A fuel cell was assembled using alkaline borohydride solutions as the fuel. The specific gravity, specific viscosity, and melting points of the borohydride solutions were evaluated. With increasing the NaBH4 concentration, the specific gravity was decreased but the viscosity was increased consistently. The effects of NaBH4 and NaOH concentrations on the cell and electrode polarizations were investigated. The increase of NaBH4 concentration improved the anode performance a little but obviously increased the cathode polarization due to the BH4- crossover. As a result, the cell polarization increased when using high concentrated borohydride solutions. According to the Nernst's equation, the increase of NaOH concentration is favorable to the anode, but negative to the cathode polarization. In principle, the cell polarization has nothing to do with the NaOH concentration according to the cell reaction NaBH4 + O-2 = NaBO2 + 2H(2)O. However, the experimental results showed that the high concentration of NaOH aggravated the cell polarization at higher current densities. (C) 2003 Elsevier B.V. All rights reserved.