Photocatalytic H2 Evolution Activity Research Articles

Properly aligned band structures in B-TiO2/MIL53(Fe)/g-C3N4 ternary nanocomposite can drastically improve its photocatalytic activity for H2 evolution: Investigations based on the experimental results

The development of new tools that could meet the demand of sustainable energy production has attracted worldwide scientific attention. Over the past few decades, significant research efforts have been carried out to efficiently reduce water to H2 (green fuel) over semiconductor photocatalysts. Numerous semiconductor photocatalysts have been employed in photocatalysis for optimum H2 production. All the techniques were chosen based on their flexibility, cost-effectiveness, and ease of availability. Recently, polymeric carbon nitride (g-C3N4) received worldwide attention in visible light photocatalysis for energy and environmental applications due to its low price, robust nature, and superior thermal stability. Nevertheless, g-C3N4 (CN) exhibits shortfalls such as high charge carrier's recombination rate and weak reduction ability. To overcome these drawbacks, herein, for the first time we have fabricated B-TiO2/MIL-53(Fe)/CN ternary composite via hydrothermal and wet-chemical methods. The resultant B-TiO2/MIL53(Fe)/CN ternary composite shows drastically improved photocatalytic activity for hydrogen evolution compared to the bare CN, B-TiO2, and MIL53(Fe) components. The B-TiO2/MIL53(Fe)/CN ternary composite produced approximately 166.3 and 581.2 μmol h−1 g−1 of hydrogen under visible light and UV–visible light irradiations, respectively, with the assistance of co-catalyst Pt. Photo-luminescence (PL) and the fluorescence (FL) spectroscopy measurements reveal that the enhanced photoactivity is due to the greatly promoted charge carrier's separation and transfer at the interfacial contact of the well-aligned three-component systems. This work will promote the design and development of efficient photocatalyst based on CN for clean energy production and environmental purification.

Simultaneous Conduction and Valence Band Regulation of Indium-Based Quantum Dots for Efficient H2 Photogeneration.

Indium-based chalcogenide semiconductors have been served as the promising candidates for solar H2 evolution reaction, however, the related studies are still in its infancy and the enhancement of efficiency remains a grand challenge. Here, we report that the photocatalytic H2 evolution activity of quantized indium chalcogenide semiconductors could be dramatically aroused by the co-decoration of transition metal Zn and Cu. Different from the traditional metal ion doping strategies which only focus on narrowing bandgap for robust visible light harvesting, the conduction and valence band are coordinately regulated to realize the bandgap narrowing and the raising of thermodynamic driving force for proton reduction, simultaneously. Therefore, the as-prepared noble metal-free Cu0.4-ZnIn2S4 quantum dots (QDs) exhibits extraordinary activity for photocatalytic H2 evolution. Under optimal conditions, the Cu0.4-ZnIn2S4 QDs could produce H2 with the rate of 144.4 μmol h−1 mg−1, 480-fold and 6-fold higher than that of pristine In2S3 QDs and Cu-doped In2S3 QDs counterparts respectively, which is even comparable with the state-of-the-art cadmium chalcogenides QDs.

Two Excited State Collaboration of Heteroleptic Ir(III)-Coumarin Complexes for H2 Evolution Dye-Sensitized Photocatalysts

Interfacial electron injection from a photoexcited surface-immobilized dye to a semiconductor substrate is a key reaction for dye-sensitized photocatalysts. We previously reported that the molecular orientation of heteroleptic Ir(III) photosensitizer on the TiO2 nanoparticle surface was important for efficient interfacial electron injection. In this work, to overcome the weak light absorption ability of heteroleptic Ir(III) photosensitizer and to improve the photoinduced charge-separation efficiency at the dye–semiconductor interface, we synthesized two heteroleptic Ir(III) complexes with different coumarin dyes, [Ir(C6)2(H4CPbpy)]Cl and [Ir(C30)2(H4CPbpy)]Cl [Ir-CX; X = 6 or 30; HC6 = 3-(2-enzothiazolyl)-7-(diethylamino)coumarin, HC30 = 3-(2-N-methylbenzimidazolyl)-7-N,N-diethylaminocoumarin, H4CPbpy = 4,4′-bis(methylphosphonic acid)-2,2′-bipyridine], as the cyclometalated ligands and immobilized them on the surface of Pt-cocatalyst-loaded TiO2 nanoparticles. Ultraviolet-visible absorption and emission spectroscopy revealed that the singlet ligand-centered (1LC) absorption and triplet 3LC emission bands of Ir-C30 occurred at shorter wavelengths than those of Ir-C6, while time-dependent density-functional-theory data suggested that the ligand-to-ligand charge transfer (LLCT) excited states of the two complexes were comparable. The photocatalytic H2 evolution activity of the Ir-C6-sensitized Pt-TiO2 nanoparticles (Ir-C6@Pt-TiO2) under visible light irradiation (λ > 420 nm) was higher than that of Ir-C30@Pt-TiO2. In contrast, their activities were comparable under irradiation with monochromatic light (λ = 450 ± 10 nm), which is absorbed comparably by both Ir-CX complexes. These results suggest that the internal conversion from the higher-lying LC state to the LLCT state effectively occurs in both Ir-CX complexes to trigger electron injection to TiO2.

