Improved oxygen evolution reaction performance with addition of Fe to form FeyCux-yCo3-xO4 and FeyNix-yCo3-xO4 (x = 0.5, 1 and y = 0.1, 0.15) spinel oxides

Transition metal spinel oxides have received renewed attention with their demonstrated usefulness as anodes for oxygen evolution reaction. The careful choice of the synthesis method and experimental conditions allow for the tailoring of the film nanostructure and surface area. We have prepared various spinel oxides, FeyCux-yCo3-xO4 and FeyNix-yCo3-xO4 (for y = 0.1 or 0.15 and x = 1 or 0.5 for both Fe-Cu and Fe-Ni containing oxides), using the thermal decomposition method. The films were analyzed using several structural, chemical and electrochemical methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The SEM analysis of FeyCux-yCo3-xO4 electrodes shows that surface is covered with grains, while the surface of FeyNix-yCo3-xO4 appears smoother and more compact. For all our compositions, the X-ray data support the existence of the spinel structure. XPS measurements were performed to study the cation distribution and surface chemical composition of the electrodes, both survey spectra and core level spectra were recorded. The high-resolution spectra for the Co, Cu and Ni 2p peaks indicate the existence of different Co2+/Co3+, Cu+/Cu2+ and Ni2+/Ni3+ ratio for these materials (note that the Fe signal was often too small in the XPS spectra to yield meaningful results). The analysis of O 1s spectra indicate that the main peak is composed of three components that can be assigned to lattice oxygen, adsorbed oxygen containing species such as hydroxides and surface bonded water. Electrochemical measurements show that when the current is corrected for the real surface area, FeyCux-yCo3-xO4 and FeyNix-yCo3-xO4 show significant enhancement with almost double the current density for the oxygen evolution reaction at 1 V under the same conditions compared to Co3O4. Fe has some synergic effect with Ni, Cu and Co, which promote the catalytic activity. A suitable combination of metal cations in the spinel structure could markedly enhance current density and thus, chemical composition plays a crucial role in the electrocatalytic activity of the materials for oxygen evolution reaction.