Unraveling Potential-Dependent Mechanistic Pathways of Urea Oxidation on Pt, Ni, and PtNi Electrocatalysts

Elucidating the reaction mechanisms of the urea oxidation reaction (UOR) is key to overcoming kinetic limitations and controlling product selectivity in alkaline media. Here, we combine online electrochemical mass spectrometry and ion chromatography to investigate high-surface-area Pt, Ni, and PtNi catalysts supported on carbon. This approach enables the unequivocal identification of seven gaseous products, six derived from UOR (N₂, NO, N₂O, CO₂, HOCN, and NO₂) and O₂ from the competing oxygen evolution reaction, as well as three solution-phase species (NO₂ ^-, NO₃ ^-, and OCN^-). At low potentials, Pt/C and PtNi/C are catalytically active, with Pt selectively promoting N₂ production. At higher potentials, NiOOH species dictate the pathways, promoting C─N bond cleavage and forming OCN^- and NO as key intermediates in the formation of more oxidized nitrogen products, including NO₂ ^- as the dominant product for Ni/C and PtNi/C. Together, these findings support a newly proposed mechanistic framework that is potential-dependent and advances the current understanding of UOR. Remarkably, the PtNi/C catalyst exhibits an early onset of oxidation at low potential while maintaining enhanced catalytic performance at higher potentials, thereby guiding the design of advanced anodes for urea-assisted water splitting and direct urea fuel cells.