OER, 4OH − → O 2 + 2H 2 O + 4e −). The OER involves a thermodynamically uphill, complex four-electron/proton transfer process, and it is the bottleneck limiting the overall efficiency of water splitting. [2] Although Ru-and Ir-based oxides show very high OER catalytic activity, their scarcity and high-cost hinder large-scale applications. [3] These problems have stimulated a wide search for earth-abundant transition-metal oxides (TM = Fe, Co, and Ni) with multi-valent states of TM cations to accelerate the OER. [1a,4] To design active electrocatalysts, efforts to understand the OER reaction mechanisms and to identify the structural and electronic factors determining the intrinsic catalytic activity are essential. Similar to the d-band center theory established for noble metal catalysis, [5] Nørskov et al. proposed that the OER kinetics on TM oxides is generally governed by the adsorption binding strength of reaction intermediates (*OH, *O, and *OOH) on the surfaces. [2a,6] Therefore, many researchers have attempted to correlate different electronic structure parameters to OER catalytic activity, including the number of electrons in the e g orbitals of TM cations (with e g = 1.2 displaying the highest OER activity), [7] the degree of TM 3d-O 2p hybridization, [8] the energy position of O 2p band center. [9] Following these guidelines, high Aliovalent doping is widely adopted to tune the electronic structure of transition-metal oxides for design of low-cost, active electrocatalysts. Here, using single-crystalline thin films as model electrocatalysts, the structureactivity relationship of Fe states doping in perovskite LaNiO 3 for oxygen evolution reaction (OER) is studied. Fe 4+ state is found to be crucial for enhancing the OER activity of LaNiO 3 , dramatically increasing the activity by six times, while Fe 3+ has negligible effect. Spectroscopic studies and DFT calculations indicate Fe 4+ states enhance the degree of Ni/Fe 3d and O 2p hybridization, and meanwhile produce down-shift of the unoccupied density of states towards lower energies. Such electronic features reduce the energy barrier for interfacial electron transfer for water oxidization by 0.2 eV. Further theoretical calculations and H/D isotope experiments reveal the electronic states associated with Fe 4+-O 2−-Ni 3+ configuration accelerate the deprotonation of *OH to *O (rate-determining step), and thus facilitate fast OER kinetics.

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Oxide thin film transistors (TFTs) represented by n‐type amorphous InGaZnOx (a‐IGZO) have revolutionized the display industry. However, the lack of p‐type counterparts hinders the development of high‐resolution displays with lower energy consumption. In this paper, we review the recent trend in the material design and devices of p‐type oxide semiconductors.