Keggin and Dawson polyoxometalates as electrodes for flexible and transparent piezoelectric nanogenerators to efficiently utilize mechanical energy in the environment

In recent years, piezoelectric nanogenerators (PENGs) have been developed as a promising energy-harvesting electronic device. However, the electrodes of most PENGs devices are precious metals, thus increasing the production cost. Here, we propose a flexible transparent PENGs with polyoxometalates (POMs) as the electrodes; it can effectively utilize ambient mechanical energy to generate electricity. Five types of polyoxometalates with different structures and compositions are selected as the electrode materials for PENGs for the first time, and the output performance of different PENGs electrode devices is tested. The PENG device with (NH4)6P2Mo18O62 as the electrode can steadily provide a high electric output with an open-circuit voltage of 2.8 mV and a short-circuit current of 8.5 µA at the bending degree of 90°. At the same time, the transmission spectrum shows that the average visible transmittance (AVT) of PENG can reach 31%, thus outperforming the benchmark for window applications. Finally, the working mechanism, force analysis, repeatability, and stability of PENG are systematically evaluated. All the studies show that this flexible transparent device has potential application prospect in wearable electronic devices.