Noble metal-free bimetallic NiCo decorated Zn0.5Cd0.5S solid solution for enhanced photocatalytic H2 evolution under visible light

As we know, noble metal (Pt, Pd and Au) with appropriate adsorption free energy of H atoms and higher work function as cocatalyst has been considered to be an effective tactic to enhance photocatalytic activity. However, they are limited severely by scarcity and high-cost. Herein, Zn_0.5Cd_0.5S solid-solution photocatalyst decorated with noble metal-free NiCo cocatalyst has been successfully obtained through one-step photochemical route. It is found that the lifespan of charge carriers of Zn_0.5Cd_0.5S@NiCo can be prolonged dramatically after modification, and the photocatalytic H₂ rate reach to 34.7  mmol g⁻¹·h⁻¹ is nearly 9 times higher than the bare Zn_0.5Cd_0.5S (λ ≥ 420 nm). The superior photocatalytic activity for ZCS@NiCo could be mainly ascribed to higher separation and transfer efficiency of photogenerated carriers by introduced bimetallic NiCo cocatalysts possessing the superior electron transfer property and reducing the onset over-potential of water reduction, which was proved by experiment. This study can provide a potential strategy to design a more efficient noble metal-free cocatalyst over photocatalyst.     

Boosting hydrogen evolution under simulated sunlight via constructing close electron transfer interface between 1D CdxZn1-xS nanorod and 2D MoS2@MoOy nanosheet

Designing an efficient non-noble metal photocatalyst, which utilizes solar energy, has great potential to produce clean energy hydrogen. The microstructural refinement of 1D Cd_0.2Zn_0.8S nanorod was induced by doping with 2D MoS₂@MoO_y layer during microwave hydrothermal treatment. The maximum H₂ production rate of the composite prepared at optimum conditions was 186 mmol g⁻¹ h⁻¹, which increased by 34.8% compared with that of Cd_0.2Zn_0.8S (138 mmol g⁻¹ h⁻¹). The apparent quantum yields of the optimized composite were 10.3% and 15.6% at 365 and 420 nm, respectively. The tight S-scheme heterojunction contributed to the separation of photogenerated electron-hole pairs effectively, as confirmed by the characterization analysis of ·OH and ·O⁻₂ radicals, surface potential under illumination and darkness and in situ XPS spectra. Moreover, the active species of sulfur coordinated-Mo⁵⁺ as low-coordinate center promoted the dissociation of water and decreased the over potential of H₂ production. Furthermore, the optimal composite showed excellent stable catalytic activity for hydrogen evolution, and the H₂ production rate was 176.7 mmol g⁻¹ h⁻¹ after five cycles (95% of the first cycle). Overall, this work provides a promising strategy for improving the effectiveness of H₂ production by preparing non-noble metal composite photocatalysts.     

A 3D peony-like sulfur-doped carbon nitride synthesized by self-assembly for efficient photocatalytic hydrogen production

Photocatalytic hydrogen evolution reaction (HER) provides a new way for the development of clean energy. Herein, a high-performance peony-like 3D structure S-doped carbon nitride (SCNx) with a large specific surface area was synthesized through a universal and non-thermal polymerization template-free approach. As an additional component, the introduction of trithiocyanuric acid in the raw material led to the formation of supramolecular intermediates through hydrogen bond self-assembly, and the sulfur was introduced into the framework of g-C₃N₄ subsequently. The charge separation lifetime of SCNx was studied by transient absorption spectroscopy, and the reason for its excellent optical performance was revealed from a dynamic perspective. Furthermore, the resulting SCNx composite material shows significant photocatalytic hydrogen release performance under visible light irradiation. In particular, the photocatalytic hydrogen rate of SCN1.0 reached 567.7 μmol/h, which was almost 53 times that of BCN, and was also 2.3 times that of SCN0 obtained by the binary self-assembly of melamine and cyanuric acid. Our finding advances the application of simple, environmentally friendly, and scalable strategy for the synthesis of high-performance sulfur-doped g-C₃N₄ photocatalysts.     

Structure-mechanism relationship for enhancing photocatalytic H2 production

Clean and renewable energy plays important role in achieving carbon neutrality and nature sustainability, especially the application of green hydrogen in new energy system. Hydrogen (H₂) produced from visible light has attracted attention owing to its high conversion efficiency and cleaner process. In this review, different photocatalyst preparation methods which can directly design the same structure were clarified. Also, different mechanism design which can realize different electron transfers were also proposed. Thus, various morphologies and different mechanisms of electron transfer have been summarized and evaluated. Also, the methods of photocatalysts’ construction were mentioned, all H₂ production reactions depend on the amount of reaction sites and photo-generate electrons. It was evident that the concentration of reaction sites and photo-generate electrons play important roles in efficient H₂ production. This review provides fundamental knowledge to design and construct variable morphologies with different electron transfer processes to enhance efficiency of H₂ production.     

