Photocatalytic hydrogen production by biomimetic indium sulfide using Mimosa pudica leaves as template

Biomimetic sulfur-deficient indium sulfide (In_2.77S₄) was synthesized by a template-assisted hydrothermal method using leaves of Mimosa pudica as a template for the first time. The effect of this template in modifying the morphology of the semiconductor particles was determined by physicochemical characterization, revealing an increase in surface area, decrease in microsphere size and pore size and an increase in pore volume density in samples synthesized with the template. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of organic sulfur (SO/SC/SH) and sulfur oxide species (SO₂, SO₃²⁻, SO₄²⁻) at the surface of the indium sulfide in samples synthesized with the template. Biomimetic indium sulfide also showed significant amounts of Fe introduced as a contaminant present on the Mimosa pudica leaves. The presence of these sulfur and iron species favors the photocatalytic activity for hydrogen production by their acting as a sacrificial reagent and promoting water oxidation on the surface of the templated particles, respectively. The photocatalytic hydrogen production rates over optimally-prepared biomimetic indium sulfide and indium sulfide synthesized without the organic template were 73 and 22 μmol g⁻¹, respectively, indicating an improvement by a factor of three in the templated sample.     

Investigation on the effect of temperature on photothermal glycerol reforming hydrogen production over Ag/TiO2 nanoflake catalyst

Photothermal reforming of biomass-derived hydrocarbons is an efficient approach to generate renewable hydrogen driven by solar. However, the current understanding of the general thermal effect on hydrogen production is limited since the photothermal and thermal radiation from solar is difficult to separate. Herein, an experimental study is carried out by synthesizing a series of photothermal catalysts composed of Ag nanoparticles supported on TiO₂ nanoflake (TNF). The structure of the Ag/TNF was examined by XRD, XPS, and HRTEM, respectively. The local temperature rise of the Ag/TNF was detected during the photothermal reforming reaction of the aqueous bio-glycerol, and its influence on H₂ yield was analyzed. By introducing different weight ratios of Ag nanoparticles on TNF, the equilibrium temperature was obviously increased due to the localized surface plasmon resonance (LSPR) effect and dynamic balance between LSPR and heat dissipation was found. It was observed that increasing the weight ratio of Ag particles could result in an increased temperature and lower hydrogen yields. In fact, such photothermal reforming hydrogen production was a synergistic effect between photogenerated-electrons and phonons. Therefore, precisely regulating the photothermal effect by controlling the metal nanoparticles loading to achieve proper thermal balance and high catalytic activity is one effective countermeasure to enhance hydrogen production.     

Boosting the photocatalytic hydrogen production of TiO2 by using copper hexacyanocobaltate as co-catalyst

The development of cheap and efficient co-catalysts is crucial to improve the performance of well-known photocatalysts towards the hydrogen evolution reaction. Here, copper hexacyanocobaltate was evaluated for the first time as a potential candidate to be used as co-catalyst coupled with conventional TiO₂. Copper hexacyanocobaltate was formed by chemical precipitation in the presence of TiO₂, without needing further treatments. The composite exhibited paramount performance towards hydrogen generation, surpassing by up to 16 times the behavior reached with bare TiO₂. This composite also overcome the performance of conventional TiO₂ modified with copper and cobalt oxides derived from copper hexacyanocobaltate. The enhanced behavior of TiO₂/Cu₃[Co(CN)₆]₂ composite was promoted by the efficient separation of photogenerated charge carries, and the faster charge transfer from photocatalyst towards species in solution, as it was proved by the photoelectrochemical characterization of the materials. Furthermore, the composite experienced a slight detriment (15%) in its hydrogen production rate after four consecutive photocatalyst tests. This variation was attributed to the slow leaching of copper in the co-catalyst caused by its partial transformation into metal hydroxides, as it was suggested by the ex-situ XPS characterization. Nevertheless, the structural characterization evinced the presence of the Cu₃[Co(CN)₆]₂ in the composite after long-term use. This study should be considered a proof of concept on a reliable route to obtain appropriate composites for hydrogen production using light as primary energy source.     

