Improving hydrogen production via water splitting over Pt/TiO2/activated carbon nanocomposite

Mesoporous TiO₂/AC, Pt/TiO₂ and Pt/TiO₂/AC (AC = activated carbon) nanocomposites were synthesized by functionalizing the activated carbon using acid treatment and sol–gel method. Photochemical deposition method was used for Pt loading. The nano-photocatalysts were characterized using XRD, SEM, DRS, BET, FTIR, XPS, CHN and ICP methods. The hydrogen production, under UV light irradiation in an aqueous suspension containing methanol has been studied. The effect of Pt, methanol and activated carbon were investigated. The results show that the activated carbon and Pt together improve the hydrogen production via water splitting. Also methanol acts as a good hole scavenger. Mesoporous Pt/TiO₂/AC nanocomposite is the most efficient photocatalyst for hydrogen production compared to TiO₂/AC, Pt/TiO₂ and the commercial photocatalyst P25 under the same photoreaction conditions. Using Pt/TiO₂/AC, the rate of hydrogen production is 7490 μmol (h g catal.)⁻¹ that is about 75 times higher than that of the P25 photocatalyst.     

Pt modified TiO2 nanotubes electrode: Preparation and electrocatalytic application for methanol oxidation

Pt nanoparticles decorated TiO₂ nanotubes (Pt/TiO₂NTs) modified electrode has been successfully synthesized by depositing Pt in TiO₂NTs, which were prepared by anodization of the Ti foil. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties. The Pt/TiO₂NTs electrode shows excellent electrocatalytic activity toward methanol oxidation reaction (MOR) in alkaline electrolyte without UV irradiation.     

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.     

TiO2 nanosheets loaded with Cu: A low-cost efficient photocatalytic system for hydrogen evolution from water

Rutile TiO₂ nanosheets were prepared by a simple solvothermal process, and Cu was loaded on the surface of TiO₂ nanosheets using the in situ photo-deposition method. Meanwhile, photocatalytic H₂ evolution from water over the as-prepared TiO₂ nanosheets loaded with Cu was explored using methanol as a sacrificial reagent. The results indicate that the TiO₂ nanosheets loaded with Cu is an efficient photocatalyst under UV irradiation. During the first 5 h, a rate of H₂ evolution of approximately 22.1 mmol g⁻¹ h⁻¹ was achieved under optimal conditions. Furthermore, for practical purposes, the photocatalytic hydrogen evolution was studied as a function of content of Cu, pH of solution, concentration of methanol and dosage of photocatalyst, respectively. At last, the photocatalytic mechanism was preliminarily discussed.     

TiO2–CdS supported CuNi nanoparticles as a highly efficient catalyst for hydrolysis of ammonia borane under visible-light irradiation

TiO₂–CdS nanotubes (NTs) were used for the first time as a support to load metal nanoparticles (NPs) for the hydrolysis of ammonia borane (AB) which is a new strategy. The TiO₂–CdS NTs support was first synthesized using a hydrothermal method, and then the CuNi NPs were loaded using a liquid-phase reduction method. The synthesized samples were characterized by XRD, SEM-EDS, TEM, XPS, ICP, UV–Vis, and PL analyses. The characterization results show that the CuNi NPs existed in the form of an alloy with a size of ~1.2 nm and uniformly dispersed on the support. Compared with their single metal counterparts, the bimetallic CuNi-supported catalysts showed a higher catalytic activity in the hydrolysis of AB under visible-light irradiation: Cu_0·45Ni_0·55/TiO₂–CdS catalyst had the fastest hydrogen evolution rate with a high conversion frequency (TOF) of 25.9 mol_H2·mol_cat⁻¹ min⁻¹ at 25 °C and low activation energy of 32.8 kJ mol⁻¹. Cu_0.45Ni_0.55/TiO₂–CdS catalyst showed good recycle performance, maintaining 99.3% and 85.6% of the original hydrogen evolution rate even after five and ten recycles, respectively. Strong absorption of visible light, improved electron–hole separation efficiency, and metal synergy between Cu and Ni elements played a crucial role in improving the catalytic hydrolysis performance of AB. The catalyst prepared in this study provides a new strategy for the application of photocatalysts.     

