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The formation of hierarchically porous metal and metal oxide monoliths by replication of hierarchically porous silica templates is reviewed. The various factors that impact the structure and properties of the synthesized materials are discussed and illustrated by the formation of new α‐Fe2O3, ZrO2, nickel, silver, and silver silicate porous monoliths. The impact of the atmosphere is addressed in the formation of Co3O4 and silver monoliths. For Co3O4, formation of the monolith under vacuum, air, argon, or nitrogen was found to dramatically change the structure of the final material. For silver, decomposition of the silver nitrate under air resulted in porous monoliths composed of silver silicates. Decomposition of silver nitrate under vacuum produced monoliths for which the chemical composition of the monolith was predominantly silver on the exterior of the monolith consisted of silver silicates in the interior of the monolith.

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Abstract

Hierarchically porous materials are of interest in a wide range of applications. If the materials are electronic or ionic conductors such materials are of interest as electrodes for use in fuel cells, flow batteries, electrocatalysis, and pseudo/supercapacitors. We have demonstrated the synthesis of hierarchically porous carbon, metal and metal oxide monoliths. Hierarchically porous silica with porosity at three length scales: 0.5-30 micrometer, 200-500 nm, and 3-8 nm, is used as a template to form these materials. The porosity of the silica template is produced by spinodal decomposition (0.5-30 micrometer), particle agglomeration (200-500 nm) and addition of surfactant or block copolymer (3-8 nm). Nanocasting: replication of all or part of the structure via one of a number of chemical replication techniques has been used to produce the carbon, metal oxide and metal replicas. The final surface areas of the materials can be as high as 1200 m2/g for carbon replicas, and >300 m2/g for metals and metal oxides. The use of the nanocasting technique allows for formation of materials that are compositionally or spatially heterogeneous.We report here results on the synthesis and characterization of hierarchically porous monoliths of carbon and, nickel and the use of some of these monoliths in catalysis and electrochemical capacitors.