CdO–CdS nanocomposites with enhanced photocatalytic activity for hydrogen generation from water

Nanocomposites of CdO–CdS have been prepared in ethylene glycol water mixture followed by heating at 300 °C. TEM and XRD studies confirmed the atomic scale mixing of CdO and CdS nanoparticles, leading to the formation of CdSO₃ phase at the interfacial region between CdO and CdS. Photocatalytic studies for hydrogen generation from water show an enhanced activity for CdO–CdS composites compared to individual components namely CdO or CdS nanoparticles. Based on optical absorption, surface area measurements, steady state and time resolved fluorescence studies, it is established that, enhanced absorption in the visible region, higher surface area and increase in lifetime of the charge carriers are responsible for the observed increase in hydrogen yield from water when composite sample was used as the photocatalyst compared to individual components. The composite sample when combined with Pt as co-catalyst exhibit a large increase in the photocatalytic activity.     

Electricity generation using solar parabolic dish system with thermoelectric generator—An experimental investigation

The present electricity grid installation cost as well as the tariff is quite high in India, particularly remote rural areas, to electrify houses. These problems can be easily solved by installing standalone systems that operate on one of the clean energy sources such as solar energy. An experimental analysis of generating electricity from a thermoelectric generator (TEG) powered by a solar parabolic dish concentrator device with aperture area and focal length of 12.6 m² and 2.42 m, respectively, is presented in this article. A TEG is made up of a thermoelectric module connected to a flat receiver by an absorber layer. The studies were carried out in Indian climatic conditions at the National Institute of Technology, Puducherry. Over a spectrum of beam radiation, the system's maximum energy conversion efficiency, as well as efficient electrical output, are evaluated and presented. The proposed system's average effective electrical efficiency is 0.424%, corresponding to the TEG's average energy conversion efficiency of 2.76%.     

Hydrogen generation from hydrolysis of aluminum/graphite composites with a core–shell structure

Hydrogen generated by hydrolysis of metal aluminum with water is promising for portable fuel cell applications. However aluminum would not react with water to yield hydrogen at ordinary conditions due to the passive oxide film formed on its surface. In the present investigation, the aluminum/graphite composite were prepared by a ball milling process in an attempt to improve the reactivity of aluminum, using sphere-shape aluminum particles and laminate graphite as the initial materials and 2 wt% NaCl as the milling-assisted agent. The TEM observation showed that the Al particles are covered by graphite to form a core–shell structure. Such a Al/graphite composite material exhibited a pronounced hydrolysis reactivity with tap water to generate hydrogen while Al alone did not react with water. The presence of graphite could lower the hydrogen generation reaction temperature below 45 °C. Increasing the reaction temperature could obtain an increased hydrogen generation rate and the maximum hydrogen generation rate of 40 cm³ min⁻¹ g⁻¹ Al was obtained when the reaction temperature was increased to 75 °C. Prolonging milling time could also improve the Al hydrolysis reactivity in the composite particularly at a relatively low temperature. The XRD results identified that the hydrolysis byproducts are bayerite (Al(OH)₃) and boehmite (AlOOH). The microstructure-related hydrolysis reaction mechanism was finally proposed.     

Photocatalytic hydrogen generation with simultaneous organic degradation by composite CdS–ZnS nanoparticles under visible light

A visible light-driven CdS–ZnS photocatalyst in the form of nanoparticles with a heterogeneous structure was synthesized using the stepped microemulsion method. The composite CdS–ZnS was capable of simultaneous photocatalytic hydrogen production and organic degradation under visible light. The ZnS deposition on CdS helped to suppress the recombination of electron/hole pairs generated on the more reactive CdS, leading to faster hydrogen production and improved stability of the CdS–ZnS in comparison to the bare CdS catalyst. Deposition of Ru on the catalyst surface further increased its photo-reactivity by about 4 times for hydrogen production. The heterostructured nanoparticles were effective in photocatalytic hydrogen production together with the degradation of model organic substances, including formic acid, methanol, and ethanol. The highest hydrogen production rate was achieved by the (CdS–ZnS)/Ru catalyst at 266 mmol/m²-h in the formic acid solution with an energy conversion efficiency of 3.05% in visible light, and the corresponding organic degradation rate in terms of the removal of chemical oxygen demand (COD) was estimated at 4272 mg COD/m²-h.     

