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Metal borides have received increased attention as potentially robust water splitting electrocatalysts. Some studies have reported synergistic electrocatalytic effects on hydrogen and/or oxygen evolution reactions (HER/OER) using mixed metal borides. This report describes the single-step, solvent-free, and rapid (few seconds) synthesis of a series of crystalline Co1−xFexB (x = 0–1) solid solutions in high isolated product yields (>80%) from exothermic, self-propagating solid-state metathesis (SSM) reactions between metal halides and elemental Mg/B reactants. Powder X-ray diffraction shows the Co1−xFexB products are single-phase with crystallite sizes near 60 nm. SEM/EDS and elemental analysis indicate products contain homogeneous Co/Fe distributions and form large micrometer-sized particle aggregates. The electrocatalytic HER with these well-structured crystalline Co1−xFexB materials in 1 M KOH shows increased HER activity at lower applied potentials as cobalt content increases. The OER activity of Co1−xFexB also generally shows improvement with increased cobalt content. Crystalline Co1−xFexB catalysts exhibit good long-term 24 h HER and OER stability in 1 M KOH. Post-electrochemistry Co1−xFexB analyses confirm the retention of product crystallinity after long term electrocatalysis. 

The reaction of CoCl₂ on carbon black with phosphorus yields crystalline CoP₃ particles on a carbon.  Low CoP₃ (5–25 mol%) content is distributed on the carbon support and shows electrocatalytic hydrogen evolution activity similar to bulk CoP₃. 

The facile solvent-free synthesis of several known metal thiophosphates was accomplished by a chemical exchange reaction between anhydrous metal chlorides and elemental phosphorus with sulfur, or combinations of phosphorus with molecular P2S5 at moderate 500 °C temperatures. The crystalline products obtained from this synthetic approach include MPS3 (M = Fe, Co, Ni) and Cu3PS4. The successful reactions benefit from thermochemically favorable PCl3 elimination. This solvent-free route performed at moderate temperatures leads to mixed anion products with complex heteroatomic anions, such as P2S64−. The MPS3 phases are thermally metastable relative to the thermodynamically preferred separate MPx/ MSy and more metal-rich MPxSy phases. The micrometer-sized M-P-S products exhibit room-temperature optical and magnetic properties consistent with isolated metal ion structural arrangements and semiconducting band gaps. The MPS3 materials were examined as electrocatalysts in hydrogen evolution reactions (HER) under acidic conditions. In terms of HER activity at lower applied potentials, the MPS3 materials show the trend of Co > Ni >> Fe. Extended time constant potential HER experiments show reasonable HER stability of ionic and semiconducting MPS3 (M = Co, Ni) structures under acidic reducing conditions.