Degradation Effects at the Porous Transport Layer/Catalyst Layer Interface in Polymer Electrolyte Membrane Water Electrolyzer

The porous transport layer (PTL)/catalyst layer (CL) interface plays a crucial role in the achievement of high performance and efficiency in polymer electrolyte membrane water electrolyzers (PEMWEs). This study investigated the effects of the PTL/CL interface on the degradation of membrane electrode assemblies (MEAs) during a 4000 h test, comparing the MEAs assembled with uncoated and Ir-coated Ti PTLs. Our results show that compared to an uncoated PTL/CL interface, an optimized interface formed when using a platinum group metal (PGM) coating, i.e., an iridium layer at the PTL/CL interface, and reduced the degradation of the MEA. The agglomeration and formation of voids and cracks could be found for both MEAs after the long-term test, but the incorporation of an Ir coating on the PTL did not affect the morphology change or oxidation of IrOx in the catalyst layer. In addition, our studies suggest that the ionomer loss and restructuring of the anodic MEA can also be reduced by Ir coating of the PTL/CL interface. Optimization of the PTL/CL interface improves the performance and durability of a PEMWE

Investigating the interface of TiOX/PGM coating of porous transport layers used in PEM electrolyzers by surface analysis

Investigating the interface of TiOx/PGM coating of porous transport layers used in PEM electrolyzers by surface analysis Chang Liu1*, Meital Shviro1, Sarah Zaccarine2, Aldo Saul Gago3, Pawel Gazdzicki3, Tobias Morawietz3, Indro Biswas3, Roland Schierholz4, Svitlana Pylypenko2, Werner Lehnert1, 5 and Marcelo Carmo1 1 Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-14): Electrochemical Process Engineering, 52425, Jülich, Germany.2 Department of Chemistry, Colorado School of Mines, Golden, CO, 80401, USA.3 Institute of Engineering Thermodynamics, German Aerospace Center (DLR), Pfaffenwaldring 38-40, Stuttgart, 70569, Germany.4 Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-9): Fundamental Electrochemistry, 52425, Jülich, Germany.5 Modeling in Electrochemical Process Engineering, RWTH Aachen University, Germany.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

Effects of Graphitic and Pyridinic Nitrogen Defects on Transition Metal Nucleation and Nanoparticle Formation on N‑Doped Carbon Supports: Implications for Catalysis

Functionalization of carbon supports with heteroatom dopants is now widely regarded as a promising route for stabilizing and strengthening the interactions between the support and metal catalysts. Tuning the type and density of heteroatom dopants allows for the tailoring of nanoscale catalyst–support interactions; however, an understanding of these phenomena has not yet been fully realized because of the complexity of the system. In this work, computational modeling, materials synthesis, and advanced nanomaterial characterization are used to systematically investigate the intriguing effect of the two most common nitrogen functionalities in the carbon-based supports on the interactions with selected transition metals toward realizing catalytic applications. Specifically, this study utilized density functional theory to evaluate adsorption energies and modes of adsorption for 12 metals located in groups 8–11 and periods 4–6 with pyridinic and graphitic N defects. Based on these results, further electronic structure investigation of the period 4 metals was conducted to elucidate periodic group trends. Experimental work included synthesis and nanomaterial characterization of a subset of materials featuring three metals each supported on two types of N-doped carbon supports and undoped graphene. Characterization of nanomaterials with scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed that N functionalities enhanced the interactions with the selected transition metals when compared to the undoped support and demonstrated that the nature of the defect influences these interactions. Both computations and experiments agreed that Fe and Co are biased toward the graphitic sites over pyridinic sites, while Ni has an affinity to both defects without a statistically significant preference. This work established a correlation between computational and experimental work and a framework that can be expanded to other metals and alternative dopants beyond nitrogen in tailoring nanoscale catalyst–support interactions for a breadth of catalytic applications

Exploring the Interface of Skin‐Layered Titanium Fibers for Electrochemical Water Splitting

Water electrolysis is the key to a decarbonized energy system, as it enables the conversion and storage of renewably generated intermittent electricity in the form of hydrogen. However, reliability challenges arising from titanium‐based porous transport layers (PTLs) have hitherto restricted the deployment of next‐generation water‐splitting devices. Here, it is shown for the first time how PTLs can be adapted so that their interface remains well protected and resistant to corrosion across ≈4000 h under real electrolysis conditions. It is also demonstrated that the malfunctioning of unprotected PTLs is a result triggered by additional fatal degradation mechanisms over the anodic catalyst layer beyond the impacts expected from iridium oxide stability. Now, superior durability and efficiency in water electrolyzers can be achieved over extended periods of operation with less‐expensive PTLs with proper protection, which can be explained by the detailed reconstruction of the interface between the different elements, materials, layers, and components presented in this work