanode benefits from solar heating, enabling the bias-free semi-artificial FDh-TE-BiVO4 device to attain a 97% faradic yield for formate production under 3-sun irradiation. This work demonstrates unassisted CO2 reduction coupled to water oxidation using only a single semiconductor light absorber through effective waste heat utilization, overcoming the challenges of (non-)complementary light absorption and IR losses in both natural and artificial photosynthesis.Graphical abstract