Fiber-shaped Co modified with Au and Pt crystallites for enhanced hydrogen generation from sodium borohydride

This work presents the study of catalytic activity of the fiber-shaped Co decorated with low amounts of Au or Pt nanoparticles for the hydrolysis of sodium borohydride in alkaline conditions. The morphology, structure and composition of the prepared catalysts were examined using Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Analysis and Inductively Coupled Plasma Optical Emission Spectroscopy.It was found that the decoration of the fiber-shaped Co with the Au or Pt nanoparticles allows enhancing of catalytic activity for the hydrolysis of sodium borohydride, compared with that of the pure fiber-shaped Co.     

Hydrogen generation from splitting water with Al–Bi(OH)3 composite promoted by NaCl

In this paper, a novel Al–Bi(OH)₃ system hydrogen-generating material is investigated. Hydrolysis experiments show that the hydrolysis properties of the Al–10 wt% Bi(OH)₃ composite are significantly improved by doping with sodium chloride, and the Al–10 wt% Bi(OH)₃–5 wt% NaCl composite has a low activation energy (10.4 kJ mol⁻¹). With the further optimization of milling time, the hydrogen yield of Al–10 wt% Bi(OH)₃–5 wt% NaCl composite reaches 1000 mL g⁻¹ in 1 min. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy and thermogravimetric analysis are applied to characterize the composite and explore the hydrolysis mechanism. The characterization results show that the activation of aluminum mainly comes from three factors: (1) The formation of alumina during ball milling plays an important role in preventing the agglomeration between Al–Bi, Al–Al and Bi–Bi; (2) Bismuth generated during ball milling can form micro-galvanic cell with aluminum to promote the corrosion of aluminum; (3) Sodium chloride as a grinding aid contributes to crush aluminum powder, and chloride ions facilitate the corrosion of aluminum in the hydrolysis process. In addition, the drying method and initial water temperature have a great influence on by-products. The composite is expected to be used in mobile emergency fuel cell due to its rapid hydrogen production capacity.     

Phase specific α-MnO2 synthesis by microbial fuel cell for supercapacitor applications with simultaneous power generation

Phase specific α-MnO₂ is synthesized by reduction of KMnO₄ in microbial fuel cell. Electrochemical characterization of synthesized α-MnO₂ in aqueous 1M Li₂SO₄ electrolyte exhibit supercapacitor behaviour with initial specific capacitance of 558 mF/g and is 3.77 times higher than its theoretical capacitance. After 50 cycles, α-MnO₂ maintained specific capacitance of 250 mF/g which is 1.69 times higher than the theoretical capacitance of 148 mF/g. Decay in the specific capacitance is noticed after 2000 cycles upto 50 mF/g.     

Enhancement of energy generation efficiency in industrial facilities by SOFC – SOEC systems with additional hydrogen production

Industry is one of the highest energy consumption sector: some facilities like steelworks, foundries, or paper mills are highly energy-intensive activities. Many countries have already implemented subsidies on energy efficiency in generation and utilisation, with the aim of decreasing overall consumption and energy intensity of gross domestic product. Meanwhile, researchers have increased interest into alternative energy systems to decrease pollution and use of fossil fuels. Hydrogen, in particular, is proposed as a clean alternative energy vector, as it can be used as energy storage mean or to replace fossil fuels, e.g. for transport.This work analyses the re-vamping of the energy generation system of a paper mill by means of reversible solid oxide cells (RSOCs). The aim is not only to increase efficiency on energy generation, but also to create a polygeneration system where hydrogen is produced. Application on a real industrial facility, based in Italy with a production capacity of 60000 t/y of paper, is analysed. First, the current energy system is studied. Then, a novel system based on RSOC is proposed. Each component of the systems (both existing and novel) is defined using operational data, technical datasheet, or models defined with thermodynamic tools. Then, the interaction between them is studied. Primary energy analysis on the novel system is performed, and saving with respect to the current configuration is evaluated. Even if the complexity of the system increases, results show that saving occurs between 2 and 6%. Hydrogen generation is assessed, comparing the RSOC integrated system with proton exchange membrane (PEM) electrolysis, in terms of both primary energy and economics. Results exhibit significant primary energy and good economic performance on hydrogen production with the novel system proposed (hydrogen cost decreases from 10 €/kg to at least 8 €/kg).     

