Highly stabilized Ag2O-loaded nano TiO2 for hydrogen production from glycerol: Water mixtures under solar light irradiation

Nano TiO₂ prepared by a hydrothermal method and silver-loaded nano TiO₂ prepared by impregnation were studied for the photocatalytic production of hydrogen from glycerol:water mixtures. The structural characteristics were revealed using XRD, EDAX, DRS, TEM, XPS, BET surface area and Raman techniques. The photocatalytic hydrogen production has been investigated under solar light irradiation. Effects of nano TiO₂ calcination temperature, silver loading, photocatalyst content, light source and Ag oxidation state on hydrogen production have been systematically studied. Maximum hydrogen production of 200 μmol h^?1 g^?1 is observed on 4wt% silver-loaded nano TiO₂ catalyst in pure water and the maximum hydrogen production of 7030 μmol h^?1 g^?1 is observed on 3wt% silver-loaded nano TiO₂ catalyst in glycerol: water mixtures. Silver-loaded nano TiO₂ reduced and photodeposited catalysts show similar hydrogen production activities in glycerol: water mixtures under solar irradiation. The optimum catalyst modified with conducting carbon materials (graphene oxide, graphene, carbon nanotubes) by a solid-state dispersion method were also studied for hydrogen production under solar light irradiation. Compared with pure nano TiO₂, a 3wt% silver-loaded nano TiO₂/graphene composite exhibited an approximately 17-fold enhancement of hydrogen production leading to hydrogen production rates of 12,100 μmol h^?1 g^?1. Based on the characterization results and hydrogen production activity on these catalysts, a structure–activity correlation has been proposed wherein the interacting Ag₂OAg phases on the surface of nano TiO₂ play an important role in maintaining a high hydrogen production activity under solar irradiation.     

Facile construction of phosphate incorporated graphitic carbon nitride with mesoporous structure and superior performance for H2 production

Novel mesoporous phosphate incorporated g-C₃N₄ (CNM-Px) polymeric material was synthesized via a facile hydrothermal-calcination method, using melamine as precursor and phosphoric acid as dopant. The successful incorporation of phosphate into the framework of g-C₃N₄ nanosheets was verified by XRD, FT-IR and XPS characterizations and the possible formation mechanism was put forward. The as-fabricated CNM-Px samples were applied to photocatalytic hydrogen evolution reaction and exhibited remarkably improved photocatalytic performance both under simulated sunlight and visible light irradiation. The concentration of phosphoric acid was also well tuned and the optimal concentration was 2.5 mol L^?1. The hydrogen evolution rate of the optimized sample CNM-P2.5 (the concentration of treating phosphoric acid was 2.5 mol L^?1) reached 8163 μmol g^?1 h^?1 under simulated sunlight irradiation, which is 3.7 times higher than that of pristine g-C₃N₄ (CNM). It also showed dramatically improved hydrogen evolution rate under visible light irradiation, which was 2105 μmol g^?1 h^?1, about 6.7 times higher than that of CNM. The excellent photocatalytic activity of CNM-Px samples is due to the synergic advantages of larger surface area and reduced recombination of photo-generated electrons and holes. This study paves the way for tailoring design and synthesis of highly active metal-free carbon nitride materials for photocatalytic hydrogen evolution.     

Synthesis and investigation of a high-activity catalyst: Au nanoparticles modified metalic Ti microrods for NaBH4 electrooxidation

A novel catalyst electrode of Au nanoparticles modified Ti microrods is synthesized through a route of hydrothermal etching and electrodeposition. As substrate, the metallic Ti microrods are in-situ etched from the Ti plate using hydrochloric acid as an etching reagent. After that, Au is prepared on the metallic Ti microrods in a form of nanoparticle by electrodeposition. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) are conducted to investigate the structure and phase composition of the Au nanoparticles modified Ti microrods (Au/Ti MRs) electrode. Besides, the electrocatalytic property of the Au/Ti MRs electrode for NaBH₄ oxidation is explored through chronoamperometry (CA) and cyclic voltammetry (CV). In alkaline solution, the Au/Ti MRs electrode displays excellent electrocatalytic property and good stability. At 0 V, there is a current density of 12.12 mA cm^?2 on the as-prepared electrode in 2 mol L^?1 NaOH and 0.1 mol L^?1 NaBH₄ that is twice as the current density on Au nanoparticles modified Ti plate electrode demonstrating huge potential for application in direct borohydride fuel cell.     

