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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