Electro/photo multi-energy triggered expanded graphite/polyethylene glycol composite phase change materials for...

In this work, we combined expanded graphite (ExG) and polyethylene glycol (PEG) to fabricate composite phase change materials (CPCMs) with effective photo/electrothermal conversion and storage, potentially applied to thermotherapy. The CPCMs were studied with varying contents of PEG (60, 70, 80, and 90%), showing good leakage-proof ability at a PEG content of up to 90% and high crystallization fractions of 94.4-98.7%. These two factors promoted a high thermal energy storage capacity of 151.1 J g^-1 for the fabricated CPCM90 (the CPCM with 90% PEG). The CPCMs also exhibited good cycling durability, high thermal stability, and elevated thermal conductivities of 3.201-7.683 W (m^-1 K^-1), which were 11.6-27.9 times above that of pure PEG. The high electrical conductivity and light absorption of ExG allowed effective electro/photothermal conversion and storage for the CPCMs. For example, the CPCM90 could be heated from the ambient to 70 °C in 390 s, as applied with a low electrical energy of 1.5 V. It also exhibited a high photothermal conversion efficiency of 84.0% at a simulated solar radiation of 1000 W m^-2. The CPCM90 was further evaluated for practical thermotherapy application as a heat eye-patch, which could maintain temperatures within 40.0-42.5 °C for 37 min. This temperature range and duration were highly desired for eye relaxation and therapy of some eye issues.