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

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.