Direct Urea Fuel Cells: A Review on Roadmap, Mechanism, Bottleneck, and Future Perspective

Direct urea fuel cells (DUFCs) have emerged as an exceptionally viable option for sustainable energy production by utilizing urine- or urea-contaminated wastewater or AdBlue as fuel. In spite of the significant theoretical gravimetric power density, the poor electro-kinetics of the urea oxidation reaction (UOR) obstruct its operational feasibility. Therefore, an improvement of the electrode materials is needed to realize a faster electro-kinetic rate to achieve the scaled-up goals of DUFCs. This review is essential to address the latest developments in urea electrolysis and its mechanistic pathways as explored by the scientific community. Consequently, a panoramic view of the origins, underlying principles, and mechanisms of the UOR-based fuel cells are also highlighted. Additionally, the contemporary progress on transition metal oxides and their alloy-based, mixed oxide-based “nanocarbon” materials, such as carbon nanotubes, and graphene-based electrocatalysts for UOR in alkaline electrolytes discussed in detail. Furthermore, upon optimizing energy efficiency and mitigating capital investments, the economic viability of various catalytic designs is also highlighted, including structural modulation and elemental doping to accelerate the rate of UOR from the very outset to the most recent findings. Finally, the significant challenges impeding the advancement of UOR catalyst-derived DUFCs are also laid out with futuristic perspectives.