Phase-change composites for bimodal solar/electromagnetic energy storage based on magnetite-modified cellulose microfibers

•Cellulose microfibers were modified with Fe3O4 nanoparticles in a tunable way.•Adsorption of lauric acid onto Fe3O4-modified fibers leads to shape-stable PCM.•Magnetic PCM composites can store thermal energy under alternating magnetic field.•Magnetite nanoparticles improves light-to-thermal conversion of PCM composites. Fe3O4-modified cellulose microfibers containing 7, 16, and 31 wt% of magnetite were prepared via co-precipitation of Fe2+ and Fe3+ salts. The magnetic phase-change composites were synthesized by adsorption of lauric acid onto the modified fibers with the highest saturation magnetization (23 emu/g) and magnetic-to-thermal conversion. The resulted composites demonstrated the saturation magnetization of 11.2 emu/g and latent heat storage capacity of 90 J/g corresponding to the loading efficiency of lauric acid of 49–51 wt%. The IR-imaging revealed the efficient accumulation of latent heat in the phase-change composite under the simulated sunlight and high frequency alternating magnetic field along with the excellent shape stability of the composites during the melting of lauric acid.