Photons to formate: Efficient electrochemical solar energy conversion via reduction of carbon dioxide

•CO2 was reduced to formate using an integrated silicon PV electrolyzer system.•The flow electrolyzer design utilized an indium cathode and an IrO2 anode.•3 cells with 109 cm2 electrodes were placed in series forming an electrolyzer stack.•Thermionic energy conversion efficiency (η) using sunlight (AM1.5) was 1.8%.•This represents the highest η for solar CO2 reduction reported to date.

The storage of solar energy as formic acid generated electrochemically from carbon dioxide has been identified as a viable solar fuel pathway. We report that this transformation can be accomplished by separating light absorption and CO2 reduction through the use of a commercial solar panel illuminated with natural AM1.5 sunlight to power a custom closed-loop electrochemical flow cell stack. Faradaic yields for formate of up to 67% have been demonstrated in this system, yielding a solar energy to fuel thermionic conversion efficiency above 1.8%.

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