The development of highly active catalyst in pH-neutral media for oxygen evolution reaction (OER) is critical in the field of renewable energy storage and conversion. Nevertheless, the slow kinetics of proton-coupled electron transfer (PCET) hinders the overall OER efficiency. Herein, we report an ionic liquid (IL) modified CoSn(OH)₆ nanocubes (denoted as CoSn(OH)₆-IL), which could be prepared through a facile strategy. The modified IL would not change the structural characteristics of CoSn(OH)₆, but could effectively regulate the local proton activity near the active sites. The CoSn(OH)₆-IL exhibited higher intrinsic OER performances than the pristine CoSn(OH)₆ in neutral media. For example, the current density of CoSn(OH)₆-IL at 1.8 V versus reversible hydrogen electrode (RHE) was about 4 times higher than that of CoSn(OH)₆. According to the pH-dependent kinetic investigations, operando electrochemical impedance spectroscopic, chemical probe tests, and deuterium kinetic isotope effects, the interfacial layer of IL could be utilized as a proton transfer mediator to promote the proton transfer, which enhances the surface coverage of OER intermediates and reduces the activation barrier. Consequently, the sluggish OER kinetics would be efficiently accelerated. This study provides a facile and effective strategy to facilitate the PCET processes and is beneficial to guide the rational design of OER electrocatalysts.

Understanding factors that influence the catalyst activity for oxygen reduction reaction (ORR) is essential for the rational design of efficient ORR catalysts. Regulating catalyst electronic structure is commonly used to fine-tune electrocatalytic ORR activity. However, modifying the hydrophilicity of catalysts has been rarely reported to improve ORR, which happens at the liquid/gas/solid interface. Herein, we report on two Co porphyrins, namely, NO₂-CoP (Co complex of 5,10,15,20-tetrakis(4-nitrophenyl)porphyrin) and 5F-CoP (Co complex of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin), and their electrocatalytic ORR features. By simultaneously controlling the electronic structure and hydrophilic property of the meso-substituents, the NO₂-CoP showed higher electrocatalytic activity than the 5F-CoP by shifting the ORR half-wave potential to the anodic direction by 60 mV. Compared with the 5F-CoP, the complex NO₂-CoP was more hydrophilic. Theoretical calculations suggest that NO₂-CoP is also more efficient than 5F-CoP to bind with an O₂ molecule to form Co^Ⅲ-O₂^·-. This work provides a simple but an effective strategy to improve ORR activity of Co porphyrins by using electron-withdrawing and hydrophilic substituents. This strategy will be also valuable for the design of other ORR molecular electrocatalysts.