Intercalated graphene oxide for flexible and practically large thermoelectric voltage generation and simultaneous energy storage

Abstract

We report a new planar-type “thermally” chargeable supercapacitor (pTCSC) that can be charged by converting thermal energy into electricity without an external electrical power supply. The pTCSC was fabricated using a facile and scalable laser irradiation on graphene oxide films intercalated by sulfate ions (SGO) to control the mobility and concentration of dissociated protons without any liquid-phase electrolytes typically used in conventional supercapacitors. We utilized the Soret effect as a dominant transport mechanism for producing a very high thermally induced voltage up to 9 mV/K, compared with typically much lower thermoelectric voltages mainly from the Seebeck effect in traditional inorganic and organic thermoelectric materials. The key parameters to obtain the strikingly high thermopower with decent electrical conductivity were identified to be the improved mobility and concentration of proton. At the same time, the harvested electrical energy was stored on the reduced SGO electrodes. With a temperature gradient of 10.5 K, our “single” pTCSC device generated a large thermally charged voltage of 58 mV without electrical power supply. We also demonstrated that an array of pTCSC can be batch-fabricated and connected together to linearly raise the output voltage as large as 2.1 V, suggesting excellent suitability for roll-to-roll mass manufacturing of practical pTCSC. We demonstrated that it is feasible to operate an electrochromic device that darkens with power supply like a smart window using the batch-fabricated pTCSC when a temperature gradient is applied. Our results suggest that the pTCSC could eliminate needs for battery replacement and wired connections to power lines for various distributed electronic systems whenever and wherever a temperature gradient is present.