Impedance Analysis and Electrochemical Measurements of A Direct Borohydride Fuel Cell Constructed with Ag Anode

Abstract

The catalytic activity of the silver metal as regards to the oxidation of borohydride for fuel cell applications was investigated by cyclic voltammetry (CV), open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). It was observed that the oxidized Ag electrode leads to the six-electron oxidation of borohydride. According the CV results, the oxides formed upon the Ag surface have catalytic effect on the oxidation of borohydride. A DBFC was constructed using Ag powder as anode and Ni powder as cathode having Nafion-117 membrane producing a voltage of 0.52 V and a power density of 45 mW /cm2 at room temperature in a %10 NaBH4 in 6 M NaOH medium as anolyte and %3.5 H2O2 solution as an oxidant. The complex plane plots of the electrochemical impedance of Ag electrodes show an apparent inductive semicircle, indicating the presence of the reaction intermediate Ag(HO)2- . Decrease of charge transfer resistances (Rct) observed in Nyquist plots was due to fast kinetics of the Ag2O/Ag couple that Ag2O reduces Ag with NaBH4.