Photocatalytic H2 Production Rate Research Articles

MoSe2-NiSe dual co-catalysts modified g-C3N4 for enhanced photocatalytic H2 generation

Solar energy conversion into hydrogen (H2) energy has attracted much attention. However, the low light utilization rate and fast carrier recombination of photocatalysts extremely limit the practical application of photocatalytic H2 production. In this paper, MoSe2-NiSe with abundant active sites and interfacial electronic structures as dual co-catalysts were assembled on g-C3N4 nanosheets (NSs) vis a solvothermal reaction process. MoSe2-NiSe/g-C3N4 NSs composite exhibited improved light absorption and photoelectrochemical properties. The photocatalytic H2 production rate of MoSe2-NiSe/g-C3N4 composite achieved 2379.04 μmol·h−1·g−1, which is 99.25, 1.44, and 3.67 times those of pure g-C3N4 nanosheets (23.97 μmol·h−1·g−1), MoSe2/C3N4 (1654.57 μmol·h−1·g−1), and NiSe/C3N4 (649.08 μmol·h−1·g−1), respectively. The apparent quantum efficiency (AQE) value of MoSe2-NiSe/g-C3N4 achieved 4.07 % under light at λ = 370 nm. The corresponding characterization and experiments proved that 2D ultrathin g-C3N4 NSs with a large surface area and short charge-transfer distance could facilitate light scattering and the transport of photoexcited electrons. MoSe2-NiSe, as a dual co-catalyst, showed strong electronic synergistic interaction between the interfaces, thus improving the conductivity and promoting the electron transfer process.

Enhanced photocatalytic H2 production performance of Au@Cu2O-Ta3N5 discrete ternary core-shell spheres

Ta3N5 owns a theoretical band structure for photocatalytic H2 production. However, the practical production performance is unsatisfactory, which is probably attributed to fast electron-hole recombination. In this study, we design novel Au@Cu2O-Ta3N5 discrete core-shell ternary nanospheres for highly efficient photocatalytic H2 production by splitting water. This catalyst is prepared by coating Cu2O on the Au nanoparticles of Au-Ta3N5 nanospheres via an illumination method. The core-shell structure irradiated for 2 h (Au@Cu2O-Ta3N5 2 h) shows higher photocatalytic H2 production rate (65.78 μmol·g−1·h−1) than Au-Ta3N5 (0.5% Au-Ta3N5, 22.43 μmol·g−1·h−1), Au-Cu2O-Ta3N5 (32.24 μmol·g−1·h−1), and fully covered Au@Cu2O-Ta3N5 5 h sample (51.27 μmol·g−1·h−1). The enhanced performance is attributed to the unique discrete core-shell structure, designed appropriate band structure, low charge transfer resistance, and high electron-hole separation ability. This study provides a novel Ta3N5-based ternary core-shell structure for high-performance H2 production.

Mo2N decorated hierarchical ZnIn2S4 with sulfur-rich vacancy photocatalyst for efficient photocatalytic hydrogen production

The development of photocatalyst is essential for achieving efficient photocatalytic water splitting for hydrogen production. Therefore, a novel Mo2N (MN) decorated ZnIn2S4 (ZIS) with sulfur-rich vacancy (Sv-ZIS) photocatalyst was rationally constructed via a facile calcining-hydrothermal method for efficient photocatalytic H2 production. The optimized photocatalyst exhibits an outstanding photocatalytic H2 production rate of 10.28 mmol·g−1·h−1, 7.52 and 3.11 times higher than that of bare ZIS and SV-ZnIn2S4 (SV-ZIS), respectively. The characterizations reveal that the presence of MN and S-vacancies improves the light absorption capacity, and facilitates the separation and migration of photogenerated carriers. Density functional theory calculations (DFT) have confirmed that MN can optimize ΔGH* to approach 0, which is favorable for photocatalytic hydrogen production. Therefore, the combined effect of MN and S-vacancies facilitates efficient photocatalytic H2 production of SV-ZIS/MN.

