High H2 Evolution Activity Research Articles

Facile synthesis of noble-metal-free MoP as an efficient catalyst for H2 evolution from formaldehyde solution

A series of MoP were synthesized by a facile solid reaction and used as catalysts for H2 evolution from alkaline HCHO solution. It was found that the as-prepared MoP catalysts exhibited high H2 evolution activity and stability. The calcination temperature had a great influence on the structure, morphology and H2 evolution activity of MoP. When the calcination temperature was 400 °C, the MoP-400 exhibited the highest H2 evolution activity. The concentration of HCHO and reaction temperature in the reaction system also affected the H2 evolution efficiency. The H2 evolution performance of MoP was better than or comparable to those of the reported noble metal catalysts. The possible mechanism of H2 evolution from HCHO was discussed.

Efficient solar hydrogen production of zinc trimesityl porphyrin-based photocatalysts

Dye-sensitized photocatalytic systems (DSPs) have emerged as a promising strategy to achieve efficient and stable solar-driven H2 evolution systems. In this work, we prepared and tested a series of zinc-trimesityl porphyrin carboxylic acid derivatives as photosensitizes in DSPs for H2 evolution. In order to unveil the influence of the anchoring group, different positions of the carboxylic acid were studied. All porphyrins were adsorbed onto platinum-doped titanium dioxide nanoparticles (Pt-TiO2 NPs) and were irradiated by a white LED source. The DSPs coated with Zn-TM(pCOOH)P(i.e. the carboxylic acid at the para-phenyl position) illustrated increased stability (2514 TONs for 1.0 × 10[Formula: see text] M) and the highest H2 evolution activity (1959 mmol g[Formula: see text] h[Formula: see text] for 1.5 × 10[Formula: see text] M). These results reveal that efficient and stable DSPs for H2 evolution can be developed by utilizing porphyrin derivatives as photosensitizers.

Co2P/CoP quantum dots surface heterojunction derived from amorphous Co3O4 quantum dots for efficient photocatalytic H2 production

Amorphous/crystalline heterostructures show excellent potential in the hydrogen evolution reaction (HER) as they can significantly facilitate surface adsorption and redox reactions. Herein, a unique amorphous Co2P/crystalline CoP quantum dots (Co2P/CoP QDs) Type-II surface heterojunction was derived from amorphous Co3O4 QDs via phosphorization. The intimate contact between Co2P QDs and CoP QDs was conducive to charge transfer, thereby promoting surface reaction kinetics. The unique structure and properties were beneficial to providing more active sites and controlling the electronic structures thus making amorphous/crystalline composites show superior photocatalytic hydrogen (H2) production performance. Additionally, the amorphous Co2P QDs had a plethora of unsaturated bonds and abundant defects; the disordered structure led to increased active sites that promoted surface reaction kinetics. Due to the synergistic effect of the quantum confinement of QDs and the surface heterojunction, the charge transfer efficiency of Co2P/CoP QDs was extremely high, and high H2 evolution activity and photostability were achieved. The maximum H2 generation rate over the Co2P/CoP QDs composite reached 11.88 mmol h−1 g−1 with an apparent quantum efficiency (AQE) of 3.88 % at 420 nm, which is roughly 20-times that of the pure Co3O4 QDs. In addition, high photostability was realized; even the photocatalyst that stood for a week reached initial photoactivity. This work offers a novel idea for reasonably establishing amorphous/crystalline photocatalysts to achieve efficient H2 evolution.

Direct Z-Scheme Heterojunction Catalysts Constructed by Graphitic-C3N4 and Photosensitive Metal-Organic Cages for Efficient Photocatalytic Hydrogen Evolution.

The demand for improving the activity, durability, and recyclability of metal-organic cages (MOCs) that work as photocatalytic molecular devices in a homogeneous system has promoted research to combine them with other solid materials. An M2L4 type photosensitive metal-organic cage MOC-Q2 with light-harvesting ligands and catalytic Pd2+ centers has been synthesized and further heterogenized with graphitic carbon nitride to prepare a robust direct Z-scheme heterojunction photocatalyst for visible-light-driven hydrogen generation. The optimized g-C3N4/MOC-Q2 (0.7 wt%) sample exhibits a high H2 evolution activity of 6423 μmol g−1 h−1 in 5 h, and a total turnover number of 39,695 after 10 h, significantly superior to the bare MOC-Q2 used in the homogeneous solution and the comparison sample Pd/g-C3N4/L-4. The enhanced performances of g-C3N4/MOC-Q2 can be ascribed to its direct Z-scheme heterostructure, which effectively improves the charge separation and transfer efficiency. This work presents a rational approach of designing a binary photocatalytic system through combing micromolecular MOCs with heterogeneous semiconductors for water splitting.

