Enhancement of the conversion of mechanical energy into chemical energy by using piezoelectric KNbO3−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 KNbO_3−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 KNbO_3−x/Nb₂O_5−x and piezoelectric KNbO_3−x respectively. The enhanced piezocatalytic activity of KNbO_3−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 KNbO_3−x/Nb₂O_5−x and KNbO_3−x respectively. The enhanced piezocatalytic activity of KNbO_3−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.