Hydrolysis and electrooxidation of sodium borohydride on novel CNT supported CoBi fuel cell catalyst

At present, Co, Bi, CoBi, and CoBi/CNT catalysts are prepared via co-precipitation method and sodium borohydride (NaBH₄) reduction method for NaBH₄ electrooxidation and hydrolysis. These Co, Bi, and CoBi catalysts are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), N₂ adsorption-desorption, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and Temperature Programmed Reduction (TPR). These catalysts are employed for NaBH₄ hydrolysis and further measurements are performed to investigate their NaBH₄ electrooxidation activity. For NaBH₄ hydrolysis, NaOH concentration, reaction temperature, NaBH₄ concentration, and catalyst amount are optimized for CoBi and CoBi/CNT catalysts. Furthermore, the rate constants (k) are found between 20 and 50 °C and the activation energy is calculated from the Arrhenius equation. The hydrogen generation rates on CoBi (95–5) and % 10 CoBi (95–5)/CNT catalysts are found as 2605.6 ml H₂ g⁻¹cat min⁻¹ and 12996 ml H₂ g⁻¹cat min⁻¹, respectively. NaBH₄ electrooxidation is investigated with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. Maximum mass activities are obtained as 5.86 mA mg⁻¹ Co for CoBi and 25.7 mA mg⁻¹ Co for CoBi/CNT catalysts. EIS and CA results are also in a good agreement with CV results in terms of stability and electrocatalytic activity of CoBi/CNT catalyst. The CoBi/CNT catalyst is believed to be a promising anode catalyst for the direct borohydride fuel cell (DBFC).