Highly elastic conductive sponges by joule heat-driven selective polymer reinforcement at reduced graphene oxide junctions

Polymer reinforcement of reduced graphene oxide (rGO) sponges is widely employed to enhance mechanical strength and elasticity. However, the surplus polymer decreases electrical conductivity by passivating the conductive surface of rGO flakes. Here we firstly report the selective polydimethylsiloxane (PDMS) reinforcement at the flake junction of rGO sponge by the Joule heating process utilizing the high electrical contact resistance. The preferential Joule heating of the junction is theoretically simulated by finite element modeling and experimentally confirmed by micro-thermal infrared imaging. The local temperature increase results in the further reduction of rGO and preferential PDMS curing at the flake junction only. The PDMS/rGO mass ratio was carefully optimized at 3.96. The electrical conductivity (0.087 S m⁻¹ at 0% strain) is more than an order of magnitude higher than that (0.00251 S m⁻¹) of the conventional oven-heated sponge with a similar PDMS/rGO mass ratio. The mechanical strength is equivalent (210.3 kPa at 70% strain), in spite of the preferential polymer coating at the rGO flake junction only, with excellent elasticity. The Joule heating method is an excellent curing strategy to selectively reinforce flake junctions for conductive elastic rGO-polymer sponges.