Formation and Applications of Hierarchically Porous Carbon, Metals and Metal Oxides Formed by Nanocasting
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Formation and Applications of Hierarchically Porous Carbon, Metals and Metal Oxides Formed by Nanocasting Franchessa M. Sayler1, Amy J. Grano1, William Scogin1, Pasha Sanders1, Jan-Henrik Smått2, Kevin H. Shaughnessy, and Martin G. Bakker1 1 Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487-0336, USA. 2 Department of Physical and Colloidal Chemistry, Åbo Akademi University, Turku, Finland 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. INTRODUCTION Hierarchically porous materials are of interest in a wide range of applications, such as fuel cells, catalysts, sensors and energy storage. The ability to control the spatial composition and the structure and scale of the pores in the material significantly impacts the properties of the materials. We have been developing methods that use hierarchically porous silica monoliths prepared by sol-gel processes as the starting point to synthesize a range of other hierarchically porous materials including metal oxides1, metals and carbon2 by "nanocasting"3: using the silica as a sacrificial template. This contribution will focus on two applications of such materials: nickel metal based hydrogenation and the functionalization of hierarchically porous carbon as current collector for manganese dioxide and iron oxide electrodes for use in aqueous supercapacitors. The former serves as a test case for evaluating the reactivity and stability of porous nickel monoliths, the latter are of interest because the electrode pair manganese dioxide/iron oxide has high charge storage capacity and optimal electrode potentials for use with aqueous electrolytes. The nanostructured nature of the current collector is expected to produce very high charge/discharge rates.
EXPERIMENTAL Synthesis
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