Journal of Energy Storage 33 (2021) 102045 2352-152X/© 2020 Elsevier Ltd. All rights reserved. Time-Controlling the Latent Heat Release of Fatty Acids using Static Electric Field Akhmad Yusuf a , Risky Afandi Putri a , Annisa Rahman a , Yunita Anggraini a , Daniel Kurnia a , Surjamanto Wonorahardjo b , Inge Magdalena Sutjahja a, * a Dept. of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha No. 10, Bandung 40132 b Dept. of Architecture, School of Architecture, Planning and Policy Development, Institut Teknologi Bandung, Jl. Ganesha No. 10, Bandung 40132 A R T I C L E INFO Keywords: Electrofreezing Fatty acid Electric feld, Latent phase change at constant temperature, Crystallisation period ABSTRACT Latent heat released during freezing of phase change material (PCM), which occurs at a constant temperature, can be modifed using an electric feld, through a process called electrofreezing. To date, the effects of the electric feld on the freezing of salt solutions or salt hydrates of inorganic PCM, such as reduction of the supercooling degree, increase of nucleation rate, and reduction of the induction time due to changes in the Gibbs free energy, have been the focus. In this paper, we describe the electrofreezing of stearic acid and lauric acid of fatty acid PCM. Because common organic PCM has relatively small or even zero supercooling, the effect of the DC electric feld on the time of latent heat release at a constant temperature and crystallization time was more pronounced. A comparison was also done with inorganic CaCl 2 ⋅6H 2 O PCM using previously published data. We propose that the two time parameters are closely related to the electrical and thermal conductivities. Different nucleation mechanisms for fatty acids and CaCl 2 ⋅6H 2 O with interactions between the crystalline sample and electric feld, as well as dissimilar Joule heating effects, have been proposed. Changes in the chemical structure and thermal stability due to electric feld treatment are evaluated using the Fourier-transform infrared spectra, the decom- position and melting temperatures, and the calculation of the latent heat of fusion. We also discuss the potential applications of lauric and stearic acids as phase change composites in thermoresponsive devices for high elec- trical to thermal energy conversion effciencies. 1. Introduction Phase change material (PCM) is an important thermal energy storage (TES) medium, especially in this energy crisis era. PCM can store and release sensible and latent heat with its relatively large latent heat storage capability around its phase transition temperature. The commonly used phase transition is from solid to liquid (melting) or vice versa (freezing) [1–3]. Both inorganic and organic PCMs have advantages and disadvan- tages, which are related to their thermophysical and chemical proper- ties. These are mainly considered in their applications. For example, water (H 2 O) or salt hydrate of inorganic PCM with general formula AB•nH 2 O generally has a relatively large supercooling degree and major phase separation during liquid to solid phase transition. It also has a relatively large latent heat of fusion per volume, relatively high thermal conductivity, and small volume changes upon melting [4]. The super- cooling of PCM leads to their inability to recover stored latent heat, which can hinder their phase change energy storage ability. Phase separation also results in the transformation of salt hydrates to other salt hydrates with lower hydrate numbers or even to anhydrous salt and water during the melting freezing process, thus reducing the storage capacity. The fatty acid of organic PCM with a chemical formula CH 3 (CH 2 ) n COOH has useful properties, such as little or no supercooling, minor phase separation, melting congruency, low toxicity, small volume changes during melting or freezing, and relatively high surface tension that allows their impregnation into a host material [5]. The melting temperature and heat of fusion of this material are dependent on the number n in the carbon chains, with a longer carbon chain resulting in a higher melting temperature and non-monotonous increase in the heat of fusion [6]. Applications of this class of PCM in the cosmetic industry, food industry, building construction, and biological application are high due to its high termal stabilization, low toxicity and biocompatibility [4]. However, the thermal conductivity of this kind of organic PCM is lower than that of inorganic PCM due to its chemical composition of * Corresponding author. E-mail address: inge@f.itb.ac.id (I.M. Sutjahja). Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est https://doi.org/10.1016/j.est.2020.102045 Received 28 July 2020; Received in revised form 27 October 2020; Accepted 2 November 2020