Bio‐Metabolism‐Driven Crystalline‐Engineering of CdS Quantum Dots for Highly Active Photocatalytic H2 Evolution

AbstractBiosynthesis was considered as a green and sustainable approach for nanomaterials fabrication. However, it is still quite challenging to fine tune the biosynthesis process for high‐quality photocatalytic nanomaterials. In this study, an aerobic approach for biosynthesis of photocatalytic CdS quantum dots (QDs) by Shewanella oneidensis MR‐1 was developed. Interestingly, it was found that by simply tuning the concentration of substrates, the crystalline structure of the CdS QDs was transformed between cubic phase and hexagonal phase. The hexagonal CdS QDs synthesized by simple substrate‐metabolism regulation exhibited high photocatalytic H2 evolution activity (21 mmol H2/g CdS/h), which was the highest record for CdS QDs. This finding demonstrated the possibility to well control the crystalline structure of biosynthesized QDs by simple bio‐metabolism regulation and provided a bio‐metabolism‐driven green route for crystalline engineering.

Crystalline carbon nitride anchored on MXene as an ordered Schottky heterojunction photocatalyst for enhanced visible-light hydrogen evolution

Carbon nitride (CN) polymer is considered as a potential material for photocatalysis, but surfers from the low photoconversion efficiency due to its high defect density. Although the defects can be limited through the crystallization of CN, the photocatalytic activity of single-component photocatalyst is still restricted by the recombination of photoexcited carriers. In our work, the ordered Schottky heterojunction of heptazine-based crystalline carbon nitride (HCN) and Ti3C2 MXene was successfully prepared through ionothermal method. The HCN/Ti3C2 composites exhibit higher photocatalytic performance than pristine HCN. Particularly, the HCNT20 sample exhibits the highest photocatalytic H2 evolution activity, which is about 8 and 2 times higher than that of bulk CN and pristine HCN, respectively. The results of charge transfer dynamics and DFT calculation reveal that the photocatalytic enhancement mechanism is primarily attributed to the synergistic effects of crystallization of CN, excellent conductivity of Ti3C2 and well-constructed Schottky heterojunction.

Salt-air template synthesis of Na and O doped porous graphitic carbon nitride nanorods with exceptional photocatalytic H2 evolution activity

Photocatalyst fabrication process plays the central role in photocatalytic hydrogen (H2) evolution reaction. Herein, we synthesize Na+ functionalized porous graphitic carbon nitride nanorods (Na-CNNR) via a facile one-pot calcination method. The morphology and size of Na-CNNR are controllable by changing the amount of sodium salt; both sodium salt and air are essential to the unique structure and oxygen doping. The obtained Na-CNNR contains abundant oxygen in the graphitic carbon nitride (CN) plane. The optimized Na20-CNNR (20 wt% Na2S2O3•5H2O to dicyanamide) photocatalyst exhibits a high surface area with enhanced visible light absorption. Besides, Na20-CNNR displays fast charge transfer and high carrier separation rate characterized by photoluminescence (PL) spectroscopy and electrochemical test. Through time-resolved transient absorption spectra analysis, the trapped unreactive electron accumulation can be highly restrained, favoring efficient active electron de-trapping and transfer. The optimized Na20-CNNR sample exhibits the highest photocatalytic H2 evolution rate of 7.46 mmol/h/g under visible light irradiation (>400 nm, 100 mW/cm2), which is up to 85 times that of the bare CN and 27 times that of Na+ doped graphitic carbon nitride nanoparticles (Na20–CNNP). Meanwhile, the cyclability tests indicate that Na20-CNNR displays robust stability over 24 h.

