Rational design of stratified material with spatially separated catalytic sites as an efficient overall water-splitting photocatalyst

The development of metal sulfide catalysts with remarkable activity toward efficient overall photocatalytic water splitting remains challenging owing to the dominant charge recombination and deficient catalytic active sites.Moreover,in the process of water oxidation catalysis,the inhibition of severe photocorrosion is an immense task,requiring effective photogenic hole-transfer kinetics.Herein,stratified Co-MnO_(2)@CdS/CoS hollow cubes with spatially separated catalytic sites were rationally designed and fabricated as highly efficient controllable catalysts for photocatalytic overall water splitting.The unique self-templated method,including a continuous anion/cation-exchange reaction,integrates a Co-doped oxidation co-catalyst(Co-MnO_(2))and a reduction co-catalyst(CoS)on the nanocubes with uniform interface contact and ultrathin two-dimensional(2D)nanometer sheets.We demonstrate that the stratified Co-MnO_(2)@CdS/CoS hollow cubes can provide an abundance of active sites for surface redox reactions and contribute to the separation and migration of the photoionization charge carriers.In particular,CoS nanoparticles dispersed on the walls of CdS hollow cubes were identified as reduction co-catalysts accelerating hydrogen generation,while Co-MnO_(2) nanosheets attached to the inner walls of the CdS hollow cube were oxidation co-catalysts,promoting oxygen evolution dynamics.Benefiting from the desirable structural and compositional advantages,optimized stratification of Co-MnO_(2)@CdS/CoS nanocubes provided a catalytic system devoid of precious metals,which exhibited a remarkable overall photocatalytic water-splitting rate(735.4(H_(2))and 361.1(O_(2))μmol h^(−1) g^(−1)),being among the highest values reported thus far for CdS-based catalysts.Moreover,an apparent quantum efficiency(AQE)of 1.32%was achieved for hydrogen evolution at 420 nm.This study emphasizes the importance of rational design on the structure and composition of photocatalysts for overall water splitting.

Accurate design of spatially separated double active site in Bi_(4)NbO_(8)Cl single crystal to promote Z-Scheme photocatalytic overall water splitting

The efficiency of photocatalytic overall water splitting was mainly limited by the slow reaction kinetics of water oxidation.How to design effective surface active site to overcome the slow water oxidation reaction was a major challenge.Here,we propose a strategy to accelerate surface water oxidation through the fabrication spatially separated double active sites.FeCoPi/Bi_(4)NbO_(8)Cl-OVs photocatalyst with spatially separated double active site was prepared by hydrogen reduction photoanode deposition method.Due to the high matching of the spatial loading positions of FeCoPi and OVs with the photogenerated charge distribution of Bi_(4)NbO_(8)Cl and corresponding reaction mechanisms of substrate,the FeCoPi and OVs on the(001)and(010)crystal planes of Bi_(4)NbO_(8)Cl photocatalyst provided surface active site for water oxidation reaction and electron shuttle reaction(Fe^(3+)/Fe^(2+)),respectively.Under visible light irradiation,the evolution O_(2)rate of FeCoPi/Bi_(4)NbO_(8)Cl OVs was 16.8μmol h^(-1),as 32.9 times as Bi_(4)NbO_(8)Cl.Furthermore,a hydrogen evolution co-catalyst PtRu@Cr_(2)O_(3)was prepared by sequential photodeposition method.Due to the introduction of Ru,the Schottky barrier between PbTiO_(3)and Pt was effectively reduced,which promoted the transfer of photogenerated electrons to PtRu@Cr_(2)O_(3)thermodynamically,the evolution H_(2)rate on PtRu@Cr_(2)O_(3)/PbTiO_(3)increased to 664.8 times.On based of the synchronous enhancement of the water oxidation performance on FeCoPi/Bi_(4)NbO_(8)Cl-OVs and water reduction performance on PtRu@Cr_(2)O_(3)/PbTiO_(3),a novel Z-Scheme photocatalytic overall water splitting system(FeCoPi/Bi_(4)NbO_(8)Cl-OVs)mediated by Fe^(3+)/Fe^(2+)had successfully constructed.Under visible light irradiation,the evolution rates of H_(2)and O_(2)were 2.5 and 1.3μmol h^(-1),respectively.This work can provide some reference for the design of active site and the controllable synthesis of OVs spatial position.On the other hand,the hydrogen evolution co catalyst(PtRu@Cr_(2)O_(3))and the co catalyst FeCoPi for oxygen evolution contributed to the construction of an overall water splitting system.

Enhanced charge separation by continuous homojunction with spatially separated redox sites for hydrogen evolution

Photocatalytic hydrogen generation represents a promising strategy for the establishment of a sustainable and environmentally friendly energy reservoir.However,the current solar-to-hydrogen conversion efficiency is not yet sufficient for practical hydrogen production,highlighting the need for further research and development.Here,we report the synthesis of a Sn-doped TiO_(2)continuous homojunction hollow sphere,achieved through controlled calcination time.The incorporation of a gradient doping profile has been demonstrated to generate a gradient in the band edge energy,facilitating carrier orientation migration.Furthermore,the hollow sphere’s outer and inner sides provide spatially separated reaction sites allowing for the separate acceptance of holes and electrons,which enables the rapid utilization of carriers after separation.As a result,the hollow sphere TiO_(2)with gradient Sn doping exhibits a significantly increased hydrogen production rate of 20.1 mmol·g^(−1)·h^(−1).This study offers a compelling and effective approach to the designing and fabricating highly efficient nanostructured photocatalysts for solar energy conversion applications.

Fabrication of morphology-controlled TiO_2 photocatalyst nanoparticles and improvement of photocatalytic activities by modification of Fe compounds

Our previous studies suggested that redox reaction proceeded separately on specific exposed crystal faces of TiO2 nanoparticles. Site-selective deposition of metal or metal oxide on TiO2 specific exposed crystal faces successfully proceeded using the unique reactivity properties on the surface of TiO2 nanoparticles under photoexcitation. A remarkable improvement ofphotocatalytic activity of shape- controlled brookite and rutile TiO2 nanorods with modification of Fe^3＋ compounds was observed under visible light. Crystal face-selective metal compound modification on exposed crystal faces of TiO2 nanorods with brookite and futile phases was successfully prepared. Brookite and rutile TiO2 nanorods prepared by site-selective modification with metal compounds should be ideal visible-light responsive TiO2 photocatalysts because of the remarkable suppression of back electron transfer from TiO2 to oxidized metal com- pounds on the surface of the TiO2 nanorod with a brookite or rutile phase. In this paper, the development of exposed crystal face-controlled TiO2 nanorods with rutile and brookite phases was described. The obtained rutile and brookite TiO2 nanorod, showing remarkably high activity for degra- dation of organic compounds compared with the photocatalytic activities of anatase fine particles （ST-01）, is one of the most active commercially available photocatalysts for environmental cleanup in Japan. The technology of visiblelight responsive treatment for morphology-controlled rutile and brookite TiO2 nanorods by crystal face-selective modification of Fe^3＋ compounds was also discussed in this paper. The Fe^3＋ compound-modified rutile and brookite TiO2 nanorods show much higher activity than conventional visible-light responsive N-doped TiO2, which is commercially available in Japan.