An experimental study on energy generation with a photovoltaic (PV)–solar thermal hybrid system

A hybrid system, composed of a photovoltaic (PV) module and a solar thermal collector is constructed and tested for energy collection at a geographic location of Cyprus. Normally, it is required to install a PV system occupying an area of about 10 m² in order to produce electrical energy; 7 kWh/day, required by a typical household. In this experimental study, we used only two PV modules of area approximately 0.6 m² (i.e., 1.3×0.47 m²) each. PV modules absorb a considerable amount of solar radiation that generate undesirable heat. This thermal energy, however, may be utilized in water pre-heating applications. The proposed hybrid system produces about 2.8 kWh thermal energy daily. Various attachments that are placed over the hybrid modules lead to a total of 11.5% loss in electrical energy generation. This loss, however, represents only 1% of the 7 kWh energy that is consumed by a typical household in northern Cyprus. The pay-back period for the modification is less than 2 years. The low investment cost and the relatively short pay-back period make this hybrid system economically attractive.     

MHD Eyring–Powell nanofluid past over an unsteady exponentially stretching surface with entropy generation and thermal radiation

This study's primary objective is to analyze the entropy generation in an unsteady magnetohydrodynamics (MHD) Eyring–Powell nanofluid flow. A surface that stretched out exponentially induced flow. The influences of thermal radiation, thermophoresis, and Brownian motion are also taken into consideration. The mathematical formulation for the transport of mass, momentum, and heat described by a set of partial differential equation is used, which is then interpreted by embracing the homotopy analysis method and with a fourth-order precision program (bvp4c). Graphical results display the consequences of numerous parameters on velocity, temperature, concentration, and entropy generation. Moreover, escalating amounts of the magnetic parameter, thermal radiation parameter, Reynolds number, and Brinkman number improve the entropy profile of the nanofluid. The rate of heat flux and the mass flux conspicuously improves for non-Newtonian fluid as compared to Newtonian fluid.     

Power generation efficiency of an SOFC–PEFC combined system with time shift utilization of SOFC exhaust heat

A microgrid, with little environmental impact, is developed by introducing a combined SOFC (solid oxide fuel cell) and PEFC (proton exchange membrane fuel cell) system. Although the SOFC requires a higher operation temperature compared to the PEFC, the power generation efficiency of the SOFC is higher. However, if high temperature exhaust heat may be used effectively, a system with higher total power generation efficiency can be built. Therefore, this paper investigates the operation of a SOFC–PEFC combined system, with time shift operation of reformed gas, into a microgrid with 30 houses in Sapporo, Japan. The SOFC is designed to correspond to base load operation, and the exhaust heat of the SOFC is used for production of reformed gas. This reformed gas is used for the production of electricity for the PEFC, corresponding to fluctuation load of the next day. Accordingly, the reformed gas is used with a time shift operation. In this paper, the relation between operation method, power generation efficiency, and amount of heat storage of the SOFC–PEFC combined system to the difference in power load pattern was investigated. The average power generation efficiency of the system can be maintained at nearly 48% on a representative day in February (winter season) and August (summer season).     

Adaptive fuzzy control with an optimization by using genetic algorithms for grid connected a hybrid photovoltaic–hydrogen generation system

The integration of significant amounts of renewable-storage hybrid power generation systems to the electric grid poses a unique set of challenges to utilities and system operators. This article deals with the designing methodology of an intelligent control based grid-connected a hybrid system composed of renewable energy source (RES) and storage system (SS). RES is a photovoltaic (PV) source and SS is a process of hydrogen transformation system (H₂TS) which composed of alkaline water electrolysis (AWE) for decomposition water by using the PV power, a tank used for gas storage and a proton exchange membrane (PEM) fuel cell (FC) to transform the H₂ to the electrical energy. The interconnection of the grid with the power generation system (PGS) is ensured through using a DC/AC hysteresis converter and it can synchronize current with the grid voltage among an independent control of active (P) and reactive (Q) power through a possibility of the Q compensation. In the proposed system, three algorithms are applied; two used inside generation and the third is used inside the grid. Perturb and observe (P&O) maximum power point tracking (MPPT) control algorithm always finds optimal power in the PV generator. A simple cascade controls loop of DC-DC boost converter and operate the FC generator to ensure maximum power and to regulate the DC Bus voltage. In addition, adaptive fuzzy logic control (FLC) unit is developed to control the DC/AC inverter, with adopting an off-line optimization based on genetic algorithms (GAs) applauded for tune different issues as scaling factors of the FLC and PIDs gains of the PV and the H₂TS control loops. Simulated results prove a big success of the proposed controls of the grid connected the hybrid PV-H₂TS with good performance.     

