High-performance flexible electrothermal Joule heaters from laser reduced F-N Co-doped graphene oxide with extended Sp2 networks

Phonons play an important role in heat generation and propagation across graphene lattice; however, this is hindered by graphene heteroatom doping which generates highly defected structures. Consequently, heteroatom doping has not been primarily explored in electrothermal materials despite presenting a cost-effective and metal-free method of improving electronic activity in flexible 2D materials. Herein, we present a facile and scalable technique for fabrication of fluorine-nitrogen co-doped laser reduced graphene oxide (FN-G) Joule heaters by ultrasonic wetchemical doping and maskless laser writing method. Films containing 6.14 at. % F and 3.22 at. % N, low sheet resistance of 24.49 O/sq. and uniquely high degree of atomic ordering indicated by an ID/IG of 0.16 were successfully fabricated. The heaters showed highly competitive transient electrothermal behaviour with a saturation temperature of 365 °C for only 9 V applied voltage, high heating rate of 385.33 °C/s, and average response time of 0.68 s. An excellent temperature distribution, low power requirement, and a net-zero degradation in the electrical and electrothermal properties even after 500 bending cycles was demonstrated. These high-performance features render the FN-G heater suitable for applications in wearable electronics powered by low voltage portable electrochemical cells.