Electrolytic Nickel Phosphide with One-Dimensional Pore Channels

Abstract

Nickel phosphide has been widely studied in various applications including electrochemical catalyst, electrode for capacitor, electrode for solar cell and electrode for lithium/sodium ion battery. It is synthesized by a variety of methods including hydrothermal/solvothermal/ionothermal method, ball milling, organometallic method, phosphorization, electroplating, etc. Among them, electroplating has many advantages such as relatively simple equipment set up, easy control of electrodeposit’s composition/thickness/structure by changing plating condition, and simplification of process scale-up. When used as electrochemical functional electrode, porous materials have great kinetic advantages such as decrease in activation overvoltage due to wide surface area and decrease in concentration overvoltage due to open mass transfer path. Well defined porous structure with esp. one-dimensional channels has been usually fabricated using porous template and the process includes at least more than three steps: the application of template, deposition, and removal of template. Apart from the relative complexity of the process, the template might be damaged in the course of experiments and is cost-prohibitive for large scale production. This work reports nickel phosphide thin films with one-dimensional pore channels, prepared by an electrochemical deposition. In particular, it is synthesized by single step process without porous template. Figure shows typical porous structure of the electrolytic nickel phosphide. Based on plating mechanism and observation of deposit’s growth pattern over time, it is suggested that the porous structure is formed by complex factors such as competitive reaction between deposit formation and gas generation, and island-type deposit growth. It was proved that the porous structure can be well controlled by plating conditions such as current density and pH. The electrochemical properties of the porous nickel phosphide thin films were investigated as an electrode for functional electrochemical devices (i.e., batteries and capacitors). The redox processes and interfacial resistance along with energy storage characteristics were analyzed through various electrochemical techniques. In this presentation, the pore formation mechanism of the electrolytic nickel phosphide and the factors governing porous structure will be proposed. In addition, the feasibility of its use as an energy storage materials will be discussed. Figure 1