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

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 Pt_1-xIr_x (0 ≤ x ≤ 1.0) and Pt _1-xRu_x (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 300 s. The arbitrarily selected j₆₀ (j after 60 s) tended to saturate at a high set potential region probably due to the deactivation by a poison of N_ads. The saturated j₆₀ at a high oxidation potential was apparently higher on Pt_1-xIr _x (x ≤ 0.8) or Pt_1-xRu_x (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 Pt_1-xNi_x (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.