Composition dependent activity of Fe1−xPtx decorated ZnCdS nanocrystals for photocatalytic hydrogen evolution

In this work, ZnCdS nanoparticles (NPs) were decorated with FePt alloy, forming nanocomposites via ethylene glycol reduction method. The photocatalytic H₂ production of the Fe_1?xPt_x–ZnCdS NPs was studied by changing the composition and weight percentage of Fe_1?xPt_x alloy in the nanocomposites under visible light (λ ≥ 420 nm) irradiation. The results showed that the hydrogen production rate of Fe_1?xPt_x–ZnCdS NPs had a significant enhancement over the pure ZnCdS (740 μmol g^?1 h^?1). The activity of the nanocomposites was dependent on the composition of Fe_1?xPt_x alloy and the highest hydrogen production rate of 2265 μmol g^?1 h^?1 was achieved by the 0.5 wt% Fe_0.3Pt_0.7–ZnCdS nanocomposites, which was even better than that of 0.5 wt% Pt–ZnCdS (1626 μmol g^?1 h^?1) under the same condition. This study highlights the significance of Pt base alloys as new cocatalysts for the development of novel composite photocatalysts.     

Monodisperse PtCu alloy nanoparticles as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Pt-M alloy nanoparticles (NPs) with well-defined size and compositions exhibit dramatically catalytic performance in chemical reactions. In this work, monodisperse PtCu NPs with controlled size and compositions were synthesized by the co-reduction method in the presence of oleylamine. These NPs have excellent catalytic activities in the hydrolytic dehydrogenation of ammonia borane (AB) and their activities were composition dependent. Among the different-composition PtCu NPs, the Cu₅₀Pt₅₀ NPs exhibit the highest catalytic activity with an initial turnover frequency of 102.5 mol_(hydrogen)·mol_(catalyst)^?1·min^?1 and an apparent activation energy of 36 kJ·mol^?1, which demonstrate the validity of partly replacing Pt by a first-row transition metal on constructing high performance heterogeneous nanocatalysts for the hydrolytic dehydrogenation of AB.     

Electrospun Pt/TiO2 hybrid nanofibers for visible-light-driven H2 evolution

One-dimensional (1D) Pt/TiO₂ hybrid nanofibers (HNFs) with different concentrations of Pt were fabricated by a facile two-step synthesis route combining an electrospinning technique and calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) results showed that the Pt nanoparticles (NPs) with the size of 5–10 nm were well dispersed in the TiO₂ nanofibers (NFs). Further investigations from the UV–Vis diffuse reflectance (DR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that some Pt ions were incorporated into the TiO₂ lattice as Pt⁴⁺ state, which contributed to the visible light absorption of TiO₂ NFs. Meanwhile, the Pt²⁺ ions existing on the surface of Pt NPs resulted in the formation of Pt–O–Ti bond at Pt NPs/TiO₂ NFs interfaces that might serve as an effective channel for improving the charge transfer. The as-electrospun Pt/TiO₂ HNFs exhibited remarkable activities for photocatalytic H₂ evolution under visible light irradiation in the presence of l-ascorbic acid as the sacrificial agent. In particular, the optimal HNFs containing 1.0 at% Pt showed the H₂ evolution rate of 2.91 μmol h⁻¹ and apparent quantum efficiency of 0.04% at 420 nm by using only 5 mg of photocatalysts. The higher photocatalytic activity could be ascribed to the appropriate amount of Pt ions doping and excellent electron-sink effect of Pt NPs co-catalysts.     

