For the cathode (Figure (a)) very few acoustic hits were observed at low current densities (e.g. Only two hits were observed across the 1 min, 10 mA cm -2 period), this is an indication of exceptionally low bubble formation with very limited acoustic activity. This trend for low amounts of bubble formation at low areal current densities continued across the first few current densities tested, although notably as the current density increased there was an increase in the number of hits occurring in each constant current step. After approximately 1500 s the number of acoustic hits increased more significantly. It is also observed that while there are hits just above the 25 dB threshold across the course of the experiment, increasing numbers of hits at higher acoustic amplitudes were observed as the current density increased.