Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels

Significance Direct capture of CO 2 from the air and its conversion to fuels using solar energy offers a means for mitigating global warming while also supporting future energy demands. Whereas natural photosynthesis converts CO 2 and water to carbohydrates, this process is only 0.5–2.0% efficient and the energy content of the resulting biomass is low. Increasing CO 2 levels in the atmosphere combined with rising energy needs motivate the search for an artificial photosynthetic system that is at least 10 times as efficient as that used by nature. Identification of light absorbers that provide a photocurrent density >10 mA cm -2 and a photovoltage >2 V are prerequisites for a >10% efficient artificial photosynthetic system.