Comparative study of the electrochemical behavior of polycrystalline and nanocrystalline Ru powder in NaOH solution

In this study, a comparison was made of the "microstructure" and the electrochemical behavior of ruthenium in the polycrystalline (pc) and nanocrystalline (nc) states. The nc-ruthenium was prepared by high energy ballmilling. X-ray diffraction patterns show crystallite size ranging from 10 to 30 nm and larger than 100 nm for nc-Ru and pc-Ru, respectively. Scanning electron microscopy showed that the milled powder is made of agglomerates of crystallites. Evaluation of the accessible surface area by gas-phase adsorption (Brunauer-Emmett-Teller method measurements) and capacitance measurements through cyclic voltammetry shows an increase of about 150% for nc-Ru compared to pc-Ru. Ru in the nanocrystalline state is more prone to oxidation than its polycrystalline counterpart. Despite this, nc-ruthenium exhibits a better resistance to corrosion than pc-ruthenium. An explanation to reconcile these two observations is proposed.