Mo2C MXene Nanosheets Made in Different Etching Solutions as Co-catalysts for Hydrogen Production

Mo2C MXene is a two-dimensional material, which can be applied as a co-catalyst to significantly enhance the photocatalytic performance of CdS for H2 production. To understand the effect of the synthesis process of Mo2C MXene nanosheets on the catalytic performance, in this paper, Mo2C MXene was made from Mo2Ga2C by hydrothermal etching in different etchants. Diverse cations (Li+, Na+, K+, or NH4+) in etchants resided on the surface of Mo2C MXene nanosheets. Then, the samples were used to construct CdS/Mo2C-MXene composites for photocatalytic H2 evolution. Among them, Mo2C MXene with Li+ shows the best photocatalytic H2 production rate of 22,048 μmol g–1 h–1 under visible light. The remarkable performance arises from the modification at the nanoscale of Mo2C MXene with Li+, thereby resulting in better photoabsorption behavior, high separation efficiency of photogenerated carriers, and fast charge transfer at the heterointerface. Moreover, the energy band structures explain that the changes of band gap and the position of the conductive band in the photocatalyst tuned by cations are also key to affect photocatalytic activities.

Synergistic effect of n-π* electronic transitions in porous ultrathin graphitic carbon nitride nanosheets for efficient photocatalytic hydrogen production

The visible light absorption capacity and active sites of graphitic carbon nitride (GCN) are crucial roles for photocatalytic hydrogen (H2) production. However, the fabrication of ultrathin GCN nanosheets with enhanced light absorption via n-π* electronic transitions remain challenging. Here, we report on the successful preparation of porous ultrathin GCN nanosheets with activating n-π* electronic transitions simultaneously by microwave heating the mixture of urea and ammonium chloride (NH4Cl) compression strategy. Such the unique structure of GCN is composed of a curved porous thin layer and has numerous wrinkles that not only largely expand visible light absorption range to ∼ 650 nm but also significantly enhance the unmber of active sites and the mobility of photoexcited charges. The highest photocatalytic H2 production rate reached 99.1 μmol h−1 under visible light irradiation (λ > 420 nm), which is 8.8 folds higher than that of pristine GCN (11.2 μmol h−1). This work presents a promising and effective strategy for the engineering of GCN, which fully utilizes n-π* electronic transitions to largely expand the visible light absorption while enhancing the active sites.

A review on energy conversion applications of graphene-based nanomaterials and environmental remediation

Graphene is popular for its striking physicochemical properties. Conversely, the application of pure graphene is greatly limited inert owing to its inert nature. Therefore, one of the greatest approaches to investigate graphene's intrinsic features is by functionalization. The highly conductive rGO (reduced graphene oxide) sheet is generally used as a suitable solid support for catalysts that not only inhibit carrier recombination but also improve carrier mobility to power a variety of solar energy conversion applications. According to various studies, the photocatalytic H2 production rate was found to be significantly increased by the potential electron storing and transferring characteristics of the rGO sheet, going from 16656 mol/h for Cu2O-TiO2 to 110968 mol/h for Cu2O-TiO2/rGO, or an increase of at least 7 times. The Cu2O-rGO-C3N4 photocatalyst 139 considerably enhanced the photocatalytic 4-nitrophenol reduction in comparison to the Cu2O-C3N4 photocatalyst alone. The oxygen reduction reaction, photocatalytic water splitting, photocatalytic degradation of organic contaminants, and polymer solar cells were only a few of the applications that rGO-based nanocomposites were used for in the current study.