Preparation of direct Z-scheme Bi2WO6/TiO2 heterojunction by one-step solvothermal method and enhancement mechanism of photocatalytic H2 production

Direct Z-scheme Bi₂WO₆/TiO₂ heterojunction photocatalyst was prepared by one-step solvothermal method. The catalyst was characterized by XRD, TEM, XPS, UV–Vis DRS, photoluminescence spectroscopy and photoelectrochemical studies. The photocatalytic hydrogen production experiments show that Bi₂WO₆ did not generate H₂ and the H₂-production rate of TiO₂ is only 0.1 mmol⋅g⁻¹h⁻¹. The hydrogen production rate of the Bi₂WO₆/TiO₂ heterojunction photocatalyst reaches 12.9 mmol⋅g⁻¹h⁻¹, which is 129 times that of TiO₂. Compared with TiO₂, the enhanced H₂-production activity of the heterojunction catalyst can be attributed to the wider light absorption range and the efficient separation and migration of carriers at the close contact interface between Bi₂WO₆ and TiO₂. Based on the work functions of Bi₂WO₆, TiO₂ and their heterojunctions, combined with the results of electron paramagnetic resonance spectroscopy and Mott-Schottky measurements, the photocatalytic H₂ production mechanism of Z-scheme heterojunction Bi₂WO₆/TiO₂ was proposed. This work provides an easy and simple way to design a binary Z-scheme photocatalyst with efficient catalytic H₂-production activity without electron mediators.     

Solar-driven multifunctional Au/TiO2@PCM towards bio-glycerol photothermal reforming hydrogen production and thermal storage

Photocatalytic hydrogen production and thermal storage are effective ways to convert solar energy into storable chemical energy and thermal energy, but they only respond to specific spectrum. In order to improve the energy conversion and storage efficiency of solar energy in the solar spectrum, hydrothermal and photo-deposition method were employed to synthesized photothermal catalyst while and Au/TiO₂@PCM composite microcapsules were fabricated by electrostatic adsorption self-assembly methods. Micro-morphologies and structures were detailed characterized by SEM, XRD, UV-Vis, etc. As calculated from the DSC results for effective, enthalpy value, the loading rates of Au/TiO₂ shell for the microcapsule were 12.6% and 15.4% corresponding to rod-shaped and sheet-shaped samples. To test their catalytic performance, the samples were dispersed in the same concentration of glycerol solution, and showed that the light to hydrogen efficiencies were 11.4‰ and 5.0‰ for ATR@PCM and ATF@PCM, respectively with the increasement of 53.8% and 56.1% comparing to their corresponding catalyst nanoparticle suspensions. Photo-thermal conversion efficiencies of ATR@PCM and ATF@PCM were 62.74% and 53.32% after 60 min-irradiations, and they were 48.22% and 25.96% higher than that of Me-PCM. Therefore, it was confirmed that the composite phase change microcapsules prepared in this study have the dual functions of energy storage and photothermal catalysis. Higher solar light to hydrogen energy conversion efficiency may be attained in future study if the stored thermal energy can be successfully employed to activate organic components for helping catalytic hydrogen generation.     

Highly efficient white-LED-light-driven photocatalytic hydrogen production using highly crystalline ZnFe2O4/MoS2 nanocomposites

