# Electrocatalysis for the Oxygen Evolution Reaction in Acidic Media: Progress and Challenges
## 3 Tailoring Strategies for Effective OER Electrocatalysts
### Electronic Structure
Although promising in terms of providing enhanced activity, such a surface reconstruction during the electrocatalysis process may be challenged by the uncertainty of the exact structure formed during reactions [87]. It should be mentioned that different kinds of crystal structures have a significant impact on the OER performance. It was proposed that monoclinic SrIrO\({}_{3}\) underwent less surface reconstruction than the pseudocubic SrIrO\({}_{3}\) owing to the better thermodynamic stability during OER tests in an acidic electrolyte [90]. Strong Ir-Ir metallic bonding and Ir-O covalent bonding in monoclinic SrIrO\({}_{3}\) together induced its high structural and compositional stability. Only about 1% of the leached Sr was detected after 30 h in a  
Figure 4: (**a**) Polyhedral model of IrO\({}_{2}\) being doped with Ni and Co [83]. (**b**) Enhanced OER activity and durability of SrRuO\({}_{3}\) by Na doping [86]. (**c**) XRD and XPS spectra of a SrIrO\({}_{3}\) film before and after 30 h of OER testing [87]. (**d**) High-angle annular dark-field (HAADF) images of the surface structural evolution of a SrIrO\({}_{3}\) film during the OER [89]. chronopotentiometry test, which was much less than that (24%) from the pseudocubic SrIrO\({}_{3}\). Additionally, [PERSON] et al. put forward another way to decrease the cation leaching and surface reconstruction of pseudocubic SrIrO\({}_{3}\) in acid media. They prepared pseudocubic, low-Ir-containing SrIr\({}_{x}\)Ti\({}_{1-x}\)O\({}_{3}\) perovskite oxides with 0 \(\leq\) x \(\leq\) 0.67. The inert Ti sites in pristine SrTiO\({}_{3}\) were activated by Ir-substitution and showed remarkable OER activity with a reserved crystal structure of Ir-SrIrO\({}_{3}\) during OER cycling [91]. For metal alloy/oxide-based electrocatalysts, the surface oxidation of metal atoms accompanied by de-alloying (surface dissolution of unstable metals) under acid OER conditions is considered to be a \"surface engineering\" strategy to design stable and efficient OER electrocatalysts. For example, [PERSON] and [PERSON] found that electrochemical de-alloying and surface oxidation treatment of IrNi\({}_{3,2}\) nanoparticle precursors can lead to the dissolution of Ni, and the formed Ni nanoparticles showed better catalytic performance than core-shell-structured IrNi@IrO\({}_{\rm X}\)[57]. In order to investigate the relationship between the reconstructed structure and the enhanced OER performance, an operando X-ray absorption spectroscopy (XAS) analysis was performed to characterize the local electronic properties under the OER process. The results show that iridium titania and d-band holes appear in the IrNiO\({}_{\rm x}\) electrocatalyst when the potential increases from 0.4 to 1.5 V\({}_{\rm{RHE}}\). More importantly, due to the higher oxidation state of iridium, the iridium oxygen bond length in IrNiO\({}_{\rm x}\) was significantly shortened. Based on this unique phenomenon, a structural model of the iridium oxygen ligand environment was proposed. The model shows that the hole-doped iridium ion sites around the electrophilic oxygen ligands form hole-doped IrO\({}_{\rm x}\) (caused by Ni leaching) during the OER. Therefore, more electrophilic oxygen ligands are susceptible to the nucleophilic attack of water molecules or hydroxyl ligands, resulting in the formation of oxygen bonds and the reduction of the kinetic energy barrier, which ultimately greatly improves the reaction activity.