Advanced reticulated ceramics in Concentrated Solar Power applications: from volumetric receivers to multifunctional integrated structures for solar fuels production and thermochemical solar heat storage

Abstract

The inherent structural advantages of highly porous ceramics like honeycombs and reticulated foams have established them as the configuration of choice in a variety of catalytic applications, the most notable being automotive exhaust aftertreatment. Coupling of These structural concepts to special material properties such as solar absorptivity enables the effective heating of gases inside such porous structures via Concentrated Solar Power (CSP). In a direct analogy to “conventional” catalytic applications, such chemically inert supports can be rendered “chemically active” by the incorporation of proper functional materials capable of performing/catalysing a variety of high-temperature reactions within their structure. Thus solar thermal collector/heat exchanger modules can be transformed to efficient, structured solar chemical receiver/reactors. Recent such reactor paradigms based on redox oxide materials are employed for water/carbon dioxide splitting for the production of hydrogen/“solar fuels” respectively via thermochemical cycles. In the present work, starting from an overview of the already wide CSP applications of reticulated ceramics, emphasis is placed on how their properties can be successfully exploited in new areas such as the thermochemical storage of solar heat via reversible redox chemical reactions. Reticulated ceramics have been employed as directly irradiated, volumetric solarabsorbing catalyst supports in solar methane reforming receiver/reactors since 1990. Today, such second- and third- generation solar reactors are the most developed ones, having been tested in the scale of few hundred kilowatts of solar input. A commonality of concern for the two thermochemical applications - solar-aided production of chemicals and solar heat storage - is the maximization of volumetric product yield; this “product” being the targeted chemical substance or the stored/released heat, respectively. In this respect, concepts on the use of reticulated ceramics for thermochemical storage within integrated thermochemical reactors/heat exchangers and on maximizing the incorporation of active material within their structure and relevant results are presented and discussed.