Hausmannite Mn3O4 as a positive active electrode material for rechargeable aqueous Mn‐oxide/Zn batteries

Batteries with manganese (di)oxide/zinc chemistry and aqueous‐based electrolytes have the potential to address energy storage demands of stationary applications primarily because of the abundant availability of Zn and Mn‐oxides, their intrinsic low cost, and the high specific/volumetric charge capacities. Herein, we report the use of Mn₃O₄ (hausmannite phase of manganese oxide) as the positive electrode material in a rechargeable near‐neutral Mn‐oxide/Zn battery configuration. Electrochemical investigations reveal that the hausmannite phase can activate for charge/discharge processes during the first 40 to 50 cycles and then a maximum capacity is obtained. This material shows excellent reversibility (~800 cycles) in keeping more than 65% of its maximum capacity. For the first time, the hausmannite activation mechanism was better understood under near‐neutral conditions. By using different characterization techniques (X‐ray powder diffraction [XRD], inductively coupled plasma‐optical emission spectrometry [ICP‐OES], X‐ray photoelectron spectroscopy [XPS], and energy dispersive X‐ray spectroscopy [EDS]) formation of Zn‐based compounds at the electrode surface was confirmed. One of the compounds formed is the layered double hydroxide (Zn₄SO₄[OH]₆ · 5H₂O) that forms as a side product. No direct evidence for intercalation of zinc ions was observed. Electrochemical experiments in different aqueous/organic electrolytes has shown that proton intercalation plays a significant role in the charge‐storage mechanism, while the activation process itself proceeds, most likely, through the formation of Zn‐species at the electrode surface.     

Concentrated solar photocatalysis for hydrogen generation from water by titania-containing gold nanoparticles

Photocatalysis is an effective way to utilize solar energy to produce hydrogen from water. Au/TiO₂ nanoparticles (NPs) have a better performance in photocatalytic hydrogen generation because of the localized surface plasmon resonance (LSPR) effect of Au/TiO₂ NPs. In the photocatalytic hydrogen generation experiments, it was found that light intensity plays a key role in the photocatalytic reaction rate of Au/TiO₂ NPs. At a light intensity of 0–7 kW/m², the reaction rate has a super-linear law dependence on the light intensity (Rate ∝ Intensityⁿ, with n > 1). However, at a light intensity of 7–9 kW/m², the dependency becomes sub-linear (n < 1). This means that the increase rate of photocatalytic rate is smaller than that of light intensity when the light intensity exceeds 7 kW/m². In addition, the finite element method (FEM) was utilized to further elucidate the role of light intensity by calculating the absorption power and nearfield intensity mapping of a Au/TiO₂ nanoparticle. The variation trend of the calculated total absorption power agrees with the photocatalytic experimental results for different light intensities. These results shed light on the utilization of concentrated solar photocatalysis to increase the solar-to-hydrogen performance of Au/TiO₂ NPs.     

Hierarchical Zn1.67Mn1.33O4/graphene nanoaggregates as new anode material for lithium‐ion batteries

Cubic spinel type Zn_1.67Mn_1.33O₄ porous sub‐micro spheres were synthesized by the calcination of solvothermally prepared Zn_xMn_1 ? xCO₃ precursor powders and evaluated as new anode materials for Li‐ion batteries for the first time. Each sphere exhibited aggregated morphology, constructed entirely from nanoparticles with a primary particle size of 11 nm. Electrochemical investigations and ex‐situ transmission electron microscopy analyses revealed that the reaction mechanism of obtained Zn_1.67Mn_1.33O₄ nanoaggregates is the combined conversion and alloying reaction, similar to that of ZnMn₂O₄ systems. In favor of the uniform porous sphere structure, these resulting Zn_1.67Mn_1.33O₄ nanoaggregates enabled the mitigation of volume change upon cycling. In addition, graphene composites with Zn_1.67Mn_1.33O₄ nanoaggregates were fabricated to improve electrical conductivity, simply by adding graphenes during solvothermal reaction for the formation of Zn_xMn_1 ? xCO₃ precursors. Zn_1.67Mn_1.33O₄/graphene composites showed a capacity of 670 mA h g^?1 higher than that of pure Zn_1.67Mn_1.33O₄ (518 mA h g^?1) after 200 cycle at a current density of 100 mA g^?1.     

