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Hybrid energy harvesters, using multiple harvesting mechanisms, have been proposed to overcome the limitations of single-mode energy harvesters. However, since the most hybrid harvesters have merely combined the energy generated by each mechanism, they could not synergistically enhance the output beyond a simple additive approach. In particular, although thermoelectric-piezoelectric hybrid energy harvesters have been explored for simultaneously utilizing ambient thermal–mechanical energy flows, the conventional design could not achieve the expected sum of separately harnessed individual energy outputs. Moreover, amplifying thermoelectric efficiency using the actively adjusted thermal energy flows through the piezoelectric beam dynamics has not been reported so far. Here, we propose an advanced design of the hybrid energy harvester that combines piezoelectricity and thermoelectricity, resulting in a higher final power generation. The piezoelectric cantilever beam was adopted to leverage oscillation-induced heat dissipation, which increases temperature gradients, prevents thermal saturation and sustains thermoelectric power generation. Cooling capabilities of thermoelectric generators were investigated with respect to cantilever designs, showing that the trapezoidal (narrow) cantilever design exhibits the highest displacement and heat dissipation. Furthermore, finite-element analysis validates the experimental findings to confirm consistent trends with the measured heat dissipation. The hybrid energy harvesting method achieves a power output of 7.619 mW in the presence of 0.5 g vibrational source, more than 50 % increase compared to the absence of vibration. The amplified thermoelectric-piezoelectric generators demonstrate their synergetic performances in powering IoT sensors and harvesting thermal–mechanical energy flows in automobile engines. This outcome highlights that rationally designed hybrid energy harvesters in considering thermal and vibrational characteristics can significantly boost the power output beyond a simple assembly.
Kim et al. (Sun,) studied this question.