Comparison of electrochemical active surface area methods for various nickel nanostructures

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 nanestructured 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 alpha-Ni(OH)(2) oxidation peak, (iii) the beta-NiOOH reduction peak and finally (iv) the beta-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.