The synthesis of ZnO/SrTiO3 composite for high-efficiency photocatalytic hydrogen and electricity conversion

Heterogeneous ZnO–SrTiO₃ nanocomposites were synthesized via a facile hydrothermal method. The highest H₂ production rate, 1317.44 μmol g^?1 within 5 h under solar-light irradiation was achieved for the Zn/Sr ratio of 9:1 of the ZnO–SrTiO₃. More interestingly though the ZnO–SrTiO₃ is a semiconducting system, it could be used as an electrolyte in the low temperature solid oxide fuel cell without electronic conducting short circuiting problem. This device displayed an open circuit voltage of 1.14 V and reached the maximum power density of 564 mW cm^?2 at 550 °C. These results are attributed to the enhanced separation of the charge-hole pairs by the heterogeneous structure of ZnO–SrTiO₃ nanocomposites, which possess obvious both heterogeneously ionic and semiconduction. This new discovery indicates a good promising candidate for both solar and hydrogen energy conversions.     

An integrated system of zinc oxide solar panels,fuel cells,and hydrogen storage for heating and cooling applications

Due to the production of hydrogen, using fuel cells for energy conversion and storing encounters safety problems. Combining high-temperature solid oxide fuel cells with photovoltaic solar panels or zinc oxide solar panels can be a good candidate to produce/convert and store the energy more efficiently for using at peak times. The current paper intends to analyze the efficiency of integration of zinc oxide solar panels and fuel cells to produce hydrogen directly. Therefore, the excess step of converting electricity to hydrogen and re-converting it to electricity, which is customarily used for the integration of the photovoltaic and solid oxide fuel cells, could be skipped. The new method paves the way for providing the required energy for heating/cooling through the floor heating and ceiling cooling systems as well as generating electricity. The article also demonstrates that it is possible to have heat during the day and night for an area of 1920 m² and 542 m². It is also possible to create coolness during the day and night for an area of 925 m² and 260 m².     

Co-extruded dual-layer hollow fiber with different electrolyte structure for a high temperature micro-tubular solid oxide fuel cell

In this study, the phase inversion-based co-extrusion method was employed to fabricate a structural-improved electrolyte/anode dual-layer hollow fiber (HF) precursor, which was then co-sintered at 1450 °C. The electrolyte structures were thoroughly investigated by varying the loading of electrolyte material (i.e. Yttria-stabilized zirconia, YSZ) with differing particle sizes (i.e. micron, sub-micron, and nano-sized) during suspension preparation. The results showed that the most promising electrolyte layer with thin, dense, gas-tight, and defect-free properties was obtained by mixing 70% submicron-YSZ and 30% nano-YSZ in electrolyte suspension (E-0.7sub0.3nano). This electrolyte formulation co-extruded with a thick nickel-oxide-YSZ (NiO-YSZ) anode layer yielded the highest bending strength of 85 MPa, providing major mechanical strength to the HF. Besides that, the nitrogen permeability value at 2.87 × 10^?6 mol m^?2 s^?1 Pa^?1 suggested that the electrolyte was gas-tight, preventing fuel and oxidant transport. The fiber was then reduced to nickel (Ni)-cermet anode. It was developed to be a complete micro-tubular solid oxide fuel cell (MT-SOFC) by depositing the lanthanum strontium cobalt ferrite (LSCF)/YSZ cathode via brush painting on the dual-layer HF. The cell was fed with hydrogen gas and yielded an open-circuit voltage (OCV) as high as 1.06 V with maximum power density of 0.243 W cm^?2, at 875 °C. Based on this test, it was found that the electrolyte structural-modified dual-layer hollow fiber-based MT-SOFC using mixed particle sizes may result in a promising OCV. However, the relatively low value for power density may be due to a less porous anode; thus, improvements in the anode's structure are required in future research.     

