Facile chemical tuning of thermoelectric power factor of graphene oxide

Abstract

Reduced graphene oxide (RGO) is known for its excellent mechanical, electrical, thermal, and optical properties and is a promising material for high efficiency thermoelectrics. Given that graphene oxidation turns a metallic graphene into semiconductor and degree of oxidation can be controlled chemically, it is hypothesized that thermoelectric performance of RGO may be tailored by its degree of reduction. This points to a potential avenue for optimizing the thermoelectric efficiency of RGO, because both its Seebeck coefficient and electrical conductivity is dependent on its band gap which is manageable. This report presents an investigation of such effects where pristine graphene oxide (GO) was reduced by hydrazine monohydrate and the degree of reduction was carefully controlled by reduction time. Raman spectroscopy, UV–visible spectroscopy and FTIR spectrometry were used for the characterization of GO and RGO samples. While the pristine GO showed a very low D/G intensity ratio in Raman spectra and was poorly conducting electrically, the time-controlled reductions successively improved the D/G intensity ratio, the Seebeck coefficient and electrical conductivity of the RGO samples. Depending on the reduction time we found that the Seebeck coefficient of the RGO can increase from 12.91 μV/K to 24.3 μV/K, electrical conductivity from 0.0084 S/m to 19.9 S/m and thermoelectric power factor from 1.40 × 10−6 μW/mK2 to 2.65 × 10−3 μW/mK2 respectively.