Unveiling asymmetric thermo–mechanical coupling for enhanced energy harvesting: a lead-free BCT–BST based pyro–piezoelectric hybrid nanogenerator

Abstract

Pyroelectric nanogenerators (PyNGs) and piezoelectric nanogenerators (PENGs) have great potential for harvesting thermal and mechanical energy, yet the combined influence of temperature and force on the output performance of pyro–piezoelectric hybrid nanogenerators (HNGs) remains insufficiently understood, limiting their optimization for multi-energy harvesting. To address this, we report a high-performance pyro–piezoelectric HNG based on a 0.55(Ba_0.9Ca_0.1)TiO₃–0.45Ba(Sn_0.2Ti_0.8)O₃ (BCT–BST) ceramic wafer exhibiting a high piezoelectric coefficient and systematically investigate its thermo–mechanical coupling mechanism. A key finding is the distinct asymmetric response of the device: compared to the pure piezoelectric output (54.4 nA), simultaneous heating and force suppressed the current by 41.4%, whereas simultaneous cooling and force enhanced it by 13.4%. This behavior is explained by the modulation of band bending caused by the interplay between pyroelectric and piezoelectric effects. Leveraging the optimal cooling-force condition, the device demonstrated rapid energy-storage capability, charging a 4.7 µF capacitor to 3 V within only 46 s. Moreover, it exhibited excellent stability during 9 h of continuous operation. This work not only reveals the great potential of lead-free ceramics in multi-source energy harvesting but also establishes a fundamental principle for designing high-performance pyro–piezoelectric HNGs.