Controllable oxygen doping and sulfur vacancies in one dimensional CdS nanorods for boosted hydrogen evolution reaction

Photocatalytic hydrogen evolution reaction (HER) on semiconductor surface has attracted a great attention in recent years for their abundant applications in solar energy conversion and environmental remediation. Even though a number of materials have been designed for HER, still suffer from little photocatalytic activity which restricts the practical applications. Introducing the vacancies and doping is an effective approach to control the electronic bandstructures of materials which in turn results the improved photocatalytic activity. In this study, we have synthesized one dimensional CdS nanorods by a solvothermal method and then developed a low temperature heating strategy to incorporate the O-doping and S-vacancies simultaneously into CdS towards visible photocatalytic H2 evolution reaction. The heat treated samples with controlled O-doping and S-vacancies offer enhanced visible light absorption and improved photogenerated charge carriers’ separation. Moreover, the S-vacancies also acted as traps to retard the electron-hole recombination rate. As a result, CdS sample treated at 200 °C for 2 hr showed a high photocatalytic H2 evolution activity of 377 μmol/g/h which is 22 times higher than 18 μmol/g/h for pure CdS sample. This work validates a simple thermal treatment method to produce S-vacancies and O-doping for the fabrication of efficient photocatalysts for solar hydrogen production.

Odd-membered cyclic hetero-polyoxotitanate nanoclusters with high stability and photocatalytic H2 evolution activity

We investigated the hydrolysis of TiIV along with naturally abundant AlIII ions and reported the formation of a stable and semiconducting nanocluster. Interestingly, this compound exhibits an unusual odd-membered ring structure and also represents the largest Al-containing polyoxotitanium cluster (PTC) observed thus far. The presence of a shell of organic ligands as well as the incorporation of hetero-AlIII ions endowed the nanocluster with high air, thermal, and pH stabilities. The present compound exhibited a record photocatalytic hydrogen evolution of 402.88 μmol g−1 h−1 among PTC materials. This work not only paves the way towards stable PTC materials but also provides new insights into the design of novel photocatalysts.

Enhanced photocatalytic H2 production performance of CdS hollow spheres using C and Pt as bi-cocatalysts

Photocatalytic H2 production from water splitting is an effective method to solve energy crisis and environmental pollution simultaneously. Herein, carbon@CdS composite hollow spheres (C@CdS-HS) are fabricated via a facile hydrothermal method using porous carbon hollow spheres (C-HS) as the template. The C@CdS-HS shows an excellent photocatalytic H2-generation rate of 20.9 mmol h−1 g−1 (apparent quantum efficiency of 15.3% at 420 nm), with 1.0 wt% Pt as a cocatalyst under simulated sunlight irradiation; this rate is 69.7, 13.9, and 3.9 times higher than that obtained with pure CdS hollow spheres (CdS-HS), C@CdS-HS, and CdS-HS/Pt, respectively. The enhanced photocatalytic H2-evolution activity of C@CdS-HS/Pt is due to the synergistic effect of C and Pt as the bi-cocatalyst. The C-HS serves not only as an active site provider but also as an electron transporter and reservoir. Moreover, C-HS has a strong photothermal effect that is induced by near infrared light, which kinetically accelerates the H2-production reaction. Additionally, the underlying charge transfer pathway and process from CdS to C−HS is revealed. This work highlights the potential application of C-HS-based nanocomposites in solar-to-chemical energy conversion.

0D/2D NiS/CdS nanocomposite heterojunction photocatalyst with enhanced photocatalytic H2 evolution activity

Photocatalytic H2 production under visible light irradiation is of paramount importance in energy transformation and ecotope conservation. Herein, a heterojunction composed of zero-dimension (0D) nickel sulfide (NiS) nanoparticle and cadmium sulfide (CdS) flower is tactfully constructed. Particularly, the obtained nanocomposite, whose molar ratio of NiS is 25%, yields a remarkable photocatalytic performance. Its H2-production rate reaches 18.1 mmol h−1 g−1, which is approximately 69.6 folds higher than that of pristine CdS. The excellent photocatalytic H2 evolution reaction (HER) activity can be mainly attributed to the intimate contact and efficient separation of photoinduced carriers across the interface. This work also presents a new direction in understanding the performance improvement in composite photocatalysts.