Designing efficient photocatalytic systems for hydrogen evolution is extremely important from the viewpoint of the energy crisis. Highly crystalline heterostructure catalysts have been established, considering their interface electric field effect and structural features, which can help improve their photocatalytic hydrogen-production activity. In this study, we fabricated a highly crystalline heterojunction consisting of ZnFe₂O₄ nanobricks anchored onto 2D molybdenum disulfide (MoS₂) nanosheets (i.e., ZnFe₂O₄/MoS₂) via a hydrothermal approach. The optimized ZnFe₂O₄/MoS₂ photocatalyst, with a ZnFe₂O₄ content of 7.5 wt%, exhibited a high hydrogen-production rate of 142.1 μmol h⁻¹ g⁻¹, which was 10.3 times greater than that for the pristine ZnFe₂O₄ under identical conditions. The photoelectrochemical results revealed that the ZnFe₂O₄/MoS₂ heterojunction considerably diminished the recombination of electrons and holes and promoted efficient charge transfer. Subsequently, the plausible Z-scheme mechanism for photocatalytic hydrogen production under white-LED light irradiation was discussed. Additionally, the influence of cocatalysts on the photocatalytic hydrogen evolution for the ZnFe₂O₄/MoS₂ heterostructure was investigated. This work has demonstrated a simplified coupling of one-dimensional or zero-dimensional structures with 2D nanosheets for improving the photocatalytic hydrogen production activity as well as confirmed that MoS₂ is a viable substitute for precious metal-free photocatalysis.     

Insights into morphology-dependent Au/TiO2catalyst in glycerol aqueous solutions towards photothermal reforming hydrogen production

Probing the effect of spatial morphology of catalyst on its photothermal catalytic performance is crucial for solar-driven renewable catalytic reforming of hydrogen production. In this study, Au nanoparticles loaded on various morphologies of TiO₂ nanoparticles were synthesized and characterized. The experimental results indicated that decorating TiO₂ with Au nanoparticles could dramatically increase its photocatalytic activities by 20–40 times. The photothermal conversion efficiency of Au/TiO₂ (12.74%–25.54%) was higher than those of TiO₂ due to the introduction of LSPR of Au nanoparticles could effectively improve the utilization of solar spectrum. Titania nanoflower (TNF) nanoparticles with high light absorption capacity, better colloidal dispersion stability, porous properties and narrow band gap represented the highest H₂ productivity (144.13 μmol·g⁻¹·h⁻¹). The coarse surface structure was also conducive to the dispersion of gold particles on the surface of the carrier and the growth rate of Au/TNF hydrogen production (40 times) which was higher than that of other morphology within 2 h. The results of glycerol photothermal hydrogen generation highlighted the effect of temperature on colloidal dispersion stability and hydrogen production capability of nanoparticle suspension. It demonstrated that the photothermal effect aroused a temperature rise that would deteriorate the dispersion stability of the suspension although a local entropy increase in the catalyst nanoparticles might occur. At the same time, the temperature rise caused by the photothermal effect efficiently produces hydrogen in the reaction temperature range. Therefore, an ideal temperature setting for maximal hydrogen generation could be validated and improved the photothermal synergistic impact on biomass-reformed hydrogen generation.     

Fast in-situ photodeposition of Ag and Cu nanoparticles onto AgTaO3 perovskite for an enhanced photocatalytic hydrogen generation

The M (M = Ag, Cu) nanoparticles were deposited by a fast in-situ photoreduction method onto the AgTaO₃ photocatalyst surface using 1, 2, and 5 wt % ratios, in order to investigate their photocatalytic properties for hydrogen production. The obtained results indicated a nanoparticles growth <20 nm in diameter during 10 min of photoreduction process for both nanoparticles. The M (M = Ag, Cu) NPs/AgTaO₃ exhibited superior photocatalytic activity than bare AgTaO₃, with an efficiency increment of around 11 and 30 times at 2 wt % ratio of Ag and Cu nanoparticles, respectively. The excellent photocatalytic activity could be related to the surface plasmon resonance effect of nanoparticles, preventing the electron-hole recombination. Additionally, the optical and photoelectrochemical characterization revealed the presence and the effect of oxidized species of the nanoparticles, with a direct impact on the transport of photogenerated charge carriers for the improvement of the photocatalytic activity.     