An effective electrocatalyst based on platinum nanoparticles supported with graphene nanoplatelets and carbon black hybrid for PEM fuel cells

A facile synthesis at room temperature and at solid-state directly on the support yielded small, homogeneous and well-dispersed Pt nanoparticles (NPs) on CB-carbon black, GNP-graphene nanoplatelets, and CB-GNP-50:50 hybrid support. Synthesized Pt/CB, Pt/GNP and Pt/CB:GNP NPs were used as electrocatalysts for polymer electrolyte membrane fuel cell (PEMFC) reactions. HRTEM results displayed very small, homogeneous and well-dispersed NPs with 1.7, 2.0 and 4.2 nm mean-diameters for the Pt/CB-GNP, Pt/GNP and Pt/CB electrocatalysts, respectively. Electrocatalysts were also characterized by RAMAN, XRD, BET and CV techniques. ECSA values indicated better activity for graphene-based supports with 19 m² g⁻¹_Pt for Pt/GNP and 55 m² g⁻¹_Pt for Pt/CB-GNP compared to 10 m² g⁻¹_Pt for Pt/CB. Oxygen reduction reaction (ORR) studies and fuel cell tests were in parallel with these results where highest maximum power density of 377 mW cm⁻² was achieved with Pt/CB-GNP hybrid electrocatalyst. Both fuel cell and ORR studies for Pt/CB-GNP indicated better dispersion of NPs on the support and efficient fuel cell performance that is believed to be due to the prevention of restacking of GNP by CB. To the best of our knowledge, Pt/GNP and Pt/CB-GNP electrocatalysts are the first in literature to be synthesized with the organometallic mild synthesis method using Pt(dba)₃ precursor for the PEMFC applications.     

Lattice-strained Pt nanoparticles anchored on petroleum vacuum residue derived N-doped porous carbon as highly active and durable cathode catalysts for PEMFCs

High cost and poor durability of Pt-based cathode catalysts for oxygen reduction reaction (ORR) severely hamper the popularization of proton exchange membrane fuel cells (PEMFCs). Tailoring carbon support is one of effective strategies for improving the performance of Pt-based catalysts. Herein, petroleum vacuum residue was used as carbon source, and nitrogen-doped porous carbon (N-PPC) was synthesized using a simple template-assisted and secondary calcination method. Small Pt nanoparticles (Pt NPs) with an average particles size of 1.8 nm were in-situ prepared and spread evenly on the N-PPC. Interestingly, the lattice compression (1.08%) of Pt NPs on the N-PPC (Pt/N-PPC) was clearly observed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), which was also verified by the shift of (111) crystal plane of Pt on N-PPC to higher angles. The X-ray photoelectron spectroscopy (XPS) results suggest that the N-PPC support had a strong effect on anchoring Pt NPs and endowing surface Pt NPs with lowered d band center. Thus, the Pt/N-PPC as a catalyst simultaneously boosted the ORR activity and durability. The specific activity (SA) and mass activity (MA) of the Pt/N-PPC at 0.9 V reached 0.83 mA cm⁻² and 0.37 A mg_Pt⁻¹, respectively, much higher than those of the commercial Pt/C (0.21 mA cm⁻² and 0.11 A mg_Pt⁻¹) in 0.1 M HClO₄. The half-wave potential (E_1/2) of Pt/N-PPC exhibited only a minimal negative shift of 7 mV after 30,000 accelerated durability tests (ADT) cycles. More importantly, an H₂–O₂ fuel cell with a Pt/N-PPC cathode achieved a power density of 866 mW cm⁻², demonstrating that the prepared catalyst has a promising application potential in working environment of PEMFCs.     

Pt stabilization on Pt/SBA-15 through surface modification using MPTMS for sulfuric acid decomposition in SI cycle to produce hydrogen

