[en] Acid-treated carbon nanotubes have a significant improvement on the phase change behavior of nanofluids through the elimination of supercooling degrees and improvement on thermal conductivity. However, it has been found that these carbon nanotubes aggregated after a single phase change cycle. In this study, this problem has been successfully solved by the incorporation of graphene oxide with acid-treated multi-walled carbon nanotubes (of diameters from 10 to 15 nm) to form an interpenetrated structure of nanofillers with good stability of at least 90 cycles. The efficacy of the carbon nanotubes and graphene oxide nanofillers with different ratios has been demonstrated to shorten the phase change duration of the nanofluids with insignificant reduction to their latent heat. The synergy of two different dimensional nanofillers prevented the aggregation of acid-treated carbon nanotubes without the use of surfactants and achieved high-energy storage capacity and reliability.