Facile synthesis of novel NH2-MIL-53(Fe)/AgSCN heterojunction composites as a highly efficient photocatalyst for ciprofloxacin degradation and H2 production under visible-light irradiation

A novel NH2-MIL-53(Fe)/AgSCN composite photocatalyst was successfully prepared by a one-step chemical precipitation method, the composite show high photocatalytic activity for antibiotics degradation and H2 evolution under visible light irradiation.

Constructing a novel multi-hierarchical TiO2/g-C3N4/Ag-AgBr photocatalyst with dual Z-scheme heterojunction utilizing Ag as the charge transfer mediator

Constructing multi-heterojunction photocatalysts with multi-sources for carrier generation and with multi-channels for carrier transmission is one of the effective methods for enhancing the photocatalytic activity. Here, a novel TiO2/g-C3N4/Ag-AgBr (TCNAAB) multi-heterojunction photocatalyst was successfully constructed by depositing Ag-AgBr nanoparticles onto 3D spherical TiO2/g-C3N4. With the optimal ratio of TiO2, g-C3N4 and Ag-AgBr, the TCNAAB-50 composite had the highest H2 evolution activity and generated 940.5 μmol g−1 of H2, which was 8.24 times and 2.72 times higher than that generated by single TiO2 and binary TiO2/g-C3N4, respectively. Meanwhile, TCNAAB-50 also exhibited the highest photocatalytic activity toward methyl orange (MO) with the degradation efficiency of 77.6% under LED light. The enhanced photocatalytic performance is attributed to the multi-sources for carrier generation and the multi-channels for carrier transmission of the constructed multi-heterojunction, which help to effectively enhance the light absorption efficiency and the carrier separation and transmission. Based upon PL spectra, photoelectrochemical properties, radical quenching experiments and electron spin resonance spectra, a novel double Z-scheme heterojunction bridged by silver was proposed. The design of high-efficiency multi-heterojunction with multi-carrier excitation sources and multi-carrier transmission channels can be employed in improving the photocatalytic activity of single or binary component photocatalysts.

Aminated silicon dioxide enriching iron-containing polyoxometalate catalyst confined in CdS for efficient H2 evolution

The rational design of an artificial system that mimics natural photosynthesis for H2 evolution remains a substantial yet engaging challenge. Efficient light absorption, charge separation and associated surface reactions are crucial aspects of semiconductor photocatalytic system for efficient water splitting. Herein, a catalyst assembly of p-SiO2-NH3-Fe11POM@CdS was constructed by partially etched SiO2-NH2 coating CdS (p-SiO2-NH2@CdS) bound iron-based polyoxometalate (Fe11POM) in the interstitial space. In the hybrid catalyst, Fe11POM acts as catalyst and p-SiO2-NH2@CdS as light-harvesting material as well as Fe11POM enrichment center, respectively. The p-SiO2-NH3-Fe11POM@CdS catalyst exhibits a high H2 evolution activity of 23.1 mmol g−1 h−1 with turnover number (TON) of 3225 and apparent quantum efficiency (AQE) of 71% under 420 nm LED illumination. The electrons transfer from p-SiO2-NH2@CdS to Fe11POM, affording electrons accumulated in Fe11POM for H2 evolution. Our strategy of building hybrid photocatalyst will provide a new way to construct efficient catalyst assembly for water splitting.

