Electrochemical responses of novel preferentially oriented platinum (100) nanoalloys for ammonia and hydrazine catalysis

Abstract

Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle under low pressure, costs only slightly higher than methanol and can easily be cracked down into hydrogen and nitrogen. At low temperature, ammonia oxidation on noble metal electrodes is a sluggish reaction and efficient catalysts are required to convert ammonia to nitrogen and hydrogen at reasonable reaction rates. In this thesis, I present polycrystalline and oriented nanoalloys synthesised at room temperature in aqueous media and their catalytic effects on the oxidation of ammonia. The electro-oxidation of ammonia on palladium-goldsilver (PdAuAgNPs) ternary nanoalloys was systematically studied in alkaline solution of potassium hydroxide (KOH) by cyclic voltammetry (CV). The PdAuAg nanoalloys were prepared through a facile synthesis with ascorbic acid as a reductant and polyvinylpyrrolidone (PVP) as a stabilising agent from aqueous solutions of PdCh/HAuCI4.3H20/AgN03 mixtures. UV-visible spectroscopy was used to confirm the complete reduction of the metal ions; absorption peaks observed at 260 nm, 285 nm and 420 nm for Ag", Au3+ and Pd2+ ions respectively, disappeared after reduction indicating a complete reduction of the metal ions to zero-valent nanoparticles. High resolution transmission electron microscopy (HR TEM) revealed the formation of crystalline nonaggregated 25-35 nm sized nanoalloys. The elemental composition of the nanoalloys measured using energy dispersive X-ray spectroscopy (EDX) showed the presence of the three elements; Pd, Au and Ag.