Title：Development of all-solid-state mediator supercapacitor

Speaker： Xiangyang Zhou（周向阳）, University of Miami

Time ：2013年7月23日（周二）14:00

Venue：南区学术报告厅

Abstract:

Advantages of all-solid-state supercapacitors (SCs) in comparison to those based on liquid electrolytes include no inherent leakage, absence of corrosion and combustion, ease of assembly and scale-up, wider temperature range, flexible geometry, and better safety. However, for the same electrode materials, a SC based on liquid electrolyte possess higher specific capacitance and specific power than a SC based on solid electrolyte. The major reasons for the low performance of all-solid-state SCs are: 1) the ionic conductivity of solid electrolytes is generally much lower than that of liquid electrolytes and 2) lack of viscosity or fluidity. The intrinsic low accessibility of solid-state electrolytes to small pores of a porous electrode results in a low utilization of the the active surface of the porous electrode. The present hypothesis-driven research is focused on the effects and mechanisms of dispersing redox pairs or mediators (I-1/I3-1, Co(III)/Co(II) complexes, ferrocene/ferricinium, etc.) into the porous electrodes of a SC. The new technique not only provides so-called molecular capacitors but also eliminates the problem of inaccessibility. The new concept is also employed to mitigate the reduction of specific power and energy at low temperatures. Cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge, long-term cyclic charge/discharge, and self-discharge tests were conducted to evaluate the SCs. In situ X-ray absorption spectroscopy (XAS) was conducted to probe the electrochemical mechanisms during the charge/discharge process. The maximum specific energy and power that can be obtained for poly(ethylene) oxide (PEO) based, all solid state supercapacitors with separators are 34 Wh/kg and 4.5 kW/kg, respectively, with respect to total device mass. Water-free an MEPESCs based on polyvinylidene fluoride (PVDF) enable a wider potential range of 3 V, a high specific energy of 67 Wh/kg, and a high specific power of 3.60 kW/kg. These values are much greater than those for other solid-state electrolyte supercapacitors and greater than those for state-of-the-art liquid electrolyte supercapacitors. In addition, it was found that hot pressing can increase the ionic conductivity of the PEO based polymer electrolytes more than one order of magnitude. This is highly desired for development of high performance electrochemical energy storage devices.

Bio of the speaker:

Dr. Xiangyang Zhou is a tenured associate professor at Department of Mechanical and Aerospace Engineering, University of Miami, a leading private research university in the US.

Dr. Zhou received his BS in Physics from Wuhan University, MS from Institute of Corrosion and Protection of Metals, Academia Sinica, and PhD in Materials Science and Engineering from University of Newcastle upon Tyne, England.

Dr Zhou is a Principal Investigator of multi-million-dollar research projects funded by The US National Science Foundation, Federal Aviation Administration, DOD, DOE, EPRI, etc. His research areas are: corrosion and corrosion fatigue in high temperature water, polymer electrolyte fuel cells, supercapacitors, catalytic hydrogen production, and atomistic simulation of solid-state electrochemical interfaces. He has served as a panelist for the US National Science Foundation and Swiss National Science Foundation, and has been a keynote speaker for international conferences. Dr. Zhou and his group have published 46 peer-reviewed articles.　　　　　　　　　　　　　　　　　　　　　　　　　　

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