Electrochemical investigation of urea oxidation reaction on beta Ni(OH)(2) and Ni/Ni(OH)(2)

Urea oxidation is the key limiting reaction in energy conversion devices based on this molecule. Ni-based catalysts are widely used to catalyze this reaction via the intermediate formation of reactive NiOOH from nickel hydroxide. In this study, beta Ni(OH)(2) urea oxidation activity is compared to that of Ni/Ni(OH)(2). Electrochemical active surface area, exchange current density, rate constant, and capacitance are estimated for these catalysts to mechanistically probe the reaction. A quantitative electrochemical analysis of urea oxidation on these catalyst surfaces yields important reaction parameters. The reaction orders of beta Ni(OH)(2) with respect to KOH and (NH2)(2)CO are 1.22 and 0.26, respectively, at a kinetically-controlled potential of 1.43 V vs. RHE. The reaction order with respect to KOH decreases gradually with potential and it is almost constant with urea. The similar trends in reaction order are observed with Ni/Ni(OH)(2). Electrochemical impedance measurements displayed lower charge-transfer resistance of beta Ni(OH)(2) indicative of faster urea oxidation kinetics. It is observed that at the potential of 1.43 V, the charge transfer resistance of beta Ni(OH)(2) (87.3 Omega cm(ECSA)(2)) lowered by a factor of similar to 1.23 compared to Ni/Ni(OH)(2) (107.6 Omega cm(ECSA)(2)). The electrochemical surface area normalized heterogeneous rate constant of beta Ni(OH)(2) is similar to 2 times higher than that of Ni/Ni(OH)(2), in line their high intrinsic urea oxidation activity, capacitance and higher electrochemical phase stability. Moreover, the electrochemical chemical mechanism is observed on both catalysts in support with earlier report [1]. (c) 2018 Elsevier Ltd. All rights reserved.