One-Step Colloidal Synthesis of Thiospinel High-Entropy Sulfide Nanoparticles—Catalysts for Improved Oxygen Evolution Reaction

High entropy materials have become of growing interest due to the synergistic benefits of the multi-metal systems, as demonstrated by the enhanced application performance of high entropy alloys, oxides, and halogens. Despite the promise of multi-metal sulfide systems in overcoming the performance barriers of their oxide counterparts, high entropy sulfides have received relatively little research interest compared to other high entropy systems. The reason for this is that many high entropy sulfide syntheses rely on complicated, multi-step, high temperature processes often resulting in large, polydisperse, or aggregated particles that lack stability and uniform compositions.<br/><br/>In this talk, I will highlight our recent success in synthesizing high entropy sulfide nanocrystals through a colloidal synthesis method using mild chemistry. We have developed two heat-up synthesis routes, creating the first examples of thiospinel high entropy sulfide nanoparticles and nanodiscs with uniform size dispersion. Through a one-step, heat up synthesis, we have demonstrated the incorporation of five or more cations (with each cation constituting at least 5% of the total cations), into the lattice of two unique systems, achieving a controllable size distribution of less than 15% while maintaining temperatures below 200° C.<br/><br/>Our first system incorporates a base of Ni, Co, and Fe cations, with additional incorporation of a variety of 2+ and 3+ metal cation (Mn, Ir, Ru, Al, Mo, Sr, Zn, Mg, In, and Cd). The method produces multiple permutations of high entropy sulfide nanoparticles that can be colloidally synthesized with only a five-minute heating time. Each of these nanoparticles show promising potential as electrocatalysts in the oxygen evolution reaction (OER) in alkaline media. Our best-performing system is the Ni-Co-Fe-Mn-In sulfide nanoparticles that are monodisperse in size (9.86 nm ± 10.9%) and show an overpotential as low as 285.5 mV at 10 mA/cm² for the OER reaction.<br/><br/>Our second system of focus is the first example of high entropy sulfide nano-discs using Ni-Co-Cu-Mn-Cr with triphenylphosphine and elemental sulfur. These nanodiscs exhibit an average diameter of 14.3 nm ± 11.3% and show promise for their performance potential due to their high surface area and unique facilitation of electron transport within the disc-like structure. Within this system, the surface ligands limit the directional growth resulting in discs. Multi-metal cation exchange allows the incorporation of various elements into the lattice including Sc, Sr, Mg, Mo, Zn, Cd, Ga, and V. High entropy metal selenides are also obtainable by replacing the elemental sulfur with elemental selenium within the synthesis. Our Ni-Co-Cu-Mn-Cr nanodiscs have also been investigated for their potential as electrocatalysts in the oxygen evolution reaction in alkaline media with overpotentials reaching as low as 340 mV at 10 mA/cm².<br/><br/>Each of our systems has shown improved performance, phase purity, and shape control compared to its unary, binary, ternary, and quaternary components. Our work provides two simplistic, low temperature, colloidal methods to the formation of highly complex, phase pure, low dispersity, gram-scalable sulfide nanocrystals.