Bridging-nitrogen defects modified graphitic carbon nitride nanosheet for boosted photocatalytic hydrogen production

Reinforcing the visible photon absorption and charge separation are the key issues to maximize the photocatalytic performance of graphitic carbon nitride. Herein, holey bridging-nitrogen-defected graphitic carbon nitride nanosheets were prepared through solid-state copolymerization and subsequently thermal annealing with melamine and hexamethylenetetramine as the precursors. Numerous pores and bridging nitrogen defects that embedded into the thin-layer framework were evidenced through comprehensive characterization. The synthesized textural and electronic structure enables the significant improvement of photocatalytic hydrogen production, with the optimized sample of D-CNNS(0.3) representing a hydrogen evolution rate of 2497.1 μmol?g^?1?h^?1 under visible light irradiation (λ > 420 nm). This is about 10.4 and 41.1 folds improvement compared with pristine nanosheets and bulk carbon nitride, respectively. Both experimental and theoretical results demonstrate the bridging nitrogen defects are beneficial to enhance photoabsorption, promote charge separation and transfer. Together with the enlarged surface area, the optimized nanosheet sample shows a dramatically improved quantum yield in visible region.     

Well-dispersed CoSx nanoparticles modified tubular sulfur doped carbon nitride for enhanced photocatalytic H2 production activity

Appropriate dispersion of cocatalyst on semiconductor for improving photocatalytic H₂ production efficiency is a challenging work in semiconductor photocatalysis. Herein, we constructed the noble-metal-free CoS_x modified tubular sulfur doped carbon nitride (SCN) photocatalysts by chemical precipitation process. The amorphous CoS_x well dispersed on SCN served as H₂ production sites, which reduced the overpotential and inhibited the recombination of photogenerated carriers by interfacial charge transfer. Maximized H₂ production rate of 573.06 μmol g⁻¹ h⁻¹ under visible light irradiation was obtained by optimizing the CoS_x loading proportion to 2.4%, which was higher than that of 0.75 wt% Pt/SCN. In addition, a possible mechanism for improved H₂ production activity was proposed based on the experiments and discussion. This work provides a new strategy to design rational structure of non-noble metal cocatalyst modified photocatalyst to further improve H₂ production performance.     

Heterostructure based on exfoliated graphitic carbon nitride coated by porous carbon for photocatalytic H2 evolution

In this contribution, the heterostructure based on exfoliated graphitic carbon nitride (ex-gCN) coated by a porous carbon layer was fabricated by a simple approach and tested as a photocatalyst for hydrogen evolution under simulated solar light illumination. Bulk-gCN was firstly exfoliated and annealed under a hydrogen atmosphere in carefully selected conditions. The catalyst with the highest photoactivity was fabricated at 400 °C for 4 h. This material exhibited about a 23-fold higher amount of photogenerated hydrogen (18.2 μmol/g) compared to reference ex-gCN (0.8 μmol/g). Boosted photoactivity could be attributed to the (i) highly developed Specific Surface Area leading to more active sites on the surface due to the porous carbon layer, (ii) better transfer, and separation of photogenerated carriers, and (iii) sufficient suppression of the recombination process. Moreover, the mechanism of photocatalytic H₂ evolution from water splitting based on a full physicochemical characterization of the studied materials was proposed.     

Ag decorated ZnO for enhanced photocatalytic H2 generation and pollutant degradation

In this study, Ag/ZnO photocatalyst is synthesized in ethylene glycol (EG) medium using a one-pot hydrothermal method, where EG serves as both a reaction medium for the synthesis and a reduction medium for silver. Standard analytical techniques such as XRD, XPS, SEM-EDX, TEM, HR-TEM FTIR, BET, and UV–Vis spectroscopy are used to characterize the synthesized samples. The XRD and HR-TEM results show that Ag has been decorated on the ZnO photocatalyst. The results show that spherical Ag/ZnO has the highest photocatalytic activity for H₂ evolution (30.1 μmol h⁻¹) and RhB degradation. The increased photocatalytic activity can be attributed to the formation of the Schottky barrier at the heterojunction interface of metal-semiconductor and the plasmonic resonance effect of silver, which results in efficient separation and transportation of photo-induced charge carriers. This research could open up new avenues for the development of advanced ZnO-based visible light photocatalytic materials to address energy and environmental challenges.     

