Effect of tunnel structure on the specific capacitance of etched aluminum foil

The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cylindrical model and two merged models, considering the fixed weight loss of etching. The maximum of specific capacitance and the corresponding optimum values for tunnel sizes at various anodization voltages were predicted. The increased size distribution and taper of tunnels were demonstrated to decrease the specific capacitance, whereas the addition of polymeric additive into the tunnel widening solution was demonstrated to increase the capacitance. The formation of merged tunnels on the etched aluminum surface, irrespective of the presence of row-merged tunnels or cluster-merged tunnels, resulted in a dramatic decrease in the specific capacitance. It is concluded that, enhancing the uniformity of tunnel size and distribution and avoiding the formation of merged tunnels are the effective approach to achieving the higher capacitance for the tunnel etched and formed aluminum foil.