Nanocellulose-based composite phase change materials for thermal energy storage: status and challenges

Thermal energy storage and utilization is gathering intensive attention due to the renewable nature of the energy source, easy operation and economic competency. Among all the research efforts, the preparation of sustainable and advanced phase change materials (PCMs) is the key. Cellulose, the most abundant natural polymer on earth, has the advantages of renewability, biodegradability, recyclability and ease of functionalization, making it a versatile candidate for newly emerging energy applications. Incorporating nanocellulose into PCMs has undergone a booming development as it can overcome the drawbacks of PCMs and form multifunctional sustainable composites. This review summarizes the use of nanocellulose including cellulose nanocrystals and cellulose nanofibers in the field of latent heat storage (LHS). Firstly, the preparation, physical properties and surface modification of nanocellulose are systematically reviewed, followed by the illustration of the preparation of nanocellulose-based materials, including films, hydrogels, foams and aerogels. Then, the fundamentals and applications of PCMs are briefly introduced. In particular, the recent progress in using nanocellulose-based materials for PCM-based LHS applications is intensively reviewed, where nanocellulose-based composite PCM slurries, capsules, fibers, films, and blocks are introduced in detail. The role of nanocellulose in preparing composite PCMs is interpreted from the perspective of its intrinsic properties. Summary and outlook are given to suggest the chances and challenges of using nanocellulose for LHS applications. This work may shed light on the innovative applications of naturally occurring polymers in sustainable energy systems and provide inspiration for the efficient utilization of sustainable thermal energy.