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 mgNi−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 NiII/NiIII redox center, better dispersion of Ni nuclei, and a low-Tafel slope. [ABSTRACT FROM AUTHOR]