(Digital Presentation) Engineering of Ni-Based Electrocatalysts for Direct Urea Oxidation

Abstract

In the water-energy nexus framework, the alternate renewable energy sources can be stored into molecular hydrogen or electricity with simultaneous water purification through wastewater electrolysis cell or wastewater fuel cell. Urea oxidation reaction (UOR) has been interrogated to enhance the energy efficiency and to recover energy from urea-rich wastewater. Nickel-based catalysts are up-to-date the most widely investigated materials as the UOR electrocatalyst. This presentation introduces our recent approaches for preparation of the UOR electrocatalysts by i) galvanostatic electro-deposition of mixed metal (oxy)hydroxide (NiFeOx or NiCoOx) with variable mixing ratios, ii) potentiostatic dealloying of commercial alloys (e.g. Ni-Fe, Fe-Ni, and Ni-Cr-Co) under variable pH, and iii) one-pot thermochemical treatment of NiFe alloy foam (NFF), both as substrate and catalyst source to create a self-supporting UOR electrocatalyst. The secondary elements (Fe and Co) were found to accelerate the formation of NiOOH (the active site for UOR), by partial charge transfer among the mixed metals. On the other hand, oxalic acid treatment of NFF generated prismatic NiFe-oxalate (O-NFF) which marked surprisingly small overpotential and Tafel slope for UOR. The coexistence of Fe and oxalate ligand simultaneously shift the surface electronic structure which in-turn affected the adsorption of reactants and desorption of products. The UOR on the engineed electrocatalysts could be further utilized for urea electrolysis (for molecular hydrogen production) or urea fuel cell.