Direct CO₂ capture and conversion to fuels on magnesium nanoparticles under ambient conditions simply using water

Converting CO₂ directly from the air to fuel under ambient conditions is a huge challenge. Thus, there is an urgent need for CO₂ conversion protocols working at room temperature and atmospheric pressure, preferentially without any external energy input. Herein, we employ magnesium (nanoparticles and bulk), an inexpensive and the eighth-most abundant element, to convert CO₂ to methane, methanol and formic acid, using water as the sole hydrogen source. The conversion of CO₂ (pure, as well as directly from the air) took place within a few minutes at 300 K and 1 bar, and no external (thermal, photo, or electric) energy was required. Hydrogen was, however, the predominant product as the reaction of water with magnesium was favored over the reaction of CO₂ and water with magnesium. A unique cooperative action of Mg, basic magnesium carbonate, CO₂, and water enabled this CO₂ transformation. If any of the four components was missing, no CO₂ conversion took place. The reaction intermediates and the reaction pathway were identified by ¹³CO₂ isotopic labeling, powder X-ray diffraction (PXRD), nuclear magnetic resonance (NMR) and in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and rationalized by density-functional theory (DFT) calculations. During CO₂ conversion, Mg was converted to magnesium hydroxide and carbonate, which may be regenerated. Our low-temperature experiments also indicate the future prospect of using this CO₂-to-fuel conversion process on the surface of Mars, where CO₂, water (ice), and magnesium are abundant. Thus, even though the overall process is non-catalytic, it could serve as a step towards a sustainable CO₂ utilization strategy as well as potentially being a first step towards a magnesium-driven civilization on Mars.