Investigation on multifunctional Au/TiO2@n-octadecane microcapsules towards catalytic photoreforming hydrogen production and photothermal conversion

Combining solar energy utilization and hydrogen production is an ideal model for renewable energy development. Especially the conversion of broad-spectrum solar energy into chemical energy of hydrogen and thermal energy can enrich solar energy storage methods. Herein, novel multifunctional Au/TiO₂@n-octadecane microcapsules with core-shell structure were design and synthesized by wet chemical reduction and electrostatic adsorption self-assembly methods for photothermal hydrogen production and thermal storage. The results showed that microencapsulation of photothermal catalysts could provide an effective reaction area and excellent dispersion stability, where hydrogen production and light to hydrogen efficiency were increased in the 43% and 0.3% respectively, compared to the nanoparticle suspension system. Based on the recorded temperature variations caused by the photothermal effect, the calculated photothermal conversion efficiency and specific absorption rate of Au/TiO₂@n-octadecane was 25.01% and 277% higher than that of Au/TiO₂ suspension. The proposed hydrogen production and thermal storage method via multifunctional microcapsules might shed some light on the study of improving full-spectrum energy conversion efficiency of solar energy.     

Photoelectrochemical hydrogen production from water/methanol decomposition using Ag/TiO2 nanocomposite thin films

Though less frequently studied for solar-hydrogen production, films are more convenient to use than powders and can be easily recycled. Anatase TiO₂ films decorated with Ag nanoparticles are synthesized by a rapid, simple, and inexpensive method. They are used to cleave water to produce H₂ under UV light in the presence of methanol as a hole scavenger. A simple and sensitive method is established here to monitor the time course of hydrogen production for ultralow amounts of TiO₂. The average hydrogen production rate of Ag/TiO₂ anatase films is 147.9 ± 35.5 μmol/h/g. Without silver, it decreases dramatically to 4.65 ± 0.39 μmol/h/g for anatase TiO₂ films and to 0.46 ± 0.66 μmol/h/g for amorphous TiO₂ films fabricated at room temperature. Our method can be used as a high through-put screening process in search of high efficiency heterogeneous photocatalysts for solar-hydrogen production from water-splitting.     

One-pot synthesis of non-noble metal WS2/g-C3N4 photocatalysts with enhanced photocatalytic hydrogen production

As an increasing number of photocatalysis are developed, non-noble metal photocatalysts that can be synthesized from earth-abundant and low-cost materials have received a great deal of attention. In this study, non-noble metal WS₂/g-C₃N₄ photocatalysts were prepared by a facile one-pot synthesis. Varying masses of tungsten disulfide (WS₂) were successfully loaded onto g-C₃N₄ and characterized by X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). These results indicated that the WS₂ was successfully synthesized and immobilized closely on the surface of g-C₃N₄ to form a sheet-like nanostructure. The H₂ generation results showed that the optimal photocatalyst was 0.3-WCN because it had the highest photocatalytic H₂ production of 154 μmol h⁻¹g⁻¹, which is 34 times higher than bare g-C₃N₄ and even higher than 0.3 wt% platinum-loaded g-C₃N₄. Additionally, the possible mechanism of the photocatalyst was studied by photoluminescence (PL), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoelectrochemical tests, which showed that the WS₂ played a key role in improving the efficiency of separation and migration of the photogenerated carriers in g-C₃N₄.     

Mesoporous composite NiCr2O4/Al-MCM-41: A novel photocatalyst for enhanced hydrogen production

