An important fact regarding the use of tungsten electrode for
voltammetric H+ and OH measurement is that tungsten offers
the ability of easy electrochemical cleaning. Namely, in the H+ concentration
range 0.1–1 102 mol dm3, H2 evolution takes place
at the potentials where only metallic tungsten is thermodynamically
stable [41] and thus the tungsten surface is expected to be
free of oxides, especially if described safety measures are undertaken
(Section 3.1). In addition, experiments performed on B type
of electrodes confirmed, in accordance with both the discussion given
earlier and the described electrode pretreatment, that linearity
and reproducibility of the results presented in Fig. 1 are not affected
by prior surface electrochemical oxidation. As the diffusion
currents are determined only by geometrical cross-section, surface
roughness is irrelevant for accurate measurements. This allows the
use of W electrode without any particular preparation procedure
for voltammetry of H2 evolution. In alkaline solutions, measurements
are based on the rate of anodic dissolution of tungsten.
These reactions are fast, and under hydrodynamic conditions oxide
is quickly removed from the surface, leaving W disk clean during
the operation. Yet again, as limiting diffusion currents are being
measured, only geometrical cross-section is relevant parameter.
In this case, application of W disk for OH measurement does
not require any particular preparation procedure, too.