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 H1 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.     

Improved H2 production of ZnO@ZnS nanorod-decorated Ni foam immobilized photocatalysts

ZnO@ZnS nanorod-decorated Ni foam was prepared as a self-supported photocatalyst for hydrogen generation through a two-step method, including the formation of the ZnO nanorod core by a hydrothermal method, and the fabrication of the ZnS shell by a sulfidation method. The impact of the ZnS shell thickness was studied, including the influence on the optical properties, surface wettability, separation of photoexcited charge carriers, and photocatalytic hydrogen generation performance. Formation of the core-shell ZnO@ZnS structure and the incorporation of the conductive Ni foam substrate can enhance the separation of photoexcited carriers of the immobilized photocatalyst. The formation of ZnO@ZnS nanorods on the Ni foam resulted in a change in the surface from hydrophobic to superhydrophilic. The porous texture of the Ni foam facilitates the effective contact between the sacrificial agent and the immobilized photocatalyst. The ZnO@ZnS/Ni foam photocatalyst that was synthesized using a sulfidation time of 4 h, (namely, NZS4), exhibited H₂ generation activity of 5860 μmol g^?1 h^?1, which is approximately three-fold that of the ZnO/Ni foam photocatalyst (named NZ). After being reused for three cycles, with a simple washing between cycles, the NZS4 photocatalyst retained 90% of its hydrogen generation activity.     

Giant enhancement of photocatalytic H2 production over KNbO3 photocatalyst obtained via carbon doping and MoS2 decoration

This paper was designed for the first time to improve the photocatalytic activity of KNbO₃ via carbon doping and MoS₂ decoration simultaneously. The efficient photocatalytic hydrogen production was realized on the MoS₂/C-KNbO₃ composite under simulated sunlight irradiation in the present of methanol and chloroplatinic acid. The optimal composite presents a H₂ production rate of 1300  μmol·g^?1·h^?1, which reaches 260 times that of pure KNbO₃. Characterization results of the synthesized composite indicates that the introduction of a small amount of carbon into the KNbO₃ lattice greatly hinders the recombination of electron-hole pairs. The decoration of MoS₂ further induces the separation of charge carriers via trapping the electron in the conduction band of C-KNbO₃, which is proven by the EIS and transient photocurrent response analyses. The remarkably enhanced separation efficiency of electron-hole pairs is believed to be the origin of the excellent photocatalytic performance, though other changes in surface area and optical property may also contribute the photocatalytic process. This study provides a feasible way for the design and preparation of novel photocatalysts with high efficiency.     

Organosilica-assisted superhydrophilic oxygen doped graphitic carbon nitride for improved photocatalytic H2 evolution

The regulation of surface wettability and heteroelement doping have been proved to be effective strategies to enhance photocatalytic H₂ evolution activity of graphitic carbon nitride (CN) based photocatalysts. Herein, we report, for the first time, an organosilica assisted method was adopted to synthesize the superhydrophilic oxygen doped graphitic carbon nitride (O–CN). The presence of organosilica induced simultaneous oxygen-containing groups grafting and oxygen doping within carbon nitride substrate. The grafted oxygen-containing groups improved the surface hydrophilicity and water adsorption. Oxygen doping tailored electronic structure and localized electron distribution, contributing to extended visible light harvesting and elevated photoelectric conversion efficiency. As a result, the H₂ generation rate of O–CN photocatalyst was 5.4 times higher than that of pristine CN photocatalyst attributed to the formation of hydrophilic groups and the oxygen doping.     

Mesoporous carbon/graphitic carbon nitride spheres for photocatalytic H2 evolution under solar light irradiation

Herein, two different photocatalytic composites based on ordered (OCS) and disordered (DCS) mesoporous hollow carbon spheres and graphitic carbon nitride (gCN) have been successfully fabricated through facile acid treatment. The influence of carbon shell morphology of the spheres on gCN loading and photocatalytic H₂ production under simulated solar light irradiation has been revealed. The amount of evolved H₂ was ~6.2 (OCS/gCN) and ~5.3 (DCS/gCN) times higher in comparison to pristine gCN. It was found that graphitic carbon nitride was much more homogenously supported onto ordered mesoporous carbon spheres than disordered ones. The deposition of gCN onto ordered carbon spheres was found to be more efficient to increase carrier concentration, enhance photogenerated charge carrier transport and separation. It is assigned to the formation of the graphitic carbon nitride/carbon heterojunction facilitating the contact surface between the two phases of hybrid. Therefore, via tuning of the morphology of carbon shell being a host for gCN it was possible to find more promising candidate as a photocatalyst in H₂ production under solar light irradiation.     