A novel photocatalyst NiCr₂O₄/Al-MCM-41, using Al-MCM-41 zeolite as a support loaded with NiCr₂O₄ was successfully prepared by a facile sol-gel method and followed by calcination at 700 °C. The photocatalytic hydrogen production through water splitting was tested under visible-light irradiation for 3 h. According to the results of hydrogen evolution, the NiCr₂O₄/Al-MCM-41 hybrid composite displayed higher hydrogen production compared with individual NiCr₂O₄ or Al-MCM-41. This revealed that NiCr₂O₄ incorporated into the Al-MCM-41 zeolite effectively facilitated the photocatalytic activity. The highest hydrogen generation was obtained from 50%NiCr₂O₄/Al-MCM-41, whose hydrogen generation (8.92 mmol/g) was enhanced up to 2.4 times as much as individual NiCr₂O₄ (3.75 mmol/g). The main reason for the enhanced photocatalytic activity of the hybrid photocatalysts was ascribed to the excellent synergistic effect of NiCr₂O₄ and Al-MCM-41 zeolite. The mesoporous Al-MCM-41 catalyst support increased the dispersion of NiCr₂O₄ with more active sites. In addition, Al-MCM-41 zeolite promoted the charge transfer and inhibited the rapid recombination of photo-generated electrons-holes as electron acceptor and donor.     

Kinetic performance of TiO2/Pt/reduced graphene oxide composites in the photocatalytic hydrogen production

Among the different alternatives to generate hydrogen, photocatalysis can play an important role since it is based on the use of solar radiation and a suitable semiconductor. Starting from the most commonly researched TiO₂ catalyst, many efforts have been devoted to improve its efficacy. This work, based on the potential of reduced graphene oxide (rGO) to carry charges and platinum nanoparticles to act as efficient traps for photogenerated electrons, assesses the performance of synthesized binary and ternary photocatalysts (TiO₂/rGO, TiO₂/Pt and TiO₂/rGO/Pt) for hydrogen generation. The addition of rGO to TiO₂ almost duplicates (1.95 factor) the hydrogen production rate compared to bare TiO₂. Moreover, the binary TiO₂/Pt photocatalyst reported the best performance, with an increase in the hydrogen production rate by a factor of 15.26 compared to TiO₂. However, the ternary catalyst performed worse than the binary TiO₂/Pt probably due to the use of non-optimized co-catalyst ratios. Since the addition of rGO reduces the cost of the catalyst, the trade-off between the catalyst performance and cost is worth of future research.     

B–N co-doped black TiO2 synthesized via magnesiothermic reduction for enhanced photocatalytic hydrogen production

In this work, B–N co-doped TiO₂ has been synthesized by a facile fast sol-gel method, and then, a controlled magnesiothermic reduction has been developed to synthesize B–N co-doped black TiO₂ under a N₂ atmosphere and at 580 °C followed by acid treatment. The prepared black TiO₂ samples were characterized by X-ray diffraction, high resolution transmission electron microscopy, Raman spectrameter, photoluminescence emission spectra, X-ray photoelectron spectroscopy, and ultraviolet–visible diffuse reflectance spectra. It shows that the prepared samples possess a unique crystalline core-amorphous shell structure composed of disordered surface and oxygen vacancies, and exhibit enhanced photocatalytic activity in hydrogen production in the methanol-water system in the presence of Pt as a co-catalyst. Under the full solar wavelength range of light, the maximum hydrogen production rate of the B–N co-doped black TiO₂ is 18.8 mmol h⁻¹ g⁻¹, which is almost 4 times higher than that of pure TiO₂.     

Photocatalytic hydrogen production from aqueous methanol solution using titanium dioxide with the aid of simultaneous metal deposition

The photocatalytic hydrogen generation from aqueous methanol solution using TiO₂ photocatalyst was investigated with the aid of simultaneous metal deposition. The photocatalytic hydrogen evolution with pure TiO₂ was very small. The simultaneous deposition for various metals was therefore evaluated. As a result, the additions of Au and Cu ions were effective for the improvement of photocatalytic hydrogen production. Methanol concentration and metal ion concentration were optimized for the system. The optimal methanol concentrations were 90 and 80 vol% in the case of addition of Au and Cu ions, respectively. Under the optimal conditions, the photocatalytic hydrogen production using TiO₂ photocatalyst with the aid of simultaneous Cu and Au deposition were approximately 25 and 120 times larger than those obtained with bare TiO₂.     

