Efficient solar fuel production with a high-pressure CO2-captured liquid feed

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We demonstrated an efficient solar photovoltaic-powered electrochemical CO2 reduction device with a high-pressure CO2-captured liquid feed. In an “air-to-barrel” picture, this device holds promise to avoid both high-temperature gaseous CO2 regeneration and high energy-cost gas product separation steps, while these steps are necessary for devices with a gaseous CO2 feed. To date, solar fuel production with a CO2-saturated liquid feed suffers from high over-potential to suppress the hydrogen evolution reaction and consequently, low solar-to-chemical (STC) energy conversion efficiency. Here, we presented a distinct high-pressure operando strategy, i.e., we took extra advantage of the high pressure in catalyst synthesis besides in the period of the CO2 reduction reaction (CO2RR). The power of this strategy was demonstrated by a proof-of-concept device in which a representative copper catalyst was first synthesized in operando in a high-pressure (50 bar) CO2-saturated KHCO3 solution, and then this high-pressure CO2-captured liquid was converted to solar fuel using the operando synthesized Cu catalyst. This Cu catalyst achieved 95% CO2RR selectivity at the recorded low potential of −0.3 V vs. RHE enabled by the combination of operando facet engineering and oxide derivation. Furthermore, this device achieved a record-high STC efficiency of 21.6% under outdoor illumination, superior to other CO2-saturated liquid-fed devices, and compared favorably to gaseous CO2-fed devices.