Pt–Me (Me = Ir, Ru, Ni) binary alloys as an ammonia oxidation anode

Abstract

Various Pt–Me (Me = Ir, Ru or Ni) binary alloys were prepared on a glassy carbon (GC) substrate by thermal decomposition and compared as the electrocatalyst for ammonia oxidation in KOH solutions. On the solid solutions of Pt1−xIrx (0≤x≤1.0) and Pt1−xRux (0≤x≤0.6), ammonia oxidation was found to begin at a lower potential (−0.6V versus Ag/AgCl) than on pure Pt by about 0.1V. During potentiostatic oxidation the current density j decreased considerably within about 300s. The arbitrarily selected j60 (j after 60s) tended to saturate at a high set potential region probably due to the deactivation by a poison of Nads. The saturated j60 at a high oxidation potential was apparently higher on Pt1−xIrx (x≤0.8) or Pt1−xRux (x≤0.4) than on Pt, which suggested a positive cooperation of Ir and Ru with Pt in the electrocatalysis. On the other hand, Ni added as a solute to Pt contributed to lower j60 with x in Pt1−xNix (0≤x≤0.7) and did not lower the starting potential of ammonia oxidation at all. The reason why Ir and Ru enhance the activity might be explained by their activity at the dehydrogenatation steps of NH3 at a lower potential, at which ammonia oxidation can never start on the surface of pure Pt.