Catalysts for the sulfuric acid (SA) decomposition, one of three reactions in Sulfur–Iodine (SI) cycle to produce hydrogen, should be active and stable in wide temperature ranges of 650–850 °C. Pt based catalysts are explored for SA decomposition, but they suffered from the severe Pt loss at the high temperature of 850 °C. Uniform platinum nanoparticles (NPs) are physically trapped within mesopores of the mesoporous SBA-15 prepared in a “one pot” method (Pt_x.x-NTS, x.x: loaded Pt wt%). Other Pt catalysts are prepared to stabilize Pt particles using 3-mercaptopropyletrimethoxysilane (MPTMS) as a stabilizing agent (Pt_x.x-TS, x.x: loaded Pt wt%). The co-assembly method in the one pot is based on the I⁺M^–S⁺ scheme in which S⁺ (Protonated block copolymer) and I⁺ (Cationic inorganic precursor) are assembled together through the M^– (PtCl₆^-) mediator. The MPTMS containing thiol group is used to modify the cationic precursors (I⁺) in order to hold the Pt nanoparticles in meso-channels as the reduced platinum metal is easy to bond with thiol groups. The prepared samples are characterized by XRD, TEM, CO Chemisorption, N₂ adsorption desorption, and ICP-OES techniques. The TEM images show that the small Pt NPs of an average size of 7.0 (±0.84 nm) are uniformly dispersed within the mesopores on the mesoporous SBA-15. The thiol stabilized Pt-TS catalysts display the exceptional catalytic stability for sulfuric acid decomposition at the high temperature of 850 °C for 50 h. The overall average metal loss is 67% for the Pt_2.0-NTS for 50 h at 76,000 mL.g_cat⁻¹.h⁻¹, while it is 16% for the Pt_2.0-TS. The metal loss of Pt/SBA-15 is significantly suppressed by the surface functionalization using MPTMS in the catalyst preparation step.     

Facile construction of 3D hyperbranched PtRh nanoassemblies: A bifunctional electrocatalyst for hydrogen evolution and polyhydric alcohol oxidation reactions

Development of highly effective and stable electrocatalysts is urgent for various energy conversion applications. Herein, a facile co-reduction approach was developed to fabricate three-dimensional (3D) hyperbranched PtRh nanoassemblies (NAs) under solvothermal conditions, where creatinine and cetyltrimethylammonium chloride (CTAC) were employed as the structure-directing agents. The as-synthesized nanocatalyst exhibited intriguing catalytic characters for hydrogen evolution reduction (HER) with a low overpotential (20 mV) at 10 mA cm⁻² and a small Tafel slope (49.01 mV dec⁻¹). Meanwhile, the catalyst showed remarkably enlarged mass activity (MA: 2.16/2.02 A mg⁻¹) and specific activity (SA: 4.16/3.88 mA cm⁻²) towards ethylene glycol and glycerol oxidation reactions (EGOR and GOR) alternative to commercial Pt black and homemade Pt₃Rh nanodendrites (NDs), PtRh₃ NDs and Pt nanoparticles (NPs). This method offers a feasible platform to fabricate bifunctional, efficient, durable and cost-effective nanocatalysts with finely engineered structures and morphologies for renewable energy devices.     

Binary CuPt alloy nanoparticles assembled on reduced graphene oxide-carbon black hybrid as efficient and cost-effective electrocatalyst for PEMFC

Addressed herein is the synthesis of binary CuPt alloy nanoparticles (NPs), their assembly on reduced graphene oxide (rGO), Vulcan XC72 (VC) and their hybrid (rGO-VC) to be utilized as electrocatalysts for fuel cell reactions (HOR and ORR) in acidic medium and PEMFC tests. The synthesis of nearly-monodisperse Cu₄₅Pt₅₅ alloy NPs was achieved by using a chemical reduction route comprising the reduction of commercially available metal precursors in a hot surfactant solution. As-synthesized Cu₄₅Pt₅₅ alloy NPs were then assembled on three support materials, namely rGO, VC and rGO-VC) via liquid phase self-assembly method. After the characterization, the electrocatalysts were prepared by mixing the yielded materials with Nafion and their electrocatalysis performance was investigated by studying CV and LSV for HOR and ORR in acidic medium. Among the three electrocatalysts tested, Cu₄₅Pt₅₅/rGO-VC hybrid showed the highest catalytic activity with ECSA of 119 m² g⁻¹ and mass activity of 165 mA mg⁻¹_Pt. After the evaluation of electrochemical performance of the three prepared electrocatalysts, their performance was then evaluated in fuel cell conditions. In similar to electrochemical activities, the Cu₄₅Pt₅₅/rGO-VC hybrid electrocatalyst showed a superior fuel cell performance and power output by providing a maximum power of 480 mW cm⁻² with a relatively low Pt loading (0.28 mg cm⁻²). Additionally, the Cu₄₅Pt₅₅/rGO-VC hybrid electrocatalyst exhibited substantially better activity as compared to Pt/rGO-VC electrocatalyst. Therefore, the present study confirmed that alloying Pt with Cu enhances the catalytic activity of Pt metal along with the help of beneficial features of rGO-VC hybrid support material. It should be noted that this is the first example of studying PEMFC performance of CuPt alloy NPs supported on rGO, VC and rGO-VC hybrid.     