Boosting the performance of visible light‐driven WO3/g‐C3N4 anchored with BiVO4 nanoparticles for photocatalytic hydrogen evolution

In this article, a ternary WO₃/g‐C₃N₄@ BiVO₄ composites were prepared using eco‐friendly hydrothermal method to produce efficient hydrogen energy through water in the presence of sacrificial agents. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet‐visible (UV‐vis), Brunauer‐Emmett‐Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The experimental study envisages the formation of 2‐D nanostructures and observed that such kinds of nanostructures could provide more active sites for photocatalytic reduction of water and their inherent reactive‐species mechanism. The results showed the excellent photocatalytic performance (432 μmol h^?1 g^?1) for 1.5% BiVO₄ nanoparticles in WO₃/g‐C₃N₄ composite when compared with pure WO₃ and BiVO₄. The optical properties and photocatalytic activity measurement confirmed that BiVO₄ nanoparticles in WO₃/g‐C₃N₄ photocatalyst inhibited the recombination of photogenerated electron and holes and enhanced the reduction reactions for H₂ production. The enhanced photocatalytic efficiency of the composite nanostructures may be attributed to wide absorption region of visible light, large surface area, and efficient separation of electrons/holes pairs owing to synergistic effects between BiVO₄ and WO₃/g‐C₃N₄. The prepared samples would be a precise optimal photocatalyst to increase their suppliers for worldwide applications especially in energy harvesting.     

A novel high specific capacity lithium‐ion capacitor battery with Li+‐doped Ni0.64Al0.64Mn0.56O2 prepared by coprecipitation method as cathode active material

Lithium‐ion capacitor battery is a late‐model energy storage system. It can combine the lithium‐ion battery with the capacitor to ensure that it has a high specific capacity and excellent large‐current discharge performance. In this paper, a novel Li⁺‐doped Ni_0.64Mn_0.64Al_0.56O₂ is synthesized by coprecipitation method and as a capacitor active material with commercialized LiNi_1/3Co_1/3Mn_1/3O₂ in different proportions forms the cathode of the lithium‐ion capacitor batteries. By analyzing the results of physical property characterization, when the mass ratio is 7:3, the crystal size of cathode material is less than 2 μm with uniform porous distribution. And, through electrochemical tests, the cathode has the greatest excellent reversibility, the lowest‐charge resistance, and the fastest‐lithium‐ion diffusion rate. Specific capacity can reach 196.34 mAh g^?1 at 0.5°C and, even at 5°C current density, it also can be 67.63 mAh g^‐1. After 110 times charge and discharge cycles, capacity retention of this cathode material at 5°C still can be over 85%.     

A BiOCl/β‐FeOOH heterojunction for HER photocatalytic performance under visible‐light illumination

β‐iron oxide hydroxide (β‐FeOOH) had been proven to be an effective co‐catalyst during H₂ evolution reaction (HER) process. In this research, a BiOCl/β‐FeOOH heterojunction was successfully synthesized by a solid‐state doping method. Then, the structure, composition, and photo‐electrochemical properties of the prepared photocatalysts were studied. For the superior HER photocatalytic activity of ultrasmall β‐FeOOH nanoparticles (NPs) and the formation of the BiOCl/β‐FeOOH heterojunction, this heterojunction photocatalyst exhibited very superior photocatalytic performance in the HER process. Especially, when the amount of incorporated β‐FeOOH NPs was appropriate, the BFOH‐2 possessed the highest photocatalytic activity in HER process, and the HER rate was about 16.64 mmol·g^?1·h^?1 during illuminated time of 6 hours under visible light. When appropriate, ultrasmall β‐FeOOH NPs were implanted into the structure of BiOCl, the BiOCl/β‐FeOOH heterojunction interfaces would form for the existence of interfacial interactions. Therefore, this BiOCl/β‐FeOOH heterojunction exhibited superior visible‐light response, fast photo‐carrier migration, and high‐efficient separation of photo‐carriers, so that the BFOH‐2 heterojunction possessed high‐efficient hydrogen evolution reaction (HER) photocatalytic activity.     

