Influence of phosphorus on the electrocatalytic activity of palladium nickel nanoalloy supported on N-doped reduced graphene oxide for ethanol oxidation reaction

Abstract

For successful commercialization of the direct ethanol fuel cell (DEFC), cheaper long-lasting lower noble metal contained anode catalyst is highly needed. For this, nitrogen-doped reduced graphene oxide (N-rGO) supported palladium-nickel alloy nano catalysts with tuned Pd:Ni ratio was synthesized using chemical co-reduction method. Aiming to have better catalytic efficacy and further reduction of cost, nonmetal phosphorus is incorporated to the most active Pd3Ni/N-rGO catalyst to prepare lower Pd contained Pd3NiP/N-rGO ternary catalyst. X-ray diffraction confirms the fcc alloy structure and microscopic study reveals precisely that spherical particles of nano dimension are well distributed on the N-rGO support. XPS analysis confirms the presence of nitrogen and phosphorus along with Pd and Ni in the catalyst matrix. Electrochemical evaluation by cyclic voltametry, chronoamperometry and electrochemical impedance spectroscopy showed that among the bimetallic catalysts studied, Pd3Ni/N-rGO catalyst exhibits synergistic and optimum electro-catalytic performance and poisoning tolerance towards ethanol oxidation reaction (EOR) in the high pH medium. But, phosphorus containing Pd3NiP/N-rGO catalyst shows even more enhanced catalytic performance (2223 mA mg−1Pd current density) than its bimetallic counterpart (1416 mA mg−1Pd current density) signifying that nonmetal phosphorus can effectively promote ethanol oxidation. Moreover, N-doped reduced graphene oxide enhances the catalyst dispersion by creating new active sites, which improves the proper utilization of noble metal Pd. Additionally, the synergistic effect between Pd, Ni and P particles and the support caused by N doping helps to enhance electrocatalytic activity and long-term stability of the catalyst.