Urea-based fuel cells and electrocatalysts for urea oxidation

Urea is a new member of hydrogen-storage materials for low-temperature fuel cells. It avoids issues of toxicity and safety compared to NH3 and hydrazine. The main limitation of urea-based fuel cells is their relatively low power densities due to the sluggish anode reactions. Rapid advances in nanocatalysts used for urea electro-oxidation have been achieved in lowering overpotential and improving activity. Urine, as a natural resource of urea, is also an environmental pollutant. Most technologies of treating urine with self-generation electricity are based on microbial fuel cells. However, microbes are only able to utilize the organic substrates rather than urea in urine. Chemical fuel cells in contrast directly oxidize urea to nitrogen gas, removing it from urine. Thus, urea-based fuel cells have been used as an alternative method to treat urine. In this Minireview, the progress in urea-based fuel cells and electrocatalysts for urea oxidation is reviewed.