Hydrogen permeation in twinning-induced plasticity (TWIP) steel

The hydrogen permeation behavior of twining-induced plasticity (TWIP) steel was studied using a Devanathan-Stachurski hydrogen permeation cell. The TWIP steel exhibited three orders of magnitude lower hydrogen permeation rate as compared to the mild steel at room temperature. The hydrogen permeation rate of the TWIP steel was 1.71 × 10^?18 mol cm^?1 s^?1 at 25 °C, but it increased with the increase in the electrolyte temperature: 5.55 × 10^?17 mol cm^?1 s^?1 at 30 °C, 6.56 × 10^?17 mol cm^?1 s^?1 at 40 °C and 8.84 × 10^?17 mol cm^?1 s^?1 at 50 °C. Interestingly, the effective hydrogen diffusivity of TWIP steel was significantly higher as compared to that of mild steel, at all the four test temperatures. Activation energy calculations suggest that the hydrogen permeation was primarily through the grain boundaries in TWIP steel, and therefore exhibited higher effective hydrogen diffusivity in comparison with mild steel.     

Biodegradation of Potamogeton pectinatus biomass by hydrogen and methane coproduction: Effect of different pretreatments and parallel factor analysis

To enhance the hydrogen and methane coproduction potential, three pretreatments (i.e., acid, alkali and cellulase) were investigated during a two-stage anaerobic fermentation using Potamogeton pectinatus biomass. The fluorescence spectral characteristics of the dissolved organic matter (DOM) from the two-stage effluents, coupled with parallel factor analysis, were studied. The maximum hydrogen proportions (42.65%) and production rate (4.1 mL h^?1) were obtained under the 0.5 mol L^?1 HCl pretreatment. The highest methane proportions (52.82%) and production rate (14.2 mL h^?1) were observed under the 0.5 mol L^?1 HCl and 10 mg g^?1 cellulase pretreatments, respectively. Combined with fluorescence spectra and parallel factor analysis, three fluorescent components were identified, and the protein-like substances were determined to be dominant. Using the acid pretreatment, the change of the maximum fluorescence intensities in the DOM was the most significant among the three pretreatments, followed by that of the cellulose pretreatment. The result indicated that the macromolecular substances in P. pectinatus can be decomposed by effective pretreatment and thereby enhances the hydrogen and methane coproduction potential. This technique represents a promising method for improving cellulosic biomass biodegradation and green energy coproduction.     

Hydrogen separation by thin vanadium-based multi-layered membranes

Thanks to their high hydrogen permeability, vanadium based alloys can be a valuable and sustainable alternative to palladium alloys, commonly employed in commercial membranes for hydrogen purification/separation. In this work, the unprecedented deposition of micrometric vanadium-based multilayers and their investigation as hydrogen selective membranes have been reported. In particular, this work describes the use of High Power Impulse Magnetron Sputtering, a technique easily scalable also for complex geometries, for the deposition of dense and crystalline Pd/V₉₃Pd₇/Pd multilayers with total thickness <7 μm onto porous alumina. These membranes showed high hydrogen fluxes in the 300–400 °C range, up to 0.26 mol m^?2 s^?1 at 300 kPa pressure difference and 375 °C, as well as an unexpected and significant resistance to hydrogen embrittlement and to syngas in operating conditions.     

