Metal Oxide-Based Materials for Urea Oxidation Reaction

An era of clean, sustainable “hydrogen energy economy” is on the horizon now. In light of this, the production route for hydrogen (H2) is indispensable. Urea oxidation reaction (UOR) is potential alternative to current water splitting system with more favourable operating conditions, cost-effectiveness and urea-rich wastewater mitigation. Metal oxides are promising electrocatalyst because of its high catalytic activity and long- term stability. The wide range of metal oxides tested as the anode material for the UOR are broadly categorized as (i) nobel metal based oxide electrocatalyst (ii) Ni- based oxide catalyst and (iii) earth abundant metal oxide catalysts. This review begins with basic reaction mechanism and key evaluation parameters involved in urea electrocatalysts. Then reported noble, Ni-based and earth-abundant metal oxides are critically reviewed. Several strategies to improve the catalytic performance which includes compositional variations, choice of synthetic routes and supporting materials are discussed in detail. The associated challenges and future opportunities are finally reviewed to understand the practical exploitation of MO based materials for the UOR.