PbTiO3 Based Single-Domain Ferroelectric Photocatalysts for Water Splitting

Abstract

Conspectus Solar-driven photocatalytic water splitting paves a way to produce green hydrogen for building a sustainable clean energy system, particularly within the framework of the carbon-neutral initiative. However, to date, the solar-to-hydrogen (STH) conversion efficiency of particulate photocatalysts falls far short of the demand of over 10% for industrial applications. Single-domain ferroelectric semiconductor materials with amazing unidirectional spontaneous polarization penetrating the bulk are promising candidates as photocatalysts for water splitting. Their existing inherent internal field set up by polarization can cause both two oppositely charged surfaces (namely, polar surfaces) and spatial separation of photogenerated charge carriers between them upon light excitation. These unique properties provide sufficient new room for flexibly engineering of bulk and surface/interface structures to enhance photocatalytic water splitting. In this Account, we offer a systematic overview of the exploration of PbTiO3 based single-domain ferroelectric photocatalysts for efficient solar water splitting. In detail, the controlled growth, surface modification, heterostructures, and Z-scheme system of single-domain PbTiO3 ferroelectrics are discussed by considering polar surfaces, spatial separation of the photoexcited charges, selective distribution of defects, and selective adsorption of reactive species. We start with the controlled synthesis of single-domain ferroelectric PbTiO3 nanoplates to realize the opposite directional transport of photoexcited charges driven by the polarized internal electric field, which can be verified by the fact that photochemical reduction/oxidation deposits occur on opposite polar surfaces. Then, we move to the selective modification of the specific polar surface to promote the transfer of photoexcited charges by applying the spatial separation effect of photoexcited charges and defects related internal screening mechanism. Furthermore, asymmetric heterostructures and Z-scheme systems are rationally designed by selective adsorption of reactive species on charged surfaces to promote charge separation and suppress redox mediator side reactions, respectively. Although significant advances have been achieved, many efforts remain needed toward the industrial production target. Based on single-domain ferroelectric photocatalysts, we present the following perspectives on the utilization of a wide solar spectrum for improving solar energy conversion efficiency. First, proper dopants can be incorporated homogeneously in the bulk to reduce the bandgap without obviously weakening ferroelectricity. Second, the epitaxial growth of narrow bandgap semiconductors on the ferroelectrics is feasible to induce additional polarization in the region close to their interface. These two aspects are anticipated to enable strong visible light absorption and charge separation efficiency. Third but not least, the assembly of Z-scheme systems with two narrow bandgap ferroelectrics is desirable to mimic natural photosynthetic systems with quantum yield approaching one unit.