Modulating electron transport at the IrO_x / TiO_x interface in proton exchange membrane water electrolysis

Abstract

Polymer electrolyte membrane water electrolysis (PEMWE) is garnering significant scientific interest for the carbon neutrality. This is attributed to its capacity to facilitate extensive-scale generation of pure green hydrogen under elevated pressure. Nonetheless, a substantial contact resistance between iridium oxide catalyst layer and Ti porous transport layer (PTL) degrades the performance and eventually increases the green hydrogen cost. The band bending phenomenon, Schottky contact, in titanium oxide (TiOx, n-type semiconductor) caused by the contact with high work function of iridium oxide (IrOx) induces the large contact resistance with high energy barrier. This study investigates how the presence of ionomer at the interface, along with IrOx, maximizes Schottky barrier by pinch-off effect, as determined through electrochemical analysis and COMSOL simulation. In light of the results, we determined that a catalyst exceeding the scale of 30 nm reduces the contact resistance between IrOx / TiOx caused by pinch-off effect, as compared to a smaller catalyst (10 nm). This work provides valuable outcomes to design optimal catalyst structure for reducing ohmic overpotential at the PEMWE.