Investigating the Interface of TiOx/PGM Coating of Porous Transport Layers Used in PEM Electrolyzers By Surface Analysis

Abstract

Titanium porous transport layer (PTL) situating at the anode side of a PEM electrolyzer is subjected to harsh oxidizing conditions such as high anode overpotential, low pH, and oxygen evolution [1, 2]. Under these conditions, titanium (Ti0) changes its oxidation state over time, which induces the formation of a thin but continuously growing layer of passivated titanium (TiOx). Consequently, the electrical conductivity of the titanium fibers is adversely affected, fatally decreasing cell performance and durability [3, 4].Here, we demonstrate a scalable and simple approach to using iridium or platinum as a protective layer for titanium-based PTLs. In this work, 4000 hour stable durability profiles are achieved when PTLs are coated with only 0.1 mg·cm-2 platinum or iridium (10 times reduction of Au or Pt typically used in current commercial electrolyzers). The real morphology of the TiOx/PGM (platinum group metal) coating interface of PTL is shown by different surface analysis methods. We found that the thickness of TiOx layer of iridium coated PTL did not further increase after the long-term operation. The results of this work show how the interface of a well-protected titanium fiber behaves against passivation after a long-term operation under real electrolysis conditions. Reference [1] M. Carmo, D.L. Fritz, J. Merge, and D. Stolten, A comprehensive review on PEM water electrolysis. International Journal of Hydrogen Energy, 2013. 38(12): p. 4901-4934.[2] K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar, and M. Bornstein, Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale, in Annual Review of Chemical and Biomolecular Engineering, Vol 10, J.M. Prausnitz, Editor. 2019, Annual Reviews: Palo Alto. p. 219-239.[3] C. Rakousky, U. Reimer, K. Wippermann, M. Carmo, W. Lueke, and D. Stolten, An analysis of degradation phenomena in polymer electrolyte membrane water electrolysis. Journal of Power Sources, 2016. 326: p. 120-128.[4] C. Liu, M. Carmo, G. Bender, A. Everwand, T. Lickert, J.L. Young, T. Smolinka, D. Stolten, and W. Lehnert, Performance enhancement of PEM electrolyzers through iridium-coated titanium porous transport layers. Electrochemistry Communications, 2018. 97: p. 96-99.