Carbon dioxide reduction at pyrite photoelectrodes for solar fuel production

Current carbon mitigation techniques favor sequestration in underground wells. Perhaps more useful is the conversion of carbon dioxide into a value added product. Herein, we demonstrate the reduction of carbon dioxide to formic acid and methanol at pyrite photoelectrodes. In the dark, pyrite exhibits metallic behavior due to the inherent dopants present in natural pyrite crystals. Under visible illumination, the catalytic waves observed by cyclic voltammetry shift in the positive direction on an electrochemical scale compared to dark electrodes. Therefore, the overpotential for reactivity is decreased by light absorption. The pyrite surface is stabilized in the presence of CO₂, while under an Ar atmosphere a black film, investigated with XPS, resulted. The Faradaic efficiencies for products observed by NMR were determined as a function of illumination wavelength and applied potential.