The Direct Borohydride Fuel Cell

Fuel cells are clean power sources for both large-scale and portable applications, as they provide a viable method for converting the chemical energy of fuel directly into electrical energy. The most developed FC is the H2‖O2 system, which uses hydrogen as fuel. However, there are some issues with the use of hydrogen, such as sourcing, safety of handling, and storage. Direct borohydride fuel cells address some of these concerns. They consist of both BH 4 − fuel, which is oxidized at the anode, and hydrogen peroxide (or O2), which is reduced at the cathode. Their many advantages, such as high theoretical specific energy (up to 17 kWh kg−1) and high theoretical cell voltage (up to 3.02 V), have attracted increasing interest. Borohydride is also available in solid state (NaBH4) or as an aqueous electrolyte up to 30 wt%, where it remains with a half-life of around 270 days at pH 13.9 (25 °C) in a strong alkaline solution. Borohydride FCs can operate under ambient conditions and in an air-free environment, which makes them convenient for portable and anaerobic applications. The main challenge to their commercialization is the selectivity of the anode catalysts and their substrate materials. Many publications have investigated noble metals (e.g. platinum, gold, palladium) as candidate materials, but none have found yet an anode catalyst able to meet the needs of both high catalytic activity toward BH 4 − oxidation and low activity toward its hydrolysis. Several improving strategies are being investigated.