Kerry Hazeldine, Photon Science Institute and the School of Chemistry, University of Manchester, UK

Photoelectron Spectroscopy Characterisation of High Entropy Sulphide Materials as Electrocatalysts

A major inhibitor in the viability of hydrogen production via electrochemical water splitting is the sluggish kinetics of the oxygen evolution reaction (OER), and the instability of non-rare earth metal oxides. To overcome this, a highly efficient, stable, and affordable electrocatalyst is required. Although noble metal oxides (IrOx, PtOx) make promising candidates with respect to their high catalytic activity, the rareness and high cost of these metals make the scalability of these materials unrealistic. Recently, an emerging class of materials, high entropy sulphides (HES), have demonstrated high activity and importantly, high stability in acidic medium; and therefore, are excellent candidate materials for electrocatalysis applications [1].

The HES system consists of two distinct sub-lattices; the anionic sub-lattice, i.e., sulphur; and the cationic sublattice which consists of five or more randomly distributed metal ions. In high entropy metal sulphides, high entropy is reached when five or more metal elements are present in concentrations above 5 mol% in the disordered sub-lattice [2]. The multi-element nature of the system gives rise to multiple redox states and increased stability through the entropy stabilisation effect. However, the structure and composition of HES and how they relate to the surface chemistry, electronic properties, and the catalytic ability of these materials are little understood.

X-ray diffraction (XRD) studies show a single-phase material; and both scanning electron microscopy and high-resolution scanning tunnelling electron microscopy coupled to energy dispersive X-ray analysis (SEM/HRSTEM-EDX) of the HES systems show a homogeneous distribution of metal ions.

Non-destructive, highly surface-sensitive photoelectron spectroscopy techniques, including X-ray photoelectron spectroscopy (XPS) and hard X-ray photoelectron spectroscopy (HAXPES), have been conducted to investigate the surface and sub-surface chemical environment, structure, and composition of the HES materials.

References

1. Qu, J., Elgendy, A., Cai, R., Buckingham, M. A., Papaderakis, A. A., de Latour, H., Hazeldine, K., Whitehead, G. F. S., Alam, F., Smith, C. T., Binks, D. J., Walton, A., Skelton, J. M., Dryfe, R. A. W., Haigh, S. J., Lewis, D. J., A Low-Temperature Synthetic Route Toward a High-Entropy 2D Hexernary Transition Metal Dichalcogenide for Hydrogen Evolution Electrocatalysis. Adv. Sci. 2023, 10, 2204488. https://doi.org/10.1002/advs.202204488
2. Buckingham, M. A., Ward-O’Brien, B., Xiao, W., Li, Y., Qu, J. & Lewis, D. J. High entropy metal chalcogenides: synthesis, properties, applications and future directions. Chem. Commun. 58, 8025–8037 (2022). doi.org/10.1039/D2CC01796B