Solar hydrogen generation from spinel ZnFe2O4 photocatalyst: effect of synthesis methods

This paper investigates solar radiation‐induced photocatalytic hydrogen generation using spinel ZnFe₂O₄ (ZFO) photocatalysts fabricated using different routes, viz., solid state reaction (SSR), polymer complex (PC), microwave sintering (μW) and self‐propagating combustion (SPC) method. The physicochemical properties of the photocatalysts like crystallinity, surface area, band gap and band energetics is studied as it influences their photochemical behavior. The study reveals a high crystallinity of the ZFO photocatalysts, those are synthesized using SSR, PC and μW methods, where SSR method yields the larger dimension crystallites of ~53 nm. The nanoparticles obtained from SPC methodology exhibit a relatively large surface area and a smaller crystallite size of around ~18 nm. Monodispersed particles with comparatively large surface area are obtained in the case of PC method. ZFO obtained from μW synthesis exhibits enhanced optical properties, thus favoring high absorption of solar photons. A relatively more negative flat band potential is displayed by the μW samples (?0.543 vs normal hydrogen electrode) as estimated from the electrochemical measurements. Consequently, these samples yield a higher quantum yield (0.19%) for hydrogen evolution even without co‐catalyst loading. On the contrary, the photocatalysts obtained by SSR and PC methods did display an enhancement in the quantum yield as compared to the μW samples but only after Pt co‐catalyst loading. Copyright © 2015 John Wiley & Sons, Ltd.     

Iron doped nanostructured TiO2 for photoelectrochemical generation of hydrogen

This paper describes the photoelectrochemical studies on nanostructured iron doped titanium dioxide (TiO₂) thin films prepared by sol-gel spin coating method. Thin films were characterized by X-ray diffraction, Raman spectroscopy, spectral absorbance, atomic force microscopy and photoelectrochemical (PEC) measurements. XRD study shows that the films were polycrystalline with the photoactive anatase phase of TiO₂. Doping of Fe in TiO₂ resulted in a shift of absorption edge towards the visible region of solar spectrum. The observed bandgap energy decreased from 3.3 to 2.89 eV on increasing the doping concentration upto 0.2 at.% Fe. 0.2 at.% Fe doped TiO₂ exhibited the highest photocurrent density, ∼0.92 mA/cm² at zero external bias. Flatband potential and donor density determined from the Mott–Schottky plots were found to vary with doping concentration from −0.54 to −0.92 V/SCE and 1.7 × 10¹⁹ to 4.3 × 10¹⁹ cm⁻³, respectively.     

Parametric study of chemical looping combustion for tri‐generation of hydrogen,heat, and electrical power with CO2 capture

In this article, a novel cycle configuration has been studied, termed the extended chemical looping combustion integrated in a steam‐injected gas turbine cycle. The products of this system are hydrogen, heat, and electrical power. Furthermore, the system inherently separates the CO₂ and hydrogen that is produced during the combustion. The core process is an extended chemical looping combustion (exCLC) process which is based on classical chemical looping combustion (CLC). In classical CLC, a solid oxygen carrier circulates between two fluidized bed reactors and transports oxygen from the combustion air to the fuel; thus, the fuel is not mixed with air and an inherent CO₂ separation occurs. In exCLC the oxygen carrier circulates along with a carbon carrier between three fluidized bed reactors, one to oxidize the oxygen carrier, one to produces and separate the hydrogen, and one to regenerate the carbon carrier. The impacts of process parameters, such as flowrates and temperatures have been studied on the efficiencies of producing electrical power, hydrogen, and district heating and on the degree of capturing CO₂. The result shows that this process has the potential to achieve a thermal efficiency of 54% while 96% of the CO₂ is captured and compressed to 110 bar. Copyright © 2005 John Wiley & Sons, Ltd.     