Hydrogen effect on 2.25Cr–1Mo–0.25V bainitic steel under aging heat treatment

In the present work, the mechanical properties and hydrogen interaction with microstructures obtained after thermal treatment of a 2.25Cr–1Mo–0.25V bainitic steel were investigated. The samples were heat-treated under two different conditions simulating shop-repairs and manufacturing procedures of reactors. The microstructures after each heat treatment showed MC, M₂C, and M₇C₃ carbides, characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The hydrogen diffusivity values after the first permeation for both conditions were 4.2 × 10^?11 m²s^?1 and 8.6 × 10^?11 m² s^?1, and the solubility was 7.4 molHm^?3 and 5.3 molHm^?3, showing the influence trapping in the behavior of permeation curves. The TDS results indicate that a greater hydrogen trapping capability can be achieved with one of the studied conditions. Tensile testing of the hydrogenated and heat-treated samples, showed that the number of heat treatment cycles has a strong influence on the loss of ductility, which is mainly due to carbide growth and coalescence.     

Synergistic effects and optimization of photo-fermentative hydrogen production of Rhodobacter sphaeroides DSM 158

The synergistic effects and optimization of pH, carbon-to-nitrogen ratio (C/N), and light intensity (I) on the photo-fermentative hydrogen production of Rhodobacter sphaeroides 158 DSM and light conversion efficiency have been investigated under different conditions of pH (6.5–8); C/N (15–35); and light intensity (35–185 W m^?2). Response surface methodology (RSM) and Box-Behnken experimental design (BBD) were used to identify the optimum values of the three key parameters of pH, C/N, and I, based on the impact on hydrogen production potential (HPP), hydrogen production rate (HPR), and light conversion efficiency $\eta$. With desirability value of 0.91, the optimum values of 7.4, 27.5, and 126 W m^?2 were identified for pH, C/N, and I respectively, with HPP, HPR and $\eta$ reaching 960 mL L^?1, 41.74 mL L^?1 h^?1, and 0.31 respectively. Regression analysis indicated a good fit between experimental and model data. The study showed that both C/N ratio and I have crucial and significant effect on the HPP, HPR and $\eta$, followed by pH, the synergistic effect of pH–I and C/NI on the light conversion efficiency ($\eta$) was significant while pH C/N was insignificant. The results and analysis obtained could be very useful for better optimizing the photo-fermentative hydrogen production.     

Hydrogen evolution in microbial electrolysis cells treating landfill leachate: Dynamics of anodic biofilm

This study investigates the potential opportunities of hydrogen evolution treating landfill leachate in a set of two microbial electrolysis cells (MEC-1 and 2) under 30 °C and 17 ± 3 °C temperatures, respectively. The system achieved a projected current density of 1000–1200 mA m^?2 (MEC-1) and 530–755 mA m^?2 (MEC-2) coupled with low cost hydrogen production rate of 0.148 L La^?1 d^?1 (MEC-1) and 0.04 L La^?1 d^?1 (MEC-2) at an applied voltage of 1.0 V. Current generation led to a maximum COD oxidation of 73 ± 8% (MEC-1) and 65 ± 7% (MEC-2) with ≥100% energy recovery. The system also exhibited a high hydrogen recovery (66–95%), pure hydrogen yield (98%) and tremendous working stability during two months of operation. Electroactive microbes such as Pseudomonadaceae, Geobacteraceae and Comamonadaceae were found in anodophilic biofim, along with Rhodospirillaceae and Rhodocyclaceae, which could be involved in hydrogen production. These results demonstrated an energy-efficient approach for hydrogen production coupled with pollutants removal.     

Assessment of the adequacy of different Mediterranean waste biomass types for fermentative hydrogen production and the particular advantage of carob (Ceratonia siliqua L.) pulp

