NixPd1−x (x = 0.98, 0.93, and 0.58) nanostructured catalysts for ammonia electrooxidation in alkaline media

Abstract The effect of Pd atomic content in Ni x Pd 1− x ( x  = 0.98, 0.93 and 0.58) nanometer-sized catalysts synthesized with modified polyol method is investigated for the electrooxidation of ammonia in alkaline media. Physicochemical characterization by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray diffraction (XRD) are carried out to identify the sizes, shapes, chemical and structural features of the catalysts. Both synthesized Ni 98 Pd 2 and Ni 93 Pd 7 are composed of large 50–100 nm Ni particles coated with finer Pd ones in the 5–20 nm range. The Ni 58 Pd 42 catalyst has smaller and narrower size distribution in the 20 nm size range, indicating that Pd stabilizes the particle size of Ni. According to XRD, Ni and Pd form two separate face-centred cubic phases with traces of β-Ni(OH) 2 . Before ammonia electrooxidation reaction, the catalysts were subjected to an electrochemical treatment that consisted of 200 potential cycles in NaNO 3 at pH 10.5 to build a layer of Ni(OH) 2 . Ammonia electrooxidation proceeds on NiOOH phase and follows the direct pathway at low concentrations and indirect pathway at higher concentrations where NiOOH is reducing and NH 3 is oxidizing. It was found that the Ni-rich compositions have higher activity towards the degradation of ammonia.