Effect of Pt loading on the hydrogen production of CNT/Pt composites functionalized with carboxylic groups

This work reports the morphological and photocatalytic hydrogen generation properties of CNT/Pt composites with and without functionalization by carboxylic/oxygen groups. The composites with and without functionalization were named f-CNT/Pt and CNT/Pt, respectively. Several f-CNT/Pt and CNT/Pt composites with different content of Pt NPs (from 0 to 30 wt%) were synthesized and analyzed by scanning electron microscopy (SEM). Those images revealed that the composites without functionalization presented higher agglomerations of Pt nanoparticles (NPs). Furthermore, the average sizes of the Pt NPs in the named f-CNT/Pt composites (2.3–2.9 nm) were lower than these in the CNT/Pt composites (2.5–3.1 nm). The hydrogen generation rates were also calculated from the decomposition of pure water under UV irradiation (365 nm) and found maximum values of 45.4 and 193.9 μmol·h⁻¹ g⁻¹ for the CNT/Pt and f-CNT/Pt composites (they contained 20 wt% of Pt NPs), respectively. Additional experiments for hydrogen generation were achieved using sodium sulfite as sacrificial agent; in this case, a maximum value of 13850 μmol·h⁻¹ g⁻¹ was obtained for the f-CNT/Pt composite. The f-CNT/Pt composites produced more hydrogen than the CNT/Pt composites because they presented higher content of defects; this was confirmed by the Raman spectra. We also showed that the Pt NPs acted as electron trap centers, which delayed the recombination of the photogenerated electrons and holes, this in turn, enhanced the hydrogen generation rates of the composites (the hydrogen generation was maximized by varying the content of Pt NPs deposited on the CNTs). The CNT/Pt composites presented here were simpler and easier to synthesize than the previous published ternary systems based on TiO₂, CNTs and Pt NPs.     

Bimetallic PtNi/g-C3N4 nanotubes with enhanced photocatalytic activity for H2 evolution under visible light irradiation

Bimetallic PtNi-decorated graphitic carbon nitride (g-C₃N₄) nanotubes were prepared through calcining the mixture of urea and thiourea in the presence of Pluronic F127, followed by deposition of bimetallic PtNi nanoparticles (NPs) via chemical reduction. It is found that the photocatalytic activity of PtNi/g-C₃N₄ nanotubes is strongly dependent on the molar ratio of Pt/Ni and the highest activity is observed for Pt₁Ni₁/g-C₃N₄. Under visible light (λ > 420 nm) irradiation, the H₂ generation rate over Pt₁Ni₁/g-C₃N₄ nanotubes is 104.7 μmol h^?1 from a triethanolamine (10 vol%) aqueous solution, which is higher than that of Pt/g-C₃N₄ nanotubes (98.6 μmol h^?1) and is about 47.6 times higher than that of pure g-C₃N₄ nanotubes. The cyclic photocatalytic reaction indicates that our Pt₁Ni₁/g-C₃N₄ nanotubes function as a stable photocatalyst for visible light-driven H₂ production. The effect of bimetallic PtNi NPs in the transfer and separation of photogenerated charge carriers occurring in the excited g-C₃N₄ nanotubes was investigated by performing photo-electrochemical and photoluminescence measurements. Our results reveal that bimetallic PtNi could replace Pt as a promising cocatalyst for photocatalytic H₂ evolution with better performance and lower cost.     

