New physical technologies for catalyst synthesis and anticorrosion protection

Abstract

Possibility of ion implantation and magnetron sputtering for the increase of catalyst activity and corrosion/oxidation stability of Ti components for PEM electrolyzer was studied. Porous and not-porous Ti samples modified by Pt deposition or implantation were investigated by transition electron microscopy (TEM), Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Near Edge Structure (XANES), potentiostatic and potentiodynamic electrochemical measurements and so on. It was found out that implantation of Pt ions (dose D ≤ 5 × 1016 ion/cm2, E = 1–50 keV) did not provide detectable increase of Ti catalytic activity and Ti stability against oxidation/corrosion due to a very low Pt surface concentration. At the lower energies (E ≤ 1 keV) and higher doses D ≥ 1017 ion/cm2 Pt surface concentration can reach 60–70% atomic but activity and stability is still rather low as the surface layer modified by Pt is very thin (less than 6 nm) and PtTi alloy which is obtained on the surface does not have high electrochemical activity. Application of magnetron sputtering for Pt films deposition is more efficient tool for the purposes mentioned above. The deposited films have a porous (porosity about 14–16%) column-like structure and a roughness factor is rather high (up to 13.44 for 26 nm Pt film) if Pt films are deposited on porous Ti. Pt films deposition provides a significant increase of porous Ti (current collector) electrochemical activity. However, such activity is not enough to use these current collectors as electrodes in PEM electrolyzers without additional catalysts but it permits to reduce catalyst loading. Because of Pt films porous structure a rather fast oxidation of Ti surface takes place at anode potentials due to contact with an electrolyte and such films do not provide necessary increase of stability. The following implantation of Ar+ ions with energies about 100–400 eV into the sputtered Pt films results in the significant increase of the stability of electrochemical parameters of Ti electrodes. However, it is necessary to underline that for the energy 400 eV we already observed a strong Pt sputtering and removal from the surface up to 50 wt. % of the initial Pt layer. At higher energies, total sputtering of Pt layer took place and stability and activity of electrodes became low. Therefore, combination of ion implantation and magnetron sputtering is a rather powerful tool for increase of Ti stability in corrosion/oxidation processes.