Title : Material challenges with proton conducting ceramics for intermediate temperature hydrogenation/dehydrogenation applications
Abstract:
Fuel cells and electrolyzers based on ceramic materials have become an integral part of power↔X technology. Amongst the different categories of ceramic materials, proton-conducting ones exhibit superior ionic conductivity in the intermediate temperature range of 400 to 700 °C. Such a broad temperature window expands the scope of integration with downstream/industrial processes such as methane generation (Sabatier process) and ammonia synthesis (Haber Bosch process) since the heat produced due to exothermic reactions can be utilized within the system. Further applications include dehydrogenation reactions like ammonia cracking and dehydrogenation of methylcyclohexane. Additionally, the broad temperature range expands the choice of materials that can be used as electrodes.
State-of-the-art proton-conducting ceramic materials are barium and strontium-based doped zirconates and cerates that require an incredibly high sintering temperature (> 1500?C) to achieve fully densified electrolyte membranes to prevent gas crossover. However, such high-temperature sintering limits the choice of materials, especially ceramic-metallic composites (cermets) that are conventionally used as fuel electrodes for ceramic material based fuel cells and electrolyzers. On the other hand, low-temperature sintering leads to insufficient densification that results in lower ionic conductivity and limited hydrogen flux, which is currently the main challenge of scaling up this technology. It is suggested that incorporation of transition and alkali metal oxides as sintering additives can induce liquid phase sintering (LPS), offering an efficient method to facilitate densification of these proton conducting ceramics. However, current research underscores that incorporating these sintering additives may lead to adverse secondary effects on the ionic transport properties of these materials since the concentration and mobility of protonic defects in a perovskite are highly sensitive to symmetry change. This presentation aims to address these challenges and discusses the strategies being adopted to develop proton-conducting ceramic materials that can achieve adequate densification at lower sintering temperatures.