Catalytic effect of EG and MoS2 on hydrolysis hydrogen generation behavior of high‐energy ball‐milled Mg‐10wt.%Ni alloys in NaCl solution—A powerful strategy for superior hydrogen generation performance

In this study, the metallurgical melting Mg‐10wt.%Ni (Mg10Ni) alloy is firstly modified by high‐energy ball milling (HEBM) and then surface catalysts expanded graphite (EG) or MoS₂ or EG‐MoS₂ are introduced to prepare Mg10Ni‐M (M = EG, MoS₂, and EG‐MoS₂) composites. The effects of surface catalysts on hydrolysis hydrogen generation of HEBM Mg10Ni alloy are comprehensively investigated. Their kinetics, rate‐limiting steps, and apparent activation energies are investigated by fitting the hydrolysis curves at different temperatures. The results indicate that the total hydrogen generation capacities of prepared Mg10Ni‐M (M = EG, MoS₂, and EG‐MoS₂) composites are 200, 170, 674, and 720 mL·g^?1 within 1 minute at 291 K. The capacity and yield of Mg10Ni are 500 mL·g^?1 and 56% within 15 minutes. The surface catalysts EG or MoS₂ or EG‐MoS₂ can distinctly elevate the initial H₂ produce rate and promote the complete hydrolysis process. The highest capacity and generation yield within 15 minutes are 740.8 mL·g^?1 and 91% obtained by HEBM Mg10Ni‐EG‐MoS₂ composite at 291 K. The surface catalysis can promote high generation yield of Mg10Ni alloy in a short time.     

Interstitial carbon doped of setaria viridis-like Znln2S4 hollow tubes for efficient the performance of photocatalytic hydrogen production

In the photocatalytic water splitting hydrogen production system, the key to efficient use of solar energy is to choose a suitable photocatalyst. As an important ternary sulfide, ZnIn₂S₄ (ZIS) has attracted wide attention because of its narrow band gap (E_g = 2.3–2.8 eV) and wide light absorption range. However, further modification was still needed. Therefore, in this work, the unique C/ZIS hollow tubes with nano-flakes were prepared by a simple solvothermal method. To a large extent, this unique structure increased the utilization of light and active sites. Moreover, the dissolution of PAN during the solvothermal process caused the carbon element to be uniformly doped into the hollow tube framework. After a series of characterization results, C/ZIS-3.0 has the best hydrogen release rate (1241.94 μmol g⁻¹ h⁻¹) and good cyclability under visible light irradiation (λ ≥ 420 nm). And its unique morphology and possible catalytic mechanism were further discussed.     

Multifunctional MoS2 ultrathin nanoflakes loaded by Cd0.5Zn0.5S QDs for enhanced photocatalytic H2 production

Two‐dimensional MoS₂ has been widely used as hydrogen evolution reaction (HER) cocatalyst to load onto nanostructured semiconductors for visible light‐response photocatalytic hydrogen production. However, its another important role as light harvester because of the band‐gap tunable property and beneficial band position has been rarely exploited. Herein, few layer‐thick MoS₂ nanoflakes with extended light absorption over the range of 400 to 680 nm and a photocatalytic HER rate of 0.98 mmol/h/g have been obtained. Then 7‐nm‐sized Cd_0.5Zn_0.5S quantum dots (QDs) are selectively grown upon ultrathin MoS₂ nanoflakes for enhanced photocatalytic H₂ generation. Upon the photocatalytic, light absorption, and charge transfer properties of the MoS₂‐Cd_0.5Zn_0.5S composites evolved with the amount of MoS₂ from 0 to 3 wt%, the multiple roles of MoS₂ as long‐wavelength light absorber, in‐plane carrier mediator, and edge site‐active HER catalyst have been revealed. An optimum H₂ generation rate of 8863 μmol/h/g and a solar to hydrogen (STH) efficiency of 2.15% have been achieved for 2 wt% MoS₂‐Cd_0.5Zn_0.5S flakes. Such a strategy can be applied to other cocatalysts with both the light response and HER activity for efficient photocatalytic property.     

Hydrogen generation from photocatalytic hydrolysis of alkali‐metal borohydrides

The controllable photocatalytic hydrolysis of alkali‐metal borohydrides is studied for hydrogen generation in this work. The results indicate that the photocatalysis of P25 TiO₂ controllably promotes the hydrogen generation rates from alkali‐metal borohydride hydrolysis. Its apparent activation energy is calculated to be reduced from 57.20 to 53.86 kJ mol^?1. This is due to the mechanism of photocatalytic hydrolysis: holes (h⁺) react with BH₄‐ and OH^? to form H₂ and B(OH)₄‐, meanwhile electrons (e^?) react with H⁺ to from H₂. In addition, Ti³⁺‐doped TiO₂ with a crystalline‐disordered core‐shell structure can be generated during the photocatalytic hydrolysis process. The consumption of e^? is identified as the rate‐limiting step in photocatalytic hydrolysis process. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of Al2O3-supported Cu-Schiff base complex as a catalyst for hydrogen generation in NaBH4 hydrolysis

