Cocatalyst For Photocatalytic Hydrogen Production Research Articles

Synthesis and recent developments of MXene-based composites for photocatalytic hydrogen production

Abstract The energy crisis has already seriously affected the daily lives of people around the world. As a result, designing efficient catalysts for photocatalytic hydrogen evolution (PHE) is a promising strategy for energy supply. Co-catalyst modification can significantly enhance the photocatalytic activity of single semiconductors, overcoming limitations posed by their narrow visible light absorption range and high electron–hole recombination rate. MXene-based composites demonstrate immense potential as co-catalysts for photocatalytic hydrogen production owing to their distinctive two-dimensional layered structure and outstanding photoelectrochemical properties, and further research and development efforts surrounding MXene-based composites will contribute significantly to the progress of sustainable energy technologies. In this review, we offer a comprehensive overview of synthesis methods for MXene and MXene-based composites, highlight illustrative instances of binary and ternary MXene-based composites in PHE, and explore potential avenues for future research and expansion of MXene-based composites.

An efficient NiS-ReS2/CdS nanoparticles with dual cocatalysts for photocatalytic hydrogen production

The construction of heterojunctions is one of efficacious ways to improve the charge transfer and suppress the recombination of photoexcited electron-hole pairs for enhancing reactive activities of photocatalysts. Ternary NiS-ReS2/CdS composites are synthesized via a one-step hydrothermal method and the heterojunction nanostructures are achieved. The NiS-ReS2/CdS photocatalyst exhibits the superior photocatalytic activity with a hydrogen production rate up to 139 mmol g−1 h−1, which is much higher than binary composites and pure CdS. The contributions of the dual cocatalysts NiS and ReS2 are verified to narrower bandgaps, lower resistances and increase photocurrent density of NiS-ReS2/CdS, promoting the absorption of visible light and the migration of photoinduced electrons. The NiS-ReS2/CdS heterostructures provide a possible dual Z-scheme path for the rapid transfer of electrons. The tailoring of the dual cocatalysts is effective to improve the photocatalytic hydrogen production.

2D MoB MBene: An Efficient Co-Catalyst for Photocatalytic Hydrogen Production under Visible Light.

Highly active and low-cost co-catalysts have a positive effect on the enhancement of solar H2 production. Here, we employ two-dimensional (2D) MBene as a noble-metal-free co-catalyst to boost semiconductor for photocatalytic H2 production. MoB MBene is a 2D nanoboride, which is directly made from MoAlB by a facile hydrothermal etching and manual scraping off process. The as-synthesized MoB MBene with purity >95 wt % is treated by ultrasonic cell pulverization to obtain ultrathin 2D MoB MBene nanosheets (∼0.61 nm) and integrated with CdS via an electrostatic interaction strategy. The CdS/MoB composites exhibit an ultrahigh photocatalytic H2 production activity of 16,892 μmol g-1 h-1 under visible light, surpassing that of pure CdS by an exciting factor of ≈1135%. Theoretical calculations and various measurements account for the high performance in terms of Gibbs free energy, work functions, and photoelectrochemical properties. This work discovers the huge potential of these promising 2D MBene family materials as high-efficiency and low-cost co-catalysts for photocatalytic H2 production.

Decorating CdS with cobaltous hydroxide and graphene dual cocatalyst for photocatalytic hydrogen production coupled selective benzyl alcohol oxidation

Coupling photocatalytic H2 evolution with benzyl alcohol (BA) oxidation to benzaldehyde (BAD) reaction allows the full utilization of the energy of light-induced electron and hole to produce fuel and valuable chemicals, which has received widespread attention recently. Herein, Co(OH)2 nanosheet array-graphene(GR) composites cocatalyst can be successfully synthesized by simple precipitation method, and then CdS nanoparticles are in situ grown in hybrid cocatalyst to finally obtain CdS-Co(OH)2-GR ternary photocatalysts. Composting of dual-cocatalyst with CdS facilitates the migration of photoinduced charge carriers of CdS, affords abundant active sites and makes the growth of CdS nanoparticles more uniform and dispersed. As a result, the CdS-Co(OH)2-GR ternary composites have shown a glorious performance, showing the H2 generation velocity of 1173.53 µmol h−1 g−1, and the conversion rate of benzyl alcohol has reached 100 % within 2 h, which has surpassed other prepared samples and most of analogous photocatalyst systems. We are confident that this study can supply a useful reference for the synthesis of dual-cocatalyst-modified semiconductor composites, and promote the development of photocatalytic coupling reaction system, in which sacrifice agents are free and energies of light-induced electron and holes can be fully utilized.

