The V 2+ /V 3+ reaction occurring at the negative electrode in the all-vanadium redox flow battery has been identified as performance limiting in the system. Given the complexity of the commercial carbon electrodes typically used for this application, a model electrode approach is adopted in this work to study electrode activity and stability. This was done using edge and basal plane pyrolytic graphite electrodes modified by electrochemical oxidation. Differential electrochemical mass spectrometry was used for the first time in this work to investigate the parasitic hydrogen evolution reaction on the oxidized carbon surfaces. The basal plane surface showed a higher faradaic efficiency for V 3+ reduction compared to that for the edge plane surface. The oxidized surfaces were subject to extended cycling, after which the basal electrode showed a dramatic loss in activity compared to the edge surface which was relatively stable. This activity loss was related to the poor mechanical stability of the basal plane surface. The electrodes were analyzed before and after cycling by different techniques including X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electron microscopy. The influences of the type of carbon and its related properties on electrode activity and stability are discussed.

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Arrays of vertical nanowires structured in Au/NiO/Au segments with 50 nm diameter are characterized by conductive atomic force microscopy to investigate unipolar resistive switching in NiO at the nanoscale. The switching cycles are characterized by extremely low power consumption down to 1.3 nW, which constitutes a significant improvement in nanowire-based resistive switching memory devices. The trend of the reset current as a function of the set resistance, typical of unipolar memories, is extended to a much wider current range than what is reported in literature, confirming the role of Joule heating in the reset process for very low reset currents

The present work suggests the use of a mixed water-based electrolyte containing sulfuric and phosphoric acid for both negative and positive electrolytes of a vanadium redox flow battery. Computational and experimental investigations reveal insights on the possible interactions between the vanadium ions in all oxidation states and sulphate, bisulphate, dihydrogen phosphate ions and phosphoric acid. In situ cycling experiments and ion-specific electrochemical impedance measurements confirmed a significant lowering of the charge-transfer resistance for the reduction of V(iii) ions and, consequently, an increase of the voltaic efficiency associated with the negative side of the battery. This increase of performance is attributable to the complexation of this oxidation state by phosphoric acid. So far, mixed acids have mainly been discussed with the focus on V(v) solubility. In this work we rationalize the impact of the mixed acids on the electrochemical efficiency opening new strategies on how to improve the cycling performance with ionic additives.