Nickel phosphide catalysts for hydrogen generation through water reduction, ammonia-borane and borohydride hydrolysis

Using hydrogen as fuel requires efficient production and retrieval from energy carriers. Here, we describe the synthesis of various pure phases of nickel phosphide and describe the growth mechanisms. A comparative study illustrates the phases’ catalytic activity towards hydrogen production through electrochemical water reduction as well as hydrogen retrieval by hydrolysis of hydrogen storage materials (ammonia-borane and NaBH₄). Charge separation between the Ni^δ+ and P^δ− sites in the various Ni–P phases plays a key role in achieving the desired efficacy of the catalytic reaction. Ni₂P exhibited a significant enhancement towards the hydrogen evolution reaction, with an overpotential of 126 mV at J= 10 mA cm⁻² in acid and 180 mV in alkaline. Ni₁₂P₅ was the most efficient catalyst, with a turnover frequency (TOF) = 23.0 min⁻¹ for hydrogen evolution from ammonia-borane, and TOF= 17.3 min⁻¹ from NaBH₄, which is in accordance with noble metal nanoparticles.