In situ synthesis of dendrimer-encapsulated palladium(0) nanoparticles as catalysts for hydrogen production from the methanolysis of ammonia borane

Addressed herein is the in situ synthesis of a PAMAM dendrimer-encapsulated palladium(0) NPs (Pd(0)/Dnd) during the methanolysis of ammonia borane (AB) and the catalytic performance of the yielded Pd(0)/Dnd nanocatalysts in hydrogen production from the methanolysis of AB under ambient conditions. A two-step procedure that includes the impregnation of Pd(II) ions via their coordination to –NH₂ groups of the dendrimer and then reduction of Pd(II) ions into the dendrimer-encapsulated Pd(0) NPs by AB during the methanolysis reaction was followed for the synthesis of Pd(0)/Dnd nanocatalysts. However, apart from the existing reports on the synthesis of dendrimer-encapsulated metal NPs, the present study includes for the first time the examination of effect of generation size (G4-G6), core type (ethylene diamine (E) or Jeffamine (P)) and terminal groups (-NH₂, –COOH and –OH) of a PAMAM dendrimer on the stability, particle size, morphology and catalytic activity of metal NPs. After finding the optimum Pd(0)/Dnd catalysts considering all these effects, a detailed kinetic study comprising the effect of catalyst and AB concentrations as well as temperature was conducted by monitoring the hydrogen production from the methanolysis of AB. The best catalytic activity in the methanolysis of AB was obtained by using a PAMAM dendrimer with generation G6, amine terminal groups and Jeffamine core (P6.NH₂) encapsulated Pd(0) NPs, providing the highest initial turnover frequency (TOF) of 55.8 mol H₂.mol Pd⁻¹.min⁻¹ and apparent activation energy (Ea^app) of 48 ± 3 kJ.mol⁻¹ at room temperature.     

Solution plasma method assisted with MOF for the synthesis of Pt@CoOx@N-C composite catalysts with enhanced methanol oxidation performance

The key to direct methanol fuel cells (DMFCs) is the anode catalyst for methanol oxidation reaction (MOR) which has good catalytic activity and stability. Pt@CoO_x@N-C catalysts were synthesized by compounding Pt nanoparticles and CoO_x with nitrogen-doped porous carbon (N-C). Pt nanoparticles were prepared by solution plasma technique. CoO_x@N-C are derived from zeolitic-imidazolate-framework-67 (ZIF-67) by heat treatment at 700 °C. For MOR, Pt@CoO_x@N-C exhibits an outstanding electrocatalytic performance (mass activity of 2400 mA mg_Pt⁻¹) and stability (70% remained after 300 cycles) under acidic condition, which owing to the synergistic effects among the Pt nanoparticles, CoO_x and nitrogen-doped porous carbon. Pt@CoO_x@N-C shows such mass activity superior to that of Pt/C (460 mA mg_Pt⁻¹) due to the fact that CoO can adsorb –OH in the solution and then assist Pt to oxidize the CO-like intermediates to CO₂ which improves the resistance to CO poisoning of Pt nanoparticles. Therefore, solution plasma method assisted with metal-organic frameworks have good development prospects on synthesis of highly efficient electrocatalysts.     

Effects of Pt3Ni alloy polyhedral and its de-alloying on CdS's performance in hydrogen evolution from water-splitting under visible light

In this paper, Pt₃Ni alloy polyhedral was synthesized through solvothermal method and loaded on the surface of CdS by photo-induced electrons. Under visible light irradiation, the photocatalytic activity for hydrogen evolution from solar water splitting was performed, Pt₃Ni/CdS showed the hydrogen evolution rate about 40.0 mmol/h/g (QE = 44.90%, λ = 420 nm), which was 1.8 times higher than that of Pt/CdS, indicating that Pt₃Ni NPs could effectively improve the hydrogen production activity of CdS. Next, the influence of de-alloyed Pt₃Ni NPs on the activity of CdS for water-splitting under visible light was investigated, the hydrogen evolution rate of de-alloyed Pt₃Ni NPs modified CdS was 46.1 mmol/h/g (QE = 52.70%, λ = 420 nm), which was 1.2 times as much as that of Pt₃Ni/CdS and 2.1 times as much as that of Pt/CdS, suggesting that de-alloyed Pt₃Ni NPs could further enhance the hydrogen production activity of CdS. In addition, the improved photocatalytic activity was mainly due to the surface unsaturation of Pt atoms in a metastable structure after de-alloying, which will expose more surface active sites of Pt, thus the fast electron hole charge transfer at the interface of CdS and de-alloyed Pt₃Ni NPs.     

