Porous Ceramics for Energy Applications

Three examples of porous ceramics in energy applications are described: catalysts, solid oxide cells (SOCs) and porous separation membranes. Ceramics offer properties, such as high temperature stability, chemical durability, conductivity, mechanical strength and abrasive resistance, which make these materials attractive for high performance applications. Porous ceramics are used directly as catalysts or as catalysts supports. Ceramic catalysts are typically oxide ceramics such as transition metal oxides (TMO), microporous zeolites and perovskites. Porous ceramics for catalysis are structured in the form of granules, extrudates, honey combs and laminates to carry catalytic active metals and offer large surface area, efficient mass and heat transfer properties, low pressure drop and appreciable mechanical strength. SOCs are ceramic electrochemical devices that convert chemical energy into electrical energy and vice versa, as fuel cells or electrolyzers. These devices consist of an electrolyte and two electrodes and the electrolyte separates the two electrodes. While the porous electrodes are mainly electronic conductors, the electrolyte is an ionic conductor. Different architectures, materials and fabrication techniques as well as the physical and structural characteristics of SOC, which influence directly the SOC performance are discussed. Porous ceramic membranes have a market in micro, ultra and nanofiltration for waste water treatment, in desalination processes and gas separation that do not allow the use of polymeric membranes. Ceramic membranes usually consist of a hierarchical porous multilayer architecture with a macroporous support and a number of additional layers that are successively reduced in pore size and thickness, depending on the application. Suitable materials, the ceramic fabrication steps and the challenges to prepare separation layers in respect to increasing demands on the membrane separation processes are explained.