Low loading platinum dispersed on Ni/C nanoparticles as high active catalysts for urea electrooxidation reaction

Abstract

Ni/C, Ni90Pt10/C and Ni95Pt5/C (Ni:Pt atomic ratios of 90:10 and 95:5) nanoparticles were investigated for urea electrooxidation reaction (UER) in alkaline media. The catalysts nanoparticles were synthesized by sodium borohydride reduction and galvanic replacement methods with 20 wt% of metals loading on carbon. The X-ray diffraction (XRD) analyses showed the presence of peaks attributed to the Ni0, Ni(OH)2 and Pt. Transmission electron microscopy (TEM) and Scanning transmission electron microscopy (STEM) images show nickel nanoparticles with an average size of about 6 nm, platinum nanoparticles smaller than 2 nm as well as platinum atoms spread on the carbon and nickel. The electromagnetic magnetic measurements results of the materials revealed that the addition of platinum to nickel change its magnetic properties, which is associated to the transfer of electrons from platinum to nickel 5d band. The catalytic activity of the materials was investigated by cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The Ni90Pt10/C material showed the highest catalytic activity for UER, on both CV and CA experiments. The higher catalytic activity of the Ni90Pt10/C could be due to a change of urea electrooxidation pathway in which platinum atoms might play an important role in order to oxidize intermediates formed during the UER, and also due to the modification of the electronic properties of nickel which could decrease the energy of poisoning species adsorption on the catalyst's surface.