Fig. 5: Gibbs free energy calculations.

a, b O₂ adsorption configurations and calculated differential charge densities on CuO (222) (a) and N–CuO (222) (b). Free energy diagrams of molecular oxygen activation process for N–CuO (c) and CuO (d). Key steps of ¹O₂ production for e N–CuO (222) and f CuO (222).