Recent advances in bismuth-based multimetal oxide photocatalysts for hydrogen production from water splitting: Competitiveness, challenges, and future perspectives

The efficient utilization of photocatalytic technology is essential for clean energy. Bismuth-based multimetal oxides (Bi2WO6, Bi2MoO6, BiVO4 and Bi4Ti3O12) have aroused widespread attention as a visible light responsive photocatalyst for hydrogen evolution due to their low cost, nontoxicity, modifiable morphology, and outstanding optical and chemical properties. Nevertheless, the photocatalytic activities of pure materials are unsatisfactory because of their relative small specific surface area, poor quantum yield, and the rapid recombination of photogenerated carriers. Therefore, some modification strategies, including morphological control, semiconductor combination, doping, and defect engineering, have been systematically studied to enhance photocatalytic H2 evolution activity in the past few years. Herein, we summarize the recent research progress on bismuth-based photocatalysts, pointing out the prospects, opportunities and challenges of bismuth-based photocatalysts. Eventually, we aims to put forward valuable suggestions for designing of bismuth-based photocatalysts applied in hydrogen production on the premise of consolidating the existing theoretical basis of photocatalysis.

Two dimensional ultrathin MoSe2 bedecked Zn0.5Cd0.5S for reinforced photocatalytic H2 generation and toxic Cr (VI) reduction

Metallic MoSe2 with distinct platinum-like electronic configuration and compelling band gap structure exhibits zero approaching Gibbs free energy for H atom, hence can be approved as an ideal cocatalysts for H2 evolution. However, the reports on MoSe2 cocatalyst still leaves much room. Here, two dimensional ultrathin MoSe2 nanosheets bedecked Zn0.5Cd0.5S nanoparticles were reported as efficient photocatalyst, in which metallic MoSe2 nanosheets cocatalyst will do duty for electron sink to promote the separation of charge carriers and prolong the electrons lifetime, thus benefiting the improved photocatalytic H2 evolution activity. As a result, Zn0.5Cd0.5S/MoSe2 composite with an optimized 9 wt% MoSe2 presents a higher H2 evolution activity of 4853.3 μmol g-1h−1, 3.57 folds of pure Zn0.5Cd0.5S sample (1361.0 μmol g-1h−1). Meanwhile, the greatly enhanced photo-reduction efficiency for toxic heavy metal Cr (VI) ion by Zn0.5Cd0.5S/MoSe2 composite further certifies the promoted separation of electron- hole pairs. These results turned out that MoSe2 is qualitied as candidate to serve as promising co-catalyst for photocatalyst energy conversion and decontamination.

2D/2D atomic double-layer WS2/Nb2O5 shell/core nanosheets with ultrafast interfacial charge transfer for boosting photocatalytic H2 evolution

Low-efficiency charge transfer is a critical factor to limit the photocatalytic H2 evolution activity of semiconductor photocatalysts. The interface design is a promising approach to achieve high charge-transfer efficiency for photocatalysts. Herein, a new 2D/2D atomic double-layer WS2/Nb2O5 shell/core photocatalyst (DLWS/Nb2O5) is designed. The atom-resolved HAADF-STEM results unravel the presence of an unusual 2D/2D shell/core interface in DLWS/Nb2O5. Taking advantage of the advanced femtosecond-resolved ultrafast TAS spectra, the average lifetime of charge carriers for DLWS/Nb2O5 (180.97 ps) is considerably shortened as compared to that of Nb2O5 (230.50 ps), strongly indicating that the 2D/2D shell/core interface enables DLWS/Nb2O5 to achieve ultrafast charge transfer from Nb2O5 to atomic double-layer WS2, thus yielding a high photocatalytic H2 evolution rate of 237.6 μmol/h, up to 10.8 times higher than that of pure Nb2O5 nanosheet. This study will open a new window for the development of high-efficient photocatalytic systems through the interface design.

