PbTiO₃ Based Single-Domain Ferroelectric Photocatalysts for Water Splitting

Conspectus Solar-driven photocatalyticwater splitting paves a way to producegreen hydrogen for building a sustainable clean energy system, particularlywithin the framework of the carbon-neutral initiative. However, todate, the solar-to-hydrogen (STH) conversion efficiency of particulatephotocatalysts falls far short of the demand of over 10% for industrialapplications. Single-domain ferroelectric semiconductor materialswith amazing unidirectional spontaneous polarization penetrating thebulk are promising candidates as photocatalysts for water splitting.Their existing inherent internal field set up by polarization cancause both two oppositely charged surfaces (namely, polar surfaces)and spatial separation of photogenerated charge carriers between themupon light excitation. These unique properties provide sufficientnew room for flexibly engineering of bulk and surface/interface structuresto enhance photocatalytic water splitting. In this Account,we offer a systematic overview of the explorationof PbTiO3 based single-domain ferroelectric photocatalystsfor efficient solar water splitting. In detail, the controlled growth,surface modification, heterostructures, and Z-scheme system of single-domainPbTiO(3) ferroelectrics are discussed by considering polarsurfaces, spatial separation of the photoexcited charges, selectivedistribution of defects, and selective adsorption of reactive species.We start with the controlled synthesis of single-domain ferroelectricPbTiO(3) nanoplates to realize the opposite directional transportof photoexcited charges driven by the polarized internal electricfield, which can be verified by the fact that photochemical reduction/oxidationdeposits occur on opposite polar surfaces. Then, we move to the selectivemodification of the specific polar surface to promote the transferof photoexcited charges by applying the spatial separation effectof photoexcited charges and defects related internal screening mechanism.Furthermore, asymmetric heterostructures and Z-scheme systems arerationally designed by selective adsorption of reactive species oncharged surfaces to promote charge separation and suppress redox mediatorside reactions, respectively. Although significant advances have beenachieved, many efforts remain needed toward the industrial productiontarget. Based on single-domain ferroelectric photocatalysts, we presentthe following perspectives on the utilization of a wide solar spectrumfor improving solar energy conversion efficiency. First, proper dopantscan be incorporated homogeneously in the bulk to reduce the bandgapwithout obviously weakening ferroelectricity. Second, the epitaxialgrowth of narrow bandgap semiconductors on the ferroelectrics is feasibleto induce additional polarization in the region close to their interface.These two aspects are anticipated to enable strong visible light absorptionand charge separation efficiency. Third but not least, the assemblyof Z-scheme systems with two narrow bandgap ferroelectrics is desirableto mimic natural photosynthetic systems with quantum yield approachingone unit.