Synergistic effect of NiFeP/NiFe2O4 heterostructure as an enhanced electrocatalyst for oxygen evolution reaction

초록

Due to increasing concerns about depletion of fossil fuels and global warming, enhancement of clean and renewable energy has attracted wide attention. Particularly, among the renewable energies, hydrogen is gaining attention as most promising alternative for future energy carrier. Electrochemical water splitting is regarded as an effective strategy due to its environmental friendly and its ability to generate high-purity hydrogen. Water electrolysis includes two electrocatalytic reactions, which are the anodic oxygen evolution reaction(OER) and the cathodic hydrogen evolution reaction(HER). However, at the OER, the large overpotentials caused by slow four-electron reaction limited large scale commercialization. Up to now, the noble metal-based OER catalysts, such as RuO2 and IrO2, have been employed as state-of-the-art OER electrocatalysts. Nevertheless, their rarity and cost disadvantage restricted large-scale application. Therefore, developing of non-noble metal-based electrocatalysts with low cost is inevitable. Recently, bimetallic oxides have emerged as a promising method to boost the electrocatalytic activity toward OER. Among various bimetallic oxides, NiFe2O4 is receiving attention owing to by its rich redox property and thermodynamical stability. However, the low intrinsic activity and inherently inferior electrical conductivity of NiFe2O4 hindered large-scale application. To overcome this issue, partial phosphidation could be powerful strategy to enhance the electrocatalytic performance. By combining NiFe2O4 with phosphide, it can modulate electronic property and induce charge redistribution. Especially, built-in electric fields between metallic phosphide and semiconductor NiFe2O4, induced Mott-schottky owing to their Fermi level differences. This further increase the electron transfers and improve the electrocatalytic activity.