Nano-enhanced phase change materials doped with carbon allotropes for thermal energy storage: a patent landscape analysis

Nano-enhanced phase change materials (NePCMs) are composites made of an organic or inorganic PCM and nanoparticles (metal, metal oxide, carbon nanotube, graphite, graphene) capable of increasing their thermal capacity or conductivity. PCMs are classified into three categories, namely organic, inorganic, and eutectic. This study focuses on the patent analysis of organic NePCMs doped with carbon allotropes for thermal energy storage. Patent searches were carried out using two databases (Espacenet, provided free of charge by the European Patent Office, and Orbit, a paid-for system provided by Questel) using precise and controlled keywords in the title/abstract/claims search fields with Boolean and proximity operators and classification codes. Classification symbols were retrieved by means of the Espacenet classification search tool and the WIPO IPCCAT system. China is the country with the highest number of patent applications filed for NePCMs with carbon allotropes, followed by the United States, Europe, and South Korea. The number of patent applications filed increased from 2016 to 2022. However, it should be noted that the figures for later years are not reliable, as applications are kept secret for the first 18 months after filing. Graphene and its derivatives are the most frequently claimed compounds in applications and granted patents, followed by carbon nanotubes. Fullerenes are rarely claimed (1.4% compared to graphene and derivatives), with an even smaller percentage claimed for other nanosized carbon materials (such as nano-onions, nanoscrolls, nanohorns, nanocones, nanowalls, and nanocoils). Approximately 30% of the applications have either expired or been revoked or withdrawn. Of the active patents, between 35% (for nanotubes) and 40% (for graphene) remain under examination. The most commonly used PCMs in combination with carbon allotropes are paraffin, stearic and lauryl acids, and lauryl alcohol.