Recent developments of strontium titanate for photocatalytic water splitting application

The high efficiency of SrTiO₃ in the reaction of heterogeneous photocatalysis needs a suitable architecture that maximises photon absorption and minimises electron loss during excitation state. In order to further enhance the migration of charge carriers during excitation state, considerable effort has to be exerted to further develop the heterogeneous photocatalysis of this SrTiO₃ under UV, visible, and solar illumination. Currently, unique and interesting features of binary photocatalyst system have gained more attention by researchers and it became a favourite research topic among various groups of scientists around the world. It was noticed that the binary photocatalyst system properties primarily depends on the nature of the surface properties, surface morphologies, as well as the role of optimum dopants amount incorporated into the SrTiO₃. Thus, this article presents a critical review of recent achievements in the photocatalytic activity of the SrTiO₃ for water splitting H₂ generation technology.     

Combined impact of varying biogas mass flow rate and rice bran methyl esters blended with diesel on a dual-fuel engine

ABSTRACT

For fetching day-to-day energy needs, current energy requirement majorly depends on fossil fuels. But ambiguous matter like abating petroleum products and expanding air pollution has enforced the experts to strive for another fuel which can be used as an alternative or reduce the applications of fossil fuels. Considering the issues, the main objective of the present study is to find the feasibility by using blends of rice bran oil biodiesel and diesel which are used as pilot fuels by blending 10% and 20% biodiesel in fossil diesel and biogas, introduced as gaseous fuel by varying its mass flow rate in a dual-fuel engine mode. An experimentation study was carried out to find the performance and emission parameters of the engine relative to pure diesel. The results were very much similar to the majority of researchers who used biodiesel and gaseous fuels in a dual-fuel engine. Brake specific fuel consumption (BSFC) of the engine was noticed to have increased, while brake thermal efficiency was on the lower side in dual fuel mode in comparison with regular diesel. In relation with conventional diesel, it was noticed that combined effect of rice bran methyl esters and varying mass flow rate of biogas showed a decrement in NO _x and smoke emissions, whereas HC and CO exhalations were on higher side when biogas and biodiesel were utilized collectively in dual-fuel engine. Hence, it was concluded that combination of blends of biodiesel and diesel and introduction of biogas in the engine can be a promising combination which can be used as a substitute fuel for addressing future energy needs.     

The effect of imidazolium ionic liquid on the morphology of Pt nanoparticles deposited on the surface of SrTiO3 and photoactivity of Pt–SrTiO3 composite in the H2 generation reaction

Photocatalytic water splitting has great potential in solar-hydrogen production as a low-cost and environmentally friendly method. Different unique techniques used to obtain photocatalysts with various modifications to improve H₂ generation have been introduced. In the present work, SrTiO₃ was successfully synthesized via the solvothermal method in the presence of ionic liquid (IL) - 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) followed by surface decoration with Pt particles using the photodeposition method. The effect of the noble metal content and presence of IL on the morphology, optical and surface properties of SrTiO₃, thereby the effectiveness of hydrogen generation, has been thoroughly examined and presented. Unexpectedly, the presence of [BMIM][Br] at the SrTiO₃ surface affected the interaction between the semiconductor surface and platinum particles formed throughout photodeposition. Platinum particles at the surface of SrTiO₃_IL were found to be in the form of 2D clusters with a size of 1 nm. In comparison, Pt deposited on SrTiO₃ photocatalyst without application of IL created larger, three-dimensional structures with a diameter exceeding 5 nm. This is the reason why the total amount of platinum deposited on the SrTiO₃_IL sample is smaller than that on SrTiO₃ and justifies a higher efficiency of hydrogen generation of Pt modified SrTiO₃ photocatalyst in comparison to SrTiO₃ prepared in the presence of IL. The mechanism of H₂ generation in the water-splitting reaction in the presence of SrTiO₃_Pt photocatalyst was discussed.     

