In today's renaissance of high-energy-density secondary batteries, lithium−sulfur (Li−S) batteries represent one of the most promising candidates for the next generation of renewable energy storage systems due to sulfur's high theoretical specific capacity of 1675 mA h g −1 and high earth abundance. However, despite decades of study, the issues associated with capacity fade via the polysulfide shuttle and sluggish kinetics remain. Through a rigorous and detailed electrochemical study of lithium polysulfides via rotating disk electrode (RDE) voltammetry, we have investigated the kinetics of the redox reactions and explored candidate catalysts to potentially overcome/mitigate the polysulfide shuttle effect. From these RDE studies, supported by comprehensive electronic structure calculations of conversion-type surface reactions, we determined that WSe 2 can effectively catalyze the polysulfide redox reaction, though further studies are necessary to improve the overall Li−S battery performance.
Water electrolysis is of interest as a sustainable way to produce clean hydrogen and oxygen fuel and help mitigate the rising problems of climate change while meeting global energy demands. High-efficiency, stable, and earth-abundant bifunctional catalysts are needed to enable more effective electrochemical cells for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Here, we investigate the synthesis, composition, performance, and mechanism of multimetal catalysts serving dual functionality in both OER and HER of water electrolysis. Through a laser synthesis method, we synthesized heterogeneous catalysts of nanocrystalline multimetallic alloy pockets embedded within an amorphous oxide matrix. We evaluated the performance and composition of a range of mixed transition-metal oxide materials for both OER and HER, ultimately synthesizing a Cr0.01Fe0.27Co0.34Ni0.38O x /C y catalyst that has a stable, high-rate, and competitive overall water splitting performance of 1.76 V at 100 mA cm–2 in an alkaline medium. Using density functional theory to gain insight as the active site and mechanism, we propose that the inclusion of a minor amount of Cr increases the degeneracy of energetic states that lowers the cost of forming the O 2 p–d bond and H 1 s–d bond due to the hybridization of s, p, and d orbitals from Cr. Using a two-electrode water electrolysis cell with a constant potential of 1.636 V to mimic the setup for fuel production, we found the catalyst to be stable at 14–15 mA cm–2 for 40 h. This laser synthesis method allowing for facile and rapid synthesis of complex multimetal systems demonstrates how doping a Fe, Co, and Ni heterogeneous amorphous/nanocrystalline structure with small amounts of Cr is important for bifunctional catalytic behavior, particularly for increasing HER functionality in advancing our understanding for future electrocatalytic design.
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