Phosphate group-mediated carriers transfer and energy band over carbon nitride for efficient photocatalytic H2 production and removal of rhodamine B

The development of effective methods that simultaneously regulate energy bands and electron transfer to realize high photocatalytic performance of graphitic carbon nitride (g-C3N4) remains a major challenge. Herein, we developed a novel strategy to construct a phosphate-group-intercalated g-C3N4 nanosheet photocatalyst that is driven by visible light. A series of characterizations confirmed that phosphate groups were inserted between the g-C3N4 layers and formed a vertical channel. A porous ultrathin nanosheet structure was formed. The synergistic effect of the phosphate-group intercalation and porous ultrathin nanosheet structure endowed this material with controllable electronic structures and upshifted the conduction bands, while facilitating photogenerated charge transfer and providing numerous active reactive sites. As a result, the g-C3N4 intercalated with phosphate groups photocatalyst exhibited high photocatalytic activity for H2 evolution and degradation of a coloured dye rhodamine B (RhB) under visible light. The maximum H2 production rate and degradation rate constant of the phosphate-group-intercalated g-C3N4 nanosheets (CNP-5) were 17-fold and 6-fold higher than those of primal g-C3N4, respectively. This study provides new insights for the incorporating atomic groups with modification effects and represents a giant leap in the construction of two-dimensional (2D) materials.

Photo-induced synthesis of ternary Pt/rGO/COF photocatalyst with Pt nanoparticles precisely anchored on rGO for efficient visible-light-driven H2 evolution

Covalent organic frameworks (COFs) have been recognized as a new type of promising visible-light-driven photocatalysts for H2 evolution, while it still is a key point to facilitate the separation and transfer of photoinduced charges for further enhancing their activities. In this work, we fabricated a new type of ternary Pt/rGO/COF photocatalysts with Pt cocatalyst precisely anchored on rGO serving as electron collector for largely enhanced H2 evolution. A series of ternary hybrid materials were obtained via one-pot photoreduction of Pt4+ and GO under visible-light irradiation in a solution the same as photocatalytic H2 evolution reaction and simultaneous self-assembling of rGO/COF heterostructure. No need isolation, the synthetic system could be further used for photocatalytic H2 evolution reaction and the results show the H2 evolution rate of Pt/rGO(20%)/TpPa-1-COF hybrid material is 19.59 mmol·g−1·h−1, 6.51 times higher than that of Pt/TpPa-1-COF. The essential role of the exclusively distributed Pt nanoparticles on rGO to the high H2 evolution activity was confirmed by various comparisons of activity for the samples with diverse Pt distribution.

Efficient photocatalytic hydrogen production of ternary composite constituted by cubic CdS, MoS2 and activated carbon

CdS is a promising photocatalyst and combining MoS2 with CdS can realize efficient photocatalytic hydrogen production. However, most of the previous researches about MoS2/CdS composites focus on hexagonal CdS. Studies on cubic CdS are still rare due to its unstability. Thus in this paper, a ternary composite CdS-MoS2/C (abbreviated as CdS-MC, M = MoS2, C = activated carbon) was synthesized by facile in-situ liquid phase precipitation of cubic CdS on MoS2/C. Based on a series of characterizations, its photocatalytic hydrogen production performance was studied. Under the irradiation of a LED lamp, a high H2 evolution activity of 879.6 μmol h−1 was achieved for the composite CdS-10%MC, which is 23.3 times that of pure CdS. In addition, its performance is much higher than that of the hexagonal CdS-MC sample (265.6 μmol/h) obtained by heat-treatment of CdS-MC at 400 °C for 1 h under N2 atmosphere. What’s more, the stability of CdS-MC was investigated and the possible reasons for its unstability were analyzed in detail. To improve the stability, a method of 4-mercaptobenzoic acid (4-MBA) modification was also managed. Finally, possible mechanism for the photocatalytic hydrogen production of CdS-MC was proposed.

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.

An all-inorganic quasi-homogenous polyoxometalate/[Mo3S13]2- system for efficient and stable photocatalytic H2 evolution.

An all-inorganic quasi-homogenous photocatalytic H2 evolution system has been developed employing Keggin-type polyoxometalate H4SiW12O40 (SiW12) as the photosensitizer and [Mo3S13]2- clusters as the catalyst. This SiW12/[Mo3S13]2- system achieves a high turnover number (TON) of 922 based on the [Mo3S13]2- catalyst in 5 h of reaction and excellent H2 evolution stability for 40 h with a high turnover number of 6876.

