Preface to the Special Issue on Hydrogen Production, Storage, Application, and Sensing.

This issue focuses on the multifaceted nature of hydrogen, exploring the latest research, advancements, and applications in this rapidly evolving field. Topics covered include hydrogen production methods, advancements in storage technologies, diverse applications, and the significance of hydrogen sensing for monitoring its environmental impact.

Identification of Suitable Mesh Size of Commercial Stainless-Steel for Electrochemical Oxygen Evolution Reaction.

The study examines the oxygen evolution reaction (OER) electrocatalytic efficiency of various stainless-steel mesh (SSM) sizes in electrolytic cells. Stainless steel is chosen due to its widespread availability and stability, making it an economically viable option. The primary objective of this investigation is to determine the optimal stainless-steel mesh size among those currently widely available on the market. The classification of stainless-steel mesh sizes as SS304 is confirmed by the minimal compositional variations observed across all mesh sizes through electron dispersive X-ray (EDX) spectra and X-ray fluorescence (XRF) analyses. Remarkably, CV experiments carried out at different scan rates indicate that SSM 200 has the maximum specific electrochemical surface area (ECSA). As a result, SSM 200 demonstrates superior performance in terms of current density response and shows the lowest overpotential in the alkaline medium compared to other stainless-steel mesh sizes. Furthermore, the SSM 200 exhibits a low overpotential of 337 mV at a current density of 10 mA/cm2 and a Tafel slope of 62.2 mV/decade, surpassing the performance of several previously reported electrodes for the OER. Stability tests conducted under constant voltage further confirm the remarkable stability of SSM 200, making it an ideal anode for electrolytic cell applications. These findings emphasize the cost-effectiveness and high stability of SSM 200, presenting intriguing possibilities for future research and advancements in this field.

Advanced High-Energy All-Solid-State Hybrid Supercapacitor with Nickel-Cobalt-Layered Double Hydroxide Nanoflowers Supported on Jute Stick-Derived Activated Carbon Nanosheets.

Developing efficient, lightweight, and durable all-solid-state supercapacitors is crucial for future energy storage systems. The study focuses on optimizing electrode materials to achieve high capacitance and stability. This study introduces a novel two-step pyrolysis process to synthesize activated carbon nanosheets from jute sticks (JAC), resulting in an optimized JAC-2 material with a high yield (≈24%) and specific surface area (≈2600 m2 g-1). Furthermore, an innovative in situ synthesis approach is employed to synthesize hybrid nanocomposites (NiCoLDH-1@JAC-2) by integrating JAC nanosheets with nickel-cobalt-layered double hydroxide nanoflowers (NiCoLDH). These nanocomposites serve as positive electrode materials and JAC-2 as the negative electrode material in all-solid-state asymmetric hybrid supercapacitors (HSCs), exhibiting remarkable performance metrics. The HSCs achieve a specific capacitance of 750 F g-1, a specific capacity of 209 mAh g-1 (at 0.5 A g-1), and an energy density of 100 Wh kg-1 (at 250 W kg-1) using PVA/KOH solid electrolyte, while maintaining outstanding cyclic stability. Importantly, a density functional theory framework is utilized to validate the experimental findings, underscoring the potential of this novel approach for enhancing HSC performance and enabling the large-scale production of transition metal-based layered double hydroxides.

Steam Catalytic Cracking of n-Dodecane to Light Olefins over Phosphorous- and Metal-Modified Nanozeolite Y.

Nanozeolite Y was synthesized without a template and modified with phosphorous (P) and metals. P was introduced via impregnation with different weight loadings (0.5, 1, and 2 wt %), while ion exchange was developed to introduce zirconium (Zr) and cobalt (Co). The physicochemical properties of the catalysts were characterized with X-ray diffraction (XRD), N2 adsorption-desorption, temperature-programmed desorption of ammonia (NH3-TPD), and 27Al and 31P solid-state nuclear magnetic resonance (NMR). The parent nanozeolite Y showed an identical XRD pattern to that of a previous study, and the modified nanozeolite Y showed a lower crystallinity. The introduction of P altered tetrahedral Al to an octahedral coordination, which affected the catalyst acidity. Then, the catalyst was evaluated to produce olefins from n-dodecane at 550, 575, and 600 °C. The conversion, gas yield, and olefin yield increased with increasing temperature. The maximum olefin yield (63%) was achieved with the introduction of 1 wt % P with the highest selectivity to ethylene. The Co-modified nanozeolite altered the zeolite structure and exhibited similar activity to the P-modified one. Meanwhile, Zr-modified nanozeolite Y caused excessive metal distribution, blocked the porous structure of the zeolite, and then reduced the catalytic activity.

