Search

Electrochemical processes, such as energy conversion and storage, water electrolysis and other electrocatalytic processes call for expensive noble metal catalysts to provide efficient performance of their systems. The use of those expensive catalysts does not allow for feasible industrial scale operation of such processes. Researchers have therefore moved their focus to non-noble metals such as nickel (Ni), which are inexpensive yet still have high catalytic performance. When evaluating electrochemical performance, it is imperative to quantify the electrochemical active surface area (ECSA) of the materials, however for Ni-based materials, this has proven to be quite challenging. In this study, four ECSA methods are compared for four Ni-based nanostructured catalysts as well as polycrystalline Ni, to determine whether one method is more representative than the other, or whether the appropriate method depends on the type of Ni being used. The tested methods were carried out in an alkaline environment and were based on (i) the double layer capacitance obtained through non-faradaic charging by cyclic voltammetry as well as the charge associated to (ii) the α-Ni(OH) 2 oxidation peak, (iii) the β-NiOOH reduction peak and finally (iv) the β-NiOOH reduction peak in the presence of oxalic acid. The methods were applied to Ni wire, various shaped Ni nanoparticles (NPs) such as triangle, urchin and spherical, as well as Ni foams. Electrochemical results of this study, along with scanning and transmission electron microscopy (SEM and TEM) and X-ray diffraction (XRD) analyses are reported and a detailed discussion on the applicability of the methods is provided. [ABSTRACT FROM AUTHOR]

• Electrochemical promotion of Ni 9 Pd nanoparticles for complete methane oxidation. • Ni 9 Pd had a Pd core/Ni-Pd double-shell structure confirmed through STEM EELS. • Higher open circuit catalytic rate on Ni 9 Pd compared to Ni and Pd. • Positive polarization between 425 and 500 °C led to significant, non-faradaic rate increase. Electrochemical promotion of Ni 9 Pd nanoparticles (NPs) with low Pd content (Ni:Pd = 9:1 atomic ratio) supported on yttria-stabilized zirconia (YSZ) solid-electrolyte was evaluated for the first time for complete methane oxidation. Electron Energy Loss Spectroscopy (EELS) showed a Pd core with a Ni first shell surrounded by 3–4 nm layer of Pd outer shell. This core double-shell structure of Ni 9 Pd NPs enhanced the catalytic activity and stability compared to mono-metallic Pd and Ni NPs under open-circuit. The reversible electrochemical promotion of Ni 9 Pd was obtained upon positive polarization between 425 and 500 °C. At 425 °C, the reaction rate increase reached 240% corresponding to apparent Faradaic efficiency of 25. On Ni 9 Pd NPs the reaction exhibited electrophobic behavior, i.e., the rate increased with anodic polarization, under all experimental conditions of this study. The results demonstrate the advantage of using Ni 9 Pd bi-metallic nanoparticles with core double-shell structure for methane complete oxidation due to the synergetic effect between Pd and Ni and very low amount of expensive Pd phase. EPOC with this type of highly dispersed and low noble metal content catalysts may find a way in the real world catalytic converters for gas exhaust treatment. [ABSTRACT FROM AUTHOR]