A method of preparing a fiber including electro-spinning onto a substrate polymer solutions from a plurality of jets to form a network of filaments, wherein at least one jet sprays onto the substrate a first chemical mixture including a carbon fiber precursor compound, and at least one other jet sprays onto the substrate a second chemical mixture comprising a sacrificial polymer and a precursor compound of a functional material; and processing the filaments on the substrate, thereby forming an arrangement of carbon fibers having the functional material deposited thereon.