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. Using hierarchically porous silica as templates, we have demonstrated the formation of hierarchically porous metal and metal oxide structures. Through the control of the synthesis conditions, we have produced partial replicas ca. 1 cubic centimeter in volume, in which two macroporous networks are separated by a nanoporous membrane. The macroporous network in the silica template is known to be bicontinuous. Our underlying model predicts that the second, induced, macroporous network should be similarly bicontinuous.
Micrometer resolution X-ray tomography of the whole sample confirms that the synthesis produces one bicontinuous macroporous network, and is consistent with the existence of a second set of macropores. Preliminary experiments were carried out using FIB/SEM serial tomography to image the second macropore network, however, the length scale of the structures is such that this approach it is unable to firmly establish that the second macropore network is bicontinuous throughout the entire sample volume.