An article by Mechanical Engineering Professor Dr. Eui-Hyeok Yang, "Out-of-plane growth of CNTs on graphene for supercapacitor applications," has been selected by the editors of Nanotechnology for inclusion in the exclusive "Highlights 2012" collection. Articles in this collection have been nominated on the basis of a range of criteria including referee endorsement, novelty, scientific impact and broad appeal. Less than 5% of articles from 2012 received this recognition.
Dr. Yang’s article describes a research innovation which may help to realize the potential of graphene—a one-atom thick sheet of carbon atoms arranged in a honeycomb pattern—as a supercapacitor. Supercapacitors are electrical components that store energy in a similar way to batteries. They are appealing because they offer drastically faster charge and discharge times. However, they generally have much lower energy-density (i.e., they hold a smaller amount of energy than a similarly massed battery). They are currently used in applications where a large amount of power is needed for a relatively short amount of time. If energy-density limitations can be overcome, supercapacitors could be used to supplement or replace batteries in order to create mobile phones or laptops that charge in seconds.
“This honor demonstrates the enormous potential of Dr. Yang’s research in the vibrant research field of next-generation batteries and superconductors,” says Dr. Michael Bruno, Dean of the Charles V. Schaefer, Jr. School of Engineering and Science. “This disruptive nanotechnology could have a positive impact on a large proportion of the population as over 90% of American adults have a mobile phone that they charge regularly.”
High surface area and low intrinsic resistance are vital for high-performance superconductors. Morphology-modified carbon nanostructures such as activated carbon (AC), mesoporous carbon (MC) and carbon nanotubes (CNTs) have large surface areas, but suffer from limited performance due to micropores and internal resistance, and therefore exhibit lower capacitance than theoretically predicted. Graphene has recently been identified as a promising material for supercapacitor applications, due to its outstanding theoretical specific surface area (SSA), extraordinary electrical properties in the planar direction (sheet resistance = ∼280 cm−2), high mechanical strength and chemical stability. In addition, graphene exhibits an intrinsic capacitance of up to 21 μF cm−2, which is the theoretical limit of carbon materials. Furthermore, recent successful development of chemical vapor deposition (CVD)-based graphene synthesis techniques facilitates the application of graphene as electrodes in lithium ion batteries and supercapacitors as well as on metal substrates in electronics. However, existing techniques for its fabrication often result in folding and overlapping of sheets, reducing the surface area which is crucial to capacitance capabilities.
In order to overcome the problem of graphene aggregation, Dr. Yang has formulated a new method for fabricating a hybrid nanostructure comprised of carbon nanotubes (CNTs) grown on graphene layers. This method minimizes self-aggregation of graphene sheets while preserving valuable conductive properties. The carbon nanotubes are grown out of the graphene sheets to prevent agglomeration while concurrently acting as current pathways which, given the high conductivity of both CNTs and graphene, is anticipated to facilitate electron transport throughout the structure during the charge–discharge process.
Future work includes a detailed investigation of electrochemical performance of the hybrid nanostructure as a function of available surface area, lifecycle performance and the development of graphene–CNT–graphene 3D multistack as a stepping stone in creating high-performance supercapacitors.
Dr. Yang is currently PI on a number of active grants in the areas of research, education and equipment, from AFOSR and NSF. He directs the Micro Device Laboratory (MDL), a Stevens's multi-user facility. He is also an Associate Editor of several journals including IEEE Sensors.
About the Department of Mechanical Engineering
The Department of Mechanical Engineering confidently addresses the challenges facing engineering now and into the future, yet remains true to the vision of the founders of Stevens Institute in 1870 as one of the first engineering schools in the nation. The department mission is to produce graduates with a broad-based foundation in fundamental engineering principles and liberal arts together with the depth of disciplinary knowledge needed to succeed in a career in mechanical engineering or a related field, including a wide variety of advanced technological and management careers. This is accomplished through a broad-based Core Curriculum of applied sciences, engineering sciences, design, management, and the humanities, coupled with a long-standing honor system.
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