Thermal enhancement and shape stabilization of a phase-change energy-storage material via copper nanowire aerogel

Low thermal conductivity (k) has limited the applications of phase change materials (PCMs). To enhance k of paraffin PCM, copper nanowire (CuNW) aerogels (CuNWAs) are fabricated and infiltrated with paraffin, inducing a ∼30% k-enhancement and good electrical conductivity σ with 2.0 wt% CuNW. The composite shows interesting behavior of shape stabilization: it permanently shrinks after each thermal cycle but is fully shape-stabilized after ∼50 cycles, showing a stable >130% k-enhancement with 6.3 wt% CuNW. To investigate the dominant factors for the k- and σ-enhancements, the filler-filler and filler-matrix interfacial bondings are studied through pre-sintering of CuNWAs. The pre-sintering induces two effects: (1) building the CuNW-CuNW bonding and a >∼200% σ-enhancement, and (2) weakening the CuNW-paraffin bonding and a ∼4% k-reduction. This filler-matrix interfacial weakening is confirmed by nanoindentation technique and computational modeling. The pre-sintering also enhances the shape-stabilization against thermal cycling. In summary, a metallic aerogel is first-ever employed to fabricate shape-stabilized electrically-conductive thermal-energy storage materials (TESMs) with >130% k-enhancement. The pre-sintered-CuNWA-paraffin composite shows an impressive σ (=14 S/m). This study also demonstrated that the fundamental dominant factors for σ- and k-enhancements are the filler-filler and filler-matrix interfacial bondings, respectively (not conjointly). This provides important insights into designing TESMs with high electronic and/or thermal conductivities, and also high durability.