Electrochemical behavior of ammonia on Ni98Pd2 nano-structured catalyst

• Ni(OH)2/Ni98Pd2 is active for the electrooxidation of un-ionized ammonia.
• Direct electron transfer mechanism at low ammonia concentrations (<100 mM).
• Indirect electron transfer mechanism at high ammonia concentrations (≥150 mM).
• 64% of ammonia is degraded after 9 h with 20 mA cm−2 electrolysis – pH 10.5.

Small amounts of Pd served as a reducing agent to produce sub-100 nm polygonally-shaped Ni98Pd2 materials in ethylene glycol. As-synthesized particles were crystallized into fcc Ni with a fraction of β-Ni(OH)2, and exhibited very low to no activity towards ammonia electrooxidation. Their catalytic activity has been significantly improved by building up a layer of Ni(OH)2 by cyclic voltammetry between −0.95 and 1.35 V vs. HgO/Hg in NaNO3 at pH 9. XPS analysis before and after the electrochemical treatment confirmed the transformation of Ni0 to higher state of oxidation. Ammonia electrooxidation on Ni(OH)2/NiPd occurred at around 1.28 V vs. HgO/Hg and was highly pH-dependent. At concentrations less than 100 mM, the direct electron transfer took place, whereas at higher ammonia concentrations it was the indirect electron transfer mechanism. A 9-h galvanostatic electrolysis at 20 mA cm−2 showed that 64% of the initial ammonia was degraded at 38% average current efficiency.