Hydrogen fuel in scramjet engines - A brief review

Due to the wide flammability range and low ignition delay of Hydrogen, it can burn rapidly and generate a large amount of thrust. It is for this reason alone that many researchers have promoted hydrogen as a potential fuel in scramjet engines. As H₂ is also environmentally safe and clean and can be produced from abundant sources, several researchers across the globe support the use of H₂ fuel. However, its lower volumetric energy density and higher flammability range also have an adverse effect in on-board storage system for aircraft propulsion applications. This review gives a brief representation of Hydrogen fueled scramjet engine as well the challenges associated with H₂ fuel. Additionally, the advantage of hydrogen as a fuel as compared to other hydrocarbon fuel is also discussed here thoroughly.     

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.     

Review on recent optimization strategies for hybrid renewable energy system with hydrogen technologies: State of the art,trends and future directions

The world is currently facing a power shortage due to the inadequacy of conventional energy sources and increased energy requirements in almost all sectors of human life. To mitigate this issue, the researchers have taken the considerable interest of researchers over the past decade in enhancing energy efficiency and viability. A hybrid renewable energy system (HRES) can efficiently produce clean energy to meet energy demand. Thus, it is extensively employed to improve power system quality, reliability, and economy, rather than solely relying on non-renewable energy sources. Nevertheless, RE sources' uncertain and intermittent nature, like wind speed and solar radiation, is associated with HRES. This problem can be solved with proper optimization by coupling HRES with energy conversion and storage devices, e.g., electrolyzer, fuel cell, and hydrogen tank, which can admirably balance power generation and energy demand. The literature is rich in employing optimization techniques on HRES with hydrogen technologies (HRES-H₂). However, a gap is found in the overall research progress of optimization approaches, considering HRES coupled with H₂ equipment. Therefore, the current study comprehensively reviews all the optimization approaches applied in this field worldwide. Further, a text mining-based software VOSviewer is used to investigate the scientific landscape of the literature body to figure out the current trends and future scope of HRES-H₂. It has been investigated that the researchers are focusing on: techno-economic optimization of HRES-H₂, developing sophisticated hydrogen infrastructure to reduce the overall cost of hydrogen fuel, introducing AI-based multi-objective optimization techniques to make the HRES-H₂ system more reliable and economically viable, and the impact of renewable and hydrogen technologies on the reduction of global warming. Lastly, an insightful of the current review highlighting the present shortcomings and opportunities of clean energy and hydrogen has been discussed, and suggestions are provided.     

Hydrogen production performance of active Ce/N co-doped SrTiO3 for photocatalytic water splitting

An efficient visible light responsive photocatalyst Ce/N co-doped SrTiO₃ was prepared via a hydrothermal method for hydrogen production. The phase structure, morphology, contents and valence states of the dopant elements, specific surface area, optical properties, and photocatalytic activity of the samples were characterized. The transient photocurrent response and electrochemical impedance spectra under visible light illumination indicated that Ce/N co-doped SrTiO₃ possessed a more intense photo-current response and lower surface resistance than N–SrTiO₃ and Ce–SrTiO₃. The water splitting rate of Ce/N-co-doped SrTiO₃ is 4.28 mmol/g/h, which is 84.49 times higher than that of pure SrTiO₃. The enhanced photocatalytic performance is due to the narrowing of the band gap of SrTiO₃ by Ce ion and N ion impurities.     

Electronic and optical properties of nitrogen and sulfur doped strontium titanate as efficient photocatalyst for water splitting: A DFT study

