Fig. 1: Evolution of surface intermediates, electronic structure and charge redistribution with potential on IrO2 surfaces.
a, Potential-dependent coverage of adsorbates on a modelled IrO2 structure from DFT calculations (left) and schematic showing the calculated structure before the rate-determining step (RDS) of water oxidation and O–O bond formation, highlighting the ambiguous oxidation states and charge distribution for this critical intermediate (right). b, Structures involved in different redox transitions from DFT calculations and the corresponding sum of average change in Bader charges (ΔQIr and ΔQO) for both CUS and bridge Ir and O atoms present at IrO2 surfaces during each redox reaction. Positive (negative) numbers indicate an increase (decrease) in the number of electrons (Supplementary Note 1 shows the detailed calculations). The blue and red shading surrounding the iridium and oxygen atoms are simple guides for the eye to indicate positive charge and negative charge, respectively, with the size and intensity of the shading reflecting the magnitude of charge change. c, Average Ir5d and O2p band centre energies of the occupied states (versus the Fermi level Ef) of surface atoms for different surface adsorbate structures (Supplementary Fig. 2 shows the separated band centres of CUS and Bri sites). The inset scheme illustrates the overlapping of Ir5d with O2p bands as the surface structure evolves with increasing applied potential and the upshift of O2p bands (Supplementary Note 1 shows the projected density of states).
