Role of Counter-Anions in Tailoring the Crystalline and Morphological Evolution of Spray-Pyrolyzed Nickel Catalysts for the Hydrogen Evolution Reaction

Nickel salts with different counter-anions were used as a model system to examine how precursor chemistry affects aerosol conversion and alkaline hydrogen evolution. Acetate, nitrate, chloride, and sulfate precursors were processed under the same spray-pyrolysis and reduction conditions. Thermogravimetric analysis showed separated dehydration and decomposition steps for acetate and distinct thermal responses for the inorganic salts. Ni_acetate showed the highest geometric HER activity among the tested electrodes, requiring overpotentials of 280.0 and 346.1 mV at 5 and 10 mA cm−2, respectively, with a Tafel slope of 136.8 mV dec−1. The comparison links precursor-dependent thermal and structural evolution with electrode performance and indicates that physical surface area alone does not account for the activity differences.