One of the most effective option of photocatalysts for water splitting is doped strontium titanate, SrTiO₃. It has a high rate of photo-generated charge transfer and limited photocatalytic activity for water splitting. The search of an appropriate photocatalyst having a high visible light absorption as well as fast charge transportation is extremely needed, however it is a difficult task. The structural, electronic and optical properties of sulfur-doped SrTiO₃ and nitrogen-doped SrTiO₃ are investigated using calculations based on density functional theory (DFT). According to the band structure calculations, the O-2p states represented the higher levels of the valence band of pure SrTiO₃. When S and N atoms are introduced into the SrTiO₃ structure on the O site, electronic structure findings indicate that doping the Sulfur (S) atoms reduced the band gap significantly, whereas doping of N atoms increased the bandgap of SrTiO₃. According to our results, the N-doped SrTiO₃ has a sufficient band gap of 2.03 eV, as well as suitable high visible light absorption and charge carrier transportation. The optical properties showed that N-doped SrTiO₃ has good photosensitivity for visible light. In addition, we have found a significant impurity state that differs from O 2p-states, which can increase photocatalytic efficiency. The results of studies of electronic band structure showed that electron-hole transportation was well consistent with the experimental data. Thus, the N-doped SrTiO₃ in this study is indeed an attractive candidate for hydrogen evolution throughout the visible light range, providing a logical base for the establishment of innovative photocatalysts.     

Efficient visible-light-driven photocatalytic H2 production over Cr/N-codoped SrTiO3

Visible-light-response Cr/N-codoped SrTiO₃ was prepared by a sol–gel hydrothermal method. The comparison studies indicate that Cr-doped and Cr/N-codoped SrTiO₃ can be synthesized by this means, but not the N-doped SrTiO₃. The theoretical calculations exhibit the defect formation energy of the Cr/N codoping into SrTiO₃ is much smaller than that of the N doping into SrTiO₃, illuminating that the incorporation of Cr can promote the N doping into the O sites in the SrTiO₃. Compared to the Cr-doped SrTiO₃, the Cr/N-codoped SrTiO₃ photocatalyst shows the high photocatalytic activities for hydrogen production with the quantum efficiency of 3.1% at 420 nm, due to the smaller band gap and much less vacancy defects.     

Advances in the development of titanates for anodes in SOFC

Solid oxide fuel cells (SOFCs) are highly efficient energy conversion devices with the advantage that a wide variety of hydrocarbon fuels can be used directly. Recently, the field of research on anodic materials of SOFC has advanced rapidly, with special emphasis on the development of materials with resistance to H₂S as well as to the formation of coke. Therefore, it is crucial to design new anodic materials with higher catalytic activity, stability, tolerance to coke deposition and to sulfur poisoning. Due to their stability in redox conditions, the titanates are among the most studied perovskites. Strontium titanate (SrTiO₃) is a good electronic conductor at low partial pressures of oxygen and during redox cycles and presents excellent dimensional and chemical stabilities as well as sulfur tolerance. However, for application as the anode in a SOFC, it must be doped to improve important properties such as the conductivity and power density. This article describes the progress in the knowledge of titanates with perovskite structure with potential application as anodes for SOFC.     

Hierarchically SrTiO3@TiO2@Fe2O3 nanorod heterostructures for enhanced photoelectrochemical water splitting

In this particular work, the fabrication of SrTiO₃@TiO₂@ Fe₂O₃ nanorod heterostructure has been demonstrated via hydrothermal growth of SrTiO₃ cubic on the rutile TiO₂ nanorod as a template and later sensitized with Fe₂O₃ for photocatalytic solar hydrogen production in a tandem photoelectrochemical cell and dye-sensitized solar cell (DSSC) module. The photocatalytic solar hydrogen production of this heterostructure was optimized by controlling the amount of Sr and Fe on the surface of photocatalyst. The details of the influencing parameters on the physicochemical and photoelectrochemical properties are discussed. It was found that the morphology and quality of the fabricated materials were greatly manipulated by the concentration of Sr and Fe. The optimized 0.025 M SrTiO₃@TiO₂@ Fe₂O₃ heterostructure exhibited a higher photoconversion efficiency with a long electron lifetime, low charge transfer resistance and large donor density at the electrode and electrolyte interface. This composite has significantly improved the photocatalytic hydrogen production, yielding 716 μmol/cm² of maximum accumulative hydrogen. These results show that morphology rendering and manipulation of energy band alignment is crucial in creating efficient heterojunctions for excellent contributions in photocatalytic applications.     