Carbon layers on Pt/TiO2 induced dramatic promotion of photocatalytic H2 production: a combined experimental and computation study

Noble metal nanoparticles (NMNPs) modified semiconductors play important roles in heterogeneous catalysis. However, for the ultra-small NMNPs (<5 nm) on TiO2, the problems of easy agglomeration and quick deactivation highlight the need for highly efficient protection of ultra-small NMNPs. Here, we introduce a novel structure of carbonized liquid crystals (CLCs) protected Pt NPs on TiO2, which involves in-situ photo-reduction of chloroplatinic acid to ultra-small Pt NPs in lamellar liquid crystals. According to the results of morphological structures, CLCs changed the contact type of Pt/TiO2 from ‘face-contact’ to ‘point-contact’, which was consistent with our simulation results. Compared with the bare Pt/TiO2, the visible-light photocatalytic H2 production rate of C–Pt/TiO2 exhibited 1.75-fold enhancement under the protection of CLCs (26.73 mmol g−1 h−1vs. 15.26 mmol g−1 h−1). Especially, the marriage of CLCs and the traditional Pt/TiO2 photocatalyst achieved long-term stability, which remained 87% of the original rate at the sixth cycle.

Controlling photocatalytic properties of Eosin Y-sensitized hydrogen evolution reaction of Cu2−xSe nanoparticles through surface band bending

Solar-driven water splitting for hydrogen (H2) production and energy conversion technologies have inspired impressive attention due to energy and environmental crises, but still challenges limit commercialization. To overcome these challenges, the visible-light-responsible noble-metal-free photocatalytic H2 production system is imperative. In this study, scalable synthesis of copper selenides which is one of promising semiconductor materials is developed and the Cu/Se compositions of the Cu2−xSe were readily controlled from copper (II) selenide (CuSe) to copper (I) selenide (Cu2Se). In addition, the synthesized copper selenides were applied to Eosin Y (EY)-sensitized photocatalytic H2 production, and Cu2Se exhibited the highest photocatalytic H2 production rate (1017.82 μmol∙g−1∙h−1) which was 21.17% higher than that of the commercial P25 (TiO2) under the same conditions. Through careful characterization and calculation, we investigated the band structures of the synthesized copper selenides with different Cu/Se molar ratio, and were able to propose the theory of enhanced surface H2-evolution kinetics based on downward band bending at equilibrium state in the EY-sensitized system.

Metal-Organic Framework Derived Terephthalate Ligand Decorated TiO2 with Various Morphologies for Efficient Photocatalytic H2 Evolution.

It has been rarely reported the morphological control of derivatives of metal-organic frameworks (MOFs) in hydrothermal conditions for photocatalytic applications. We report here a family of highly efficient composite photocatalysts composed of terephthalic acid/terephthalate (TPA) ligand and TiO2 with various morphologies (e. g., nanoparticles, nanosheets, and nanorods). The composites are synthesized by a simple one-step hydrothermal method in various solvents (i. e., H2 O, HF, H2 SO4 , HCl, and HNO3 ) using Ti-based MOF (MIL-125(Ti)) as precursor. The formation mechanism of composite materials with different morphological features is discussed. Impressively, the composite of TiO2 nanoparticles/TPA synthesized using H2 O as solvent under hydrothermal condition exhibits the highest photocatalytic H2 activity among the studied materials, with a photocatalytic H2 production rate of 6.38 mmol g-1 h-1 , which is approximately 7.5-fold higher than pure TiO2 (Degussa, P25) and prominent apparent quantum efficiency (AQE) of 65 % at 365 nm. Furthermore, the mechanism of boosted photocatalytic H2 production is discussed.

Robust construction of CdSe nanorods@Ti3C2 MXene nanosheet for superior photocatalytic H2 evolution

With energy shortage and environmental pollution, photocatalytic hydrogen production is one of the most important ways to convert solar energy into chemical energy, and its key technology lies in the development of efficient, highly stable and low-cost photocatalysts. In this study, binary heterojunction photocatalysts consisting of CdSe nanorods and Ti3C2 MXene nanosheet were constructed via a one-step in situ hydrothermal method. When the content of Ti3C2 MXene was 10 wt%, a maximum photocatalytic H2 production rate of 763.2 μmol g−1 h−1 was achieved, which was 6 times higher than that of pure CdSe and no noticeable decline of the photocatalytic activity was observed after five recycling cycles. Based on XPS, UPS, in-situ XPS, KPFM, DFT theoretical calculations and photocatalytic experiments, the mechanism of charge transfer and photocatalytic hydrogen production in CdSe-MXene composites were proposed. This work not only presents the potential of earth-abundant MXene materials in the construction of high efficiency and low-cost photocatalysts for hydrogen production, but also opens avenues to fabricate more MXene-based composites for solar energy conversion.