Bubble generation in micro-volumes of “nanofluids”

We report experimental investigation of a transparent flat mini evaporator heated by laser beam. The influence of non-absorbing and absorbing nanoparticles immersed in pure water, and heat absorbing fluid on the heat transfer intensification was analyzed. Nanoparticles may initiate vaporization and boiling of fluid at low heat input. Providing specific task and conditions the nanoparticles may be used in passive or active modes. Passive mode assumes that nanoparticles do not generate thermal energy and improve bubble nucleation conditions due to additional nucleation of the fluid, thus decreasing boiling/vaporization temperature thresholds. Active mode assumes that nanoparticles act as converters of optical energy into thermal one.     

Al–Li3AlH6: A novel composite with high activity for hydrogen generation

A novel material for hydrogen generation with high capacity of H₂ generation has been successfully prepared by ball milling the mixture of Al and home-made fresh Li₃AlH₆ powder. Its theoretical capacity of hydrogen released is higher than that of pure Al. Results obtained have shown conversion efficiency of Al–Li₃AlH₆ composite can be close to 100% by increasing the content of Li₃AlH₆. When the content of Li₃AlH₆ is 20 wt%, the maximum hydrogen generation rate and hydrogen yield are 2737.6 mL g⁻¹ min⁻¹ and 1513.1 mL g⁻¹, respectively, at room temperature. By XRD, SEM analyses and reaction heat measurements, it demonstrates that the additive Li₃AlH₆ can provide an additional source of H₂ and an alkaline environment (LiOH) as well as additional heat to promote the Al/H₂O reaction. Therefore, the Al–Li₃AlH₆ composite has a very high activity and high capacity of hydrogen released.     

Hydrogen generation by hydrolysis of NaBH4 with efficient Co–P–B catalyst: A kinetic study

Amorphous catalyst alloy powders in form of Co–P, Co–B, and Co–P–B have been synthesized by chemical reduction of cobalt salt at room temperature for catalytic hydrolysis of NaBH₄. Co–P–B amorphous powder showed higher efficiency as a catalyst for hydrogen production as compared to Co–B and Co–P. The enhanced activity obtained with Co–P–B (B/P molar ratio = 2.5) powder catalyst can be attributed to: large active surface area, amorphous short range structure, and synergic effects caused by B and P atoms in the catalyst. The roles of metalloids (B and P) in Co–P–B catalyst have been investigated by regulating the B/P molar ratio in the starting material. Heat-treatment at 773 K in Ar atmosphere causes the decrease in hydrogen generation rate due to partial Co crystallization in Co–P–B powder. Kinetic studies on the hydrolysis reaction of NaBH₄ with Co–P–B catalyst reveal that the concentrations of both NaOH and catalyst have positive effects on hydrogen generation rate. Zero order reaction kinetics is observed with respect to NaBH₄ concentration with high hydride/catalyst molar ratio while first order reaction kinetics is observed at low hydride/catalyst molar ratio. Synergetic effects of B and P atoms in Co–P–B catalyst lowers the activation energy (32 kJ mol⁻¹) for hydrolysis of NaBH₄. The stability, reusability, and durability of Co–P–B catalyst have also been investigated and reported in this work. It has been found that by using B/P molar ratio of 2.5 in Co–P–B catalyst, highest H₂ generation rate of about ∼4000 ml min⁻¹ g⁻¹ can be achieved. This can generate 720 W for Proton Exchange Membrane Fuel Cells (0.7 V): which is necessary for portable devices.     

