Nickel's Effect on Iron Oxide for Oxygen-Evolution Reaction

Abstract

The efficiency of NiFe (hydr)oxides as catalysts in oxygen-evolution reactions (OER) in basic solutions is widely recognized. This study focuses on the OER activity of Fe foam in the presence of Ni ions without any effort to enhance or optimize the activity. After the addition of Ni(II) nitrate, significant changes in the electrochemical behavior were observed. A distinct peak corresponding to the Ni(II)/(III) oxidation appeared at an onset potential of 1.36 V, overlapping with the OER. The reduction peak for the Ni(III)/(II) couple was observed at 1.26 V. The onset of the OER occurred at 1.45 V, indicating a reduction in the OER overpotential by 110 mV after the addition of Ni species. The decrease and positive shift for Ni(II)/(III) toward higher potentials during OER suggest that Ni(III) species in proximity to other Ni species are more stable, whereas Ni species interspersed among Fe ions, likely incorporated into the FeHxOy structure, are more active for OER. Surface analysis revealed a Fe to Ni atomic ratio of 100:2, determined using energy-dispersive X-ray (EDX) analysis. However, bulk composition analysis through inductively coupled plasma mass spectrometry (ICP-MS) detected a Fe to Ni atomic ratio of 100:0.7. In situ Raman spectroscopy shows the characteristic peak for NiO(OH) appeared at potentials greater than 1.40 V. This study highlights the potential of incorporating Ni species into Fe (hydr)oxide structures to enhance OER activity and could lead to the development of more efficient and durable catalysts for industrial applications, such as water splitting and renewable energy storage.