Reversible thermochromic polymers have emerged as compelling candidates in recent years, captivating attention for their application in heat detection systems. This comprehensive review navigates through the multifaceted landscape, intricately exploring both the virtues and hurdles inherent in their integration within these systems. Their innate capacity to change colour in response to temperature fluctuations renders reversible thermochromic nanocomposites promising assets for heat detection technologies. However, despite their inherent potential, certain barriers hinder their widespread adoption. Factors such as a restricted colour spectrum, reliance on external triggers, and cost considerations have restrained their pervasive use. For instance, these polymer-based materials exhibit utility in the domain of building insulation, where their colour-changing ability serves as a beacon, flagging areas of heat loss or inadequate insulation, thus alerting building managers and homeowners to potential energy inefficiencies. Nevertheless, the limited range of discernible colours may impede precise temperature differentiation. Additionally, dependency on external stimuli, such as electricity or UV light, can complicate implementation and inflate costs. Realising the full potential of these polymer-based materials in heat detection systems necessitates addressing these challenges head-on. Continuous research endeavours aimed at augmenting colour diversity and diminishing reliance on external stimuli offer promising avenues to enhance their efficacy. Hence, this review aims to delve into the intricate nuances surrounding reversible thermochromic nanocomposites, highlighting their transformative potential in heat detection and sensing. By exploring their mechanisms, properties, and current applications, this manuscript endeavours to shed light on their significance, providing insights crucial for further research and potential applications.

Thermal energy storage (TES) plays a vital role in advancing energy efficiency and sustainability, with phase change materials (PCMs) receiving significant attention due to their high latent heat storage capacity. Nevertheless, conventional PCMs face critical challenges such as leakage, phase separation, and low thermal conductivity, which hinder large-scale applications. Encapsulation strategies have been developed to address these issues, and bio-based composite materials are increasingly recognised as sustainable alternatives. Materials such as lignin, nanocellulose, and biochar, as well as hybrid formulations with graphene and aerogels, show promise in improving thermal conductivity, mechanical integrity, and environmental performance. This review evaluates bio-based encapsulation approaches for PCMs, examining their effectiveness in enhancing heat transfer, durability under thermal cycling, and scalability. Applications in solar energy systems, building insulation, and electronic thermal regulation are highlighted, as are emerging AI-driven modelling tools for optimising encapsulation performance. Although bio-based PCM composites outperform conventional systems in terms of thermal stability and multifunctionality, they still face persistent challenges in terms of cost-effectiveness, scalability, and long-term reliability. Future research on smart, multifunctional PCMs and advanced bio-nanocomposites is essential for realising next-generation TES solutions that combine sustainability, efficiency, and durability.

The freight transport sector, which primarily relies on heavy-duty diesel vehicles, accounts for approximately 25–30% of worldwide transport-related greenhouse gas (GHG) emissions, underscoring the critical need for decarbonisation. Hydrogen fuel cell commercial vehicles (HFCVs), otherwise, are emerging as a viable alternative for long-haul freight, strengthened by advancements in fuel cell technology and supportive national energy policies. Meanwhile, the battery electric vehicles (BEVs) excel in short- to medium-duty applications due to their high efficiency, but encounter challenges related to charging delays, infrastructure requirements, and reliance on the electrical grid. However, the HFCVs provide rapid refuelling and extensive ranges; yet they face obstacles due to elevated hydrogen prices, insufficient refuelling infrastructure, and fragmented policies. This review offers a comparative evaluation of hydrogen fuel cell vehicles, battery electric vehicles, and diesel vehicles in terms of technical, environmental, and economic factors, encompassing range, efficiency, lifecycle emissions, and infrastructure expenses. Moreover, this review outcome has indicated that China surpasses others in adoption due to robust national strategies at the same time, Europe gains from the Green Deal and Fit-for-55, and North America progresses through industry-led initiatives but faces challenges from fragmented regulations, with readiness indices of 3.8, 3.7, and 3.3, respectively. Realising scale necessitates synchronised policy, infrastructural investment, and intersectoral collaboration. This review study also provides empirical insights to inform sustainable freight transition strategies and emphasises HFCVs as a feasible alternative for decarbonising long-haul transportation.