First principles investigations on the stability and catalytic reactivity of Cu2O surfaces

Cu$_{\mathrm{2}}$O is an attractive candidate as a next-generation photocatalyst for CO$_{\mathrm{2}}$ reduction because of its high solar spectrum absorption coefficient and small electron affinity. It is observed experimentally, by Electron Paramagnetic Resonance (EPR) and Scanning x-ray fluorescence microscopy (SXFM), that the surface Cu atoms have various oxidation states, and different sites have different affinities for CO$_{\mathrm{2}}$ and intermediate products. In this work, we employ first principles density functional theory (DFT) calculations to calculate the free energies of various low-index Cu$_{\mathrm{2}}$O surfaces and further identify the change of surface Cu oxidation states upon the creation of surface defects and during the photocatalytic process. The reactivity of Cu$_{\mathrm{2}}$O surfaces with various defect types and concentrations are also predicted.