Cyclic voltammetry as a technique for determining the surface area of RuO2 electrodes

The variation of voltammetric charge with real surface area was investigated for RuO2-coated titanium foils with a view to establishing an electrochemical technique for the estimation of the latter. Errors involved in determining accurate values for real area by the B.E.T. technique were attributed to blocking of pores by adsorbed H2O and OH species whose removal, even under vacuum conditions, requires temperatures high enough to cause sintering. The anodic or cathodic charge values associated with a standard voltammetric sweep, 0.3 V to 1.25 V at 0.01 Hz, were similar for acid and base (1.0 mol dm−3 H2SO4 or NaOH) and correlated reasonably well with real surface area for different oxide loadings, annealing temperatures, etc. The high interfacial charge and capacitance values (about 1.35 C m−2 and 142 μF cm−2, respectively, for RuO2 surfaces annealed at 425° C) are attributed to a combination of ionic double layer effects and surface redox processes. For this type of microporous electrode, surface area is determined largely by the oxide loading and the annealing temperature, and the basis of a convenient (if approximate) electrochemical technique for evaluating real surface area is outlined.