Direct formation of metal layer on anion exchange membrane using electroless deposition process

In this work, a novel electroless deposition process on the anion exchange membrane (AEM) is proposed. AEM surface has a positively charged functional group, which in general does not allow the catalyst particle, such as Pd, to be formed on the surface. Hence, a different strategy from the conventional catalyzation process was required. We found that the sensitization process using Sn-containing solution, which is widely applied in the electroless plating on nonconductive substrates, hindered the Pd particle modification, which hence inhibited the following deposition reaction. Our several experiments and density functional theory analyses suggest that for Pd particle modification, anion in the bath turned out to play a key role. In particular, Cl⁻ provides the sufficiently strong connection between the precursor Pd²⁺ and positive functional group of the substrate. This leads to favorable deposition of Pd catalyst particles and metal layer formation on the AEM. Therefore, we conclude that just a single pre-treatment to immerse the AEM films into PdCl₂/HCl solution is capable to perform electroless plating on it. We applied the novel process to the electrode formation, such as Pt and Ni-P, on the AEM for hydrogen evolution reaction (HER) as a case study. Both Pt and Ni-P was successfully formed on the AEM. The electrochemical measurements show that those electrodes are able to serve as the catalytic electrode for HER. The electroless process proposed here opens possibility of the direct metal fabrication on ion exchange membrane surface.