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.     

Efficient photocatalytic hydrogen generation by Pt modified TiO2 nanotubes fabricated by rapid breakdown anodization

Photo-assisted hydrogen generation studies of platinum loaded titanium (IV) oxide nanotubes suspended in ethanol–water mixture were carried out at room temperature. The TiO₂ nanotubes synthesized by rapid breakdown anodization technique were loaded with Pt nanoparticles by chemical reduction of aqueous chloroplatinic acid solution using sodium borohydride. The chemisorption (active) surface area of the synthesized nanocomposites for hydrogen was measured by pulse chemisorption method using temperature programmed desorption reduction oxidation equipment and found to decrease with increase in platinum loading in the range 1–10 wt%. The platinum supported nanotube composites were characterized for phase and morphology by XRD, TEM and SEM. The hydrogen generated by the photocatalytic reduction of water from water–ethanol mixture at different wavelengths of incident light, using the Pt-TiO₂ nanocomposite photocatalyst, was determined by using a proton exchange membrane based hydrogen meter. The highest hydrogen generation efficiency was observed at 1–2.5 wt% of Pt loading. The maximum photocatalytic hydrogen generation of 0.03 mol/h/g of Pt-TiO₂ was observed with a 64 W UV light source (λ = 254 nm). The photoluminescence property of the Pt loaded TiO₂ has been correlated with the hydrogen generation efficiency and the reaction mechanism briefly discussed.     

Significant improvement of photocatalytic hydrogen generation rate over TiO2 with deposited CuO

TiO₂ photocatalyst with deposited CuO (CuO-TiO₂) was synthesized by the impregnation method using P25 (Degussa) as support, and exhibited high photocatalytic hydrogen generation activity from methanol/water solution. A substantial hydrogen evolution rate of 10.2 ml min⁻¹ (18,500 μmol h⁻¹ g⁻¹_catalyst) was observed over this efficient CuO-TiO₂ with optimal Cu content of 9.1 mol% from an aqueous solution containing 10 vol% methanol; this improved hydrogen generation rate is significantly higher than the reported Cu-containing TiO₂, including some Pt and Pd loaded TiO₂. Optimal Cu content of 9.1 mol% provided maximum active sites and allowed good light penetration in TiO₂. Over this efficient CuO-TiO₂, the hydrogen generation rate was accelerated by increasing the methanol concentration according to Freundlich adsorption isotherm. However, the photocatalytic hydrogen generation rate was suppressed under long time irradiation mainly due to accumulation of by-products, reduction of CuO and copper leaching, which requires further investigation.     

Preparation and photocatalytic properties of HLaNb2O7/(Pt,TiO2) perovskite intercalated nanomaterial

A novel perovskite intercalated nanomaterial HLaNb₂O₇/(Pt, TiO₂) is fabricated by successive intercalated reaction of HLaNb₂O₇ with [Pt(NH₃)₄]Cl₂ aqueous solution, n-C₆H₁₃NH₂/C₂H₅OH organic solution and acidic TiO₂ colloid solution, followed by ultraviolet light irradiation. The gallery height and the band gap energy of HLaNb₂O₇/(Pt, TiO₂) is less than 0.6 nm and 3.14 eV, respectively. The photocatalytic activity of HLaNb₂O₇/TiO₂ is superior to that of unsupported TiO₂ and is enhanced by the co-incorporation of Pt. The photocatalytic hydrogen evolution based on HLaNb₂O₇/(Pt, TiO₂) is 240 cm³ h⁻¹ g⁻¹ using methanol as a sacrificial agent under irradiation with wavelength more than 290 nm from a 100-W mercury lamp. High photocatalytic activity of HLaNb₂O₇/(Pt, TiO₂) may be due to the host with rare earth La element and perovskite structure, the quantum size effect of intercalated semiconductor and the coupling effect between host and guest.     

