Phase and chemical state tuning of FeNi oxides for oxygen evolution reaction

Advancing and deploying the Fe Ni-based catalyst, the state-of-the-art pre-electrocatalysts, for oxygen evolution reactions（OER）still suffer from unclear chemical state correlation to the catalytic ability, as evidenced by the variedly reported performance for the different Fe Ni structures. Herein, we contributed the phase and redox chemical states tuning of Fe Ni oxides by the surface microenvironment regulation for the OER catalysis that was realized by the urea-assisted pyrolysis and molybdenum-doping technique by integrating molybdenum into the iron–nickel metal-organic precursor. Driven by the complicated and compromised atmosphere, namely, the oxidation state driven by the Mo doping and reduction ability induced by the urea-assisted pyrolysis,could transfer confined Fe Ni oxides to hybrid phases of Fe2O3 and FeNi3 alloy, and the resultant compromised chemical states by the charge redistribution imparted very high electrocatalytic performance for OER compared with the control samples. The insitu Raman spectroscopy and post-XPS analysis confirmed the facile Fe/Ni oxyhydroxide active phase formation resulting from the proper phase and chemical states, and theoretical analysis disclosed the microenvironment regulation resulting in the charge redistribution forming the electron accumulation and depletion sites to accelerate the oxygen-species to oxyhydroxide-species transformation and enhance the electronic state density near the Fermi level by significantly reducing the energy barrier. The work not only showed the importance of surface chemical state tunning that can basically answer the varied performance of Fe Ni catalysts but also revealed an effective approach for fine-tuning their catalytic properties.