Researchers at the WPI Advanced Institute for Materials Research, Tohoku University (Japan) have developed nanoporous metal/oxide hybrid electrodes for supercapacitors that offer high specific capacitances and charge/discharge rates. Their paper appears in the journal Nature Nanotechnology.
Electrochemical supercapacitors can deliver high levels of electrical power and offer long operating lifetimes but their energy storage density is too low for many important applications. Pseudocapacitive transition-metal oxides such as MnO2 could be used to make electrodes in such supercapacitors, because they are predicted to have a high capacitance for storing electrical charge while also being inexpensive and not harmful to the environment. However, the poor conductivity of MnO2 (10–5–10–6 S cm–1) limits the charge/discharge rate for high-power applications.
Here, we show that hybrid structures made of nanoporous gold and nanocrystalline MnO2 have enhanced conductivity, resulting in a specific capacitance of the constituent MnO2 (~1,145 F g–1) that is close to the theoretical value. The nanoporous gold allows electron transport through the MnO2, and facilitates fast ion diffusion between the MnO2 and the electrolytes while also acting as a double-layer capacitor.
—Lang et al.
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| The Ragone plot of the power (P) and energy (E)densities of the NPG/MnO2-based supercapacitors (solid blue circle, green triangle and red square for the plating time of 5, 10 and 20 minutes, respectively) in 2M Li2SO4 aqueous electrolyte. Source: Lang et al. Click to enlarge. |
Resources
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Xingyou Lang, Akihiko Hirata, Takeshi Fujita & Mingwei Chen (2011) Nanoporous metal/oxide hybrid electrodes for electrochemical supercapacitors. Nature Nanotechnology 6, 232–236 doi: 10.1038/nnano.2011.13