Photoelectrochemical water splitting on highly smooth and ordered TiO2 nanotube arrays for hydrogen generation

To improve the photoelectrochemical (PEC) water splitting efficiency for hydrogen production, we reported the fabrication of lotus-root-shaped, highly smooth and ordered TiO₂ nanotube arrays (TiO₂ NTs) by a simple and effective two-step anodization method. The TiO₂ NTs prepared in the two-step anodization process (2-step TiO₂ NTs) showed better surface smoothness and tube orderliness than those of TiO₂ NTs prepared in one-step anodization process (1-step TiO₂ NTs). Under illumination of 100 mW/cm² (AM 1.5, simulated solar light) in 1 M KOH solution, water was oxidized on the 2-step TiO₂ NTs electrode with higher efficiency (incident-photon-to-current efficiency of 43.4% at 360 nm and photocurrent density of 0.90 mA/cm² at 1.23 V_RHE) than that on the 1-step TiO₂ NTs electrode. The effective photon-to-hydrogen conversion efficiency was found to be 0.18% and 0.49% for 1-step TiO₂ NTs and 2-step TiO₂ NTs, respectively. These results suggested that the structural smoothness and orderliness of TiO₂ NTs played an important role in improving the PEC water splitting application for hydrogen generation.     

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.     

TiO2 nanotubes incorporated with CdS for photocatalytic hydrogen production from splitting water under visible light irradiation

The CdS/TiO₂ composites were synthesized using titanate nanotubes (TiO₂NTs) with different pore diameters as the precursor by simple ion change and followed by sulfurization process at a moderate temperature. Some of results obtained from XRD, TEM, BET, UV–vis and PL analysis confirmed that cadmium sulfide nanoparticles (CdSNPs) incorporated into the titanium dioxide nanotubes. The photocatalytic production of H₂ was remarkably enhanced when CdS nanoparticles was incorporated into TiO₂NTs. The apparent quantum yield for hydrogen production reached about 43.4% under visible light around λ = 420 nm. The high activity might be attributed to the following reasons: (1) the quantum size effect and homogeneous distribution of CdSNPs; (2) the synergetic effects between CdS particles and TiO₂NTs, viz., the potential gradient at the interface between CdSNPs and TiO₂NTs.     

Microwave assisted synthesis of silver nanoparticles and its application in sustainable photocatalytic hydrogen evolution

Large amounts of photocatalysts are needed for the generation of solar hydrogen (H₂) and eco-friendly synthetic alternatives are essential. Here, we use glycerol as solvent and reducing agent, and food grade corn starch as stabilizing agent for the preparation of silver nanoparticles (Ag NPs) by microwave irradiation. The Ag NPs were also synthesized using various proportions of glycerol/water mixtures. The Ag NPs were loaded onto commercial TiO₂ NPs to study the photogeneration of H₂. Characterization was carried out by UV–vis, XRD, TEM, UV–Vis DRS, and RBS. Stable Ag NPs after 320 days of aging with diameters from 2.9 to ~44 nm were prepared under several experimental conditions. Finally, TiO₂@AgNPs showed that the rate of evolved H₂ is stable, much higher than pure TiO₂ NPs and proportional to the amount of Ag NPs loaded. The present study introduces a new sustainable and eco-friendly strategy for designing low-cost photocatalysts for H₂ generation.     

A novel photoelectrochemical cell with self-organized TiO2 nanotubes as photoanodes for hydrogen generation

A photoelectrochemical (PEC) cell with an innovative design for hydrogen generation via photoelectrocatalytic water splitting is proposed and investigated. It consisted of a TiO₂ nanotube photoanode, a Pt/C cathode and a commercial asbestos diaphragm. The PEC could generate hydrogen under ultraviolet (UV) light-excitation with applied bias in KOH solution. The Ti mesh was used as the substrate to synthesize the self-organized TiO₂ nanotubular array layers. The effect of the morphology of the nanotubular array layers on the photovoltaic performances was investigated. When TiO₂ photocatalyst was irradiated with UV-excitation, it prompted the water splitting under applied bias (0.6 V vs. Normal Hydrogen Electrode, NHE.). Photocurrent generation of 0.58 mA/cm² under UV-light irradiation showed good performance on hydrogen production.     

