Along with the climate degradation, hydrogen has been considered as prospective energy in place of fossil fuels. This is because it does not produce harmful waste to environment as well as has high energy density compared to other energy sources. The most general way to create hydrogen is water electrolysis which is the process of using external electrical driving force to decompose water into oxygen and hydrogen. This process requires significant amount of driving force (referred as overpotential in perspectives of electrochemistry) to decompose water. Therefore, noble metal catalysts such as platinum (Pt) and iridium (Ir) has been introduced to lower the driving force for efficient water decomposition. However, the use of noble metal becomes issues due to high cost and scarcity. In this context, many studies have been conducted to discover non-noble metal catalysts with comparable activity to Pt. According to literatures, transition metal phosphide (TMP) has been known as electrocatalysts which shows high activity and more stable operation in acidic environment than transition metal. Nevertheless, the conventional fabrication of TMP such as phosphidation is too troublesome due to high temperature, long reaction time and toxic gas during fabrication process. Furthermore, it is less likely to achieve TMP with high contents of phosphorus (P) which has intimate relationships to activity toward hydrogen evolution reaction (HER). To overcome this problem, the novel TMP fabrication method using electrochemical redox reaction of nickel and phosphorus is introduced.

Nickel phosphide (NiP) was prepared on nickel foil using electrochemical cyclic voltammetry (CV) deposition. In anodic current region of CV profiles, nickel is oxidized to nickel ions, resulting in the presence of nickel ions in the electrolyte. On the other hand, hydrogen evolution and the co-reduction of nickel phosphide are observed in the cathodic current region. In other words, successive CV enables oxidized Ni ions to be reduced with P to form NiP alloys. With this successive CV, NiP was obtained and characterized by SEM, XPS and other electrochemical protocols. Furthermore, this method was applied to other transition metal to verify its applicability. For commercialization, as-fabricated NiP was expected to be a cathode with high activity in proton exchange membrane water electrolysis.