Optimal Ni loading towards efficient CH4 production from H2 and CO2 over Ni supported onto fibrous SBA-15

The transformation of SBA-15 into fibrous type SBA-15 (F-SBA-15) as well as the influence of Ni loadings (1, 3, 5, and 10 wt%) towards an efficient CH₄ production from H₂ and CO₂ were explored. The synthesized catalysts were characterized using XRD, BET, ICP-MS, FTIR, FESEM-EDX, TEM, and in-situ FTIR adsorbed pyrrole. Increasing Ni loadings onto F-SBA-15 support promoted excellent performance towards CO₂ methanation. The efficacy in CO₂ methanation over Ni/F-SBA-15 increased with a sequence of 1%Ni/F-SBA-15 < 3%Ni/F-SBA-15 < 5%Ni/F-SBA-15 ≈ 10%Ni/F-SBA-15, indicating the superior performance and stability of 5%Ni/F-SBA-15. The increasing trend was due to the fibrous morphology of support which enhanced the quantity of SiONi bond, triggered better Ni dispersion, strengthen metal-support interaction, and increased the basicity. However, higher Ni loadings (10 wt%) onto F-SBA-15 slightly declined the performance and stability of CO₂ methanation due to the limited spaces for substitution of Ni species with the silanol groups of F-SBA-15 upon the bulk Ni phase, poorer Ni dispersion, weaker metal-support interaction, and lower basicity. The new finding of combination between fibrous SBA-15 (F-SBA-15) with an optimum Ni loading contributed towards an outstanding performance and thus could be applied in various applications.     

Enhancement in photocatalytic H2 evolution utilizing the synergistic effect between dual cocatalysts and heterojunctions

Expediting electrons-holes separation and surface reaction kinetics is deemed to be pivotal factor to determine the photocatalytic performance. Decoration of reductive and oxidative cocatalysts on semiconductors is a resultful approach for motivating electrons-holes separation and surface reaction kinetics. In this work, a ternary 2.4%-(CoSe₂@NiS-1)/CdS photocatalyst was developed. Among this compound, reductive cocatalyst CoSe₂ not only acted as electron trapping center by extracting photogenerated electrons, but also constructed Schottky junction with CdS to accelerate migration of photogenerated carriers and inhibit the backflow. Meanwhile, oxidative cocatalyst NiS forming p-n type heterojunction with CdS served as hole-trap center to boost transport and consumption of photoinduced holes. Integrating of dual cocatalysts and heterojunctions played synergistic effect in promoting the photocatalytic performance and photo-corrosion stability. 2.4%-(CoSe₂@NiS-1)/CdS achieved H₂ evolution of 1413.9 μmol and maintained at 85.47% after six cycles. It's expected that this work can provide an insight into designing high active solar energy conversion system.     

Efficient photocatalytic hydrogen production by doped ZnS grown on Ni foam as porous immobilized photocatalysts

Ni-doped ZnS nanomaterials were decorated on the surfaces of porous Ni foam as immobilized photocatalysts for H₂ production by a solvothermal process. Effects of the Ni dopant content on the photocatalytic hydrogen production activity, morphology, optical property, crystalline properties, surface wetting, and photocurrent were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), photocurrent response, and contact angle meter. The surface changed from hydrophobic to superhydrophilic by decorating Ni-doped ZnS on the NiO/Ni foam substrate. A mechanism is proposed to elucidate the band positions of ZnS and NiO, together with the transfer of photoinduced electrons among ZnS, NiO, and Ni foam. The Ni-doped ZnS/NiO/Ni foam photocatalyst NZ5 showed much higher photocatalytic activity because of the matched band structure and the high conductivity of Ni foam. Meanwhile, the porous texture and superhydrophilic nature of the photocatalyst favor the light trapping, effective mass transfer of reactant molecules, and provide large contact area. Ni doping leads to a decreased band gap. The highest photocatalytic H₂ generation activity reached 2500 μmol/g⁻¹ h⁻¹. After being operated for 3 cycles, the activity of the third run was 85% of that obtained at the first run.     

