The effective surface pH during reactions at the solid–liquid interface

In this work the activity of protons directly at the solid–liquid interface during a heterogeneous reaction is demonstrated without introducing any pH measurement device, in non-buffered and buffered solutions. Due to a simple approach we can experimentally demonstrate the relation between reaction rate and surface pH directly from the cyclic voltammograms. Clearly, the pH at a solid–liquid interface can be quite different from the bulk in unbuffered or insufficiently buffered solutions even at moderate reaction rates, in particular in the pH range of 4 to 10. However, at the given mass-transport conditions, well controlled by a rotating disk electrode, a buffer concentration of 10− 2 M is already sufficient to pin the surface pH to the bulk value at reaction rates of up to 1 mA cm− 2.

Research highlights
► Surface pH measurement in-situ without an extra device.
► The surface pH effect is demonstrated directly via the experiment.
► Unbuffered or insufficiently buffered solutions are critical to handle.
► Surface pH in solutions of pH 4 to 10 changes even at moderate reaction rates.
► Demonstration of relation between buffer concentration, reaction rate and surface pH.