Photocatalytic hydrogen production in the water/methanol system using Pt/RE:NaTaO3 (RE = Y,La, Ce,Yb) catalysts

Perovskite type RE-doped NaTaO₃ (where RE represents Rare Earths elements like Y, La, Ce, Yb) catalysts, derived from solid state synthesis method, have been used for the photocatalytic hydrogen production from water using methanol as sacrificial agent. The photocatalytic activity of NaTaO₃ in H₂ production is improved on its doping with Y, La or Yb elements. In contrast, Ce-doped sample shows a worsening of the photoactivity, which is even lower than the un-doped catalyst. The characterization of the materials reveals that the monoclinic structure and the presence of Ce⁴⁺ do not favour to increase the performance of NaTaO₃. Previous reports proved that La-doping boosted the water splitting photoactivity of NaTaO₃. However the results of this work reveal an increase in the H₂ production by the use of Y as dopant. This enhancement in the photoactivity could be related with the modification of the opto-electronic properties of NaTaO₃ with the inclusion of RE elements (Y, La, Yb) in the orthorhombic structure of this perovskite. Moreover, the catalytic activity of all the RE-doped samples is further increased on their modification with Pt nanoparticles (NPs) loading that act as photo-generated electron scavenger facilitating the reduction reactions.     

The TiO2/Mn0.2Cd0.8S hollow heterojunction with Mn/Cd bimetallic synergy towards photocatalytic hydrogen production enhancement

The TiO₂/Mn_0.2Cd_0.8S hollow heterojunction with Mn/Cd bimetallic synergy is prepared via a continuous chemical-hydrothermal-etching method. There, the TiO₂ shell and Mn_0.2Cd_0.8S nanoparticles were deposited by continuous chemical-hydrothermal method on the surface of SiO₂ template, and subsequently the SiO₂ template was etched via a chemical method. Evaluated by HER, the as-prepared TiO₂/Mn_0.2Cd_0.8S hollow heterojunction exhibits an obvious photocatalytic enhancement to about ~5822.94 μmol/g∙h(~40 folds of TiO₂, ~7 folds of Mn_0.2Cd_0.8S), which can be mainly ascribed to that, the narrow band gap of Mn_0.2Cd_0.8S can increase the visible light energy utilization, the TiO₂/Mn_0.2Cd_0.8S heterojunction and Mn/Cd bimetallic synergy can separate/transfer the photo-generated charge carriers efficiently, and the sufficient specific surface areas and actives from 3D hollow structure can promote the charge carrier diffusing into water quickly for achieving H₂ generation. Additionally, the hollow 3D structure can provide a decent physical-chemical stability to improve the photocatalytic stability.     

Photocatalytic hydrogen production from aqueous methanol solution with CuO/Al2O3/TiO2 nanocomposite

The photocatalytic hydrogen production from aqueous methanol solution was investigated with ZnO/TiO₂, SnO/TiO₂, CuO/TiO₂, Al₂O₃/TiO₂ and CuO/Al₂O₃/TiO₂ nanocomposites. A mechanical mixing method, followed by the solid-state reaction at elevated temperature, was used for the preparation of nanocomposite photocatalyst. Among these nanocomposite photocatalysts, the maximal photocatalytic hydrogen production was observed with CuO/Al₂O₃/TiO₂ nanocomposites. A variety of components of CuO/Al₂O₃/TiO₂ photocatalysts were tested for the enhancement of H₂ formation. The optimal component was 0.2 wt% CuO/0.3 wt% Al₂O₃/TiO₂. The activity exhibited approximately tenfold enhancement at the optimum loading, compared with that with pure P-25 TiO₂. Nano-sized TiO₂ photocatalytic hydrogen technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy.     

