Hierarchical nanostructures are usually a combination of multiscale, multidimensional nanostructures such as nanowires, nanoparticles, nanosheets, nanopores and so on. Hierarchical nanostructures are expected to overcome the limitations of simple single-scale nanostructures. However, simple geometric combinations or a mixture of those multidimensional nanomaterials cannot be called true hierarchical nanostructures. To be functional hierarchical nanostructures, smart structuring or organization of each nanomaterial should be carried out to obtain ultimate performance compared with single component nanomaterials. To satisfy those requirements, functional hierarchical nanostructures should not only have a large surface area but also enhanced electrical, chemical, mechanical and optical performance.

This book has introduced recent developments in hierarchical nanostructuring especially for highly efficient energy device applications. Surface and electrical properties are the primary concerns in most energy devices. Maximizing efficiency in energy devices can be achieved by either new material development or functional structuring. Hierarchical functional nanostructuring has rapidly gained interest to achieve an increase in surface area and favourable electrical properties.