Recovery of borohydride from metaborate solution using a silver catalyst for application of direct rechargable borohydride/peroxide fuel cells

This study aims at the investigation of a suitable catalyst for the electrochemical reduction mechanism of metaborate into borohydride with the hope of the construction of rechargeable direct borohydride/peroxide fuel cell. A passive direct borohydride/peroxide fuel cell with Ag anode and Pt/C cathode was constructed. Its maximum power density was calculated as 7 mW cm⁻² at a cell voltage of 0.5 and a current density of 11 mA cm⁻². Recycling of the metaborate, the co-product of the borohydride oxidation, to the borohydride is the major issue in order to achieve the rechargeable borohydride fuel cells. Accordingly, the NaBO₂ solution was electrolyzed with the use of Ag electrodes for this purpose. The converted borohydride were determined by the cyclic voltammetry using Au and Ag electrodes which are highly selective for this purpose. The cyclic voltammetric curves revealed the peaks which indicated the conversion of NaBO₂ into NaBH₄. The presence of NaBH₄ was also verified iodometrically after the electrolysis. It was observed that there was 10% conversion after 24 h of electrolysis which reached up to 17% after 48 h. These data are very promising in the quest of the construction of a rechargeable direct borohydride fuel cell.