Bio-based phase-change materials for thermal energy storage: Recent advances, challenges, and outlook

This review systematically examines recent advances (2022–2025) in bio-based phase change materials (PCMs) for thermal energy storage (TES). Emphasis is placed on renewable PCMs derived from fatty acids, plant oils, and biowaxes, highlighting progress in synthesis strategies, structural modifications, performance enhancement, and techno-environmental sustainability. Nanofiller incorporation, including graphene nanoplatelets and boron nitride, has improved thermal conductivity by up to 400 %, while advanced encapsulation techniques ensure over 95 % enthalpy retention across 1000 cycles. Life cycle assessments (LCAs) reveal 40–60 % lower CO₂-equivalent emissions compared to paraffin-based PCMs, underscoring environmental benefits. Application-driven case studies demonstrate significant impacts: energy savings of up to 25 % in HVAC-integrated building envelopes, peak temperature reductions of 10–15 °C in battery thermal management, and prolonged heat retention of 4–5 h in solar thermal systems. Nonetheless, challenges remain in oxidation stability, long-term durability, leakage mitigation, scalability, and cost competitiveness. The review distinguishes incremental improvements from transformative innovations, contrasts bio-based with petrochemical PCMs, and identifies hybrid TES systems as emerging solutions. A commercialization-focused roadmap aligns challenges with industry initiatives and technology readiness levels, offering short-, medium-, and long-term strategies. Overall, this work provides an evidence-based synthesis to accelerate the transition of bio-PCMs from laboratory research to scalable, low-carbon TES applications.