Fabrication of NbN-Coated Porous Titanium Sheets for PEM Electrolyzers

Abstract

Porous titanium sheets are attractive for application as the porous transport layer (PTL) for polymer electrolyte membrane (PEM) water electrolyzers. However, the titanium passivation increases its surface contact resistance, deteriorating the electrolyzer performance. A solution for long-term operation has been to coat titanium-based PTLs with platinum or gold, which considerably increases PEM electrolyzer costs. To overcome this limitation, a NbN coating is proposed as an alternative to decrease materials costs while avoiding titanium surface oxidation. Therefore, porous titanium sheets of ca. 250 μm were powder metallurgically produced by tape casting and then sputter-coated with a NbN thin film. A systematic investigation of NbN film deposition on porous titanium sheets by reactive magnetron sputtering was undertaken. Coating microstructure and constitution were evaluated before and after electrochemical characterization. First electrochemical characterizations throughout cyclic voltammetry and potentiodynamic polarization curves demonstrate that the addition of NbN coatings decreases titanium surface oxidation and improves electrochemical performance of the porous titanium sheets. These results indicated that NbN-coated PTLs are promising candidates for PEM electrolyzer application.