3D-nano-hetero-structured n/n junction,CuO/Ru–ZnO thin films,for hydrogen generation with enhanced photoelectrochemical performances

Hydrogen, derived from solar-water splitting, is a clean and renewable fuel for which per gram energy storage capacity is even higher than fossil fuels. Towards the development of a viable technology for above conversion, this report describes enhanced performance in photoelectrochemical water splitting using uniquely evolved nano-hetero-structured bilayered thin films, CuO/Ru–ZnO as photoanode. Grown over ITO (In:SnO₂) glass substrates by using low-cost and easily up-scalable wet chemical methods, films were characterized for microstructure, optical behaviour and surface characteristics, using XRD and other spectral measurements viz. FESEM, AFM, TEM, UV–Visible Spectroscopy, EDX and XPS. Against monolayered pristine films of CuO and ZnO, bilayered films yielded a major gain in PEC water splitting photocurrent, on being used as working electrode in PEC cell, in conjunction with platinum counter electrode and saturated calomel reference electrode (electrolyte solution 0.1 M NaOH solution, pH 13, temperature 30 ± 3.6 °C). Films with 1% Ru-incorporation yielded highest photocurrent (2.04 mA/cm²). Enhanced photoactivity of bilayered films was found correlated with increments in light absorption, charge carrier density and film surface area, coupled with reduced electrical resistivity. The study highlights an important role played by Ru added in ZnO overlayer, apparently existing as RuO₂ nanoparticles dispersed in ZnO lattice, in hole-transfer from valence band of CuO underlayer to electrolyte, thereby imparting a significant boost on photocurrent generation.     

Performance evaluation of hydrogen generation system with electroless-deposited Co–P/Ni foam catalyst for NaBH4 hydrolysis

In this work, the performance of a hydrogen generation system with an electroless-deposited Co–P/Ni foam catalyst for NaBH₄ hydrolysis was evaluated. The performance of a hydrogen generator using a combination of Co/γ-Al₂O₃ and Co–P/Ni foam catalysts was also evaluated in order to address the shortcomings with the individual catalysts. The generator had high conversion efficiency, fast response characteristics, and strong catalyst durability. Hydrogen generation tests were performed to investigate the effect of the composition of the NaBH₄ solution on the hydrogen generation properties. The generator's conversion efficiency decreased with an increase in the amount of solute dissolved in NaBH₄ solution because of the accumulation of precipitates on the catalyst, and NaOH concentration had a greater effect on the hydrogen generation properties than did NaBH₄ concentration. According to these results, the hydrogen generation system with the Co–P/Ni foam catalyst is suitable as a hydrogen supplier for proton exchange membrane fuel cells owing to the strong durability and inexpensive cost of the catalyst.     

Hydrogen generation through rolling using Al–Sn alloy

Mechanically treated aluminum-tin (Al–Sn) alloy, a novel hydrogen-generating material, was fabricated and found to react directly and immediately with water at room temperature. The maximum yield of hydrogen per unit volume of alloy was 2259 mL/cm³ (0.202 g/cm³). The mass ratio of the generated hydrogen and the Al–Sn alloy material was 4.86%. This percentage is much higher than that of traditional hydrogen storage alloys and can compete with metal hydrides. The combination of Al–Sn alloy powder and carbon nanotubes (CNTs) produced a new kind of Al–Sn/CNT composite that also reacts with water at room temperature. Al–Sn/CNT composites were synthesized using a high temperature and high-pressure method. When CNT content was held constant, composites with single-walled CNTs had higher reaction rates than those with multi-walled CNTs. The effects of mechanical treatment and CNT addition on enhancing the reaction between Al–Sn alloys or Al–Sn/CNTs and water were also analysed.     

Photocatalytic hydrogen generation from water—Organic solutions using polytungstates

Illumination of polytungstate (PT) solutions, containing organic compounds results in the formation of photoreduced tungsten species and the evolution of hydrogen. Photocatalytic hydrogen generation from water-ethanol solutions using PT was studied in detail. Prolonged irradiation of this solution leads to the formation of hydrogen and acetaldehyde in a stoichiometric ratio. Absorption and ESR spectra of the photolyte indicate the subsequent formation of one- and two-electron reduced decatungstates. The addition of colloidal platinum to the system results in the increase in rate of hydrogen evolution. The dependences of the rate of hydrogen generation on a number of parameters (pH, concentrations of reagents, amounts of colloidal Pt, temperature) were studied. A mechanism of the process was proposed involving the formation of two-electron reduced PT and its subsequent reoxidation yielding hydrogen in the presence of colloidal platinum.