Sodium borohydride determination by measurement of open circuit potentials

Sodium borohydride has been gaining increasing interest as energy source for direct borohydride fuel cells. One of the difficulties in the research on borohydride-based systems is related to the knowledge of the borohydride concentration. When immersed in sodium borohydride alkaline solutions, some materials are characterised by electrode responses that allow monitoring the borohydride content. Thirteen materials are tested for this purpose using a simple and relatively precise potentiometric titration technique that may be applied for in situ analysis of a variety of borohydride solutions. Thermodynamic treatment of measured open circuit potentials helps defining the electrode processes, being supported by additional measurements in hydrogen saturated solutions with no borohydride present. Tested materials are classified according to their borohydride response, which is higher for platinum, palladium, gold, copper, nickel, and graphite. For these selected materials a microelectrode array sensor for in situ borohydride monitoring is proposed.