NANOSTRUCTURED Ni₅P₄ FILMS AS AN EFFICIENT NON-NOBLE BIFUNCTIONAL ELECTROCATALYST FOR FULL WATER SPLITTING

The electrocatalytic water splitting reaction is considered one of the easiest and cleanest methods to obtain hydrogen gas, which is considered to be an alternative fuel for fuel cell vehicles and more. However, high overpotentials in both hydrogen (HER) and oxygen evolution reaction (OER) are required in order to obtain adequate amounts of hydrogen. Furthermore, in both reactions, low abundant and expensive materials as Pt for the HER and IrO₂ / RuO₂ for the OER are used due to their high activity to the respective reaction. Recently, metal rich phosphides such as FeP, Ni₂P, CoP and more have shown great potential as HER catalysts with stable behavior in acid as well as in base due to their special properties.

Here we demonstrate the utilization of nickel phosphide (Ni₅P₄) as a catalyst for the hydrogen (HER) and oxygen evolution reaction (OER) in strong acidic and alkaline environment¹. The catalyst can be easily grown in a 3D hierarchical structure directly on a nickel substrate, thus making it an ideal candidate for practical water splitting devices. The activity of the catalyst towards the HER, together with its high stability especially in acidic solution, makes it one of the best non-noble materials described to date. Furthermore, Ni₅P₄ was investigated in the OER and showed competitive performance compared to pristine nickel, iridium or platinum. The practical relevance of Ni₅P₄ as a bifunctional catalyst for the overall water splitting reaction was demonstrated, with 10 mA cm⁻² achieved below 1.7 V.

(1) Ledendecker, M.; Krick Calderón, S.; Papp, C.; Steinrück, H.-P.; Antonietti, M.; Shalom, M. Angewandte Chemie International Edition 2015, 54, 12361.