# Electrocatalysis for the Oxygen Evolution Reaction in Acidic Media: Progress and Challenges
## 3 Tailoring Strategies for Effective OER Electrocatalysts
### Electronic Structure  
Incorporation of heteroatoms or groups will destroy the periodicity of the lattice, resulting in the modification of the local coordination environment and the electronic structure of active sites [35; 82]. This change can effectively regulate the adsorption energy of reaction intermediates and improve the intrinsic activity of electrocatalysts. One of the effective strategies is to incorporate easily soluble non-noble metals, which suffer in-situ dissolution to form an amorphous structure, and increase the degree of coordination unsaturation of the metal in the active center during the oxygen evolution reaction [67]. [PERSON] et al. chose Ni and Co as the dopants to substitute 50% of the precious metal Ir. The Ni-Co co-doped IrO\({}_{2}\) showed a low overpotential of 285 mV at a current density of 10 mA\(\cdot\)cm\({}^{-2}\) (Figure 4a) [83]. Besides Ir-based catalysts, researchers have also done a lot of work on Ru-based catalysts [84]. For example, SrRuO\({}_{3}\) exhibited low OER activity in acid electrolytes due to rapid Sr leaching and Ru dissolution at high potential ranges in 0.1 M HClO\({}_{4}\)[85]. Surprisingly, incorporating a small amount of Na\({}^{+}\) into the lattice of SrRuO\({}_{3}\) by substituting Sr\({}^{2+}\) results in significantly enhanced OER performance, both in terms of activity and stability (Figure 4b) [86]. The doped sample exhibited 85% of activity retention after a stability test, which was assigned to the stabilization of Ru centers with a positive shift in dissolution potentials and less distorted RuO\({}_{6}\) octahedra. Preparation of a perovskite ABO\({}_{3}\) structure (or A\({}_{2}\)BB\({}^{\prime}\)O\({}_{6}\)) and regulation of the valence band structure of B-site cations (usually Ir and Ru) by the atoms at A-site cations have commonly been used to improve the performance of the OER in recent years. Catalysts with  
Figure 3: (a) Low- and high-magnification transmission electron microscope (TEM) images, a Nyquist diagram, and the steady-state polarization curve of the IrO\({}_{2}\)/Sb-SnO\({}_{2}\) catalyst [37]. (b) Bode plot from the electrochemical impedance spectroscopy (EIS) of TaC-supported IrO\({}_{2}\)[79]. (c) Diagram of the process by which the \(\alpha\)-MnO\({}_{2}\) substrate induces the lattice strain of IrO\({}_{2}\)[45]. this perovskite structure can greatly reduce the usage of noble metals. Pseudocubic SrIrO\({}_{3}\) was the first AlrO\({}_{3}\) single perovskite oxide reported for usage as an OER electrocatalyst in acid media [87]. It was found that the formation of IrO\({}_{\text{x}}\) by Sr leaching on the surface of SrIrO\({}_{3}\) through surface reconstruction was responsible for the enhanced OER activity (Figure 4c). The active surface area increased significantly owing to the formation of IrO\({}_{\text{x}}\) groups on the surface of catalysts during cycling. Moreover, the intrinsic activity of Ir in the SrCo\({}_{0.9}\)Ir\({}_{0.1}\)O\({}_{3-8}\) electrocatalyst was more than two orders of magnitude higher than that of IrO\({}_{2}\) and approximately 10-fold higher as compared with the unmodified benchmark SrIrO\({}_{3}\)[88]. The observed high activity was attributed to the surface reconstruction through Sr and Co leaching during the electrochemical cycling, which contains a large number of oxygen vacancies with corner-shared and under-coordinated IrO\({}_{\text{x}}\) octahedrons in the oxide crystal lattice. Furthermore, surface reconstruction of AlrO\({}_{3}\) (A = Sr or Ba) perovskite oxides was visualized by atomic-resolution scanning transmission electron microscopy (Figure 4d) [89]. Leading of Sr or Ba happened by applying an anodic current, resulting in surface roughening and a structure change by the continuous formation of the mosaic-shaped, Sr-deficient IrO\({}_{\text{x}}\) on the surface. Moreover, the lattice strain induced by the substitution of smaller lanthanides or yttrium atoms can effectively decrease the adsorption energy toward oxygen-containing intermediates [51].