PtxCo1−x alloy NPs prepared by colloidal tool-box synthesis: The effect of de-alloying on the oxygen reduction reaction activity

In the presented work we investigate the influence of de-alloying carbon supported Pt_xCo_1−x alloy nanoparticles (NPs) on their oxygen reduction reaction (ORR) activity. In our study we used a modification of a recently developed colloidal synthesis approach in order to prepare NPs of similar size, i.e. around 2 nm in diameter, but varying initial Pt:Co ratios. The results show that using a surfactant is favorable to control the initial Pt:Co ratio. The initial composition of the catalyst however is lost upon introduction into an acid environment, i.e. the well-known effect of chemical de-alloying occurs. Interestingly, despite the fact that due to de-alloying almost all Co is removed from the Pt_xCo_1−x NPs, a clear trend of increasing ORR activity with increasing initial Co content is observed. The results indicate that the process of chemical de-alloying is favorable for producing active ORR catalysts.     

Increased interface effects of PtFe alloy/CeO2/C with PtFe selective loading on CeO2 for superior performance in direct methanol fuel cell

Here, a simple two-step solvothermal approach has been employed to synthesize PtFe alloy (or Pt)/CeO₂/C with PtFe (or Pt) selective loading on CeO₂ nanoparticles. In addition, the selective loading of PtFe alloy or Pt nanoparticles on the surface of CeO₂ is achieved under weak alkaline environment, which is mainly attributed to the opposite electrostatic force between H⁺ enriched on the surface of CeO₂ particles and OH⁻ covered with carbon supporters. As-prepared PtFe alloy (or Pt)/CeO₂/C catalysts with two-stage loading structures show more excellent electro-catalytic efficiency for methanol oxidation as well as duration compared with commercial Pt/C and PtCeO₂/C with random loading structure. Further, single-cell assembly based on Pt₃Fe/CeO₂/C as the anode catalyst exhibits a maximum power density of 31.1 mW cm⁻², which is 1.95 times that of an analogous cell based on the commercial Pt/C. These improved performances with considerable low Pt content (<0.3 mg cm⁻²) are mainly ascribed to the abundant three phase interfaces (PtCeO₂ carbon) induced by the selective and efficient dispersion of Pt nanoparticles on ceria.     

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.     

Ag–Pt bimetallic composite supported on defective C3Nx nanosheets for plasmon hot electron-mediated photocatalytic H2 evolution

Combining the strong localized surface plasmon resonance (LSPR) of metallic Ag and the chemically reactive Pt co-catalyst, the Ag–Pt bimetallic composite was prepared and then coated on the surface of the exfoliated defective graphitic carbon nitride nanosheets (C₃N_x NS) for plasmon hot electron-mediated photocatalytic H₂ evolution. Under the visible light irradiation, the sample of (1:2) Ag–Pt/C₃N_x NS exhibits the highest activity (1.25 mmol g⁻¹ h⁻¹), which is 35.7 and 1.7 times higher than that of Ag/C₃N_x NS and Pt/C₃N_x NS, respectively. Moreover, the apparent quantum efficiency (AQE) of (1:2) Ag–Pt/C₃N_x NS reaches 3.3% at 420 nm. The boosted photocatalytic capacity may be ascribed to the utilization of the advantages of the LSPR effect of Ag particles and the Schottky barrier between Pt and C₃N_x NS, resulting in more electrons participate in the reduction reaction to boost the photocatalytic H₂ evolution performance.     