Tuning semiconductor LaFe0.65Ti0.35O3-δ to fast ionic transport for advanced ceramics fuel cells

Heterostructure and their associated properties like band energy, band bending, and interface play a vital role in the conduction of charge carriers. Enhancement of ionic conductivity has been observed by the semiconductor SrTiO₃ and ionic conductor heterostructure formation, such insightful effect may be beneficial for electrolyte application in solid oxide fuel cells. Herein we report the formation of semiconductor and ionic materials heterostructure of LaFe_0.65Ti_0.35O_3-δ (LFT) and Sm and Ca co-doped cerium oxide Ce_0.8Sm_0.05Ca_0.15O_2-δ (SCDC) with three folds enhancement in the ionic conductivity. When LFT-SCDC heterostructure was applied in the fuel cell, LFT-SCDC work as a good electrolyte and achieve a maximum power output density of 0.98 W/cm². LFT-SCDC maintains the ionic and electronic conduction, the presence of electrons, their blockage and the fast promotion of ion transport play a key role in physical interpretation in realizing outstanding performance and understanding the mechanism of semiconductor electrolyte ceramics fuel cells. The constructed heterostructure between two different constituent phases of LFT and SCDC has established strong band bending at heterointerface, leading to the fast ionic transport in the interface. The combination of UV–visible spectroscopy and ultraviolet photoelectron spectroscopy (UPS) determine the band structure of both constituents, where the creation of oxygen vacancies are supported by X-ray photoelectron spectroscopy (XPS). It is revealed by the various investigation of electrical properties of LFT-SCDC heterostructure that it has both electronic and ionic behavior, where the built-in electric field formed by band energy alignment helps to enhance the transport of ions.     

A two-pronged strategy to modulate the porosity of porous carbons for capacitors: The relative effects of the texture and fuel properties of carbonaceous matter

Based on the search for a novel method to modulate the texture properties of porous carbon, it is essential to demonstrate the relative influence of texture and fuel properties (i.e., the general term of volatile, fixed carbon, ash, elements, and calorific value) of carbonaceous matter. Herein, H₃PO₄ activation was applied to fabricate pine sawdust-derived porous carbons (PC-T; T can be 450, 500, 550, and 600) with various fuel and texture properties. Afterward, the pore architectures recorded for PC-T were adjusted using the CO₂ activation procedure; that is, PC-T-derived porous carbons (PC-TC) were obtained. PC-TC showed a significant increase in texture properties (e.g., specific surface area and total pore volume) and specific capacitance compared to PC-T. In the three-electrode configuration, PC-550C achieved high specific capacitance values (e.g., 230.78 F/g at 0.5 A/g). The assembled PC-550C-based symmetrical supercapacitor achieved an impressive specific capacitance of 172.12 F/g upon 0.5 A/g. Interestingly, it equally delivered high energy density (23.91 Wh kg⁻¹) and power density (47.30 kW kg⁻¹), respectively. Further, the specific surface area of the PC-TC samples depends not only on the fuel properties of the PC-T samples but also on the texture properties of the PC-T samples. Superior fabricability and variable texture properties enable the two-pronged strategy (i.e., sequential H₃PO₄–CO₂ activation) for producing bulk senior and multi-level porous carbons.     

Improved separation efficiency of photogenerated carriers for Fe2O3/SrTiO3 heterojunction semiconductor

To investigate the mechanisms of the improvement on separation efficiency of photogenerated carriers, a Fe₂O₃/SrTiO₃ heterojunction semiconductor with an improved separation efficiency was successfully prepared. The heterojunction semiconductor was characterized with X-ray diffraction (XRD), UV–vis absorption spectrum, scanning electron microscope (SEM) and surface photovoltage (SPV) spectroscopy. The energy band diagrams of Fe₂O₃ and SrTiO₃ were determined with X-ray photoelectron spectroscopy (XPS), based on which the conduction band offset (CBO) between Fe₂O₃ and SrTiO₃ was quantified to be 1.26 ± 0.03 eV. The recombination of photogenerated carriers was investigated with photoluminescence (PL) spectrum, which indicates that the formation of Fe₂O₃/SrTiO₃ decreases the recombination. Thus the improved separation efficiency is mainly due to the energy difference between the conduction band edges of Fe₂O₃ and SrTiO₃, and the decreased electron-hole recombination for Fe₂O₃/SrTiO₃.     

