Bidirectional anisotropic bacterial cellulose/polyvinyl alcohol/MXene aerogel phase change composites for photothermal conversion enhancement

The issues of inherent low thermal conductivity, slow heat transport rate and easy leakage are critical challenges for accelerating solar-thermal energy harvesting and storage for organic solid-liquid phase change materials (PCMs). Aerogel carriers with thermal conductivity enhancement based on ice temple methods show favorable potential for PCMs solar thermal applications. Comparing with disordered and unidirectional freezing, bidirectional freezing can assemble efficiently in multiple dimensions and result in long-range ordered structures. In this paper, bacterial cellulose/polyvinyl alcohol/MXene aerogels were constructed by bidirectional freezing. The anisotropic PCMs composites were from vacuum impregnation PEG into aerogel networks. By controlling crystallization and growth of ice crystals through the dual temperature gradients, the PCMs composites obtained enhanced heat transfer efficiency in horizontal and vertical directions. Bidirectional aligned PCMs with PDMS wedge angle of 0° and 20° exhibit high thermal conductivity of 0.716 W m−1 K−1 and 0.768 W m−1 K−1, which were 184% higher than that of PEG, and photothermal conversion efficiency of 55.17% and 76.91%. Remarkably, the PCMs composites with a 20° PDMS wedge angle also exhibited a high PCM loading capacity (96.3%) and a high enthalpy (157.7 J/g). The results show that bidirectional anisotropic PCMs composites have excellent overall performance and are expected to improve solar thermal application. •Bidirectional aligned BC/PVA/MXene-PEG PCMs composites were developed.•The assembly of Ti3C2 MXene in long-range oriented structures allows faster heat transfer and enhanced light absorption.•The thermal conductivity of bidirectional aligned PCMs with 20° PDMS wedge angle were 184% higher than that of PEG.•The PCMs composites achieved good photothermal conversion efficiency of 76.91%.•The composites exhibited high PCM loading capacity of 96.3%.