Zinc Negative Electrode for Direct Borohydride Fuel Cells

Zinc is evaluated as negative electrode for the direct electrochemical oxidation of sodium borohydride. Open-circuit potential measurements, cyclic voltammetry, chronoamperometry, and chronopotentiometry are used to characterise the electrode behaviour, namely the oxidation reaction at the Zn/BH4- interface. Two consecutive oxidation steps are identified and a possible working mechanism is proposed. A relatively low electrocatalytic activity of Zn for borohydride oxidation is indicated. A laboratory direct sodium borohydride/hydrogen peroxide fuel cell using a Zn anode is studied at room temperature. Cell voltages of 2.14 V and short-circuit currents of 1050 mA cm-2 are reported but cell stability is limited to 6 hours operation. Specific energies and maximum capacities (based on total H2O2 weight) of 2553 mWh kg-1 and 1438 mAh kg-1, respectively, are obtained. A maximum power density of about 470 mW cm-2 at a cell voltage of 1.1 V and current density of 426 mA cm-2 is reported.