The electrolysis of water has promise as a sustainable energy source to meet global energy demands while mitigating climate change. However, the reaction requires efficient and stable catalysts to accelerate the sluggish kinetics of the oxygen evolution reaction (OER) due to its high overpotentials. Common OER catalysts are Ru/Ir precious metal-based, but their rarity and cost make them impractical for long-term, high-volume use. Recently, non-precious transition metal OER catalysts have been studied for their ability to form improved absorption energies for reaction intermediates that are key to facilitate oxygen production. As it is still largely unknown how the specific catalyst structure in more complex mixed metal oxides affects activity, small variations in the catalyst processing method can have dramatic influence over performance, especially for those methods that form amorphous, nanocrystalline, or metastable phases that are more ill-defined or disordered. Here we investigate a laser-induced thermal voxel (LITV) method as a facile synthetic route enabling the rapid creation of diverse, heterogenous, transition metal OER electrocatalysts consisting of nanocrystalline metallic alloy pockets embedded within an amorphous mixed oxide matrix consistent with reactive force-field Monte Carlo calculations. By evaluating various complex transition metal electrocatalysts and their structure, we were able to synthesize a stable Fe0.63Co0.19Ni0.18Ox/Cy catalyst with a Tafel slope of 38.23 mV dec−1 and overpotential of 247 mV, a performance similar to IrO2. We determined that higher iron content and a less crystalline structure in the secondary matrix decreases the charge transfer resistance and is beneficial for electrocatalytic activity. This conclusion is supported by density-functional theory calculations showing distorted active sites in ternary metal catalysts are key for lowering overpotentials for OER. We hope to continue investigating to find non-precious metal HER catalysts that perform in alkaline medium along with OER, which is a particular problem for electrolysis cell design.

Single-step laser-induced thermal voxel synthesis of multimetal, oxygen evolution electrocatalysts

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ACS Fall 2022

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