Photocatalytic hydrogen production over CuO and TiO2 nanoparticles mixture

Cheap and efficient photocatalysts were fabricated by simply mixing TiO₂ nanoparticles (NPs) and CuO NPs. The two NPs combined with each other to form TiO₂/CuO mixture in an aqueous solution due to the opposite surface charge. The TiO₂/CuO mixture exhibited photocatalytic hydrogen production rate of up to 8.23 mmol h⁻¹ g⁻¹ under Xe lamp irradiation when the weight ratio of P25 to CuO was optimized to 10. Although the conduction band edge position of CuO NPs is more positive than normal hydrogen electrode, the TiO₂/CuO mixture exhibited good photocatalytic hydrogen production performance because of the inter-particle charge transfer between the two NPs. The detailed mechanism of the photocatalytic hydrogen production is discussed. This mixing method does not require a complicated chemical process and allows mass production of the photocatalysts.     

Enhancing hydrogen evolution of water splitting under solar spectra using Au/TiO2 heterojunction photocatalysts

An effective improvement of hydrogen evolution from water splitting under solar light irradiation was investigated using quantum dots (QDs) compounds loaded onto a Au/TiO₂ photocatalyst. First, Au/TiO₂ was prepared by the deposition-precipitation method, and then sulfide QDs were loaded onto the as-prepared Au/TiO₂ by a hydrothermal method. QDs were loaded onto Au/TiO₂ to enhance the energy capture of visible light and near-infrared light of the solar spectrum. The results indicated that the as-prepared heterojunction photocatalysts absorbed the energy from the range of ultraviolet light to the near-infrared light region and effectively reduced the electron-hole pair recombination during the photocatalytic reaction. Using a hydrothermal temperature of 120 °C, the as-prepared (ZnS–PbS)/Au/TiO₂ photocatalyst had a PbS QDs particle size of 5 nm, exhibited an energy gap of 0.92 eV, and demonstrated the best hydrogen production rate. Additionally, after adding 20 wt % methanol as a sacrificial reagent to photocatalyze for 5 h, the hydrogen production rate reached 5011 μmol g⁻¹ h⁻¹.     

Pt nanoparticles supported on titanium iron nitride nanotubes prepared as a superior electrocatalysts for methanol electrooxidation

Titanium iron nitride (Ti_0.95Fe_0.05N) supports with one-dimensional (1D) hollow and porous nanotubes(Ti_0.95Fe_0.05N NTs)are prepared by a two-step method, including hydrothermal method followed post-nitriding treatment. Pt nanoparticles (NPs) are further supported on Ti_0.95Fe_0.05N NTs for methanol electrooxidation. The experimental results reveal that the prepared material is Ti_0.95Fe_0.05N NTs with high purity, and this support is characterized by a porous tubular structure with hollow walls and large specific surface area. The X-ray photoelectron spectroscopy (XPS) pattern shows the strong interaction between the robust Ti_0.95Fe_0.05N NTs support and uniform Pt NPs catalyst. In addition, the electrochemical data demonstrate that Ti_0.95Fe_0.05N NTs loaded Pt NPs (Pt/Ti_0.95Fe_0.05N) display greatly improved activity and stability than that of Pt/C catalyst. The significantly enhanced durability of the hybrid electrocatalysts and electrochemical surface area (ECSA) preservation of the catalyst are observed after the accelerated durability test (ADT). The experimental data verify that the introducing of Fe can tune the electronic structure of Pt atoms, which contributes to the strengthened activity and stability of the Pt catalyst for the methanol oxidation reaction.     

