Study On Electrochemical Oxidization Effect Of BH₄～- In DBFC With Cu Anode

Because of energy need all over the world is increasing continuouslyand high interest to new energy in many markets, fuel cell will become anew growing opportunity in energy industry. As for much merits such asclean,high performance,low noise,high reliability, fuel cell had becomea new important energy form and received much attention. As to its highcapability (5.67 Ah·g^-1, NaBH₄-based),high output voltage (theoreticalvalue 1.64V),high hydrogen storage(10.8wt%), Direct Borohydride FuelCell (DBFC) received more and more attention.The Cu anode was used for the experimental DBFC with carboncathode and Nafion^?117 membrane, and a 0.1 mol·L^-1 KCl Hg/Hg₂Cl₂electrode was used as the reference electrode. Electrochemical oxidationbehaviors of BH₄^- ion on Cu electrocatalyst has been studied through threeelectrochemical measurements which is Open-Circuit Potential,CyclicVoltammetry(CV),Electrochemical Impedance Spectroscopy (EIS). Electrochemical oxidization effect of BH₄^- in the presence of thiourea on Cuelectrode with cyclic voltammogram (CV) and electrochemical impedancespectra(EIS) have been studied. Accordingly to the feature of DBFC, anequivalent circuit was proposed to fit the EIS experimental data. Throughthe research and analysis in experiments, main conclusions achieved areshowed as following:(1)The relationship of open-circuit potentials and borohydrideconcentrations is not linearity. When the concentrations of borohydrideincrease, open-circuit potentials become larger at first, then become lower.In this paper, the maximum open-circuit potentials is -0.93V when theconcentrations of borohydride is 1.0 mol·L^-1.(2) Electrochemical oxidization effect of BH₄^- on Cu electrode withelectrochemical impedance spectra(EIS) have been studied. Through theresult of EIS, we know that: the value of parameter in equivalent circuitdepend on the concentrations of borohydride; the reaction of DBFC iscontrolled by electrochemical polarization in higher frequency andconcentration polarization in lower frequency.(3) Electrochemical oxidization effect of BH₄^- in the presence ofthiourea on Cu electrode with cyclic voltammogram(CV) andelectrochemical impedance spectra(EIS) have been studied. When the sweeping rate of CV was 40mV/s, the results of CV experiments displayedthat oxidation peak of BH₄^- with thiourea was markedly increased thanwithout thiourea. Accordingly to the feature of DBFC, an equivalent circuitwas proposed to fit the EIS experimental data. The fitted results indicatedthat the equivalent circuit (R(Q(RW))) was fitted very well with theexperimental data and the results had good accuracy. Both CV and EISexperimental results showed that appropriate concentration of thiourea couldinhibit the side reaction of catalytic hydrolysis of BH₄^- yielding H₂ at DBFCanode.