Dual non-metal atom doping enabled 2D 1T-MoS2 cocatalyst with abundant edge-S active sites for efficient photocatalytic H2 evolution

Metal–organic frameworks (MOFs) materials featured large specific surface area, unique porous structure and highly crystalline nature which rendered them ideal catalysts in solar light conversion. Generally, the catalytic H2 generation activity of the MOFs was rather low which restricted its application. The effective co-catalyst introduction could enhance its overall performance via reducing the overpotential of hydrogen production while facilitating charges transfer and increasing reactive sites. Herein, an two-dimensional (2D) O,P–MoS2 nanosheets cocatalyst with adequate edge-S active sites and high 1T-phase content were fabricated via co-doping of O and P atoms. Rational coupling the 2D O, P–MoS2 nanosheets with 2D NH2-MIL-125(Ti) nanoplate can afford greatly improved photocatalytic H2 production rate of 339.3 μmol⋅g−1⋅h−1, which was 11.6 and 6.7 times of pure NH2-MIL-125(Ti) and NH2-MIL-125(Ti)/commercial MoS2 composite, respectively. DFT calculation revealed that the edge-S serve as the active sites for H∗ adsorption rather than the plane-S and O sites in O, P–MoS2 or the O and S sites in O–MoS2. Compared with the commercial MoS2 with completely 2H-phase, the dual-doping can create higher-density unsaturated edge-S atoms and more 1T phase which can improve the reactivity of NH2-MIL-125(Ti) via inducing the breaking of Mo–S bonds and providing higher electrical conductivity. Dual non-metal atom doping of MoS2 cocatalyst featured abundant edge-S active centers and high concentration of 1T-phase offered a facile and effective method to developing highly efficient catalysts toward solar-energy conversion.

In-situ fabrication of Bi2S3/g-C3N4 heterojunctions with boosted H2 production rate under visible light irradiation

The limited response region of visible light and the fast recombination of photo-induced carriers severely confine the photocatalytic behavior of the original g-C3N4. In this work, using thioureas and bismuth citrate as precursors, Bi2S3/g-C3N4 heterojunction photocatalytic materials were successfully in-situ constructed by a one-step solid phase method. Suffering from 4 h visible-light shining, the amount of H2 evolution over 1.5 wt% Bi2S3/g-C3N4 heterojunctions has reached 826.2 μmol·g−1, and the H2 production rate over Bi2S3/g-C3N4 heterojunctions achieves 236.1 μmol·g−1·h−1, which is 7 times as high as that of the pure g-C3N4. Construction of Bi2S3/g-C3N4 not only adjusts the band structures but also improves the visible light response capacity of g-C3N4. The rapid transfer of photogenerated charge pairs between Bi2S3 and g-C3N4 interfaces facilitates the separation of photo-excited charge pairs, sequentially boosting the photocatalytic H2 production rate. Combined with the various characterization and analysis results, the reasonable and possible mechanism for enhancement in the performance of Bi2S3/g-C3N4 heterojunction photocatalytic materials was proposed. This work offers potential insight into the boosted photocatalytic performance of g-C3N4 for H2 production exposure to visible light by constructing the heterojunctions to efficiently separate the photo-induced charge pairs.

