Binary and nanostructured NiMn perovskite fluorides as efficient electrocatalysts for urea oxidation reaction

Urea electrolysis holds tremendous promise to provide green and sustainable energy and environmental solutions, because it can simultaneously remedy urea-containing wastewater and provide energy-saving hydrogen. However, the development of this emerging technology remains challenging mainly due to a dearth of high-performance electrocatalysts for efficient urea oxidation reaction (UOR). Perovskite fluorides have the advantages of intrinsic 3D diffusion pathways, robust architecture, and tunable chemical composition, thus receiving increasing attention in many applications. In this work, the UOR performances of a series of ABF₃ samples (A = K; B = Ni/Mn, Ni/Co, Co/Mn) with various compositions are investigated in a systematic fashion for the first time. Among the binary samples, KNMF41 (Ni/Mn atomic ratio = 4:1) is the optimal sample with reduced overpotential (reaching 100 mA cm^-2 at 1.43 V), low Tafel slope (40 mV dec^-1), enhanced reaction rate constant (6.3 × 10⁵ cm³ mol^-1 s^-1), and high turnover frequency (TOF, 0.19 s^-1 at 1.60 V) toward urea oxidation. By comparing with NiCo and CoMn samples, the binary NiMn design is confirmed to endow the perovskite fluoride with higher electrocatalytic activity, thanks to the directed adsorption of urea molecules on the adjacent NiMn active sites. This work presents a targeted synthetic strategy for obtaining efficient electrocatalysts.