Production of high capacity porous nickel borides via novel molten salt electrolysis

Abstract

This work focused on producing Ni-boride powders via the novel boron diffusion method called CRTD-Bor (cathodic reduction and thermal diffusion-based boriding) and their electrochemical examinations. The nickel specimens with mesh geometry were borided through the whole cross-section at 1000 °C and 200 mA/cm² for 2 h and held inside of the molten electrolyte for 1 h of phase homogenization. After the boriding treatment, the fully boron diffused specimens were ground via a ball mill and cold-pressed. The structural characterizations of the Ni-boride powders were carried out by using X-ray diffractometry (XRD), scanning electron microscopy (SEM). The results demonstrated that the powders were composed of NiB, Ni₄B₃, Ni₂B, and Ni₃B, where Ni₄B₃ was dominant. To examine the electrochemical behaviors of produced electrodes, cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques were performed through the standard three-electrode system. The CV experiment was conducted within the potential range of 0–0.45 V, over 2000 cycles at 200 mV/s. While a 76 % increase in areal capacitance (Ca) was detected until the 1000th cycle, this value remained constant afterward. Ca was calculated as 1500 mF/cm² at 10 mV/s. At different scan rate experiments, the b value was found as 0.65, representing the system was under mixed control, namely both capacitive and faradaic. The charge/discharge behavior was investigated via GCD at different current densities (0.1–0.01 A/cm²). According to data obtained from GCD, the energy and power density values were calculated as 57.5 mWh/cm² and 3450 mW/cm² at 0.01 A/cm², respectively.