An overview of utilizing water-in-diesel emulsion fuel in diesel engine and its potential research study

The need for more efficient energy usage and a less polluted environment are the prominent research areas that are currently being investigated by many researchers worldwide. Water-in-diesel emulsion fuel (W/D) is a promising alternative fuel that could fulfills such requests in that it can improve the combustion efficiency of a diesel engine and reduce harmful exhaust emission, especially nitrogen oxides (NO_x) and particulate matter (PM). To date, there have been many W/D emulsion fuel studies, especially regarding performance, emissions and micro-explosion phenomena. This review paper gathers and discusses the recent advances in emulsion fuel studies in respect of the impact of W/D emulsion fuel on the performance and emission of diesel engines, micro-explosion phenomena especially the factors that affecting the onset and strength of micro-explosion process, and proposed potential research area in W/D emulsion fuel study. There is an inconsistency in the results reported from previous studies especially for the thermal efficiency, brake power, torque and specific fuel consumption. However, it is agreed by most of the studies that W/D does result in an improvement in these measurements when the total amount of diesel fuel in the emulsion is compared with that of the neat diesel fuel. NO_x and PM exhaust gas emissions are greatly reduced by using the W/D emulsion fuel. Unburnt hydrocarbon (UHC) and carbon monoxide (CO) exhaust emissions are found to be increased by using the W/D emulsion fuel. The inconsistency of the experimental result can be related to the effects of the onset and the strength of the micro-explosion process. The factors that affect these measurements consist of the size of the dispersed water particle, droplet size of the emulsion, water-content in the emulsion, ambient temperature, ambient pressure, type and percentage of surfactant, type of diesel engine and engine operating conditions. Durability testing and developing the fuel production device that requires no/less surfactant are the potential research area that can be explored in future.     

The synthesis,properties, and potential applications of CoS2 as a transition metal dichalcogenide (TMD)

Cobalt disulfide (CoS₂) is an attractive member of the dichalcogenides family, which has attracted a lot of attention due to its abundance of constituents and its special properties such as semi-metallic conductivity and large surface area. Particularly, the high theoretical capacity of CoS₂ is so beneficial for energy storage systems such as different types of batteries, supercapacitors, and dye-sensitized solar cells (DSSCs). Furthermore, CoS₂ has the lowest chemisorption energy for atomic hydrogen among other pyrite types. In this review, different methods for the synthesis of CoS₂ are discussed and the role of CoS₂ as an active electrode material for various applications such as different kinds of batteries, supercapacitors, DSSCs, an electrocatalyst for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR) reactions, and as a component in the sensor's construction is investigated. Moreover, several solutions to solve the challenges of using CoS₂, such as volume changes during cycling or aggregation of nanoparticles, are presented and discussed. We hope that this information will be beneficial for many researchers around the world and suggest promising paths for future projects.     

Experimental parameters affecting the photocatalytic reduction performance of CO2 to methanol: A review

Photocatalytic conversion of CO₂ into value‐added hydrocarbon fuels and/or useful chemical products, using solar energy, has been the focus of active research, owing to its tremendous potential to provide a green fuel (eg, methanol) and simultaneously mitigate global warming by reducing CO₂ levels in the atmosphere. CO₂ photocatalytic reduction yields various hydrocarbon products. In this paper, we focus on methanol as it is an easily transportable energy‐dense fuel with multifarious applications in the automobile, industrial, and petrochemical sector. The photocatalytic conversion rate of CO₂ to methanol depends on 3 factors: the photocatalyst used, photoreactor design, and experimental parameters (or variables). The last factor—experimental parameters—forms the basis of this review paper. These parameters include the reaction temperature, CO₂ pressure, solvent used, intensity, wavelength, and duration of the incident light, concentration of organic impurities adsorbed on catalytic surface, addition of hole scavengers, type of reductant used, catalyst loading method, catalyst concentration, and the dissolved oxygen concentration. There have been numerous published works aiming to improve the methanol formation rate by optimizing these experimental parameters. In this paper, we consolidate and review these parameters, and investigate how optimizing them can enhance the photocatalytic conversion rate of CO₂ into methanol, thus ushering in the era of a green methanol‐based economy.     

