  Water electrolysis in a microsystem is observed and analyzed on a short-time
scale ~10 us. Very unusual properties of the process are stressed. An extremely
high current density is observed because the process is not limited by the
diffusion of electroactive species. The high current is accompanied by a high
relative supersaturation S>1000 that results in homogeneous nucleation of
bubbles. On the short-time scale only nanobubbles can be formed. These
nanobubbles densely cover the electrodes and aggregate at a later time to
microbubbles. The effect is significantly intensified with a small increase of
temperature. Application of alternating polarity voltage pulses produces
bubbles containing a mixture of hydrogen and oxygen. Spontaneous reaction
between gases is observed for stoichiometric bubbles with the size smallaer
than 150 nm. Such bubbles disintegrate violently affecting the surface of
electrodes.
