Nanoporous Metals for Supercapacitor Applications

Abstract

Supercapacitors have received great attentions among various energy storage devices both in academic and practical applications. They show high power densities and can be fully discharged or charged in seconds which are suitable for large instantaneous current densities. The performance is highly dependent on the specific surface area and conductivity of the electrode materials. Nanoporous metals-based electrode materials with a large internal surface area and excellent conductivity have been widely investigated in supercapacitors. In this chapter, we summarize the research progress of pure nanoporous metals, pseudo-capacitive materials (metal oxides, conductive polymer)/nanoporous metals composites in supercapacitors. By introducing nanoporous structures into electrode materials, the 3D bicontinuous porous structure and the high conductivity of the nanoporous metal-based framework benefit the electron--proton transport and electrolyte permeation, giving rise to ultrahigh specific capacitance. The pseudo-capacitive materials can also be deposited on the nanoporous metals by surface oxidize/oxyhydroxide. The surface oxyhydroxide and the internal nanoporous metal framework form a homogeneous and stable hybrid structure. The mixed-valence oxyhydroxide composite has been prepared by dealloying ternary Ni–Cu–Mn alloy. This hybrid composite electrode exhibits an ultrahigh specific capacitance of 627 F/cm3 and a very large operating potential window of 1.8 V in an aqueous electrolyte. The MnO2/NPG composite electrode gives a high specific capacitance of 601 F/g even based on the total mass of gold and MnO2. The conductive polymer/NPG composites have been developed into all-solid-state supercapacitor electrode and gives excellent electrochemical performance. Asymmetric capacitors based on nanoporous metal electrodes have also been fabricated to further improve the performance of supercapacitors. All of the related works have been reviewed in this chapter. The summary part of this chapter gives a brief prospective and the roadmap in the field of nanoporous metals-based electrode materials about toward a practical supercapacitor.