Electroactivity of NiCr Catalysts for Urea Oxidation in Alkaline Electrolyte

Inexpensive Ni-based catalysts have shown comparable urea oxidation activity to that of precious metals in an alkaline electrolyte. We investigated the urea oxidation on binary NiCr catalysts supported on a carbon matrix in 1 m KOH and 0.33 m urea. The amount of Cr was optimized in the catalyst layer, and it was found that the catalyst with 40 % Cr (Ni₆₀Cr₄₀/C) exhibits the highest urea oxidation activity of 2933 mA mg_Ni ⁻¹ at 0.55 V; with an onset potential of 0.32 V vs. Ag/AgCl. Chronoamperometry curves of NiCr catalysts show stability over 2000 s in oxidizing urea. A lower charge-transfer resistance of 3.3 Ω cm² at 0.40 V was calculated on Ni₆₀Cr₄₀/C compared to that on Ni/C (13 Ω cm²). The exceptionally high mass activity of Ni₆₀Cr₄₀/C is attributed to its improved charge-transfer kinetics, enhanced surface coverage of Ni^II/Ni^III redox center, better dispersion of Ni nuclei, and a low-Tafel slope.