Spontaneous Unassisted Conversion of CO2 to Multicarbon Liquid Products on Green Rust Mineral

Direct low-pressure, low-temperature conversion of CO2 to multicarbon (C>2) products is a quite challenging process due to the high stability of CO2 molecules and the difficulty in achieving the C-C coupling between intermediate steps, which are kinetically slow. Electrocatalysts reported to date have required at least 800-1000 mV overpotentials to achieve even moderate faradaic conversion efficiencies (FE). Here, we report on a hydrothermal iron mineral, namely green rust (GR), a Fe corrosion product that forms under anaerobic conditions, as a highly potent catalyst capable of spontaneously reducing CO2 to multicarbon liquid products, such as erythritol (C4), lactate (C3), malonate (C3), and others, without the application of any external input. Under a small external potential bias, GR achieves FE in excess of 250% at overpotentials of only ~100 mV, which is a new benchmark for spontaneous (unassisted) and electrocatalytic CO2 conversions. Our results show that the high intrinsic activity of GR is probably due to its unusual band structure with an electron affinity of ~3.2 eV, which is the lowest among all commonly known oxides and sulfides in the aqueous electrolyte.