Synergistic effect of {101} crystal facet and bulk/surface oxygen vacancy ratio on the photocatalytic hydrogen production of TiO2

Anatase titanium dioxide (TiO₂) nanocrystals with different percentages (up to 95%) of exposed {101} facet and different concentration ratios of bulk single-electron-trapped oxygen vacancies (SETOVs) to surface oxygen vacancies (SOVs) were prepared by alcohol-thermal method with nanotube titanic acid as the precursor in combination with solid-state reduction by NaBH₄. The as-prepared TiO₂ nanocrystals were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and ultraviolet–visible light spectrometry. The effects of the percentage of crystal facets and the concentration ratio of bulk SETOVs/SOVs on the photocatalytic hydrogen production rate of TiO₂ nanocrystals were investigated with positron annihilation lifetime spectroscopy as well as photocurrent test. Findings indicate that the percentage of the exposed {101} facets of the as-prepared TiO₂ nanocrystals and their concentration ratios of bulk SETOVs/SOVs can be well tuned by properly adjusting the amount of NaBH₄ and the reduction reaction time as well. Increasing percentage of the {101} facet of anatase TiO₂ nanocrystals contributes to improving their photocatalytic hydrogen production activity, because the {101} facets of the anatase TiO₂ nanocrystals possess enriched electrons and can act as the reduction sites to enhance the reduction reaction of H⁺ affording H₂ in the sacrifice system of splitting water. Both the bulk SETOVs and SOVs contribute to the improvement of the light absorption while SOVs can facilitate the separation of photogenerated charges, thereby adding to the photocatalytic activity. However, the bulk SETOVs and excessive SOVs are also the combination centers of photogenerated charges, which means it is essential to maintain a suitable concentration ratio of the bulk SETOVs/SOVs so as to enhance the light absorption and achieve the best separation efficiency of photogenerated charges and achieve the best photocatalytic activity for hydrogen production. Particularly, when anatase TiO₂ nanocrystal with a high percentage (95%) of exposed {101} facet is reduced by NaBH₄ at a mass ratio of 2: 1 for 20 min, the resultant reduced H-TiO₂ nanocrystal (denoted as H-TiO₂-R20(2:1)) provides the highest photocatalytic hydrogen productive rate. Furthermore, the combination of 0.5% Pt/H-TiO₂-R20(2:1) with 0.5% Pt/WO₃ can split water to simultaneously produce H₂ and O₂, showing promising potential for splitting water affording hydrogen and oxygen.     

Design,modelling and optimal power and hydrogen management strategy of an off grid PV system for hydrogen production using methanol electrolysis

Hydrogen used as an energy carrier and chemical element can be produced by several processes such as gasification of coal and biomass, steam reforming of fossil fuel and electrolysis of water. Each of these methods has its own advantage and disadvantage. Electrolysis process is seen as the best option for quick hydrogen production. Hydrogen generation by methanol electrolysis process (MEP) gained much attention since it guarantees high purity gas and can be compatible with renewable energies. Furthermore, due to its very low theoretical potential (0.02 V), MEP can save more than 65% of electrical energy required to produce 1 kg of hydrogen compared to water electrolysis process (WEP). Electrolytic hydrogen production using solar photovoltaic (PV) energy is positioned to become as one of the preferred options due to the harmful environmental impacts of widely used methane steam reforming process and also since the prices of PV modules are more competitive.In this paper, hydrogen production by MEP using PV energy is investigated. A design of an off grid PV/battery/MethElec system is proposed. Mathematical models of each component of the system are presented. Semi-empirical relationship between hydrogen production rate and power consumption at 80 °C and 4 M concentration is developed. Optimal power and hydrogen management strategy (PHMS) is designed to achieve high system efficiency and safe operation. Case studies are carried out on two tilts of PV array: horizontal and tilted at 36° using measured meteorological data of solar irradiation and ambient temperature of Algiers site. Simulation results reveal great opportunities of hydrogen production using MEP compared to the WEP with 22.36 g/m² d and 24.38 g/m² d of hydrogen when using system with horizontal and tilted PV array position, respectively.