Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 24, Issue 42, Pages 6717-6728Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201401284
Keywords
pseudocapacitors; mesoporous materials; vanadia; ITO nanocrystals; ALD
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Funding
- center for Molecularly Engineered Energy Materials (MEEM), an Energy Frontier Research Center - US Department of Energy (D.O.E.), Office of Science, Office of Basic Energy Sciences [DE-SC0001342]
- center for Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DESC0001160]
- NSF [CHE-0840531]
- NIH, California NanoSystems Institute, UCLA [1S10RR23057]
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Solution processing of colloidal nanocrystals into porous architectures using block co-polymer templating offers a simple yet robust route to construct materials with open porosity and high surface area. These features, when realized in materials that show efficient redox activity and good conductivity, should be ideal for electrochemical energy storage because they allow for efficient electrolyte diffusion and ample surface and near-surface redox reactions. Here, a route to synthesize nanoporous pseudocapacitors is presented using preformed ITO nanocrystals to make a conductive scaffold, coated with a conformal layer of vanadia deposited using atomic layer deposition (ALD). Two vanadia thicknesses are deposited, 2 and 7 nm, to examine the kinetics of Li+ diffusion into vanadia in a system where all other chemical and structural parameters are fixed. Porosity measurements show that the internal surface area of 2 nm vanadia samples is fully accessible; whereas for the 7 nm vanadia, there is some pore blockage that limits electrolyte diffusion. Despite this fact, composites with both thick and thin vanadia layers show high levels of pseudocapacitance, indicating fast diffusion of Li+ through even the 7 nm thick vanadia. This work thus sets a minimum accessible length-scale of 7 nm for intercalation pseudocapacitance in orthorhombic V2O5.
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