A method was created for electroless deposition of conformal ultrathin (<20 nm) metal oxides on the high-surface-area walls of commercial carbon nanofoam papers, typically 0.1–0.3 mm thick. The resulting ultrathin metal oxides rapidly take up and release electrons and ions, thereby storing energy at 300–600 Farads per gram of oxide, while the carbon nanofoam paper serves as a three-dimensional current collector and defines a pre-selected porous electrode architecture.

Nanoscale metal oxide coatings on 3D carbon nanoarchitectures.

The high surface-to-volume ratio of oxide-painted carbon nano-foam enables footprint-normalized capacitances of 1–10 F-cm-2 addressable within tens of seconds — a time scale of relevance for hybrid electric vehicles. Pairing MnOx-carbon nanofoam with FeOx-carbon nanofoam yields an energy-storage device with an extended operating voltage in mild aqueous electrolytes (~2 V). This device provides technologically relevant energy and power density, while also being low-cost, safe to operate, and environmentally benign. Device-ready electrode structures exhibit up to 10-fold increased electrochemical charge storage.

The combination of high-performance electrode materials and aqueous electrolytes results in energy-storage devices that are composed of inexpensive components, safe to operate, environmentally friendly, and relevant in energy and power density.

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