Continuous Production of Ethylene from Carbon Dioxide and Water Using Intermittent Sunlight

By Ren, Dan; Loo, Nicholas Wei Xian; Gong, Luo; Yeo, Boon Siang
Published in ACS Sustainable Chemistry & Engineering

Abstract

The large-scale deployment of efficient artificial photosynthesis systems to convert carbon dioxide (CO2) into carbon-based fuels and chemical feedstocks holds great promise as a way to ensure a carbon neutral cycle. While catalysts have been developed for the pertinent half-reaction of CO2 reduction to C2 molecules, an integrated system for this purpose has never been designed and built. In this work, we demonstrate an energetically efficient formation of ethylene directly from CO2 and water (H2O) using solar energy at room temperature and pressure. A two-electrode cell (electrolyzer) was designed, and cell parameters such as electrolyte and voltage were optimized. Oxide-derived copper (Cu) and iridium oxide (IrOx) were used as electrocatalysts respectively in the cathode and anode. Coupling this electrolyzer with silicon solar panels under laboratory 1 sun illumination (100 mW/cm2), we show that CO2 could be facilely reduced to ethylene with a faradaic efficiency of 31.9%, partial current density of 6.5 mA/cm2, and a solar-to-ethylene energy efficiency of 1.5%. When liquid fuels such as ethanol and n-propanol were included, the total solar-to-fuel efficiency was 2.9%. These outstanding figures-of-merits are the state-of-the-art. We also introduced insoluble chelating agents in the electrolyte to capture contaminants such as dissolved iridium ions, and thus significantly improved the longevity of the electrolyzer. Compared to previously reported solar-to-fuel setups which were only tested under simulated sunlight, our system, when coupled with a rechargeable battery, could run and produce ethylene continuously using only intermittent natural sunlight.

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