Flexocatalytic driven Water Splitting: Unprecedented Hydrogen Production by Symmetry invariant ZnIn2S4 Nanosheets

Abstract

Flexocatalytic water splitting offers an intriguing avenue for “sustainable hydrogen” generation and has potential to overcome several inherent limitations of photocatalytic, electrocatalytic, and even piezocatalytic methods. In particular, flexocatalysis does not necessitate a non-centrosymmetric crystal structure, unlike piezocatalysis which allows to choose from a large materials database. In this context, centrosymmetric 2D zinc indium sulfide (ZnIn2S4) nanosheets were utilized as an active material for flexoelectric-driven water-splitting. Notably, utilizing methanol as a sacrificial agent under an ultrasonic frequency of 40 kHz, an unprecedented H2 evolution rate of 60 mmol g-1 h-1 (0.120 mmol h-1) was achieved without using a co-catalyst, demonstrating the practical viability of the ZnIn2S4 (ZIS) nanosheets. FEA (finite element analysis) simulation reveals that induced flexoelectric polarization developed over the ZIS nanosheets due to inhomogeneous stress distribution that facilitates the progressive water-splitting reaction. A series of control experiments with electrochemical impedance spectroscopy, and surface potential studies were conducted to bestow mechanistic insights into the flexocatalytic-driven water splitting over ZIS nanosheets. The density functional theory corroborates the experimental findings, revealing that applying stress on the catalyst lowers the Gibbs free energy, promoting H2 production over ZIS nanosheets. Thus, the present study presents the symmetry invariant pathway for transforming mechanical energy into H2 production, thereby paving the potential way for sustainable and economically feasible H2 production.