Soutenance thèse Garance Cossard
Mme garance Cossard soutiendra sa thèse intitulée "Stratégies de structuration d'anode autosupportée à base d'acier inoxydable pour l'électrolyse de l'eau à membrane échangeuse d'anions"
| Water electrolysis is one of the most promising production routes for low-carbon dihydrogen (H2). In recent years, Anion Exchange Membrane Water Electrolysis (AEMWE) has attracted considerable interest as this novel technology has the potential to overcome the shortcomings of current state-of-the-art electrolyzers. This work focused on the anode side of the electrolyzer, where the Oxygen Evolution Reaction (OER) – producing dioxygen (O2) – is taking place, and targeted both the development of active OER catalysts and the identification of effective and promising implementation strategies of such materials in an AEMWE system. In industrial electrolysis, Porous Transport Layers (PTL) are used for electrical conductivity, mass transport and catalyst support. While these structures are usually inert for the reaction, it was reported that commercial stainless steel PTL worked efficiently for the OER without the need for conventional catalyst addition. This is possible because stainless steel undergoes significant surface reconstruction into highly active NiFe (oxy)hydroxides, under operating conditions (in alkaline media and at high oxidative potential). Still, to consider AEMWE as a viable and competitive hydrogen production route, it should match or outperform the characteristics of the state-of-the-art electrolysis technologies, in terms of performance, durability and cost. This work explores means of upgrading commercial stainless steel PTL to increase their OER activity and their utilization in an AEMWE system. As a first approach, Co3O4 spinel particles were deposited on the PTL using a thermal decomposition synthesis route. The spinel-decorated PTL beneficiated from a significant increase in specific surface area and from a favorable surface chemistry and texture, and consequently, of intrinsic catalytic activity. Yet, when implemented in the AEMWE single cell, the thick spinel oxide layer considerably reduced the conductivity between the anode and its current collector, which greatly hindered the practical performance of the catalyst. To alleviate this effect, Physical Vapor Deposition (PVD) was used to direct the catalyst deposition only on the membrane-side of the PTL. Concurrently, the use of PVD as a novel preparation route for Raney-like catalysts was explored. Incorporating the Raney-like NiFe films on the PTL lead to an effective increase in specific surface area and OER activity. The success of the implementation of such materials in the AEM single cell was proven to depend on several cell components. More precisely, to beneficiate from the addition of the layer, it needs to have minimal interaction with the membrane, which can block mass transport and thus poison the sputtering-deposited catalyst. One way of mitigating the catalyst poisoning by the membrane, and more generally, to maximize its utilization, is to rightfully choose the morphology of the PTL. In state-of-the-art hydrogen technologies, so-called Microporous Layer (MPL) – constituted of small and well-distributed pores - are used in that regard. The final approach of this PhD involved the use of powder sintering as a way of forming a stainless steel-based MPL on the surface of the commercial PTL. While this PTL modification allows for a significant increase in specific surface area, the structural reconstruction of the surface occurring during sintering was proven to be detrimental for the OER activity. The developed materials structure and properties were characterized using several techniques (SEM, TEM, XRD or XPS). Their catalytic activity was assessed both using the 3-electrode cell (for a 0.07 cm2 surface), to probe more intrinsic properties of the catalysts, and the 2-electrode AEM single cell (25 cm2), to evaluate its behavior in conditions closer to industrial application. While this study successfully highlighted the materials strengths and weaknesses, it also allowed to identify efficient implementation strategies of anode catalyst in AEMWE. |
Infos lieu
La thèse aura lieu le 13 novembre à 13:30 à l'auditorium du bâtiment IMAG (150 place du torrent, Saint Martin d'Hères).