Dual PCM integrated thermoelectric generator for harvesting energy from ambient temperature variations

Traditional thermoelectric generators (TEGs) rely on external heat sources and heat sinks to maintain a thermal gradient and generate electrical power. Here, we present a dual phase change material (PCM) integrated TEG system that generates an internal temperature gradient without a defined hot or cold side. Two PCMs with different melting points are positioned on opposite sides of the TEG, enabling the system to create repeatable thermal hysteresis during heating and cooling cycles. To improve the thermal conductivity of the PCM, we developed a hybrid composite PCM containing graphene nanoplatelets and copper metal wool, achieving a thermal conductivity of 0.98 W m^-1 K^-1 while maintaining a latent heat of 160-170 J g^-1. Prototype testing under ambient-like temperature variations demonstrated stable and repeatable voltage generation, with open-circuit voltages exceeding 10 mV for 100-130 minutes. Composite PCMs provided faster and more uniform thermal responses than pure PCMs, enabling more predictable output. This dual PCM-TEG harvester represents a novel operational concept of passive energy harvesting, enabling conversion of low-grade, non-directional ambient thermal fluctuations into electrical power. The approach is well-suited for low-power autonomous sensors and IoT devices where external thermal gradients are unavailable.