For the first time, transition metal-based chalcogenides conforming to the definition of high entropy materials, are synthesized, with the multicomponent occupation being utilized on both cationic and anionic sublattices. The pentlandite-structured (Co,Fe,Ni)₉S₈ and (Co,Fe,Ni)₉(S,Se)₈ compositions are obtained using a two-stage, solid-state reaction method. Room temperature structural analysis (XRD, SEM, Raman) in both cases indicates the presence of a homogeneous, single-phase, Fmm structure, with a profound effect of Se addition on the lattice parameters. The obtained materials possess an excellent electrical conductivity of 10⁵ S m⁻¹, and slightly negative Seebeck coefficient values, resulting from their metallic character, combined with a low thermal conductivity of 2.5 W m⁻¹ K⁻¹, especially when compared with conventional analogues. The optical measurements reveal very promising behavior in the UV/vis range. The electrochemical sensitivity towards hydrazine and acetaminophen is also presented, making them potentially interesting for sensor devices. Based on the DFT analysis of various sub-systems, the origins of the observed transport and optical behavior are explained. Furthermore, it is shown that the application of the high-entropy principle to both sublattices simultaneously allows for extensive tailoring of the band structure, allowing these materials to be optimized with respect to the given application, including thermoelectric and photoelectrochemical devices and catalysis, e.g., the hydrogen evolution reaction.

The multi-component approach to materials design is gaining increasing popularity in energy-conversion-oriented applications. This study describes a 5-component multimetallic chalcogenide compound with a pentlandite structure that recently became increasingly interesting in terms of electrocatalytic water splitting. The solubility limit of Se in the trimetallic Co₃Fe₃Ni₃S₈ system was determined along with the potential effect of this additive on the material's intrinsic properties. This was followed by an unprecedented approach, an attempt to fabricate solid electrodes using the inductive hot-pressing method. The effects of the consolidation conditions on the morphology and final properties of the material are discussed in detail. Tailoring both the chemical composition and processing conditions (initial grain size, sintering temperature) can lead to the optimization of highly efficient electrocatalysts for water splitting. The best electrodes were characterized at elevated current densities of 120 mA cm⁻², showing low overpotentials (240 mV versus RHE) but with rather low electrochemical active surface area and moderately optimal reaction kinetics. It was therefore shown that using multi-component compositions resulted in good intrinsic properties of the materials toward hydrogen production, together with high density and vacancy concentrations provided by the sintering process, thus producing an efficient electrocatalyst using a simple, scalable method without any additional processing.

With electrocatalysis being the very foundation of multiple energy conversion technologies, the search for more effective, and affordable catalysts is becoming increasingly important for their further development. Recently, the multicomponent approach, together with the electronic structure calculations, have established themselves as promising ways of designing such materials. In the presented study, both these approaches are combined, leading to the development of a unprecedented (Co,Fe,Ni)₃Se₄ chalcogenide catalyst. Based on the extensive density functional theory calculations (DFT), and structural data, the impact of the multi-element atomic arrangement is discussed, and the possible benefits of such a design strategy are identified. The transport and catalytic properties of the materials are studied, showing excellent charge transfer capabilities, combined with very high catalytic activity with regard to the hydrogen evolution reaction (HER), as evidenced by the current densities of 120, 500, and 1000 mA cm⁻² at overpotentials of 250, 360, and 450 mV. Of importance, all these results are achieved for the bulk-type electrode, obtained by a simple and scalable process, a considerable advantage over most of the state-of-the-art electrocatalysts, requiring costly and time-consuming nano-structuring of the electrode layer.

Since pentlandites are among the most promising catalysts for hydrogen evolution reactions (HER), in this study, we investigated the influence of different cobalt, iron, and nickel substitutions in the cationic sublattice and the form of the material (powder, ingot, sintered pellet) on catalytic performance. This complements previous results regarding a multi-component approach in these chalcogenides. It was shown that in the case of sulfur-rich pentlandites with a non-equimolar ratio of Co, Fe, and Ni, the impact of intrinsic material properties is smaller than the surface-related effects. Among powder forms, catalysts based on a combination of Fe and Co perform the best. However, in volumetric forms, extremely high contents of individual metals are favorable, albeit they are associated with active precipitations of foreign phases. The presence of these phases positively affects the recorded currents but slows down the reaction kinetics. These findings shed light on the nuanced interplay between material composition, form, and HER properties, offering insights for tailored catalyst design.