Long-term photochemical stability of heteroaromatic dye-functionalised g-C3N4via covalent linkage for efficient photocatalytic hydrogen evolution

In this study, three typical D–π–A type heteroaromatic organic dyes containing carbazole (CBZ), phenothiazine (PTZ), and phenoxazine (POZ) moiety as electron donor cores and linked to g-C3N4 with amide covalent bonds were synthesized. Thereafter, we studied the long-term photochemical stability and degradation mechanism of the associated dye-sensitised g-C3N4 with covalent linkage or weak interaction. The results revealed that most of the dyes degraded and became unstable after absorption on g-C3N4 under light irradiation. Interestingly, after the target dyes were linked to g-C3N4 with amide covalent bonds, the photostability could be effectively promoted and improved to high levels of stability. For POZ-S dye covalent bond-linked sample g-C3N4/POZ-S, ∼90.5% percent of the dyes were reserved, whereas only ∼25.3% remained for the physically absorbed dye sample g-C3N4+POZ-S after 30 min of irradiation aging test. Moreover, the obtained g-C3N4/POZ-S sample exhibited enhanced H2 evolution activity with photocatalytic H2 production rates that were approximately 96- fold of that of pure g-C3N4. Then, we applied various instrumental analysis and DFT calculation to clarify the mechanism involved with dye photostability and degradation pathway. The typical decarboxylation process was confirmed, and such an unfavourable reaction process could be effectively inhibited if the target dye is linked to g-C3N4 with amide covalent bond instead of the weak interaction. Overall, the existed covalent bond is the key factor for enhancing both the photochemical stability and photocatalytic activity of organic dye-sensitised g-C3N4 for hydrogen evolution.

Efficient photocatalytic H2 generation over In2.77S4/NiS2/g-C3N4 S-scheme heterojunction using NiS2 as electron-bridge

Herein, In2.77S4/NiS2 heterojunction was firstly synthesized through an in-situ solvothermal method, then it was introduced to the surface of g-C3N4 to construct a ternary In2.77S4/NiS2/g-C3N4 S-scheme heterojunction via a simple physical solvent evaporation process. The investigation shows that the ternary In2.77S4/NiS2/g-C3N4 heterojunction exhibits an excellent light harvesting ability from 200 nm to 800 nm for the metallic-like NiS2 and the narrower bandgap of In2.77S4, it also has a better charge carrier separation and migration property compared to single and binary components. According to the photocatalytic tests, the photocatalytic H2 production rate over 20 wt% In2.77S4/NiS2/g-C3N4 can attain 7481.7 μmol·g−1·h−1, 52.5, 33.8 and 28.5 times higher than that of g-C3N4, In2.77S4 and In2.77S4/g-C3N4 respectively. Further investigation shows that the charge carriers transfer between g-C3N4 and In2.77S4 follows a S-scheme transfer route on the basis of the photoelectrochemical tests and density functional theory (DFT) calculations. In addition, NiS2 as an electron-bridge can further improve the charge transfer between the interface of g-C3N4 and In2.77S4, making more useful electrons and holes with strong REDOX capacity participating the surface reactions. What’s more, In2.77S4/NiS2 can also induce more electrochemical active sites, which can lead to a faster surface H2 releasing kinetics by reducing the overpotential of H2 evolution. This work offers an effective method for the designing novel g-C3N4-based S-scheme heterojunctions by introducing a charge-bridge to facilitate the charge carrier transfer between different photocatalysts.

In-situ sulfidation to fabricate NiSx modified g-C3N4/NiO composite for efficient photocatalytic hydrogen production under visible-light

