Transition metal borides (TMBs) have shown feasibility as electrocatalysts for the water splitting reaction in place of currently used precious metals. The electrocatalytic performance, low production cost, high durability due to corrosion resistivity, wear resistivity, oxidation inertness, and the ability to be used in broad pH ranges owing to the chemical stability are all driving forces to the development of TMBs as a sustainable electrocatalytic alternative. The synthesis method predominantly determines the characteristics of TMBs such as particle size, morphology, chemical composition, surface area, and available active surface sites which consequently affect the electrocatalytic activity. Solid-state metathesis (SSM) is an alternative to the traditional high temperature, mechanochemical, and solution-phase chemical reduction syntheses, providing a potentially useful route for rapid solvent-free formation of TMBs as highly crystalline and nanometer sized crystallites. Among transitional metals, iron, cobalt, and nickel are three earth abundant metals and electrocatalysts incorporating them have been widely studied. The present study examines the formation of metal monoborides of iron, cobalt and nickel via hot wire SSM ignition reactions using two different precursor pathways that change the boron source, reactions of transition metal chloride (MCl2) with MgB2, and with Mg+B elements. Single phase FeB and CoB were synthesized from both reaction routes, while single phase NiB can be only yielded from Mg+B reactions. Products contain small crystallites (300-500 nm), although the particle aggregation results in wide range of particle size distribution (2-70 µm). The resultant TMBs have moderate surface areas (&lt;10 m2/g), which reveal that the products are non-porous solids. Electrochemical studies show a moderate electrocatalytic activity of FeB, CoB, and NiB for both oxygen evolution reaction (OER) (10 mA cm-2 at ~1.8 V) and hydrogen evolution reaction (HER) (10 mA cm-2 at ~500 mV) in OER and HER overpotentials increasing as CoB &lt; NiB &lt; FeB.

Investigation of energetic solid-state metathesis reactions for the formation of iron, cobalt and nickel borides and their electrocatalytic activities

ACS Spring Meeting 2021

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