Intrinsic borohydride fuel cell/battery hybrid power sources

The electrochemical oxidation behaviors of NaBH4 on Zn, Zn–MH, and MH (metal-hydride) electrodes were investigated, and an intrinsic direct borohydride fuel cell (DBFC)/battery hybrid power source using MH (or Zn–MH) as the anode and MnO2 as the cathode was tested. Borohydride cannot be effectively oxidized on Zn electrodes at the Zn oxidation potential because of the poor electrocatalytic ability of Zn for borohydride oxidation and the high overpotential, even though borohydride has the same oxidation potential of Zn in an alkaline solution. The borohydride can be electrochemically oxidized on Ni and MH electrodes through a 4e reaction at a high overpotential. Simply adding borohydride into an alkaline electrolyte of a Zn/air or MH/air battery can greatly increase the capacity, while an intrinsic DBFC/MH(or Zn)–MnO2 battery can deliver a higher peak power than regular DBFCs.