Graphitic carbon nitride is a very potential photocatalytic catalyst for H2 production, but its practical application is seriously limited by the fast recombination of photogenerated carriers and insufficient utilization of surface charge. In order to solve these problems, herein, a series of g-C3N4-NiO-NiSx photocatalysts were synthesized by first calcining the precursor to load NiO on g-C3N4 and subsequently partial sulfidation of NiO into NiSx in situ via a hydrothermal process. Under the irradiation of visible light, the photocatalytic H2 production rate of g-C3N4-NiO-0.4T can be up to 1248.1 μmol·g−1·h−1 using triethanolamine as sacrificial agent. In addition, recycling test also confirmed g-C3N4-NiO-0.4T has excellent photostability. It is believed that the formation of p-n junction between NiO and g-C3N4 and the presence of NiSx promote the spatially fast separation of photogenerated carriers, while the abundant interface of NiS2 and NiS also leads to the good proton trapping ability. These two factors jointly determine the efficient H2 production of the composite photocatalysts. Furthermore, the detailed energy band structure and plausible photocatalytic mechanism of g-C3N4-NiO-NiSx are also proposed. This work can offer a new route and useful reference for the design and research of high efficiency composite photocatalysts for H2 production.

Accelerating electron transport in Eosin Y by bidentately bridging on BaSnO3 for noble-metal-free photocatalytic H2 production

The separation and transport of photogenerated carriers is regarded as a curial factor in photocatalytic H2 production. As known in solar cells and photoelectron-chemistry, to strengthen the electron conduction for effective utilization of carriers, the electron transport material (ETM) is widely applied. Herein, inspired by the function of ETM, we adopted barium stannate (BaSnO3, labeled as BSO) as an excellent ETM which had the merits of high electron mobility, suitable conduction band position and simple preparation, to adjust the carrier kinetics of dye Eosin Y (EY)-sensitized photocatalytic system. Detailly, the photocatalytic system with the spatial separation sites of photogenerated carriers excitation and water reduction reaction was elaborately constructed, that was, dye EY-sensitized BSO (EY/BSO) for photocatalytic H2 production. The photocatalytic H2-production rate of EY/BSO (257 μmol·h−1·gEY−1) in the absence of noble metals was 28.6 times higher than that of single EY (∼9 μmol·h−1·gEY−1) under visible-light irradiation. With systematic and comprehensive characterizations, the formed electron transport channel by the bidentate bridging of EY on BSO could accelerate the transfer of photogenerated electrons from EY to BSO, promoting the effective separation of photogenerated carriers for the enhanced photocatalytic performance. Moreover, the water reduction reaction for H2 production proceeded on the surface of BSO that acted as the H2-evolution cocatalyst, avoiding the use of high-cost noble metals. Furthermore, based on the well-proved ETM-based concept in the EY/BSO system, La-doped BaSnO3 (LBSO) with better electron transport ability was adopted to construct EY/LBSO system (344 μmol·h−1·gEY−1) which showed better photocatalytic activity than EY/BSO.

Engineering a phase transition induced g-C3N5/poly (triazine imide) heterojunction for boosted photocatalytic H2 evolution

g-C3N5, as a novel carbon nitride-based photocatalyst, has attracted widespread attention in H2 production. Constructing g-C3N5-based heterojunctions has proved to be an effective method to boost the photocatalytic H2 evolution activity. Nevertheless, the current engineering methods for constructing g-C3N5-based heterojunctions generally suffer from the cumbersome multi-step pathways. Herein, g-C3N5/poly (triazine imide) (PTI) heterojunction was successfully constructed by one-step molten-salt approach. This unique molten-salt method can simultaneously induce the formation of g-C3N5 and promote the phase transition from g-C3N5 to PTI. The relative contents of PTI in the g-C3N5/PTI heterojunction can be regulated readily by changing the calcination temperature. Our results demonstrated that the optimal g-C3N5/PTI heterojunction exhibits highest photocatalytic H2 production rate of 2326.8 μmol g−1h−1, which is 2.7 and 6.7 times those of pure g-C3N5 and PTI, respectively. The improved photocatalytic activity of g-C3N5/PTI is mainly attributed to the charge transport pathway provided by S-scheme heterostructure and the construction of the hierarchical structure, which ensure charge separate and migrate sufficiently. This work provided a tractable strategy for the construction of novel metal-free g-C3N5-based heterojunctions with enhanced photocatalytic performance and may inspire the design and synthesis of other semiconductor heterojunction photocatalysts.

