Bifunctional energy materials based on cellulose ionic complexes toward low-grade heat and photon energy storage

Discovering energy materials for low-grade heat and photon energy storage would advance the energy utilization from natural resources. Here, the ionic complexes based on cellulose and azobenzene-containing surfactant are presented as a new class of phase change materials for achieving this objective. Such materials could accomplish the energy charging in two different ways. Under UV light, the ionic complexes store photon energy and low-grade heat via the photoisomerization of azobenzene and the induced isothermal phase change at room temperature. While, without light condition, they could be employed for storing low-grade heat through a gradual phase change below 100 °C, by taking advantage of the intermolecular interaction changes. In the two different energy charging ways, the gravimetric energy densities for low-grade heat storage upon heating and photoinduced energy storage are up to 202 J/g and 152 J/g, respectively. The stored energy could be fast released as heat under Vis light irradiation. In addition, the fabrication of gold nanoparticles is proved to be a highly effective method for the fast energy charging under UV light. This work provides a new physicochemical principle for the development of energy storage materials based on biomolecules, which would also advance the economic value of cellulose as biomass resource.