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

Abstract

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), N-2 adsorption-desorption, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and Temperature Programmed Reduction (TPA). 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 degrees 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 2605.6ml H-2 g(-1)cat min(-1) and 12996 ml H-2 g(-1)cat min(-1), respectively. NaBH4 electrooxidation is investigated with cyclic voltammetry (CV), chronoampemmetry (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).