The capability to engineer materials in nanometer scales has brought unprecedented technological advancements in various fields. Energy storage devices, in particular, have demonstrated significant improvements in their performances derived from superior capabilities of nanostructured electrodes, but systematic control of the nanomaterials remains a challenge. This dissertation discusses fabrication of highly controlled, bicontinuous composite nanostructures using block copolymer self-assembly and their evaluations as electrode materials in energy applications. Three-dimensionally arranged block copolymers were utilized as the structure-directing frameworks to produce highly porous and interconnected carbonaceous structures. The bottom-up fabrication process allowed versatile control of the nanostructures with high degrees of freedom in the structure dimensions, morphologies, and compositions. In Chapter 2, supercapacitor electrodes were prepared with integration of phenolic resin to the polymer network to produce heteroatom-doped carbon nanostructures. Their structural dimensions were controlled to facilitate the electrolyte accessibility and diffusion within the electrode nanostructures, which lead to superior performances. In Chapter 3, electrocatalyst materials were fabricated with incorporation of platinum precursors to develop composite nanostructures of platinum particles embedded in carbon matrix. Morphology control of the composite structure enhanced the catalytic activity and durability of the noble metal particles. In Chapter 4, various carbon-metal nanostructures were prepared with diverse noble metal nanoparticles, and multi-metallic carbon composites were demonstrated by simultaneously introducing multiple noble metal precursors to the polymer framework. Overall, the nanofabrication process discussed in this thesis provides a simple yet versatile approach in producing well-defined nanostructures with controlled dimensions, morphologies, and compositions, and the electrochemical evaluations suggest novel perspectives in design and fabrication of electrode nanostructures.