Design and fabrication of Fe₂O₃/FeP heterostructure for oxygen evolution reaction electrocatalysis

The production of an inexpensive, highly active electrocatalyst for a simple oxygen evolution reaction (OER) based on earth-abundant transition metals is still a major challenge. In addition, the ambiguity of the water splitting reaction (hydrogen evolution and OER) is a hurdle in the manufacture of suitable catalysts for the efficient water electrolysis process. Here, the synthesis of iron oxide/iron phosphide (Fe₂O₃/FeP) heterostructure and its counterparts Fe₂O₃ and FeP as cheap electrocatalysts for water electrolysis is presented. Characterization techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were used to analyze the structure of these electrocatalysts. Heterostructure Fe₂O₃/FeP has been shown to be a more active electrocatalyst than its counterparts. It initiates OER at a remarkably low potential of 1.49 V vs. reverse hydrogen electrode (RHE). For this electrocatalyst, a current density of 10 mA/cm² is achieved at an overpotential of 264 mV for OER in 1.0 M potassium hydroxide solution and the value of the Tafel slope is 47 mV dec⁻¹, outperforming its complements (Fe₂O₃ and FeP) under similar conditions. The results obtained are superior to those of previously reported Fe-based OER electrocatalysts. The Fe₂O₃/FeP electrocatalyst has proven its long-term stability by driving OER at 1.65 V (vs. RHE) for about 12.5 h.