Abstract
Nickel phosphide (Ni-P) films as a catalytic cathode for the hydrogen evolution reaction (HER) of a water splitting were fabricated by a pulse-reverse electrodeposition technique. The electrochemical behaviors for the electrodeposition of Ni-P were investigated by the characterization of peaks in a cyclic voltammogram. The composition of the electrodeposited Ni-P alloys was controlled by adjusting duty cycles of the pulse-reverse electrodeposition. The HER electrocatalytic properties of the Ni-P electrodeposits with an amorphous phase as a function of phosphorous contents existing in Ni-P were electrochemically characterized by the analysis of overpotentials, Tafel slopes, and electrochemical impedance spectrometry. Additionally, the elemental Ni-embedded crystalline Ni3P was prepared by an annealing process with the amorphous Ni69P31 electrodeposit with high contents of phosphorus. The crystalline structure with Ni inclusions in the matrix of Ni3P was formed by the precipitation of excess Ni. The electrocatalytic properties of crystalline Ni3P with elemental Ni inclusions were also investigated by electrochemical characterization.
Highlights
Research on environmentally friendly renewable energy has been conducted to replace fossil fuels with limited reserves
The overpotentials at -10 mA/cm2 and Tafel slopes of the amorphous Nickel phosphide (Ni-P) electrodeposits for hydrogen evolution reaction (HER) were reduced from -396 and 120 mV/dec to -317 and 97 mV/dec, as the contents of phosphorous in Ni-P increased from Ni75P25 to Ni69P31
The improvement of electrocatalytic properties in amorphous Ni-P electrodeposits with increase in the contents of phosphorous can be achieved by the reduction of the H2 desorption energy
Summary
Research on environmentally friendly renewable energy has been conducted to replace fossil fuels with limited reserves. Hydrogen energy (H2) with high gravimetric density has been researched as a candidate for an environmentally friendly sustainable energy source (Kapdan and Kargi, 2006; Nikolaidis and Poullikkas, 2017). Electrochemical water splitting operating in a sustainable manner, such as wind and solar power, has been applied to produce green hydrogen as a promising approach. Water splitting is a chemical reaction in which water is separated into hydrogen and oxygen by applying an electric current. The representative technologies of electrochemical water splitting can be categorized in alkaline water electrolysis (AEL), proton exchange membrane electrolysis (or polymer electrolyte membrane) (PEMEL), and solid oxide electrolysis (SOEL) (Brisse et al, 2008; Carmo et al, 2013; David et al, 2019; Shiva Kumar and Himabindu, 2019; Brauns and Turek, 2020).
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