Photothermal effect of carbon dots for boosted photothermal-assisted photocatalytic water/seawater splitting into hydrogen

Herein, carbon dots were loaded on the surface of hollow tubular carbon nitride (CDs/TCN) via a two-step route of hydrothermal and calcination processes for photothermal-assisted photocatalytic water/seawater splitting into hydrogen full spectrum light irradiation. The introduction of CDs promotes the separation and transfer rate of photogenerated carriers, and provides active sites for the hydrogen precipitation reaction. Most importantly, with the assistance of the thermal insulation effect of TCN, the photothermal effect of CDs can greatly increase the surface temperature of CDs/TCN composite system, thus enhancing the photocatalytic H2 production performance. All the synthesized CDs/TCN composites exhibited efficient photocatalytic H2 production rates, the highest of which reached 12.94 mmol h−1 g−1 and 11.92 mmol h−1 g−1 from water and seawater splitting, respectively. This study provides a new idea for enhancing the photothermal-assisted photocatalytic water splitting into hydrogen using CDs with photothermal effect.

Z-scheme g-C3N4/ZnO heterojunction decorated by Au nanoparticles for enhanced photocatalytic hydrogen production

The construction of heterojunction photocatalysts is an effective and widespread approach to solving global environmental issues. Herein, we designed and fabricated a Z-scheme g-C3N4/ZnO/Au heterojunction using a simple chemical method for photocatalytic H2 production under UV–Visible light irradiation. The g-C3N4/ZnO/Au-2 composite has an optimal photocatalytic H2 production rate of 46.46 μmol∙g−1∙h−1, representing 25.2-fold and 30.4-fold enhancements compared with a g-C3N4/ZnO-2 composite and bare g-C3N4, respectively. The decorated Au nanoparticles not only enhance the absorption of visible light by the LSPR effect, but also act as an electron mediator to accelerate the electrons transfer from ZnO to g-C3N4. The improved photocatalytic activity of the g-C3N4/ZnO/Au-2 composite can be attributed to the effectively suppressed recombination of photogenerated electron and hole pairs. The mechanism of the photocatalytic hydrogen evolution process had been studied by UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Ultraviolet photoemission spectroscopy (UPS), photoluminescence (PL), transient photocurrent responses, electrochemical impedance spectroscopy (EIS), and electron spin resonance (ESR). This work provides a strategy for the design and synthesis of an environmentally friendly Z-scheme heterojunction for photocatalytic H2 evolution applications.

Enhanced photocatalytic H2 evolution based on a polymer/TiO2 film heterojunction

Polymer heterojunctions have emerged as promising photocatalysts for the photocatalytic hydrogen evolution. However, they are usually used in the form of suspended powder due to the low solubility and lack of anchoring groups to hybridize with inorganic semiconductor oxides. Yet polymer film heterojunctions with convenient separation and recycling potential are more suitable for large-scale water splitting. Herein, a new solution-processable polymer PDBCOOH with biphenyl as the electron donor and diketopyrrolopyrrole (DPP) containing carboxyl group as the electron acceptor has been designed and synthesized. Surface anchoring of PDBCOOH to TiO2 films through covalent bonding formed polymer-TiO2 film heterojunctions that achieved a recorded photocatalytic H2 production rate of 11.9 mmol/m2/h without Pt co-catalyst and was 88.8 times higher than that of pristine TiO2 film. Transient absorption spectroscopy confirms ultrafast polymer excited state electron injection into TiO2, long-lived charge separated state, and unity yield of polymer hole regeneration. Photoelectrochemical experiments combined with density functional theory calculation further demonstrate that polymer PDBCOOH/TiO2 film heterojunctions not only accelerate the charge transfer but also significantly improve the hydrogen evolution rate and stability of the photocatalysts. This work offers a new strategy for obtaining stable and efficient photocatalysts by using the covalent anchoring strategy of polymer/TiO2 film heterojunction.