Platinum interlayers reduce charge transport barriers between amorphous Ir-oxide OER electrocatalysts and the porous transport layer
Moritz Geuß, Lukas Löttert, Andreas Hutzler, Julian Schwarz, Jaroslava Nováková, Ivan Khalakhan, Miran Gaberšček, Karl J. J. Mayrhofer, Simon Thiele, Serhiy Cherevko
Abstract
• Platinization thickness on the PTL influences OER performance for amorphous IrO x . • Potential and platinization-dependent semicircle observed in Nyquist plots. • Impedance spectra corroborate Schottky junction between Ti-PTLs and amorphous IrO x . • Diode equation can be used to fit additional overpotentials for non-platinized PTLs. • Observed integral Ir dissolution independent of platinization of PTLs. Significant research efforts are dedicated to reducing the iridium loading in proton-exchange membrane water electrolyzers. Recently, the focus shifted toward better understanding the interplay between the titanium porous transport layers (PTLs) and the Ir-oxide-based catalyst layers, where significant performance losses were observed for low-loaded anodes based on intrinsically highly active but poorly conductive amorphous IrO x . In the presented study, a gas-diffusion electrode half-cell setup is used to promote an understanding of the underlying phenomena leading to this low performance. The influence of the PTL platinization on the performance of realistic porous transport electrodes (PTEs) for the oxygen evolution reaction (OER) is investigated by gradually increasing the platinum layer thickness for PTEs based on amorphous and rutile Ir-oxide. Electrochemical measurements show a beneficial influence of platinization on the activity for amorphous, but not for rutile Ir-oxide. Impedance analysis corroborates the formation of a Schottky-type interface between the PTL and the amorphous IrO x catalyst layers, depending on the PTL’s platinum layer thickness. We presume that this heterogeneous Schottky-type interface induces an additional voltage drop and influences the utilization of the catalyst layer, leading to increased overpotentials. The measurements were complemented by inductively coupled plasma mass spectrometry showing constant integral amounts of Ir dissolving from the catalyst layers during the OER, independent of the platinization. Transferring the obtained knowledge to single cells, the whole composite anode, including e.g. the interplay between PTL and catalyst layer, must be optimized in conjunction to achieve optimum OER performance and long-term stability.