Remarkably enhanced hydrogen evolution of g-C3N4 nanosheet under simulated sunlight via AgPt alloy co-catalyst with low amount of Pt

The development of low-cost co-catalysts matched with proper photocatalysts to enhance the photocatalytic hydrogen evolution performance is highly demanded. Herein, the AgPt bimetallic alloy nanoparticles with small amounts of Pt were decorated on g-C3N4 nanosheets (AP-CN) via the NaBH4 reduction method, which were further used as catalysts towards photocatalytic hydrogen evolution from water under AM1.5 irradiation. Compared to mono-metallic co-catalysts, bimetallic AgPt alloy nanoparticles exhibited excellent co-catalytic performance. The optimum AP-CN photocatalyst with 0.5 wt% Pt exhibited photocatalytic hydrogen evolution rate of 3507.89 μmol g−1·h−1, which even surpassed that of the commonly-used photocatalyst 1.0 wt% Pt in-situ photo-deposited on g-C3N4. Meanwhile, the AP-CN showed excellent photocatalytic activity and durability after four experimental cycles. The enhanced activity and stability could be attributed to the synergistic effect between plasmonic metal Ag and Pt, which promoted the transfer and separation of photoinduced charge carriers. Besides, the theoretical results based on DFT calculation also verified that AgPt alloys have better performance of desorbing hydrogen and adsorbing H atoms. This work provides a feasible idea for the development of inexpensive and efficient bimetallic co-catalysts for photocatalytic hydrogen production through water splitting.

Amorphization-induced reverse electron transfer in NiB cocatalyst for boosting photocatalytic H2 production

Regulating the electron density distribution of active sites to accelerate catalytic process is of great significance to explore high-efficiency cocatalysts for photocatalytic hydrogen production. In this work, a novel strategy of amorphization-induced reverse electron transfer is proposed to optimize the electronic structure of Ni active site in nickel boride (NiB) cocatalyst to promote the photocatalytic hydrogen-production activity of TiO2. Herein, the NiB nanodots (0.5–1 nm) with an amorphous structure can perfectly be anchored onto TiO2 surface via a novel-designed light-induced route. The resulting amorphous-NiB/TiO2 sample achieves the photocatalytic H2-production rate of 2334.0 μmol h−1 g−1, which is 1.8 times higher than that of the traditional crystalline-NiB/TiO2 photocatalyst. The experimental and theoretical investigations confirm that the amorphization of NiB can induce the reverse electron transfer from B to Ni, which can promote the hydrogen desorption process of the Ni active site to boost the H2-production efficiency. This work paves a new way for active site optimization and delivers in-depth insights for the exploration of high-efficient hydrogen-production cocatalysts.

Solid-state synthesis of ZnS/ZnO nanocomposites and their decoration with NiS cocatalyst for photocatalytic hydrogen production

Herein was demonstrated the facile solid-state synthesis of ZnS/ZnO nanocomposites using planetary ball milling followed by subsequent thermal treatment. X-ray diffraction analysis has shown that the ZnS/ZnO products are nanocrystalline with an estimated crystallite size of less than 60 nm. A transmission electron microscope has demonstrated the presence of spherical heterostructures and core-shell structured ZnS/ZnO nanocomposites with the size being 40–80 nm in diameter. Fourier transform infrared spectroscopy analysis confirmed the presence of Zn–O and Zn–S bonds. The formation of a thin boundary between the ZnS and ZnO phases, where the sulfur oxidation state varies from −2 to +6, was determined by X-ray photoelectron spectroscopy. Degradation of methylene blue and Orange II organic dyes was used to assess the photocatalytic activity of ZnS/ZnO nanocomposites, and the nanocomposites of ZnS/ZnO, with a mass ratio of ∼1:1, demonstrated the highest visible light photocatalytic activity. For photocatalytic hydrogen production experiments, the surface of ZnS/ZnO nanocomposites was in situ decorated with NiS nanoparticles, where the mass content of NiS was 1.5%. The presence of NiS cocatalyst promotes the separation and transfer of photogenerated charges, thereby increasing the photocatalytic activity of ZnS/ZnO nanocomposites during hydrogen generation. The apparent quantum efficiency of photocatalytic hydrogen generation using ZnS/ZnO-3h-NiS photocatalyst was equal to 1.13%. This contribution shows the possibility to prepare nano-structured photocatalysts via mechanochemistry.

Enhanced Photocatalytic Hydrogen Production of ZnIn2S4 by Using Surface-Engineered Ti3C2Tx MXene as a Cocatalyst.

