Effects of silicone oil additives on hydrogen adsorption and tunnel formation of aluminium foil

•Large bubbles adsorbed on Al foil will decrease the corroded regions sharply.•Corroded regions in silicone-oil contained electrolyte were relatively uniform.•Symmetry and distribution of the etched tunnels were improved accordingly.•Narrow etched tunnels were clearly longer than those of the large tunnels.•The specific surface area of the etched aluminium foil was considerably enhanced. This study investigated the adsorption of hydrogen bubbles and tunnel formation on aluminium foil during direct current (DC) electrochemical etching in an electrolyte with and without silicone oil additive. The results indicated that the etched tunnels obtained in the electrolyte containing silicone oil were more uniformly distributed with a more consistent size and length. This was attributed to the additive ability to facilitate the desorption of large bubbles on the aluminium surface, resulting in uniform corroded regions. Moreover, the generated narrow tunnels can accelerate the hydrogen evolution inside the tunnels, resulting in increasing the length of the etched tunnels.