Electrochemical applications of graphene are of great interest to many researchers as they can potentially lead to crucial technological advancements in fabrication of electrochemical devices for energy production and storage, and highly sensitive sensors. There are many routes towards fabrication of bulk quantities of chemically modified graphenes (CMG) for applications such as electrode materials. Each of them yields different graphene materials with different functionalities and structural defects. Here, we compare the electrochemical properties of five different chemically modified graphenes: graphite oxide, graphene oxide, thermally reduced graphene oxide, chemically reduced graphene oxide, and electrochemically reduced graphene oxide. We characterized these materials using transmission electron microscopy, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry, which allowed us to correlate the electrochemical properties with the structural and chemical features of the CMGs. We found that thermally reduced graphene oxide offers the most favorable electrochemical performance among the different materials studied. Our findings have a profound impact for the applications of chemically modified graphenes in electrochemical devices.
Kingon, A. I.; Nemanich, R. J.; and Cross, J. S., "Direct studies of domain switching dynamics in thin film ferroelectric capacitors" (2005). Alexei Gruverman Publications. 16.
Kingon, A. I.; Nemanich, R. J.; Tagantsev, A. K.; Cross, J. S.; and Tsukada, M., "Mechanical stress effect on imprint behavior of integrated ferroelectric capacitors" (2003). Alexei Gruverman Publications. 11.
Nemanich, R. J.; and Cross, J. S., "Three-dimensional high-resolution reconstruction of polarization in ferroelectric capacitors by piezoresponse force microscopy" (2004 A combination of vertical and lateral piezoresponse force microscopy ͑VPFM and LPFM, respectively͒ has been used to map the out-of-plane and in-plane polarization distribution, respectively, of ͑111͒-oriented Pb(Zr,Ti)O 3 -based ͑PZT͒ ferroelectric patterned and reactively-ion-etched capacitors. While VPFM and LPFM have previously been used to determine the orientation of the polarization vector in ferroelectric crystals and thin films, this is the first time the technique has been applied to determine the three-dimensional polarization distribution in thin-film capacitors and, as such, is of importance to the implementation of nonvolatile ferroelectric random access memory. Sequential VPFM and LPFM imaging have been performed in poled 1 ϫ1.5 m 2 PZT capacitors. Subsequent quantitative analysis of the obtained piezoresponse images allowed the three-dimensional reconstruction of the domain arrangement in the PZT layers of the capacitors. It has been found that the poled capacitors, which appear as uniformly polarized in VPFM, are in fact in a polydomain state as is detected by LPFM and contain 90°domain walls. Despite the polycrystallinity of the PZT layer, regions larger than the average PZT grain size are found to have the same polarization orientation. This technique has potential for clarifying the switching behavior and imprint mechanism in micro-and nanoscale ferroelectric capacitors.
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