Graphitic Mesoporous Carbon Thin Film Prepared By Rapid Thermal Annealing for Micro-Supercapacitors

Abstract

The miniaturization of electronic devices led to the advent of on-chip power sources with high energy and power density requirement. The development of such miniaturized energy devices further requires the preparation and/or processing of thin films (down to a few nanometers) of active material. Mesoporous carbon possessing both high porosity and conductivity are desired for such applications. However, obtaining thin films of mesoporous carbon on various substrates using commercially viable approaches requires further improvement and investigation. We have adapted rapid thermal annealing (RTA) as a novel approach to obtain mesoporous carbon. RTA enables rapid heating to temperatures up to 1200oC in just a few seconds and therefore provides a route for complete carbonization within a few minutes. Carbon precursor films comprised of brush block copolymers (BBCP) as sacrificial templates and phenol formaldehyde (PF) resin as a carbon source were prepared. In particular, the self-assembly of polydimethylsiloxane-b-polyethylene oxide (PDMS–b-PEO) BBCP and PF resin led to the formation of microphase-segregated film on various substrates including Si wafer, fused silica, and stainless steel. The PDMS domain in the BBCP fostered strong adhesion to the substrate even after annealing. RTA enabled complete carbonization of the precursor film within only 5 minutes, whereas conventional methods require approximately 500 minutes. Rapid processing at 1000oC resulted in the formation of mesoporous carbon with higher degree of graphitization, which is difficult to achieve with conventional carbonization method. The device prepared via RTA has a capacitance value of 7.0 mF/cm2 at 100mV/s, which is one of the highest values obtained for nanometer-thick carbon-based electrodes. These electrodes maintained a quasi-rectangular shape during the potential vs current scan, even at a scan rate of 20 V/s, which suggests that these materials are promising candidates for applications requiring very high-power density. The mesoporous carbon structure having high porosity and high conductivity can be further utilized as supports for the deposition of pseudo-capacitance materials to further boost the energy density of the device. Figure 1