Acidity modifications of nanozeolite-Y for enhanced selectivity to olefins from the steam catalytic cracking of dodecane.

Nanozeolite-Y was synthesized in the absence of a templating agent with several modification methods. The parent nanozeolite-Y was prepared with different sodium (Na) contents and crystallization conditions. Then, the parent nanozeolite-Y was modified by ion exchange, calcination, and steam treatment. The treatment caused insignificant changes to the ratio of alumina and silica but altered the zeolite acid sites. The Lewis and Brønsted acidity changed after the treatment depending on the modification approach, as indicated by the FTIR spectroscopy of pyridine. The ammonia temperature programmed desorption (NH3-TPD) confirmed that the acid sites consisted of weak and medium sites, which decreased after modifications. Moreover, the solid-state nuclear magnetic resonance (NMR) spectroscopy revealed that the position of Al shifted from tetrahedral to a combined octahedral and pentahedral framework. The catalytic evaluation for dodecane cracking at 550 °C shows the gas yield as the main product with naphtha as a side product. The gas yield consisted of 50% light olefins from ethylene to butene. However, the process yielded 9% of coke that led to faster catalyst deactivation because of nanozeolite-Y evolution and product transformation.

Recent Progress in Carbonaceous and Redox-Active Nanoarchitectures for Hybrid Supercapacitors: Performance Evaluation, Challenges, and Future Prospects.

Due to advancements in technology, the energy demand is becoming more intense with time. The rapid fossil fuels consumption and environmental concerns triggered intensive research for alternative renewable energy resources, including sunlight and wind. Yet, due to their time-dependent operations, significant electric energy storage systems are required to store substantial energy. In this regard, electrochemical energy storage devices, like batteries and supercapacitors (SCs), have recently attracted much research attention. Recent developments in SCs demonstrated that hybrid SCs (HSCs), which combine the excellent properties of batteries and SCs, increase the specific energy, specific power, specific capacitance, and life span. Carbonaceous and redox-active materials have been explored as efficient electrode materials for applications in HSCs, ultimately enhancing their electrochemical performances. The HSCs performance significantly depends on the porosity, specific surface area, and conductivity of the electrode materials. This review article gives an overview of recent advances in developing HSCs with high specific power, specific energy, and long cyclic-life. The fabrication of various HSCs materials using carbonaceous and redox-active nanoarchitectures and their characterization are explored in-depth, including electrode development, basic principles, and device engineering. A proper investigation has been conducted regarding state-of-the-art materials as HSC electrodes. This review focuses on the most up-to-date, cutting-edge, electrode materials for HSCs and their performance. The possibilities for novel electrode materials and their impact on the HSCs performance for future energy storage are also discussed.

Electrochemical Reduction of CO2 to C1 and C2 Liquid Products on Copper-Decorated Nitrogen-Doped Carbon Nanosheets.

Due to the significant rise in atmospheric carbon dioxide (CO2) concentration and its detrimental environmental effects, the electrochemical CO2 conversion to valuable liquid products has received great interest. In this work, the copper-melamine complex was used to synthesize copper-based electrocatalysts comprising copper nanoparticles decorating thin layers of nitrogen-doped carbon nanosheets (Cu/NC). The as-prepared electrocatalysts were characterized by XRD, SEM, EDX, and TEM and investigated in the electrochemical CO2 reduction reaction (ECO2RR) to useful liquid products. The electrochemical CO2 reduction reaction was carried out in two compartments of an electrochemical H-Cell, using 0.5 M potassium bicarbonate (KHCO3) as an electrolyte; nuclear magnetic resonance (1H NMR) was used to analyze and quantify the liquid products. The electrode prepared at 700 °C (Cu/NC-700) exhibited the best dispersion for the copper nanoparticles on the carbon nanosheets (compared to Cu/NC-600 & Cu/NC-800), highest current density, highest electrochemical surface area, highest electrical conductivity, and excellent stability and faradic efficiency (FE) towards overall liquid products of 56.9% for formate and acetate at the potential of -0.8V vs. Reversible Hydrogen Electrode (RHE).

Experimental and Theoretical Study on the Interchange between Zr and Ti within the MIL-125-NH2 Metal Cluster.