Cu-Schiff base complex which we previously synthesized (Kilinc et al., 2012) is supported on Al₂O₃. The prepared catalyst is characterized by using SEM, XRD, BET, and FT-IR methods. And Al₂O₃-supported complex is used as a catalyst in NaBH₄ hydrolysis reaction for hydrogen generation. NaBH₄ hydrolysis reactions are investigated depending on the concentration of NaBH₄ and NaOH, temperature, percentage of Cu complex, and amount of catalyst. Maximum reaction rates are 44,453.33 and 57,410.00 mL H₂/g.cat.min at 30°C and 50°C, respectively. The activation energy of NaBH₄ hydrolysis reaction is found as 225,775 kJ^.mol^?1. All the experimental results and literature comparisons show that Al₂O₃-supported Cu-Schiff base complex is a very effective catalyst in NaBH₄ hydrolysis for H₂ generation.     

A hybrid power generation system: solar‐driven Rankine engine–hydrogen storage

This paper reports on the feasibility of a hybrid power generation system consisting of a solar energy‐driven Rankine engine and a hydrogen storage unit. Solar energy, the power for the hybrid system, is converted into electrical power through a combination of a solar collector, a tracking device to maintain proper orientation with the sun and a Rankine cycle engine driving an electrical power generator. Excess electricity is utilized to produce hydrogen for storage through electrolysis of water. At the solar down time, the stored hydrogen can be used to produce high‐quality steam in an aphodid burner to operate a turbine and with a field modulated generator to supplement electric power. Case studies are carried out on the optimum configuration of the hybrid system satisfying the energy demand. A numerical example based on the actual measured solar input is also included to demonstrate the design potential. Copyright © 2001 John Wiley & Sons, Ltd.     

Zn‐Al hydrotalcite‐derived CoxZnyAlOz catalysts for hydrogen generation by auto‐thermal reforming of acetic acid

Auto‐thermal reforming (ATR) of acetic acid (HAc) is considered as a promising route for hydrogen generation from renewable resources, while oxidation, coking, and sintering need to be addressed for durable catalysts in ATR. In the current work, Zn‐Al hydrotalcite‐derived Co_xZn_yAlO_z catalysts were prepared by co‐precipitation and evaluated in a fixed‐bed tubular quartz continuous‐flow reactor. The Co_0.70Zn_3.30AlO_{5.5 ± δ} catalyst presented a HAc conversation near 100% and a stable hydrogen yield near 3.01 mol‐H₂/mol‐HAc. The characterization results of XRD, H₂‐TPR, BET, SEM, XPS, and TG indicated that the hydrotalcite structure was obtained via co‐precipitation method; over the hydrotalcite‐derived mixed oxides, (a) the specific surface area was increased with high dispersion of Co, (b) the phases of ZnO with spinel of ZnAl₂O₄,CoAl₂O₄, Co₃O₄, and ZnCo₂O₄ were beneficial to improve resistance to coking and oxidation, and (c) the relative stability of Co species over ZnO and spinel phases helps to suppress sintering. Meanwhile, ratio of O/C and temperatures near 0.28 and 650 °C, respectively, were also evaluated and proposed as optimized conditions for hydrogen generation, and the durable Co_0.70Zn_3.30AlO_{5.5 ± δ} catalyst produced a rate of 114.9 mmol‐H₂/s/g‐catalyst in a 15‐hour ATR test, showing promising potential for hydrogen generation.     

