High energy demand is one of the main issues towards global decarbonization since fossil fuels still limit mobility and industry sectors. In this scenario, hydrogen as an energy vector is critical to reaching the net zero emission targets [1]. The hydrogen economy relies on the electrochemical water-splitting involving the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode of electrolyzers. The sluggish kinetics of the OER dictates the overall efficiency of electrochemical water-splitting because it comprises four proton-coupled electron transfer steps with different reaction intermediates. High-cost and low-abundant platinum-group-metal (PGM) catalysts such as RuO₂ and IrO₂ are required to enhance OER activity, highlighting the importance of developing new cost-effective PGM-free materials for OER to spread the electrolyzers applications [1,2]. High-entropy oxides (HEOs) are an emerging class of materials consisting of five or more metals in equimolar or near-equimolar ratios, which are incorporated in a single lattice that exhibits modulable properties. The synergistic interaction in the single lattice has indicated HEOs as a promising candidate for applications within electrocatalysis [3]. We propose different synthesis strategies to optimize the spinel-type transition metal HEOs based on Mg, Mn, Fe, Co, and Ni in this work. Several methods have been used, such as the co-precipitation approach and rapid quenching after the heat treatment step. Different calcination conditions and near-equimolar ratios were investigated. The structure, composition, and morphology of the prepared HEOs were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG and DTA), and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The electrochemical performance was accessed by rotating disk electrode experiments in an alkaline medium (at pH=14), by performing linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) measurements.

References

[1] M. Chatenet, B.G. Pollet, Dario R. Dekel, F. Dionigi, J. Deseure, P. Millet, R.D. Braatz, M. Z. Bazant, M. Eikerling, I. Staffell, P. Balcombe, Y. Shao-Horn, H. Schäfer, Chem. Soc. Rev., 2022,51, 4583-4762.

[2] C. Santoro, A. Lavacchi, P. Mustarelli, V. Di Noto, L. Elbaz, D. R. Dekel, F. Jaouen, ChemSusChem, 2022, 15, e202200027.

[3] K. L. Svane, J. Rossmeisl, Angew. Chem. Int. Ed. 2022, 61, e202201146.