Highly efficient thermo-electrochemical energy harvesting from graphene–carbon nanotube ‘hybrid’ aerogels

Three-dimensional scaffold assemblies consisting of thermally reduced graphene oxide nanosheets and small-diameter carbon nanotubes were synthesized as potential ‘all carbon’ thermo-electrochemical energy harvesters. The facile hydrothermal–solvothermal synthesis route in which organic wet chemistry used was to inter crosslink the well-dispersed graphene oxide nanosheets with carbon nanotubes followed by freeze-drying to produce monolithic aerogel networks with ultralow densities, tunable mesoscopic pore sizes, tailorable functionality and morphology. They exhibited high electrical conductivity due to multiplex topologies owing to the integration with carbon nanotubes, which has high density of states at van Hove singularities, accompanied by expected larger surface area and sufficient edge plane sites, which in-turn enhance surface adsorption and rapid ion transportation. We conducted thermoelectric and thermo-electrochemical power generation from these ‘hybrid’ aerogel materials and using two different designs of galvanic thermo-cells. Consequently, higher Seebeck (electronic; Se as well as ionic; Sion) coefficients and thermopower generation was measured that confirmed low thermal responsiveness attributed to smaller domain size generated by hierarchical mesoporosity and open network. These multiple features demonstrate significant potential of these novel electrodes in galvanic thermocells for low-grade thermal energy harvester with higher relative conversion efficiency.