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

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 (IrO x ) 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.

Si photocathode with Ag-supported dendritic Cu catalyst for CO2reduction

“…This type of cathode contamination by metals from the counter electrode has been observed previously in CO2 electrolysis cells and appears to be only partially mitigated by the use of an anion conducting membrane. 24 Replacing the IrO2 counter electrode with Pt exacerbated the contamination effect with H2 production becoming dominant after only 2 days (Fig. S19c, ESI, shows XPS observation of Pt on the photocathode).…”

“…Although far fewer in number compared to water splitting, there have been a number of recent demonstrations of solarpowered CO2R, some of which have reported overall energy conversion efficiencies above 1%. [18][19][20][21][22][23][24][25][26] Notably, most of these demonstrations employ photovoltaic elements which are isolated from the electrochemistry; exceptions are studies which use an illuminated photoanode to drive the water oxidation reaction (OER) with a dark cathode employed for CO2R. 20,21 Urbain et al reported a CO2 reduction prototype reactor containing a Si photoanode coupled to Ni foam as an OER catalyst and a Cu foam with Zn flakes as the cathode with a solar to syngas conversion efficiency of 4.3%.…”

Effects of Electrolyte Anions on the Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper (100) and (111) Surfaces

“…Reducing CO 2 emission from the use of fossil fuels is urgently needed to prevent undesirable global warming . Using renewable electricity and catalysts for the electrochemical reduction of CO 2 to chemicals and fuels offers a promising approach to reduce our reliance on fossil fuels . Copper‐based catalysts are particularly attractive for such a purpose owing to their unique ability to reduce CO 2 to ethylene and ethanol .…”

Solar-powered synthesis of hydrocarbons from carbon dioxide and water

“…Development of improved systems for CO 2 conversion has been an area of intense activity, with significant emphasis placed on EC design and on discovery of improved CO 2 reduction (4, 5) and H 2 O oxidation (6) catalysts based on nonprecious earthabundant elements. PV-EC systems for solar-driven CO 2 RRs have also been reported (7-9); however, only two such systems have provided appreciable selectivity for reduced carbon compounds containing C-C bonds (10,11). Among the PV-EC systems for CO 2 conversion, the most efficient one generates the C 1 feedstock CO (not hydrocarbons) using a GaInP/GaInAs/Ge PV cell (9).…”