Photo-reduction synthesis of Cu nanoparticles as plasmon-driven non-semiconductor photocatalyst for overall water splitting

Plasmon-induced photo-electron generated from the surface plasmon resonance effect in metal nanoparticles has attracted tremendous interest in photocatalysis. However, semiconductors are still leading role and plasmonic metal nanoparticles are just co-catalysts in photocatalytic system. Herein, we demonstrate that an alternative pathway via constructing single Cu nanoparticles is available for robust photocatalytic overall water splitting under full-spectrum irradiation. Plasmonic Cu nanoparticles are prepared using a photo-reduction method, and identified by X-ray diffraction patterns and X-ray photoelectron spectroscopy. Importantly, the photocatalyst exhibits a stable and high activity for O2 and H2 evolution in four consecutive runs. Our findings may provide a new strategy to develop the plasmon photocatalytic system and offer opportunities for extending the non-semiconductor photocatalysts field.

Enhancing H2 evolution and molecular oxygen activation via dye sensitized BiOBr0.9I0.1 under visible light

Sensitization with a dye has great potential for dealing with the photoexcited charge recombination problem for photocatalysts. One of the main factors affecting the dye-sensitization performance is the absorption capacity of semiconductor for dye. Specific surface area of semiconductors and pH values of reaction system are critical for the absorption capacity. Herein, we firstly developed a BiOBr0.9I0.1 solid solution via a facile and fast sacrificial template method. The prepared BiOBr0.9I0.1 has distinct advantages, e.g. loose and rich porous structure, more oxygen vacancies (OVs), and a large specific surface area, which result in strong adsorption for dye molecules. Sensitized by Rhodamine B (RhB), the prepared BiOBr0.9I0.1 photocatalyst shows remarkably improved high activity for H2 evolution, which is 27.9 times than that of the dense structured BiOBr0.9I0.1 under a direct photocatalytic process. By lowing the pH of RhB solution, the absorption ability is further improved because of the protonation of dye. At low pH, the prepared BiOBr0.9I0.1 can efficiently activate the molecular oxygen to produce superoxide radicals (O2−), resulting a super high dye-sensitized degradation activity for tetracycline hydrochloride (TCH) and methyl orange (MO) pollutants, outperforming most catalysts reported under similar conditions by the direct photocatalytic reaction. The present method represents a new direction in the development of dye-sensitization nanomaterials with good performance for energy and environment applications.

Metal–Organic Frameworks Integrate Cu Photosensitizers and Secondary Building Unit-Supported Fe Catalysts for Photocatalytic Hydrogen Evolution

We report here the synthesis of a series of metal-organic frameworks (MOFs), FeX@Zr6-Cu, comprising cuprous photosensitizing linkers (Cu-PSs) and catalytically active FeII centers supported on secondary building units (SBUs) for photocatalytic H2 evolution. Close proximity (∼1 nm) between Cu-PS and SBU-supported Fe sites and stabilization of Fe sites by periodically ordered SBUs led to exceptionally high H2 evolution activity for FeX@Zr6-Cu, with turnover numbers of up to 33 700 and turnover frequencies of up to 880 h-1. Photocatalytic H2 evolution activities of FeX@Zr6-Cu correlate with the lability of X counteranions, suggesting that open coordination environments of Fe sites generated by labile X groups facilitate the formation of Fe-hydride intermediates before hydrogen evolution. This work highlights the potential of using MOFs to integrate Earth-abundant components for solar energy utilization.

Controlled Growth and Bandstructure Properties of One Dimensional Cadmium Sulfide Nanorods for Visible Photocatalytic Hydrogen Evolution Reaction.

One dimensional (1D) metal sulfide nanostructures are one of the most promising materials for photocatalytic water splitting reactions to produce hydrogen (H2). However, tuning the nanostructural, optical, electrical and chemical properties of metal sulfides is a challenging task for the fabrication of highly efficient photocatalysts. Herein, 1D CdS nanorods (NRs) were synthesized by a facile and low-cost solvothermal method, in which reaction time played a significant role for increasing the length of CdS NRs from 100 nm to several micrometers. It is confirmed that as the length of CdS NR increases, the visible photocatalytic H2 evolution activity also increases and the CdS NR sample obtained at 18 hr. reaction time exhibited the highest H2 evolution activity of 206.07 μmol.g−1.h−1. The higher H2 evolution activity is explained by the improved optical absorption properties, enhanced electronic bandstructure and decreased electron-hole recombination rate.