The conversion of agro-industrial byproducts, residues and microalgae, which are representative or adapted to the Mediterranean climate, to hydrogen (H₂) by C. butyricum was compared. Five biomass types were selected: brewery’s spent grain (BSG), corn cobs (CC), carob pulp (CP), Spirogyra sp. (SP) and wheat straw (WS). The biomasses were delignified and/or saccharified, except for CP which was simply submitted to aqueous extraction, to obtain fermentable solutions with 56.2–168.4 g total sugars L^?1. In small-scale comparative assays, the H₂ production from SP, WS, CC, BSG and CP reached 37.3, 82.6, 126.5, 175.7 and 215.8 mL (g biomass)^?1, respectively. The best fermentable substrate (CP) was tested in a pH-controlled batch fermentation. The H₂ production rate was 204 mL (L h)^?1 and a cumulative value of 3.9 L H₂ L^?1 was achieved, corresponding to a H₂ production yield of 70.0 mL (g biomass)^?1 or 1.6 mol (mol of glucose equivalents)^?1_. The experimental data were used to foresight a potential energy generation of 2.4 GWh per year in Portugal, from the use of CP as substrate for H₂ production.     

Long-term effect of carbon nanotubes on electrochemical properties and microbial community of electrochemically active biofilms in microbial fuel cells

Carbon nanotubes (CNTs) have been widely exploited to improve anodic performance, but information is needed on their long-term stability for improvement. Herein, we prepared a novel CNTs-modified graphite felt (CNTs-GF) by a simple and scalable process and evaluated its long-term performance using anaerobic sludge as inoculum. the MFC with CNTs-GF yielded a sustained enhancement of power output, increasing from 1.93 ± 0.09 W m^?2 after 1 month to 2.10 ± 0.05 W m^?2 after 3 months and reaching 2.00 ± 0.10 W m^?2 after 13 month, indicating the enhancement in electricity generation by the CNTs was not declined over one year. However, the bare GF showed a declining tendency of performance during 13 months. The long-term enhancement can be explained by the facts that the CNTs-GF was beneficial to electrochemically active biofilms (EABs) growth and interacted better with EABs and increased the extracellular electron transfer. Community analysis showed an increase in Geobacter in response to CNTs modification. These results demonstrated that CNTs modification could sustain a superior long-term enhancement in MFC performance.     

Graphite coating on alumina substrate for the fabrication of hydrogen selective membranes

Development of composite membranes is a suitable alternative to improve the hydrogen flux through palladium membranes. The porous substrate should not represent a barrier to gas permeation, but the roughness of its surface should be sufficiently smooth for the deposition of a thin and defect-free metal layer. In this study, the performances of the modification of the outer surface of an asymmetric alumina hollow fibre substrate by the deposition of a graphite layer were evaluated. The roughness of the substrate outer surface was reduced from 120 to 37 nm after graphite coating. After graphite coating, the hydrogen permeance through the composite membrane produced with 2 Pd plating cycles was of 1.02 × 10^?3 mol s^?1 m^?2 kPa^?1 at 450 °C and with infinite H₂/N₂ selectivity. Similar hydrogen permeance was obtained with the composite membrane without graphite coating, also at infinite H₂/N₂ selectivity, but 3 Pd plating cycles were necessary. Thus, graphite coating on asymmetric alumina hollow fibres is a suitable alternative to reduce the required palladium amount to produce hydrogen selective membranes.     

Facile synthesis of Ti3+ doped Ag/AgITiO2 nanoparticles with efficient visible-light photocatalytic activity

We successfully synthesized novel Ti³⁺ doped TiO₂ and Ti³⁺ doped Ag/AgITiO₂ nanoparticles with efficient visible-light photocatalytic activity for hydrogen production by facile one-step solvothermal method. The as-prepared Ti³⁺ doped TiO₂ nanoparticles displayed excellent visible-light absorption and visible-light driven hydrogen production activity (115.3 μmol g^?1 h^?1), while the commercial TiO₂ had no visible-light response. Moreover, the as-prepared Ti³⁺ doped Ag/AgITiO₂ nanoparticles in this experiment showed highly enhanced visible-light absorption and efficient visible-light driven activity for hydrogen (571.0 μmol g^?1 h^?1), which was 4.95 times as high as that of the as-prepared TiO₂ nanoparticles. And the surface areas of the as-prepared TiO₂ and Ti³⁺ doped Ag/AgITiO₂ catalysts were up to 138.829 m² g^?1 and 102.988 m² g^?1, much higher than that of the commercial TiO₂ (55.516 m² g^?1). Finally, the visible-light photocatalytic mechanism of the Ti³⁺ doped Ag/AgITiO₂ nanoparticles for hydrogen generation was also proposed in detail.     

