Self‐Reconstruction of Sulfate‐Containing High Entropy Sulfide for Exceptionally High‐Performance Oxygen Evolution Reaction Electrocatalyst

Abstract

Novel earth-abundant metal sulfate-containing high entropy sulfides, FeNiCo-CrXS 2 (where X = Mn, Cu, Zn, or Al), are synthesized via a two-step solvothermal method. It is shown that sulfate-containing FeNiCoCrMnS 2 exhibits superior oxygen evolution reaction (OER) activity with an exceptionally low overpotential of 199, 246, 285, and 308 mV at current densities of 10, 100, 500, and 1000 mA cm -2 , respectively, and surpassing its unary-, binary-, ternary-, and quaternary-metal counterparts. The electrocatalyst yields exceptional stability after 12 000 cycles and 55 h of durability even at a high current density of 500 mA cm -2 . Various in situ and ex situ analyses are used to investigate the self-reconstruction of the sulfides during the OER for the first time. The resulting metal (oxy)hydroxide is believed to be the true active center for OER. The remaining sulfate also contributes to the catalytic activity. Density function theory calculation is in good agreement with the experimental result. The extraordinary OER performance of the high entropy sulfide brings a great opportunity for desirable catalyst design for practical applications.

High entropy metal chalcogenides: synthesis, properties, applications and future directions

“…5(a) and (b)). 48 It is important to note here that the main catalytic site (Fe 3+ ) was found to be stabilised by the high entropy cocktail effect of the presence of multiple cations. Increasing the number of metals in these materials was found to decrease the overpotential required to reach 100 mA cm À2 .…”

“…Another technique is based on a solvothermal process where the solvated metal salts are heated with a sulphur source (thioacetamide) present in the solution at a significantly lower temperature (150-160 1C) than elemental annealing, but still over an extended timeframe (18 h). 48 A further method of synthesising HE metal chalcogenides is through high energy ball milling of the constituent metal sulphides, often known as mechanical alloying. In this method, pre-synthesised metal sulphide materials are ball milled for between 60 h and 110 h. This method has the significant advantage of not requiring any external heating steps, and can rely on the energy generated by asperity contacts in the ball milling alone.…”

“…For example, with the FeNiCoCrMnS 2 HEMC the Fe 3+ species was found to be crucial for the oxygen evolution reaction (OER), due to the high affinity of iron to oxygen and the fast electron transfer between the Fe and the absorbed oxygen species. 48 Further analysis of the HE material after OER found that the valence of the metal species was driven towards the 3+ oxidation state. Other significant alterations were also observed such as an initial reduction in crystallinity (over 30 minute period of OER activity), followed by gaining in crystallinity (by 9 hours of OER activity), this 'self-reconstruction' of the HE metal chalcogenide material is also accompanied by a change in morphology from a 'yolk-shell' structure to a significantly more porous sponge-like morphology, with a catalytic oxyhydroxide layer formed on the surface.…”

“…High Entropy metal sulphides have the widest range of applications reported to date for the non-oxide HE metal chalcogenides, having been demonstrated as thermoelectric materials, 47,57 catalytic electrodes for both the oxygen evolution 48,51 and CO 2 reduction 49 reactions, and as electrodes in Li-ion batteries. 52 Thermoelectric energy generation is the most common application of these non-oxide HE metal chalcogenides and will be discussed together with the telluride and mixed chalcogenide systems in the next section.…”

Design and Synthesis of Hollow Nanostructures for Electrochemical Water Splitting

“…As an emerging type of advanced functional materials, high‐entropy alloys (HEAs) are composed of four or more metal elements. [ 63 , 64 ] In view of the unique properties like high entropy effect, large lattice distortion, and cocktail effect, high‐entropy materials (HEMs) derived from HEAs manifest great potential as promising electrocatalysts, such as FeNiCoCrMnS 2 [ 65 ] and CoFeNiMnMoPi. [ 66 ] It is believed that the combination of hollow structure with HEMs can shed some light on the design of efficient water‐splitting electrocatalysts.…”