A novel pathway toward efficient improvement of the photocatalytic activity and stability of CdS-based photocatalyst for light driven H2 evolution: The synergistic effect between CdS and SrWO4

It has been a research hot spot how to efficiently heighten the photocatalytic activity and stability of CdS-based photocatalysts for H₂ evolution. Here, SrWO₄/CdS nanoparticles which contained CdS/SrWO₄ heterojunctions were prepared. Meanwhile, their photocatalytic performance and stability were investigated in detail for H₂ evolution. At last, the photocatalytic mechanism of the SrWO₄/CdS nanoparticles was discussed roughly. The results show that the photocatalytic performance of CdS can be heightened significantly due to introduction of SrWO₄. The fastest evolution rate of H₂ over the SrWO₄/CdS nanoparticles is 392.5 μmol g⁻¹ h⁻¹, which is 5.8 times as high as that over the pure CdS nanomaterial. More interestingly, the SrWO₄/CdS nanoparticles possess excellent stability. The evolution rate of H₂ over the photocatalyst used 10 times can be up to 473 μmol g⁻¹ h⁻¹, which is the same as that over the once used sample, even is 37% higher than that over of the fresh one. In contrast, after used five times, the photocatalytic activity of the pure CdS nanomaterial is only 57% of that of the fresh sample. This study will supply a new idea for the design and development of highly stable and efficient CdS-based photocatalysts for H₂ evolution in the future.     

PtxNi1−x nanoparticles as catalysts for hydrogen generation from hydrolysis of ammonia borane

We report on Pt_xNi_1−x (x = 0, 0.35, 0.44, 0.65, 0.75, and 0.93) nanoparticles as catalysts for hydrogen generation from hydrolysis of ammonia borane (NH₃BH₃). The Pt_xNi_1−x catalysts were prepared through a redox replacement reaction with a reverse microemulsion technique. The structure, morphology, and chemical composition of the obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) equipped with energy dispersive X-ray (EDX), and inductively coupled plasma emission spectroscopy (ICP). The results show that the diameters of the Pt_xNi_1−x nanoparticles are about 2–4 nm, and the Pt atomic contents in the catalysts were 35%, 44%, 65%, 75%, and 93%, respectively. It is found that the catalytic activity toward the hydrolysis of NH₃BH₃ is correlated with the composition of the Pt_xNi_1−x catalysts. The annealing of Pt_0.65Ni_0.35 at 300 °C for 1 h increases the crystallinity of the nanoparticles, but shows almost the same activity as that without annealing. Among the as-prepared Pt_xNi_1−x nanoparticles, Pt_0.65Ni_0.35 displays the highest catalytic performance, delivering a high hydrogen-release rate of 4784.7 mL min⁻¹ g⁻¹ and a low activation energy of 39.0 kJ mol⁻¹.     

Morphology effect of MnO2 promoter to the catalytic performance of Pt toward methanol electrooxidation reaction

Three MnO₂ samples with different well-defined morphologies including nanoplates, nanorods and corallines are prepared through a simple chemical precipitation method and used as the promoter/support for Pt electrocatalysts (denoted as Pt/MnO₂P, Pt/MnO₂-R and Pt/MnO₂C, respectively). The morphology effects of MnO₂ to the catalytic properties of Pt for methanol oxidation reaction (MOR) are intensively investigated. Results show that the catalytic properties of Pt are strongly dependent on the morphology of the promoter. Pt/MnO₂-R with MnO₂ nanorods as the promoter shows the highest catalytic properties among the MnO₂-promoted catalysts. The mass-specific activity and intrinsic activity of Pt in Pt/MnO₂-R catalyst is 0.51 A mg⁻¹_Pt and 11.54 A m⁻²_Pt, which is ca. 1.89 and 2.18 times that of commercial Pt/C catalysts (0.27 A mg⁻¹_Pt and 5.29 A m⁻²_Pt), respectively. Change in the electronic structure of Pt is responsible for the enhancement in the catalytic properties of Pt/MnO₂-R.