Developing efficient and stable photocatalysts is crucial for photocatalytic hydrogen production. Cocatalyst loading is one of the effective strategies for improving photocatalytic efficiency. Here, Ti3C2Tx (Tx = F, OH, O) nanosheets have been adopted as promising cocatalysts for photocatalytic hydrogen production due to their metallic conductivity and unique 2D characterization. In particular, surface functionalized Ti3C2(OH)x and Ti3C2Ox cocatalysts were synthesized through the alkalization treatment with NaOH and a mild oxidation treatment of Ti3C2Fx, respectively. ZnIn2S4/Ti3C2Tx composites, which were fabricated by the in-situ growth of ZnIn2S4 nanosheets on the Ti3C2Tx surface, exhibited the promoted photocatalytic performance, compared with the parent ZnIn2S4. The enhanced photocatalytic performance can be further optimized through the surface functionalization of Ti3C2Fx. As a result, the optimized ZnIn2S4/Ti3C2Ox composite with oxygen functionalized Ti3C2Ox cocatalyst demonstrated excellent photocatalytic hydrogen evolution activity. The characterizations and density functional theory calculation suggested that O-terminated Ti3C2Ox could effectively facilitate the transfer and separation of photogenerated electrons and holes due to the formation of a Schottky junction, with the largest difference in work function between ZnIn2S4 and Ti3C2Ox. This work paves the way for photocatalytic applications of MXene-based photocatalysts by tuning their surface termination groups.

MoS2 as a Co-Catalyst for Photocatalytic Hydrogen Production: A Mini Review.

Molybdenum disulfide (MoS2), with a two-dimensional (2D) structure, has attracted huge research interest due to its unique electrical, optical, and physicochemical properties. MoS2 has been used as a co-catalyst for the synthesis of novel heterojunction composites with enhanced photocatalytic hydrogen production under solar light irradiation. In this review, we briefly highlight the atomic-scale structure of MoS2 nanosheets. The top-down and bottom-up synthetic methods of MoS2 nanosheets are described. Additionally, we discuss the formation of MoS2 heterostructures with titanium dioxide (TiO2), graphitic carbon nitride (g-C3N4), and other semiconductors and co-catalysts for enhanced photocatalytic hydrogen generation. This review addresses the challenges and future perspectives for enhancing solar hydrogen production performance in heterojunction materials using MoS2 as a co-catalyst.

Unraveling novel Cu/CuxP@N-doped C composite as effective cocatalyst for photocatalytic hydrogen production under UV and visible irradiation

Rational design and fabrication of effective multi-component cocatalyst for high performance photocatalytic hydrogen production via water-splitting have been investigated. Herein, polyaniline-derived N-doped carbon encapsulated copper/copper phosphide nanoparticles (Cu/CuxP@NC) was facilely prepared by a single-step phosphorization-pyrolysis route. Homologous Cu/CuxP heterostructure with a diameter ∼ 20 nm was successfully wrapped with N-doped carbon layers. The resultant Cu/CuxP@NC is utilized as a cocatalyst of host photocatalysts like TiO2 and g-C3N4 for H2 generation. The optimal Cu/CuxP@NC/TiO2 composites exhibited a hydrogen evolution rate (HER) of 12.45 mmol.h−1 g−1 which is 145-fold higher than TiO2 alone. Interestingly, the Cu/CuxP@NC composite also improved the activity of g-C3N4 to produce 285 µmol.h−1 g−1 of H2 under visible light where no H2 was evolved over pure g-C3N4. The photocatalytic performance of the presented Cu/CuxP@NC/TiO2 was superior than carbon-free Cu/CuxP/TiO2 nanocomposite. Such improved activity is attributed to the N-doped carbon layer that plays a pivotal role in suppressing the recombination of the photogenerated electron-hole pairs. Thus, Cu/CuxP@NC cocatalyst composite can efficiently capture the photoexcited electrons from the conduction band of TiO2 or g-C3N4, accelerating the charge separation process. This study provides a low-cost and competitive cocatalyst to substitute noble metals in photocatalytic reactions.

Surface-Engineered Ni(OH)2/PtNi Nanocubes as Cocatalysts for Photocatalytic Hydrogen Production

Exposure of specific crystallographic planes as catalyst surfaces has been reported to effectively affect the performance of noble metal cocatalysts used for photocatalytic hydrogen production via water splitting. However, the performance of noble metals for hydrogen production in alkaline solutions is usually 2 orders of magnitude lower than that in acidic media because of the weak dissociative adsorption ability of noble metals to water molecules, which may greatly limit their applications in photocatalytic hydrogen production. In this research we report a Pt-based composite cocatalyst (Ni(OH)2/PtNi nanocubes), designed by separating the dissociative sites of water molecules from active sites for photocatalytic hydrogen production. Compared with PtNi nanocube-loaded CdS, Ni(OH)2/PtNi nanocube-modified CdS exhibits a much higher photocatalytic performance for hydrogen production in alkaline solutions. This study provides a method for synthesizing highly active water-splitting/reducing photocatalysts under alkaline conditions.

