The procedure for the preparation of microcapsules consisting of the phase change material, octadecane and a carbon based container was based on previous work. To form the composite shell using graphene oxide and carbon nanotubes, 10 ml of graphene oxide dispersion (2.0 mg/ml, GO Graphene) was set to pH 2 by hydrochloric acid (37%, Sigma Aldrich) in a 14 ml vial and 3.0 mg of multiwall carbon nanotubes (Sigma Aldrich) were added. The resulting mixture was sonicated using a sonicator probe (1.25 cm probe, Qsonica model Q700, 20 kHz) placed 0.5 cm into the liquid for 10 minutes at an amplitude of 30%, 5 seconds on, 5 seconds off. An ice bath was used to prevent overheating by keeping the temperature of the suspension below 40 o C.