Novel self-supported MoS2/FeS2 nanocomposite as an excellent electrocatalyst for hydrogen evolution

The development of earth-abundant electrocatalysts to replace high-cost precious metal Pt for water splitting to generate H2 is a hot topic in the researches on clean energy. Among them, MoS2 nanostructures have intrigued great interest for its low cost and potential high performance. However, due to the intrinsically low conductivity, its H2 evolution activity is not satisfactory as an applicable electrocatalyst. Herein we report a novel MoS2/FeS2 nanocomposite grown directly on carbon cloth by a facile method based on simple one-step chemical vapor deposition, which has significantly improved H2 evolution performance compared to its pure MoS2 nanosheets counterpart. Such self-supported MoS2/FeS2 nanocomposite electrode exhibits a relatively low overpotential of 134 mV at a current of 10 mA cm−2, a quite small Tafel slope of 76.8 mV⋅dec−1 and excellent electrocatalytic durability in 0.5 mol L−1 H2SO4. The remarkably high H2 evolution activity could be ascribed to the fully exposed and increased number of active sites, enhanced charge transfer rate between MoS2 nanosheets and FeS2 nanoparticles in the composite, and the 3D self-supported structure. This strategy to prepare MoS2/FeS2 nanocomposite with controllable morphology and highly active microstructure would provide a new way for the improvement of the electrocatalytic H2 evolution activity and durability of MoS2.

Ni(acac)2/Mo-MOF-derived difunctional MoNi@MoO2cocatalyst to enhance the photocatalytic H2evolution activity of g-C3N4

It is essential to construct bifunctional composite cocatalysts with earth-abundant metals for efficient transfer and separation of charge carriers, thus leading to the development of a photocatalyst with high H2 evolution activity. Herein, MoNi@MoO2 composite cocatalysts were prepared by annealing Ni-doped Mo-MOF, and then decorating with g-C3N4 by grinding. The obtained MoNi@MoO2-8 %/g-C3N4 photocatalyst exhibited an optimum H2 evolution rate of as high as 1.359 mmol g−1 h−1, 6.0 and 3.7 times than those of Ni/g-C3N4 and MoO2-8 %/g-C3N4, respectively. This improved activity can be ascribed to the bifunctional roles of MoNi@MoO2 and synergy between MoNi and MoO2. MoO2 acts as a reservoir to store electrons from g-C3N4; MoNi acts as surface-active sites to trap electrons from MoO2 and increase the proton reduction kinetics. This study would promote the development of other high-efficiency bifunctional cocatalysts to increase the photocatalytic H2 evolution performance.

Colloidal CdS and CdZnS nanocrystal photocatalysts with massive S2--adsorption: one-step facile synthesis and highly efficient H2-evolution performance.

Colloidal CdS and CdZnS nanocrystals (NCs) with massive S2--adsorption were synthesized via a one-step synthetic method. In the absence of a cocatalyst, the as-obtained colloidal CdS-NC photocatalyst achieves a superb H2-evolution rate of 6.86 mmol h-1 g-1 and an apparent quantum efficiency of 52.8% under visible light.

Facile synthesis of sulfur-doped polymeric carbon nitride/MoS2 face-to-face heterojunction for highly efficient photocatalytic interfacial charge separation

The notorious rapid recombination of photoinduced electron-hole limits the further application of polymeric carbon nitride (PCN) based photocatalysts. Face-to-face heterojunction composed of dissimilar 2D nanomaterials has been explored as a feasible way to facilitate the charge separation of PCN at the atomically well-defined hetero-interface. However, the conventional exfoliation-assembling process is tedious and time-consuming. Herein, a 2D/2D face-to-face heterojunction (MCN) has been constructed between sulfur (S)-doped polymeric carbon nitride nanosheets (SCN) and ultrathin molybdenum disulfide (MoS2) via a facile hydrothermal-polymerization method to overcome the recombination of photoinduced electron-hole pairs. The as-prepared MCN face-to-face heterojunction facilitated charge transport for the intimate interface contact and enhanced the separation of charge carriers, thus exhibiting high H2 evolution activity (2120 μmol h−1 g−1) without any other co-catalyst and high efficient degradation of dye. This work provides a facile protocol for synthesis of 2D/2D carbon nitride based photocatalysts towards future energy technology innovation.