A nanoreactor based on SrTiO3 coupled TiO2 nanotubes confined Au nanoparticles for photocatalytic hydrogen evolution

A TiO₂ nanotube-based nanoreactor was designed and fabricated by facile two steps synthesis: firstly, hydrothermal synthesized SrTiO₃ was deposited on TiO₂ nanotubes (TiO₂NTs). Secondly, the Au nanoparticles (NPs) were encapsulated inside the TiO₂NTs followed by vacuum-assisted impregnation. The as-synthesized composites were characterized using Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and Ultraviolet–visible absorption spectroscopy (UV–vis). The photocatalytic performance was evaluated by the hydrogen evolution reaction. The results revealed that the SrTiO₃ modified TiO₂NTs confined Au NPs (STO-TiO₂NTs@Au) achieved an enhanced hydrogen evolution rate at 7200 μmol h⁻¹ g⁻¹, which was 2.2 times higher than that of bald TiO₂NTs@Au at 3300 μmol h⁻¹ g⁻¹. The improved photocatalytic activity could be attributed to the synergistic effect of the electron-donating of SrTiO₃ and TiO₂NTs confinement. The as-designed nanoreactor structure provides an example of efficient carriers' separation photocatalyst.     

Structural properties of CuO/TiO2 nanorod in relation to their catalytic activity for simultaneous hydrogen production under solar light

CuO was introduced into porous TiO₂ nanorod through impregnation method. Before the impregnation step, TiO₂ nanorod was hydrothermally synthesized from TiO₂ powder in aqueous NaOH solution and followed by thermal treatment at 450 °C. The structures and properties of impregnated samples were characterized using various techniques, including XRD, BET, XAS, TEM, and UV-DRS. Their photocatalytic performance on simultaneous hydrogen production from pure water and aqueous methanol solution was also investigated under solar light. It was found that CuO/TiO₂ nanorod possessed a high surface area, good photocatalytic property and excellent hydrogen generation activity. Incorporation of Cu ions into the lattice framework of anatase TiO₂ nanorod enhanced the efficiency in visible region at 438–730 nm. Moreover, the XAS results showed that some Cu ions formed solid solution in the TiO₂ nanorod (Cu_xT_1−xO₂). However, the excessive incorporation of Cu ions did not improve any ability of anatase TiO₂ nanorod for production of hydrogen from pure water splitting. This could be due to the excessive CuO agglomeration at outside-pores which blocked the sensitization of TiO₂ nanorod. Only 1% Cu/TiO₂ nanorod was found to be a remarkable and an efficient photocatalyst for hydrogen production under solar light from both pure water and sacrificial methanol splitting. The highest rate of hydrogen production of 139.03 μmol h⁻¹ g_catalyst⁻¹ was found in sacrificial methanol which was 3.24% higher than in pure water.     

High photocatalytic hydrogen production over the band gap-tuned urchin-like Bi2S3-loaded TiO2 composites system

A new system using Bi₂S₃-loaded TiO₂ photocatalysts (Bi₂S₃/TiO₂) was developed to enhance the production of hydrogen. The Bi₂S₃ (5, 10, 15 wt%) particles in an urchin-like morphology with a length of about 2∼3 μm and a diameter of 15–20 nm, which can absorb all wavelengths in UV–visible radiation, were prepared by solvothermal method and loaded onto nano-sized TiO₂ (10∼15 nm) for photocatalysis on hydrogen production. The evolution of H₂ from methanol/water (1:1) photo splitting over the Bi₂S₃/TiO₂ composite in the liquid system was enhanced, compared with that over pure TiO₂ and Bi₂S₃. In particular, 14.2 ml of H₂ gas was produced after 12 h when 0.5 g of a 10 wt% Bi₂S₃/TiO₂ composite was used. On the basis of cyclic voltammetry (CV) results, the high photoactivity was attributed to the increase of band gap in the Bi₂S₃/TiO₂ composite, due to the decreased recombination between the excited electrons and holes.