Thermotherapy has emerged as one of the most promising treatments for arthritis, a prevalent, crippling, painful bone disease. This demands more flexibility, energy-efficiency, safety, and light-weight in thermotherapy packs and hot clothing. Heteroatom doping is a metal-free, cost-effective way to improve carrier concentration and hence electrical and thermal conductivity in reduced Graphene Oxide (rGO) thus rendering it suitable for wearable joule heaters. However, the current doping techniques result in complex chemical structures that hinder phonon propagation and suffer other problems such as low yield, low scalability, and rigidity of the final product. Here, we disclose a novel and facile, low-temperature technique for nitrogen doping and photoreduction of graphene oxide (GO) films for high-performance, flexible graphene-based electrothermal heaters. The nitrogen atoms are introduced into the GO lattice with the aid of ultrasonic power in a wet chemical doping phase and maskless, automated, rapid CO2 laser scanning is used for the concurrent removal of oxygen-containing functional groups and the rearrangement of nitrogen atoms in the graphene lattice. X-ray Photoelectron Spectroscopy (XPS) studies reveal up to 5.43% nitrogen dopant concentration with a high carbon to oxygen ratio of 16, while Raman studies uniquely show improved atomic ordering with ID/IG ratio of 0.51 in the nitrogen-doped Laser reduced graphene oxide (N-LrGO) films. The fabricated N-LrGO heater has a sheet resistance of 26 O/sq. and attains a higher steady-state temperature of up to 245.7 °C at a low driving voltage of 9 V with a low power demand of 0.7 Wcm−2 and a heating rate of 103 °C/s. Its excellent temperature distribution and high flexibility join with the scalability of the preparation technique to demonstrate great potential for its incorporation with next-generation wearable electronics powered by low voltage portable energy storage devices. |
