Imaging of Ionic Channels in Proton Exchange Membranes by the Nickel Replica Method

An imaging method for ionic channels in proton exchange membranes in wet conditions is reported. The ionic channels were replicated by the electrodeposition of nickel and then observed using scanning electron microscopy (SEM). The fidelity of the replica to the channels was confirmed by comparison of the SEM image of the nickel deposit to the transmission electron microscopy and atomic force microscopy image of the ionic channels using a sulfonated hydrocarbon block copolymer membrane, which keeps continuous ionic channels even in dry condition. By use of this method, the morphology of the ionic channels in a Nafion membrane in wet conditions was successfully observed. The nickel replica showed a continuous network of 5-10 nm wide channels, which is close to the reported value estimated using small-angle X-ray spectroscopy.