## 1 Introduction  
The demand for efficient energy storage and effective electromagnetic interference (EMI) shielding materials has significantly increased with climate change and the rapid development of technology on electronic devices and systems. Nowadays, a significant challenge is to reduce the cooling and heating demands of buildings and the practical solution is finding new materials that can improve these properties of the building components [1]. Moreover, the need for buildings capable of mitigating the effects of electromagnetic waves has become increasingly critical in our technology-infused surroundings. The swift advancement of electronic devices has heightened concerns about electromagnetic radiation,as it can interfere with device performance and potentially affect human health [2]. In response to these challenges, the design of advanced materials with multifunctional properties has emerged as a promising strategy for achieving diverse and effective solutions in building constructions. Phase change materials (PCMs) such as paraffins have gained significant attention in the construction industry for their potential applications in energy storage and thermal management systems. PCMs can improve the thermal performance of buildings when integrated into various construction components, such as concrete, gypsum, or ceramic bricks [3]. By incorporating PCMs into these materials, it is possible to mitigate rapid fluctuations in indoor temperatures, thereby decreasing energy losses and lowering heating and cooling requirements without compromising comfort levels. However, these materials are still limited for practical applications due to some drawbacks related to their leakage during the phase transition and low thermal conductivity [4]. Carbonaceous composites, which are also conductive materials, act as effective shape-stabilized materials for PCMs (SS-PCMs) leading to effective thermal storage and parallel EMI shielding systems [5; 6; 7]. Paraffin octadecane, a well-known PCM with a melting point of 28 \({}^{\circ}\)C and high latent heat storage capacity, is an ideal component for thermal energy storage applications [8]. However, its leakage during the phase transition and low thermal conductivity limits its practical applications. To address this issue, researchers have developed composite materials that incorporate octadecane within a carbonaceous matrix, thereby stabilizing its shape and enhancing its thermal and mechanical properties. Such materials encase the PCM, enabling it to remain in its molten state without movement even at high temperatures [9; 10]. Some carbonaceous materials, that were used for the effective stabilization of PCMs, are activated carbons, carbon foams, graphite, graphene, single-wall nanotubes, multi-walled nanotubes and carbon nanofibers [6; 7; 11; 12; 13]. On the other hand, multi-walled carbon nanotubes (MWCNTs) are renowned for their exceptional electrical conductivity, mechanical strength, and thermal conductivity [14; 15]. When integrated with SS-PCMs, MWCNTs can significantly enhance the thermal conductivity and electromagnetic interference (EMI) shielding effectiveness of the composite material [13; 16; 17; 18; 19; 20; 21; 22; 23]. [PERSON] et al. showed an enhancement in thermal conductivity with the introduction of carbon nanotubes as a filler in paraffin/expanded perlite [16]. [PERSON] et al. found that the thermal conductivity of montmorillonite/MWCNTs/paraffin composite is 34% greater than that of montmorillonite/paraffin composite and 65% higher than that of pure paraffin [17]. [PERSON] et al. achieved a 29% increment of polyethylene/paraffin wax thermal conductivity by adding 3% MWCNTs [21]. [PERSON] et al. also showed an improvement in the thermal conductivity of paraffin by adding graphene nanoplatelets (GNPs) and CNT nanoparticles [22]. [PERSON] et al. [13] showed that the effective thermal conductivity of Ultrathin Graphite Hybrid Foams composites can be further enhanced by growing extensive CNT networks directly from the graphite struts into the pore spaces.