Direct\nLaser Writing\nof Multimetal Bifunctional Catalysts\nfor Overall Water Splitting

Abstract

Water electrolysis is of interest\nas a sustainable way\nto produce\nclean hydrogen and oxygen fuel and help mitigate the rising problems\nof climate change while meeting global energy demands. High-efficiency,\nstable, and earth-abundant bifunctional catalysts are needed to enable\nmore effective electrochemical cells for the hydrogen evolution reaction\n(HER) and oxygen evolution reaction (OER). Here, we investigate the\nsynthesis, composition, performance, and mechanism of multimetal catalysts\nserving dual functionality in both OER and HER of water electrolysis.\nThrough a laser synthesis method, we synthesized heterogeneous catalysts\nof nanocrystalline multimetallic alloy pockets embedded within an\namorphous oxide matrix. We evaluated the performance and composition\nof a range of mixed transition-metal oxide materials for both OER\nand HER, ultimately synthesizing a Cr_0.01Fe_0.27Co_0.34Ni_0.38O<i>_x</i>/C<i>_y</i> catalyst that has a stable, high-rate, and\ncompetitive overall water splitting performance of 1.76 V at 100 mA\ncm^–2 in an alkaline medium. Using density functional\ntheory to gain insight as the active site and mechanism, we propose\nthat the inclusion of a minor amount of Cr increases the degeneracy\nof energetic states that lowers the cost of forming the O 2 p–d\nbond and H 1 s–d bond due to the hybridization of s, p, and\nd orbitals from Cr. Using a two-electrode water electrolysis cell\nwith a constant potential of 1.636 V to mimic the setup for fuel production,\nwe found the catalyst to be stable at 14–15 mA cm^–2 for 40 h. This laser synthesis method allowing for facile and rapid\nsynthesis of complex multimetal systems demonstrates how doping a\nFe, Co, and Ni heterogeneous amorphous/nanocrystalline structure with\nsmall amounts of Cr is important for bifunctional catalytic behavior,\nparticularly for increasing HER functionality in advancing our understanding\nfor future electrocatalytic design.