Surface assembly of cobalt species for simultaneous acceleration of interfacial charge separation and catalytic reactions on Cd0.9Zn0.1S photocatalyst

Although photocatalytic water splitting has excellent potential for converting solar energy into chemical energy, the challenging charge separation process and sluggish surface catalytic reactions significantly limit progress in solar energy conversion using semiconductor photocatalysts. Herein, we demonstrate a feasible strategy involving the surface assembly of cobalt oxide species (CoOx) on a visible-light-responsive Cd0.9Zn0.1S (CZS) photocatalyst to fabricate a hierarchical CZS@CoOx heterostructure. The unique hierarchical structure effectively accelerates the directional transfer of photogenerated charges, reducing charge recombination through the smooth interfacial heterojunction between CZS and CoOx, as evidenced by photoluminescence (PL) spectroscopy and various electrochemical characterizations. The surface cobalt species on the CZS material also act as efficient cocatalysts for photocatalytic hydrogen production, with activity even higher than that of noble metals. The well-defined CZS@CoOx heterostructure not only enhances the interfacial separation of photoinduced charges, but also improves surface catalytic reactions. This leads to superior photocatalytic performances, with an apparent quantum efficiency of 20% at 420 nm for visible-light-driven hydrogen generation, which is one of the highest quantum efficiencies measured among noble-metal-free photocatalysts. Our work presents a potential pathway for controlling complex charge separation and catalytic reaction processes in photocatalysis, guiding the practical development of artificial photocatalysts for successful transformation of solar to chemical energy.

Graphitic Carbon Nitride Decorated with Nickel(II)-(3-Pyridyl) Benzimidazole Complexes and Pt Nanoparticles as a Cocatalyst for Photocatalytic Hydrogen Production from Water Splitting

Graphitic carbon nitride (g-C3N4) is regarded as a promising and suitable photocatalyst in the progress of hydrogen evolution from water splitting by employing visible-light irradiation. Neverthele...

CoP QD anchored carbon skeleton modified CdS nanorods as a co-catalyst for photocatalytic hydrogen production

An important strategy to improve the performance of catalysts is loading nanoparticle co-catalysts of better dispersion and conductivity. In this work, the ZIF-67-derived CoP quantum dot (QD) anchored graphitized carbon skeleton as a co-catalyst is loaded on CdS nanorods (NRs), while the CoP QDs derived from ZIF-67 are anchored to the carbon skeleton under phosphation and carbonization simultaneously. The porous, graphitized carbon skeleton can not only disperse CoP QDs, increasing active sites for the hydrogen reduction reaction, but also provide electron transfer channels, promoting electron transfer and increasing conductivity. In addition, the metallicity of CoP QDs makes it possible to form Schottky junctions, which is beneficial to the electron transfer at the interface. The results show that the composite photocatalyst can extensively improve the photocatalytic activity and stability, the H2 production rate is 104 947 μmol h-1 g-1 under visible light irradiation (λ ≥ 400 nm), up to 55.2 times that of bare CdS NRs, the apparent quantum yield (AQY) reaches a high value of 32.16% at 420 nm, and the structure of the photocatalyst did not change after the reaction. This work provides an innovative method for the preparation of highly efficient noble metal-free photocatalysts for the conversion of solar energy into hydrogen energy, which has bright prospects in industrial application.

Chromium-titanium nitride as an efficient co-catalyst for photocatalytic hydrogen production

The synergistic effect of ternary chromium-titanium nitride significantly promotes photocatalytic hydrogen production of cadmium sulfide.

Co-doped Mo-Mo2C cocatalyst for enhanced g-C3N4 photocatalytic H2 evolution

Molybdenum rich molybdenum carbide (Mo-Mo2C) has recently been confirmed as a highly effective non-noble-metal cocatalyst to boost the photocatalytic activity of g-C3N4 for water splitting. However, the activity of Mo-Mo2C is still much lower than that of Pt noble metal based cocatalysts for photocatalytic hydrogen production (PHE). This work reports a highly active cobalt (Co) doped Mo-Mo2C cocatalyst (Co(Mo-Mo2C)) for PHE. The hydrogen production rate of 2.0 wt.% optimal Co(Mo-Mo2C) loaded g-C3N4 (2.0 wt.% Co(Mo-Mo2C)/g-C3N4) photocatalyst can be as high as 11,291 μmol h−1 g−1, at 6.7% apparent quantum efficiency (AQE) at 420 nm, which is 1.4 times greater than that of 2.0 wt.% Pt/g-C3N4 photocatalyst. Catalyst characterizations have pointed out that Co doped Mo-Mo2C cocatalyst is able to efficiently suppress photo-generated charge recombination, thus improving the interfacial charge transfer rate. This research provides novel ideas and technical approaches for designing a noble-metal-free, efficient and environmentally friendly cocatalyst for photocatalytic H2 evolution via water reduction.

