Electroactive defects induced by Nickel oxide on nanostructured Ru oxide

Ruthenium oxide is amongst the most active materials for the cathodic hydrogen evolution. Its stability in acidic media is mostly due to high conductivity of the crystalline phase. The ability of Ru (and other transition metals, e.g. Ir, Rh, Co) to assume different valency states allows for pseudocapacitive behaviour. This feature is enhanced in amorphous RuO2. Doping and chemical mixing of RuO2 with other elements is a suitable way to increase crystal defects and thus modify the number or energy profile of surface active sites. Reducing the size of the crystallites points to the same goal. In the present work, both strategies have been applied. Ruthenium oxide was synthesized by a new sol-gel route in almost non-aqueous media. Nickel was used as a structure-breaking element. Catalyst powder suspensions were deposited onto Ti platelets and tested in acidic solution. Non-electrochemical techniques (XRD, XPS, SEM) were used to monitor morphology, composition and crystal defects. Although nickel stability in acidic solutions cannot be assessed, evidence for RuO2 modifications will be shown. Electrochemical techniques (cyclic voltammetry, quasi-stationary curve, steady state chronoamperometry) were used to investigate the electrochemical response of the surface towards HER. Different behaviours are observed depending on the oxide surface composition. An attempt to separate truly electrocatalytic from geometric effects will be described.