585 divacancy-defective germanene as a hydrogen separation membrane: A DFT study

As sustainable and clean energy, hydrogen is the most attractive and promising energy source in the future. Membrane separation is attractive due to its high hydrogen separation performance and low energy consumption. Van-der-Waals-corrected density functional theory (DFT) calculations are performed to investigate the hydrogen separation performance of 585 divacancy-defective germanene (585 germanene). It is found that the 585 germanene presents a surmountable energy barrier (0.34 eV) for hydrogen molecule passing through the membrane, and that membrane exhibits extremely high selectivity for H₂ molecules over CO, CO₂, N₂, CH₄ and H₂S molecules in a wide range of temperatures. Meanwhile, the hydrogen permeance of 585 germanene can reach 1.94 × 10^?7 mol s^?1 m^?2 Pa^?1 at the low limit temperature of methane reforming (at 450 K), which is higher than the industrially acceptable gas permeance. With high selectivity and permeance, the 585 germanene is a promising candidate for hydrogen separation.     

Hydrogen production by steam methane reforming in a membrane reactor equipped with a Pd composite membrane deposited on a porous stainless steel

With the aim of producing hydrogen at low cost and with a high conversion efficiency, steam methane reforming (SMR) was carried out under moderate operating conditions in a Pd-based composite membrane reactor packed with a commercial Ru/Al₂O₃ catalyst. A Pd-based composite membrane with a thickness of 4–5 μm was prepared on a tubular stainless steel support (diameter of 12.7 mm, length of 450 mm) using electroless plating (ELP). The Pd-based composite membrane had a hydrogen permeance of 2.4 × 10^?3 mol m^?1 s^?1 Pa^?0.5 and an H₂/N₂ selectivity of 618 at a temperature of 823 K and a pressure difference of 10.1 kPa. The SMR test was conducted at 823 K with a steam-to-carbon ratio of 3.0 and gas hourly space velocity of 1000 h^?1; increasing the pressure difference resulted in enhanced methane conversion, which reached 82% at a pressure difference of 912 kPa. To propose a guideline for membrane design, a process simulation was conducted for conversion enhancement as a function of pressure difference using Aspen HYSYS^®. A stability test for SMR was conducted for ～120 h; the methane conversion, hydrogen production rate, and gas composition were monitored. During the SMR test, the carbon monoxide concentration in the total reformed stream was <1%, indicating that a series of water gas shift reactors was not needed in our membrane reactor system.     

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.     

Co(OH)2 nanoparticles deposited on reduced graphene oxide nanoflake as a suitable electrode material for supercapacitor and oxygen evolution reaction in alkaline media

In this work, cobalt hydroxide nanoparticles are simply synthesized (size is about 50 nm) and deposited on the reduced graphene oxide nanoflake by the hydrothermal method. Then, the ability of glassy carbon electrode modified with this low-cost nanocomposite is examined as a supercapacitor and oxygen evolution electrocatalysts in 2.0 mol L^?1 KOH by a three-electrode system. The modified electrode as a pseudocapacitor with potential windows of 0.35 V, exhibits a powerful specific capacitance (235.20 F g^?1 at 0.1 A g^?1 current density), energy density, stability (about 90% of the initial capacitance value maintain after 2000 cycles at 1.0 A g^?1) and fast charge/discharge ability. Furthermore, the modified electrode displays a good electrocatalytic activity for oxygen evolution reaction with a current density of 10.0 mA cm^?2 at 1.647 V, small Tafel slope of 56.5 mV dec^?1, good onset potential of 1.521 V vs. RHE and suitable durability.