Enhanced hydrogen generation at designed heterojunctions of Cu2ZnSnS4-rGO-MoS2 through interface engineering

Here, we are reporting interface engineering to create designed heterojunctions in Cu₂ZnSnS₄-rGO-MoS₂ (CZTS-reduced graphene oxide-MoS₂), in which abundant high density of nanoscale interfacial contacts are formed. It has been achieved via two-step optimized electrodeposition approach. Further, as-prepared materials have been characterized by microscopic, spectroscopic and electroanalytical techniques. Finally, the concept of generation of designed heterojunctions and synergetic effect were tested for electrocatalytic and photoelectrocatalytic hydrogen generation. The electron-hole pair recombination has been reduced, since the fast transport of photoexcited electrons of CZTS to MoS₂ through reduced graphene oxide interfacial contacts. Further, the synergetic effect of increased charge separation between rGO and more catalytically active sites from MoS₂ has been attributed to enhanced hydrogen generation.     

Insight into the effect of In addition on hydrogen generation behavior and hydrolysis mechanism of Al‐based ternary alloys in distilled water—A new active Al‐Ga‐In hydrolysis hydrogen generation alloy

(Al2Ga)‐xIn (x = 0, 2, 4, 6, 8 wt%) ternary aluminum (Al) alloys with different weight ratio of In for hydrolysis H₂ generation were prepared by melting‐casting technique. The phase compositions and microstructures of Al‐rich alloys were investigated by X‐ray diffraction (XRD) and high resolution scanning electron microscope (HR‐SEM) equipped with an energy dispersive spectrometer (EDS). The effect of In addition ratio on microstructures and H₂ generation performance were investigated, and the hydrolysis mechanism for Al‐Ga‐In ternary Al‐based alloys has been proposed. Al phase as matrix phase in the Al‐Ga‐In ternary alloy mainly determines the hydrolysis behavior, and the second phase In strongly promotes the hydrolysis process. The increase of In content can accelerate the H₂ generation rate as well as the final capacity and generation yield in neutral water. The generation yields for (Al2Ga)‐x In (x = 2, 4, 6, 8 wt%) alloys at 50°C are 0.56, 0.59, 0.62, and 0.66, respectively. The raising hydrolysis temperature can elevate the initial hydrolysis rate, final H₂ generation capacity, and yield. The H₂ generation capacities of (Al2Ga)‐8In alloy at 50°C, 60°C, and 70°C are 262, 290, and 779 mL·g^?1, respectively.     

Dehydrogenation properties of doped LiAlH4 compacts for hydrogen generator applications

Lithium aluminum hydride (LiAlH₄) is an attractive hydrogen source for fuel cell systems due to its high hydrogen storage capacity and the moderate dehydrogenation conditions. In this contribution, TiCl₃- and ZrCl₄-doped LiAlH₄ powders are prepared and pelletized under different compaction pressures in a uniaxial press. At constant 80 °C and a hydrogen partial pressure of 0.1 MPa, the maximal hydrogen release of suchlike LiAlH₄ compacts amounts to 6.64 wt.%-H₂ (gravimetric capacity) and 53.88 g-H₂ l⁻¹ (volumetric capacity). The hydrogen release properties of the doped LiAlH₄ compacts are studied systematically under variation of the compaction pressure, temperature and hydrogen partial pressure. Furthermore, the volume change of doped LiAlH₄ compacts during dehydrogenation as well as their short-term storability are investigated (shelf life).     

Novel synthesis of Zn2GeO4/graphene nanocomposite for enhanced electrochemical hydrogen storage performance

For the first time, a novel technique of preparing Zn₂GeO₄ nanostructures has been developed by using chemical precipitation method of GeCl₄ as a Ge precursor and acacen as a capping agent. Uniform and fine Zn₂GeO₄ nanoparticle was synthesized. The optimized Zn₂GeO₄ nanostructures anchored onto graphene sheets and Zn₂GeO₄/graphene nanocomposite synthesized through pre-graphenization, successfully. Hydrogen storage capacities of Zn₂GeO₄ nanoparticle and Zn₂GeO₄/graphene nanocomposite were compared, for the first time. Obtained results represent that Zn₂GeO₄/graphene nanocomposites have higher electrochemical hydrogen storage capacity than Zn₂GeO₄ nanoparticles. It was found that the synergistic effect between Zn₂GeO₄ nanoparticles and graphene sheets can improve the electrochemical performance of this hybrid composite electrode. After 29 cycles, the discharging capacities of the electrode reached to 2695 mAh/g. These results indicate that the Zn₂GeO₄/graphene nanocomposite can be potentially applied for electrochemical hydrogen storage.