An alkaline microfluidic fuel cell based on formate and hypochlorite bleach

An alkaline microfluidic fuel cell is demonstrated employing an alkaline version of a formic acid anode and a sodium hypochlorite cathode. Both sodium formate fuel and sodium hypochlorite oxidant are available and stable as highly concentrated solutions, thereby facilitating fuel cell systems with high overall energy density. Sodium hypochlorite is commonly available as hypochlorite bleach. The alkaline anodic half-cell produces carbonate rather than the less-desirable gaseous CO2, while sustaining the rapid kinetics associated with formic acid oxidation in acidic media. Both half-cells provide high current densities at relatively low overpotentials and are free of gaseous products that may otherwise limit microfluidic fuel cell performance. The microfluidic fuel cell takes advantage of a recently developed membraneless architecture with flow-through porous electrodes. Power densities up to 52 mW cm−2 and overall energy conversion efficiencies up to 30% per single pass are demonstrated at room temperature using 1.2 M formate fuel and 0.67 M hypochlorite oxidant. The alkaline formate/hypochlorite fuel and oxidant combination demonstrated here, or either one of its individual half-cells, may also be useful in conventional membrane-based fuel cell designs.