Figure 4.

a) The relationships between overpotential (at 10 mA cm⁻²) and O‐Vcancies concentration. Reproduced with permission.^{[ 55 ]} Copyright 2020, ACS Publications. b) XPS characterization (O 1s) for HRO and YRO. Reproduced with permission.^{[ 57 ]} Copyright 2022, Royal Society of Chemistry. c) Calculated free energies for oxygen vacancy formation (V_O) of different RuO₂‐based electrocatalysts, illustrating that the co‐doping of W and Er into the RuO₂ lattice is beneficial to suppress oxygen vacancy formation. V_O for W_0.2Er_0.1Ru_0.7O_2‐δ exceeds the free energy of the redox couple H₂O/O₂ (1.23 eV) by far, implying that this catalyst is not prone to degradation under the harsh anodic operation conditions in the acidic oxygen evolution reaction (OER). Reproduced with permission.^{[ 58b ]} Copyright 2021, Wiley‐VCH. (d) Lines showing the mass activity of RuO₂ and all co‐doped composites at 1.7 V vs RHE. Reproduced with permission.^{[ 58a ]} Copyright 2020, ACS Publications. e) Calculated free‐energy diagrams at 1.5 V for RuO₂ (110) (black line) and that supported on either TiO₂ (blue line) or D‐TiO₂ substrate (red line). Reproduced with permission.^{[ 54 ]} Copyright 2022, ACS Publications. f) Sr 3d and Co 2p XPS for SrCo_0.9Ir_0.1O_3−δ before and after the electrochemical tests. g) HRTEM images of pristine and cycled SrCo_0.9Ir_0.1O_3−δ (by 5 cycles, scale bar, 5 nm). f,g) Reproduced with permission.^{[ 60 ]} Copyright 2019, Springer Nature.