Energy Focus: Designed imperfections in graphene maximize charge-storage potential of supercapacitors
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Designed imperfections in graphene maximize charge-storage potential of supercapacitors
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ew materials have been so extensively evaluated for electrical energy-storage applications as graphene; since 2009, over 1000 articles have highlighted the advantages that this two-dimensional (2D) carbon material possesses as a supercapacitor electrode. However, a single sheet of graphene cannot power a practical device, and few-layer graphene (FLG) or graphene-containing composites offer more practical solutions. Although graphene has unique electronic and mechanical behavior and has exceptional promise as a supercapacitor electrode material, the defect-free, ideal structures have a finite maximum charge-storage capability threshold. In an attempt to overcome this barrier, several previous research efforts have simulated the benefits of defects on the electronic and charge-storage properties of graphene. Most of that work, to date, has been solely computational, and few results have provided empirical backing of the modeling simulations. Recently, researchers from Clemson University were able to assemble graphene (FLG) electrodes with well-tailored defects into practical-scale supercapacitors. While it may appear counterintuitive, imperfections in the sp2-bonded graphene sheet—such as holes, vacancies, and atom dopants—offer critical benefits that are absent in the perfect graphene structure. Such disruptions of the π–π carbon bonds affect the density of states of the entire graphene sheet and enhance metallic conductivity of the (originally semiconducting) material. Density functional theory simulations point to higher quantum capacitance in materials with tailored defects; this, in turn, enhances graphene’s maximum charge-storage capability. Pores in the 2D sheets also enable ion transport perpendicularly through to the sheet planes of FLG and ensure high rate capabilities and power densities. Ramakrishna Podila, who heads the Laboratory of Nano-biophysics at Clemson University, underscores the significance of
Normalized Current Density (mA s/V sm2)
Energy Focus
Voltage (V)
Cyclic voltammograms show that nitrogen-doped graphene foams (NGFs) and structurally defective Ar+ plasma processed graphene foams (PGFs) both outperform their pristine graphene foam (GF) counterpart. Flexible supercapacitor pouch cells can incorporate these foams into commercially viable energy-storage devices. Credit: Advanced Materials.
this work. “Defect configuration in graphene is critical to achieving high-energy density supercapacitors beyond quantum capacitance limitations. In the right configuration, defects allow [the] electrolyte to access the interlayer spaces in few-layer graphene. This can increase the energy density as there is plenty of room in the middle.” Jingyi Zhu, Anthony S. Childress, Mehmet Karakaya, and Apparao M. Rao—all of Clemson University—joined Podila for this effort. They collaborated with Sushmita Dandeliya and Anurag Srivastava (of ABV-Indian Institute of Information Technology and Management) and Ye Lin (Univers
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