Stable electrochemical urea oxidation on Ruddlesden–Popper oxide catalysts

Urea oxidation reaction (UOR) is a crucial process for the efficiency of urea-based energy conversion technologies, including electrocatalytic water splitting and urea fuel cells. These technologies are considered alternatives to the traditional hydrogen production methods due to lower overpotentials and higher cost-effectiveness. However, sluggish UOR kinetics currently limit the practical applications of these technologies. In this study, we investigated the influence of electrolyte composition and temperature on the performance of Ruddlesden-Popper complex oxides in UOR. Our findings demonstrate that the formation of a carbonate layer at the electrode surface is a critical factor limiting UOR kinetics. This layer is mainly composed of carbonates of alkali metal from the solution and can be eliminated at elevated temperatures due to increased solubility. Specifically, we found that LaSrNi₀.₅Co₀.₅O_4±δ catalyst exhibited superior electrocatalytic activity (6 mA cm⁻² at 1.45 V vs. RHE with loading 100 µg cm⁻²) operating at 60 °C in 5 M KOH. Moreover, changing the solution to cesium hydroxide, we were able to avoid the creation of a non-conductive layer due to higher solubility of the cesium carbonate, thus stabilizing the catalytic reaction.