Direct seawater splitting by photo-piezoelectric coupling based on surface protonated perovskite

Photocatalytic water splitting for hydrogen evolution has become one of the most important and effective ways to produce green and renewable hydrogen energy, the centre of which is the efficient, stable and inexpensive photocatalyst. The part of perovskite oxides have a wide range of properties such as ferroelectricity, piezoelectricity and pyroelectricity, as well as good photoresponsivity and chemical stability, which are promising for catalytic conversion applications. In this study, the Ruddlesden-Popper (RP) phase perovskite La2NiO4 is investigated from enhanced charge separation as well as accelerated surface redox reaction rates. In the case of the existence of piezoelectric response of La2NiO4, the photo-piezoelectric coupling strategy not only realize the catalytic pure water splitting, but also greatly improve the efficiency. The lattice structure is twisted when the catalyst is subjected to external stress and the electric dipole moment is no longer zero. The resulting piezoelectric potential not only enables the free charge in the bulk phase to migrate directionally, but also inhibits the recombination of photogenerated carriers, which ultimately achieves highly efficient photo-piezoelectric coupling for water splitting for hydrogen production. In addition, the protonation of the catalyst surface is used to further enhance the interfacial reaction of the catalysts, which improves the solution-catalysts contact efficiency and generates vacancy defects to strengthen the spontaneous polarization of the lattices, contributing to the enhancement of the redox reaction rate. This optimization strategy of surface protonation treatment combined with photo-piezoelectric coupling is not only applicable to nanocatalyst powders but also has a significant enhancement effect in perovskite ceramic membranes. When La2NiO4 powders are sintered into the porous ceramic membrane and the surface is protonated with 0.006 mol L−1 hydrochloric acid, the hydrogen production rate of seawater splitting under the photo-piezoelectric coupling condition can reach 7750.41 μmol m−2 h−1. This study contributes to further understanding of photo-piezoelectric coupling catalysis, leading to a new solutions for expanding the application of coupled multifield water splitting for hydrogen evolution.