Optimum Ni:Co weight ratio for Pd-Nix-Coy/rGO catalyst nanoparticle for borohydride electro-oxidation in direct borohydride fuel cells

Abstract

The main purpose of this study is to investigate the optimum Ni:Co weight ratio for Pd₁₀-Ni_x-Co_y/rGO catalyst nanoparticles for borohydride oxidation reaction (BOR) electrooxidation in direct borohydride fuel cells (DBFCs). A facile solvothermal procedure was employed for the synthesis of Pd₁₀-Ni_x-Co_y nanoparticles supported on reduced graphene oxide (rGO). Prepared catalysts were characterized by various physical and electrochemical techniques. The crystalline phases of the catalysts were identified by X-ray diffraction. The morphology of the catalysts was identified by transmission electron microscopy (TEM). Inductively coupled plasma (ICP) was used to characterize the percentage of the metals in catalysts. Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to characterise graphene and graphene oxide. The Cyclic voltammetry (CV)was used to calculate the electrochemical surface area (ECSA) of three Pd₁₀-Ni_x-Co_y/rGO catalysts. The results show that there is not much difference between the ECSA of three electrocatalysts. Activity, stability and performance with respect to NaBH₄ oxidation of prepared Pd₁₀-Ni_x-Co_y/rGO were analyzed in the half cell and the single cell setups. The highest activity at 0.5 V was found on the Pd₁₀-Ni₆₀-Co₃₀/rGO catalyst with 272 mA/cm² which is approximately 1.13 and 1.31 times higher than those of Pd₁₀-Ni₄₅-Co₄₅/rGO and Pd₁₀-Ni₃₀-Co₆₀/rGO respectively. The power density of 55.9 mW cm⁻² was achieved at 25 °C on DBFC with the Pd₁₀-Ni₆₀-Co₃₀/rGO anodic catalyst which is 11% and 31% higher than those DBFCs with Pd-Ni₄₅-Co₄₅/rGO and Pd-Ni₃₀-Co₆₀/rGO respectively.