The low efficiency of oxygen evolution reaction (OER) is regarded as one of the major roadblocks for metal-air batteries and water electrolysis. Herein, a high-performance OER catalyst of NiFe_0.2 (oxy)hydroxide (NiFe_0.2-O_xH_y) was developed through topotactic transformation of a Prussian blue analogue in an alkaline solution, which exhibits a low overpotential of only 263 mV to reach a current density of 10 mA cm^-2 and a small Tafel slope of 35 mV dec^-1. Ex-situ/operando Raman spectroscopy results indicated that the phase structure of NiFe_0.2-O_xH_y was irreversibly transformed from the type of α-Ni(OH)₂ to γ-NiOOH with applying an anodic potential, while ex-situ/operando ⁵⁷Fe Mössbauer spectroscopic studies evidenced the in-situ production of abundant high-valent iron species under OER conditions, which effectively promoted the OER catalysis. Our work elucidates that the amount of high-valent iron species in-situ produced in the NiFe (oxy)hydroxide has a positive correlation with its water oxidation reaction performance, which further deepens the understanding of the mechanism of NiFe-based electrocatalysts.

氧气释放反应（OER）的低效率被认为是金属空气电池和水电解的主要障碍之一。本文中，通过在碱性溶液中对普鲁士蓝类似物进行定势转化，开发了一种高性能的NiFe _0.2（羟基）氢氧化物OER催化剂（NiFe _0.2 -O _x H _y），该催化剂表现出只有263 mV的低超电势才能达到10 mA cm ^-2的电流密度和35 mV dec ^-1的小Tafel斜率。易地/ operando拉曼光谱结果表明，由NiFe的相结构_0.2 -O _X ħ _ÿ被不可逆地从类型变换α -Ni（OH）₂，以γ -NiOOH与施加阳极电位，而易地/ operando ⁵⁷的Fe穆斯堡尔光谱研究证明的原位OER下生产大量的高价铁物质的条件，有效地促进了OER催化。我们的工作阐明了在NiFe（羟基）氢氧化物中原位生成的高价铁种类的数量与其水氧化反应性能成正相关，这进一步加深了对NiFe基电催化剂机理的认识。