Surface partially oxidized MoS2 nanosheets as a higher efficient cocatalyst for photocatalytic hydrogen production

In this study, a novel MoO3@MoS2/TiO2 photocatalyst with higher photocatalytic hydrogen production efficiency was prepared via a hydrothermal followed by quenching method. The prepared composites were characterized by X-ray diffraction (XRD), Raman spectroscopy, UV–Vis Spectrophotometers, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic performance for hydrogen evolution was also investigated. The results show that MoS2-340 °C/TiO2 exhibits excellent photocatalytic hydrogen production efficiency (4669 μmol g−1 h−1), which is 5.8 times higher than that of unquenched MoS2/TiO2 under the same conditions. MoO3 on the surface and edges of large layered MoS2 creates more traps adjacent to the joint. More photogenerated electrons can be enriched during the photocatalytic reaction, which achieve the purpose of exposing more active sites.

Hollow CoSe2 nanocages derived from metal–organic frameworks as efficient non-precious metal co-catalysts for photocatalytic hydrogen production

Hollow structured CoSe2 nanocages are developed as efficient co-catalysts for photocatalytic hydrogen productions.

2D/2D heterojunction of Ti3C2/g-C3N4 nanosheets for enhanced photocatalytic hydrogen evolution.

Photocatalytic hydrogen evolution from water has received enormous attention due to its ability to address a number of global environmental and energy-related issues. Here, we synthesize 2D/2D Ti3C2/g-C3N4 composites by electrostatic self-assembly technique and demonstrate their use as photocatalysts for hydrogen evolution under visible light irradiation. The optimized Ti3C2/g-C3N4 composite exhibited a 10 times higher photocatalytic hydrogen evolution performance (72.3 μmol h-1 gcat-1) than that of pristine g-C3N4 (7.1 μmol h-1 gcat-1). Such enhanced photocatalytic performance was due to the formation of 2D/2D heterojunctions in the Ti3C2/g-C3N4 composites. The intimate contact between the monolayer Ti3C2 and g-C3N4 nanosheets promotes the separation of photogenerated charge carriers at the Ti3C2/g-C3N4 interface. Furthermore, the ultrahigh conductivity of Ti3C2 and the Schottky junction formed between g-C3N4/MXene interfaces facilitate the photoinduced electron transfer and suppress the recombination with photogenerated holes. This work demonstrates that the 2D/2D Ti3C2/g-C3N4 composites are promising photocatalysts thanks to the ultrathin MXenes as efficient co-catalysts for photocatalytic hydrogen production.

Novel metal doped carbon quantum dots/CdS composites for efficient photocatalytic hydrogen evolution.

Carbon quantum dots (CDs) are rising stars for photocatalytic applications due to their low toxicity and excellent electron transfer characteristics. Doping with heteroatoms is expected to adjust the band levels and electron transfer properties of CDs, and understanding the effect of doping on CDs can aid the rational preparation of highly efficient CD-based photocatalysts. Herein, we prepared a series of metal atom (Zn, Co, Bi, Cd, or Ti) doped CDs by pyrolysis and explored the photocatalytic application of these metal doped CDs for the first time. The metal doped CDs were combined with CdS nanowires as a co-catalyst for photocatalytic hydrogen production. The Bi, Cd and Ti doped CDs/CdS composites show much better hydrogen production performance than the undoped CDs/CdS composite. Among these composites, Bi-CDs/CdS presents the optimal interfacial charge separation and the best hydrogen production performance. The hydrogen evolution rate of Bi-CDs/CdS is 4.2 times and almost one time higher than that of pure CdS and undoped CDs/CdS, respectively. Bi doping can make the CDs metallic and promote the charge transfer of CDs. Such a great enhancement originates from the outstanding electron transfer properties of Bi-doped CDs, as well as the effective charge separation between Bi-doped CDs and CdS. Bi doping was demonstrated to be an effective strategy for optimizing the photocatalytic activity of CD based composites.