Metal-organic framework derived Ni/Mo2C/Mo2TiC2Tx@NC as an efficient electrocatalyst for enhanced hydrogen production

Metal-organic framework's (MOF) shortcomings, such as poor conductivity, poor stability, and easy aggregation, impede its development in various application fields. Ni/Mo₂C/Mo₂TiC₂T_x@NC, a high-performance electrocatalyst for hydrogen evolution reaction, was prepared by incorporating a Mo₂TiC₂T_x MXene conductive matrix into MOF (namely C–Y). The Ni/Mo₂C/Mo₂TiC₂T_x@NC electrocatalyst demonstrates a remarkable HER ability with an overpotential of 105 and 134 mV and Tafel slope of 58 and 75 mV dec⁻¹ at a current density of 10 mA cm⁻² in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. The outperformed HER activity of Ni/Mo₂C/Mo₂TiC₂T_x@NC catalyst is ascribe to the introduction of conductive Mo₂TiC₂T_x MXene as a carrier to improve the poor conductivity of MOF, the synergistic effect of Ni and Mo₂C nanoparticles, and the protective effect of the carbon layer. The work not only provides an experimental approach to address the problem of poor conductivity of MOF, but also provides a high-performance electrocatalyst for HER reactions. By utilizing MOFs and MXene as the precursor and the conducting carrier, our work provides some experimental reference for fabrication of multi-component inexpensive electrocatalysts.     

Mixed-valence molybdenum ion incorporated graphitic carbon nitride with high photocatalytic H2 evolution activity

The graphitic carbon nitride (CN) incorporated with mixed-valence molybdenum ion has been prepared via in-situ copolymerization to improve the photocatalytic H₂ evolution performance. The introduced Mo species existed in mixed valence of Mo⁴⁺ and Mo²⁺ state and its content could be tuned by simply adjusting amount of added MoCl₅ in the preparation procedure. The incorporated mixed-valence Mo ions contributed to narrowed band gap, increased electron density and elevated electron motion kinetics, resulting in extended visible light response, promoted separation and transportation of photoexcited charge carriers. The obtained CN–Mo photocatalyst with an optimal content of Mo ions (0.41 wt%) exhibited a robust H₂ production activity up to 1.44 mmol h⁻¹ g⁻¹, 18 times higher than that of pristine counterpart.     

Synergistic catalytic effect of SrTiO3 and Ni on the hydrogen storage properties of MgH2

Study on the synergistic catalytic effect of the SrTiO₃ and Ni on the improvement of the hydrogen storage properties of the MgH₂ system has been carried out. The composites have been prepared using ball milling method and comparisons on the hydrogen storage properties of the MgH₂ – Ni and MgH₂ – SrTiO₃ composites have been presented. The MgH₂ – 10 wt% SrTiO₃ – 5 wt% Ni composite is found to has a decomposition temperature of 260 °C with a total decomposition capacity of 6 wt% of hydrogen. The composite is able to absorb 6.1 wt% of hydrogen in 1.3 min (320 °C, 27 atm of hydrogen). At 150 °C, the composite is able to absorb 2.9 wt% of hydrogen in 10 min under the pressure of 27 atm of hydrogen. The composite has successfully released 6.1 wt% of hydrogen in 13.1 min with a total dehydrogenation of 6.6 wt% of hydrogen (320 °C). The apparent activation energy, E_a, for decomposition of SrTiO₃-doped MgH₂ reduced from 109.0 kJ/mol to 98.6 kJ/mol after the addition of 5 wt% Ni. The formation of Mg₂Ni and Mg₂NiH₄ as the active species help to boost the performance of the hydrogen storage properties of the MgH₂ system. Observation of the scanning electron microscopy images suggested the catalytic role of the SrTiO₃ additive is based on the modification of composite microstructure.     

The 2D RGO-NiS2 dual co-catalyst synergistic modified g-C3N4 aerogel towards enhanced photocatalytic hydrogen production

The two-dimension RGO (reduced graphene oxide)-NiS₂ dual co-catalyst synergistic modified g-C₃N₄ nanosheets aerogel is synthesized via the continuous thermal oxidation etching-hydrothermal method-freeze drying process. The results of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) imply that the RGO-NiS₂ dual co-catalyst is introduced into the aerogel system successfully. The photocatalytic activity of the RGO-NiS₂ synergistic modified g-C₃N₄ aerogel remarkably exhibits an enhancement of 67 times than that of simplicial g-C₃N₄. Further, the photocatalytic process and the mechanism of the photocatalytic hydrogen production enhancement are studied, which is ascribed to RGO-NiS₂ dual co-catalyst synergistic modification, including the Pt-like behavior of the NiS₂ and the high conductivity and large specific surface area of the RGO.