Constructing 0D/2D Z-Scheme Heterojunction of CdS/g-C3N4 with Enhanced Photocatalytic Activity for H2 Evolution

0D/2D Pt-C3N4/CdS heterojunction photocatalyst were fabricated with CdS quantum dots interspersed on g-C3N4 nanosheets via successive ionic layer absorption process. The obtained Pt-C3N4/CdS Z-scheme heterojunction with Pt cocatalyst deposited on g-C3N4 nanosheets exhibited H2 production rate of 35.3 mmol g−1 h−1, which is 3.1 times higher than that of Pt-CdS/C3N4. The enhanced photocatalytic activity are attributed to the Z-scheme charge carrier transfer mechanism with stronger redox ability. The photocatalytic mechanism of the CdS/g-C3N4 composite is investigated and demonstrated in this work. It may provide unique insights to design 0D/2D Z-scheme heterojunction photocatalyst systems using a facile method for highly efficient H2 production. Schematic illustration of charge transfer modulated by the metal cocatalyst selective deposition on heterojunction-type II (a) and direct Z-Scheme mechanisms (b) over the C3N4/CdS heterostructure composites under visible light irradiation.

Building sp carbon-bridged g-C3N4-based electron donor-π-acceptor unit for efficient photocatalytic water splitting

sp hybrid carbon is emerging as a promising unit for covalent modification of organic frameworks and conductive polymers, and has been widely concerned in conjugated polymer catalysts because it can be used to construct π-electron conjugated system. Herein, we provide a simple and effective post reaction strategy to activate g-C3N4 via coupling reactions. The grafted g-C3N4 exhibits improved light absorption and separation of charges, and better water dispersibility along with increased co-catalyst loading sites, which accelerate photocatalytic hydrogen evolution. Photocatalytic H2 evolution activity of UCN-BTD and UCN-BF, in which terminal amino groups are grafted with 2,1,3-benzothiadiazole,5-(1-propyn-1-yl) or 2,1,3-benzoxadiazole,5-(1-propyn-1-yl), reveals the important role of sp hybrid carbon and electronegativity of the acceptor. The optimized UCN-BTD photocatalyst showed a significant improvement in photocatalytic hydrogen evolution performance (122 μmol·h−1), which is nearly five times of that of the pristine g-C3N4. This work provides insights for the preparation of g-C3N4-based donor-π-acceptor unit constructed with different conjugated structures.

Assemble of Bi-doped TiO2 onto 2D MoS2: an efficient p–n heterojunction for photocatalytic H2 generation under visible light

Fabrication of noble‐metal‐free, efficient and stable hybrid photocatalyst is essential to address the rapidly growing energy crisis and environmental pollution. Here, MoS2 has been used as the co-catalyst on Bi-doped TiO2 to form a novel heterostructure to increase the utilization of the photogenerated charge carriers for improving photocatalytic H2 evolution activity through water reduction. Significantly increased photocatalytic H2 generation has been achieved on the optimized MoS2/Bi-TiO2 nanocomposite (∼512 μmol g–1) after 4 h of visible light illumination, which is nine times higher than that of the pristine TiO2 (∼57 μmol g–1). The measurements of photocurrent, charge transfer resistance and photo-stability of MoS2/Bi-TiO2 photoanode imply that charge separation efficiency has been improved in comparison to the pure MoS2 and TiO2 photoanodes. Further, the Mott–Schottky study confirmed that a p–n heterojunction has been formed between n-type MoS2 and p-type Bi-doped TiO2, which provides a potential gradient to increase charge separation and transfer efficiency. On the basis of these experimental results, this enhanced photocatalytic activity of MoS2/Bi-TiO2 heterostructures could be ascribed to the significant visible light absorption and the efficient charge carrier separation. Thus, this work demonstrates the effect of p–n junction for achieving high H2 evolution activity and photoelectrochemical water oxidation under visible light illumination.

Rational designing 0D/1D Z-scheme heterojunction on CdS nanorods for efficient visible-light-driven photocatalytic H2 evolution

Rational design and construction of unique transmission channel in photocatalyst system is of great significance for promoting the efficient spatial separation of photo-induced charge carriers. This work reports a novel 0D/1D direct Z-scheme heterojunction photocatalyst synthesized by in-situ anchoring W18O49 QDs onto the surface of CdS NRs. Due to this unique structural design, both bulk and surface photogenerated carriers are separated efficiently, achieving a dramatically improved photocatalytic H2 evolution performance. The optimal of H2 production rate of the W18O49/CdS heterostructure is as high as 55.24 mmol·h−1·g−1, with lactic acid as sacrificial reagents under visible light irradiation, which is approximately 110.5 and 3.7 times as that of pure CdS NRs and Pt/CdS, respectively. Even in the absence of hole scavengers, the optimal WCS300 composite exhibits an obvious photocatalytic H2 evolution activity accompanied by the generation of considerable H2O2. This work provides a new protocol for the development of efficient photocatalyst systems.

