Preparation of Magnetically Driven Nickel Phosphide Nanowires and Their Electrochemical Properties

In this study, nickel phosphide nanowires with various structures and compositions were fabricated for the first time via magnetically-assisted liquid phase synthesis. The curvature and aspect ratio of the nanowires largely depended on the strength of the magnetic field applied during synthesis. Their phosphorus content together with the morphology were significantly modified according to the pH and reducing agent concentration. Nanowires with different structures and phosphorus contents were preliminarily tested for their capabilities to serve in general electrochemical applications. The degree of reaction (i.e., amount of reaction charge) increased with increases in the reaction area and phosphorus content of the nanowires. The rate characteristics of the reaction showed a peculiar increasing trend for a small reaction surface area and low phosphorus content. A change in the ohmic overpotential according to the nanowire curvature (aspect ratio) and porosity was suggested to be the reason for this unusual trend. Electrodes with high phosphorus contents or high reaction surface areas rapidly deteriorated during repetitive redox reactions. Based on the results for the degradation degree, the effect of the reaction surface area dominated that of the phosphorus content in the deterioration of the nickel phosphide nanowires.

Electrocatalytic Properties of Pulse-Reverse Electrodeposited Nickel Phosphide for Hydrogen Evolution Reaction

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.

One-Step Synthesis of Bifunctional Nickel Phosphide Nanowires as Electrocatalysts for Hydrogen and Oxygen Evolution Reactions

The Ni2P nanowires were simply synthesized via a rapid one-step hydrothermal approach, in which deionized water, red phosphorus, nickel acetate, and hexadecyl trimethyl ammonium bromide were used as the solvent, phosphor and nickel sources, and active agent, respectively. The as-synthesized Ni2P nanowire clusters were composed of uniform nanowires with length of about 10 μm and diameter of about 40 nm. The Ni2P nanowires exhibited enhanced electrocatalytic activity for both hydrogen evolution reaction and oxygen evolution reaction This work provides good guidance for the rational design of nickel phosphides with unique nanostructures for highly efficient overall water splitting.