Phase change materials for cold energy storage: Insights from three decades of research trends, advancements, and future directions

Phase change materials (PCMs) for cold energy storage provide an effective means of improving energy efficiency in refrigeration, cold chain logistics, building cooling, and pharmaceutical storage. However, a quantitative overview of the evolution of this research field over time remains limited. This study presents a bibliometric analysis of global research on PCM-based cold energy storage published between 1994 and 2024. A total of 769 peer-reviewed documents were retrieved from the Scopus database and analysed using the Bibliometrix package in R and VOSviewer. The results show a growth in publications after 2015, with annual output increasing from fewer than 20 papers per year before 2012 to over 120 papers in 2024. China dominates the field, accounting for approximately 43% of total publications, followed by India and several European countries. Contributions from African countries, on the other hand, remain below 2%. Keyword co-occurrence and network analyses identified ten major thematic clusters, with strong emphasis on thermal conductivity enhancement, nanocomposite PCMs, system optimisation, ice storage integration, and cold chain applications. Despite these advances, persistent research gaps were observed in subcooling control, long-term thermal stability, large-scale system integration, and region-specific applications in developing economies. This study provides a quantitative mapping of research trends, collaboration patterns, and thematic evolution in PCM-based cold energy storage. The findings provide evidence-based guidance for researchers, funding bodies, and policymakers, highlighting the need for targeted investment and collaborative research to accelerate the deployment of reliable, scalable, and low-carbon cooling technologies.