Porous ceria for high temperature catalytic applications demands structural integrity concomitant with sinter resistance and improved gas permeability. The current state of the art hinges on complex synthesis methodologies which are not only expensive but also lack flexibility in pore tailorability. Hence, the development of porous scaffolds through low-cost processes without compromising on the functionality is in order. Herein, we demonstrate porous ceria with an open porosity of 88% developed through camphene assisted freeze casting for the first time. Microstructural evolution with different building blocksmicrometre-sized particles and short fibres were also studied. Preliminary catalytic activity obtained via temperature programmed reduction exemplified similar profiles showing no effect of the initial building blocks on the activity.
Polymer-derived processing of ceramics (PDC) is an efficient technique to prepare porous nanocomposites with precise control over their phase composition and in relation to the Si-based ceramic matrix containing free carbon. The microstructure of these nanocomposites can be fine-tuned at the molecular scale for obtaining necessary properties by tailoring the chemical configuration of the preceramic polymer. In the present work, vanadiumbased nanocomposites were synthesized as oxygen reduction reaction (ORR) catalysts with the objective of elucidating the effect of microstructure changes on catalytic efficiency. For this purpose, a single-source precursor (SSP) was synthesized by crosslinking phenyl-and hydrido-substituted polysiloxane and vanadium acetylacetonate followed by pyrolysis at 1100 °C. The resulting solid was composed of sparsely distributed nanodomains of vanadium carbide (VC) crystals precipitated within an amorphous silicon oxycarbide (−Si−O−C−) matrix. High-temperature treatment of the pyrolyzed samples beyond 1300 °C induced the crystallization of β-SiC as well as VC. Furthermore, Raman spectroscopy confirmed the segregation of sp 2 -hybridized, turbostratic free carbon. The samples exposed to 1300 °C revealed a specific surface area of 239 m 2 /g. The electrocatalytic activity of the sample heat-treated at 1300 °C showed the best performance with respect to the ORR performance with onset potential (E o ) and half-wave potential (E 1/2 ) values of 0.81 and 0.72 V, respectively. In addition, improved kinetics with a Tafel slope of 57 mV/dec and enhanced current density in the diffusion-controlled region (I d ) of 3.7 mA/cm 2 were observed for this sample. The increase in E o was attributed to the optimal interfacial characteristics between the VC and SiOC matrix with better embedment of VC with free carbon through V−C bonds. The higher E 1/2 and faster kinetics are because of the higher electronic conductivity caused by the free carbon effectively connecting metallic VC crystallites. Besides, the higher specific surface area of this sample enhanced I d .
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