Superior sponge-like carbon self-doping graphitic carbon nitride nanosheets derived from supramolecular pre-assembly of a melamine–cyanuric acid complex for photocatalytic H2 evolution

The photocatalytic evolution of hydrogen (H2) from water splitting is considered a promising route to overcome the energy crisis, and the key lies in the preparation of efficient photocatalysts. Herein, superior ordered sponge-like carbon self-doped graphitic carbon nitride (g-C3N4) nanosheets (SCCNS) were prepared via a combined strategy of melamine–cyanuric acid complex supramolecular pre-assembly and solvothermal pre-treatment using ethylene glycol (EG) aqueous solutions (EG:water = 50:50 vol.%) as a solvent and carbon doping source. The following pyrolysis converts the naturally arranged melamine–EG–cyanuric acid supramolecular intermediates to highly crystalline SCCNS with large specific surface areas. The optimal SCCNS-180 exhibits superior photocatalytic H2 evolution activities (∼4393 and 11 320 μmol h−1 g−1) when irradiated with visible light and simulated sunlight; these values are up to ∼17- and ∼18-fold higher than that of bulk g-C3N4. The quantum efficiency of SCCNS-180 at λ = 420 nm can reach 6.0%. The excellent photocatalytic performance of SCCNS-180 derives from its distinct ordered sponge-like nanosheet structure with highly crystallinity and the carbon doping, leading to its improved optical absorption, accelerated photoinduced electron–hole pair transfer and separation rate and enlarged specific surface area (134.4 m2 g−1).

Engineering MoS2 Cocatalysts as Active Sites over Porous P‐Doped g‐C3N4 Nanosheets to Enhance Photocatalytic Hydrogen Production

Development of noble‐metal‐free cocatalysts is still a research hotspot to promote the photocatalytic H2 evolution performance of graphite‐phase carbon nitride (CN). Herein, 2D MoS2 nanosheets are used as a low‐cost cocatalyst and loaded onto porous P‐doped CN nanosheets (PCNNSs) to fabricate a 2D/2D noble‐metal‐free MoS2/PCNNSs photocatalyst via a simple in situ immersion pyrolysis method. The optimal H2 evolution rate of the MoS2/PCNNSs sample reaches 1741 μmol g−1 h−1, which is almost 2 times that of Pt/PCNNSs (976 μmol g−1 h−1). The outstanding activity mainly stems from the extended light absorption from 420 nm to the near‐infrared 800 nm owing to MoS2 and P doping, as well as faster separation of photogenerated electrons and holes due to the close contact between PCNNSs and MoS2 induced by in situ fabrication method. This work unfolds new opportunities for the modification of cocatalysts to realize higher photocatalytic H2 evolution activity.

Improved Light Harvesting and Efficiency for Overall Water Splitting by Embedding TiO2 Transition Layer in GaP/Ga2O3/Ga2Se3 Multijunction Photocatalyst

Photocatalytic water splitting to generate hydrogen has attracted great attention due to its potential for conversion and storage of solar energy. To obtain high efficiency of water splitting under solar irradiation, the catalyst should have good enough absorption in the visible region, excellent charge transfer ability, and satisfied stability during the photoreaction. Herein, the significant absorption promotion of the catalyst to a longer wavelength is achieved by simultaneously in situ selenylation and phosphorization of Ga2O3. The formation of narrow‐bandgap Ga2Se3 and GaP layers makes the catalyst absorb visible light up to 640 from 282 nm. In addition, by embedding a TiO2 transition layer between Ga2O3 and Ga2Se3, better crystal match in the catalyst is accomplished, which leads to better structural stability and the formation of better charge transfer route. Compared with GaP/Ga2O3/Ga2Se3, the GaP/TiO2/Ga2O3/TiO2/Ga2Se3 photocatalyst exhibits a much higher photocatalytic H2 evolution activity and achieves a higher apparent quantum efficiency (≈4% at 430 nm). Moreover, the TiO2 transition layer also reduces the crystal mismatch between GaP and Ga2O3. Herein, the advantage of utilizing the transition layer in multijunction photocatalyst to increase the photocatalytic activity and strengthen the stability of the assembled catalyst for overall water splitting is demonstrated.