Hydrogen storage performance of lithium borohydride decorated activated hexagonal boron nitride nanocomposite for fuel cell applications

A safe and cost effective material for hydrogen storage is indispensable for developing hydrogen fuel cell technology to reach its greater heights. The present work deals with hydrogen storage performance of lithium borohydride decorated activated hexagonal boron nitride (LiBH₄@Ah-BN) nanocomposite. where a facile chemical impregnation method was adopted for the preparation of LiBH₄@Ah-BN nanocomposite. The prepared nanocomposite was subjected to various characterization techniques such as X-ray Diffraction (XRD), Micro-Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDX), Brunauer–Emmett–Teller (BET) Studies, CHNS-Elemental Analysis and Thermo Gravimetric Analysis (TGA). From BET studies, it is confirmed that, there is an enhancement in the specific surface area of LiBH₄@Ah-BN nanocomposite (122 m²/g) compared to Ah-BN (70 m²/g). The hydrogen storage ability was examined using a Sieverts-like hydrogenation setup. An excellent hydrogen storage capacity of 2.3 wt% at 100 °C was noticed for LiBH₄@Ah-BN nanocomposite. The TGA study indicates the dehydrogenation profile of stored hydrogen in the range of 110–150 °C. The binding energy of stored hydrogen (0.31 eV) lies in recommended range of US-DOE 2020 targets for fuel cell applications. The present investigation demonstrates the preparation of LiBH₄@Ah-BN nanocomposite based hydrogen storage medium which has remarkable cycling stability and hydrogen storage capacity. Hence these desirable traits make LiBH₄@Ah-BN nanocomposite as a potential hydrogen storage candidate for fuel cell applications in near future.     

Influence of fuel properties and composition on NOx emissions from biodiesel powered diesel engines: A review

Biodiesel has proved to be an environment friendly alternative fuel for diesel engine because it can alleviate regulated and unregulated exhaust emissions. However, most researchers have observed a significant increase in NO_x emissions with biodiesel when compared to petrodiesel. The exact cause of this increase is still unclear; however, researchers believe that the fuel properties have been shown to effect the emissions of NO_x. The present work reviews the effect of fuel properties and composition on NO_x emissions from biodiesel fuelled engines. The paper is organised in three sections. The first section deals with the NO_x formation mechanisms. In the following section, the reasons for increased NO_x emissions of biodiesel fuel are discussed. After this, the influence of composition and fuel properties on NO_x emissions from biodiesel fuelled engines has been reviewed. Finally, some general conclusions concerning this problem are summarised and further researches are pointed out.     

Effects of partial substitutions of cerium and aluminum on the hydrogenation properties of La(0.65−x)CexCa1.03Mg1.32Ni(9−y)Aly alloy

Hydrogen in metal hydrides could be one of the promising energy storage mediums to address the intermittent nature of renewable energy. To convert the hydrogen energy to electricity, the storage system has to be coupled with a fuel cells system. Hence, it is important to design a hydrogen storage system that meets the operating requirements for a fuel cell system. In this work, the effects of partial substitution of both cerium and aluminum on the hydrogenation properties of La_(0.65−x)Ce_xCa_1.03Mg_1.32Ni_(9−y)Al_y alloys were investigated simultaneously using factorial design. Both Ce and Al additions greatly improved the reversibility of hydrogen storage capacity. However, the maximum hydrogen storage capacity and absorption kinetics can be reduced by the additions. As Ce and Al gave opposite effects on the absorption and desorption plateaus, they could be used to tune the properties of the alloys to the desired operating conditions for fuel cell applications.