Enhancement of the conversion of mechanical energy into chemical energy by using piezoelectric KNbO_3−x with oxygen vacancies as a novel piezocatalyst

Abstract

Synthesis of new piezoelectric materials to harness the vibrational and thermal energies may contribute to solve the current increasing energy demands. KNbO3 is a known piezo- electric material that exhibits poor piezocatalytic activity owing to the scarcity of charge carriers in it. In order to enhance the charge carrier density in KNbO3, extra electrons were added to KNbO3 lattice. Extrinsic piezoelectric KNbO3−x having extra electrons in the lattice was synthesized via the reaction between Nb2O5 and KBH4 at elevated temperatures. The KNbO3 nanostructures formed at 450 and 550 °C contained feebly piezoelectric KNbO3−x/Nb2O5−x and piezoelectric KNbO3−x respectively. The enhanced piezocatalytic activity of KNbO3−x is demonstrated by the production of hydrogen from water by harnessing the mechanical vibrations and the observed hydrogen production rates are 0.05 and 3.19 ml h−1 g1 for KNbO3−x/Nb2O5−x and KNbO3−x respectively. The enhanced piezocatalytic activity of KNbO3−x can be attributed to the enhancement of the charge carrier density resulting from the creation of oxygen vacancies in KNbO3 that lead to enhancing the electronic conductivity as well as charge carrier separation. It is demonstrated that the piezocatalytic activity can be boosted by augmenting the charge carrier density in piezoelectric materials by synthesizing them under highly reducing reaction conditions.