This study aims to investigate the effect of replacing Ti with Zr in the SBU of MIL-125-NH2 . We were able to replace Ti with Zr in the mixed metal synthesis of MIL-125-NH2 , for the first time. After experimentally confirming the consistency in their framework structure and comparing their morphology, we related the femtosecond light dynamics with photocatalytic CO2 visible light conversion yield of the different variants in order to establish the composition-function relation in MIL-125 vis a vis CO2 reduction. Introducing Zr to the system was found to cause structure defects due to missing linkers. The lifetime of the charge carriers for the mixed metal samples were shorter than that of the MIL-125-NH2 . The study of CO2 photocatalytic reduction under visible light indicated that the NH2 group enhances the photocatalytic activity while the Zr incorporation inside the MIL framework introduces no significant improvements. In addition, the material systems were modelled and simulated through DFT calculations which concluded that the decrease of the photocatalytic activity is not related to the system electronic structure, insinuating that defects are the culprit.

Trends and Prospects in UiO-66 Metal-Organic Framework for CO2 Capture, Separation, and Conversion.

Among thousands of known metal-organic frameworks (MOFs), the University of Oslo's MOF (UiO-66) exhibits unique structure topology, chemical and thermal stability, and intriguing tunable properties, that have gained incredible research interest. This paper summarizes the structural advancement of UiO-66 and its role in CO2 capture, separation, and transformation into chemicals. The first part of the review summarizes the fast-growing literature related to the CO2 capture reported by UiO-66 during the past ten years. The second part provides an overview of various advancements in UiO-66 membranes in CO2 purification. The third part describes the role of UiO-66 and its composites as catalysts for CO2 conversion into useful products. Despite many achievements, significant challenges associated with UiO-66 are addressed, and future perspectives are comprehensively presented to forecast how UiO-66 might be used further for CO2 management.

Mixed Dimensional Nanostructure (UiO-66-Decorated MWCNT) as a Nanofiller in Mixed-Matrix Membranes for Enhanced CO2 /CH4 Separation.

Mixed-matrix membranes (MMMs) with combination of two distinct dimensional nanofillers (such as 1D-3D, 2D-3D, or 3D-3D, etc.) have drawn special attention for gas separation applications due to their concerted effects on gas permeation and mechanical properties. An amine-functionalized 1D multiwalled carbon nanotube (NH2 -MWCNT) with exceptional mechanical strength and rapid gas transport was crosslinked with an amine-functionalized 3D metal-organic framework (UiO-66-NH2 ) with high CO2 affinity in a Schiff base reaction. The resultant crosslinked mixed-dimensional nanostructure was used as a nanofiller in a polysulfone (PSf) polymer matrix to explore the underlying synergy between 1D and 3D nanostructures on the gas separation performance of MMMs. Cross-sectional scanning electron microscopy and mapping revealed the homogenous dispersion of UiO-66@MWCNT in the polymer matrix. The MMM containing 5.0 wt. % UiO-66@MWCNT demonstrated a superior permeability 8.3 Barrer as compared to the 4.2 Barrer of pure PSf membrane for CO2 . Moreover, the selectivity (CO2 /CH4 ) of this MMM was enhanced to 39.5 from the 28.0 observed for pure PSf under similar conditions of pressure and temperature.

The validity of laser diffraction system to reproduce hydrometer results for grain size analysis in geotechnical applications.

The grain size analysis plays a significant role in any geotechnical study. The grain size analysis, by means of sieving, is usually used for coarse material of particle size > 75 µm. For the fine material; the sedimentation methods are frequently adopted (e.g., hydrometers). Other methods also exist such as electron microscopy, digital image analysis and laser diffraction. The fine geomaterials commonly undergo agglomeration which makes the recognition of individual grain size using digital image analysis or electron microscopy challenging. To facilitate and enhance the grain-size analysis, this study was conducted using the Laser Diffraction System (LDS). Seven samples with different nature (composition and texture) and sources were analyzed by hydrometer and LDS. For LDS, various factors were studied such as air pressure, sonication, dilution, refractive index, and distribution method (volume or number). The results were compared qualitatively and quantitatively based on soil classification systems, fractal dimensions, and other parameters. Furthermore, this study provided a novel criterion to determine which LDS distribution method (volume or number) is to be used depending on the Liquid Limit. A combined sieve-LDS system is recommended to obtain the entire grain size distribution. It is concluded that the LDS is a viable technique that can replace the time-consuming hydrometer method to assess the grain-size distribution.

Highly Efficient Permeation and Separation of Gases with Metal-Organic Frameworks Confined in Polymeric Nanochannels.

This work demonstrates the confinement of porous metal-organic framework (HKUST-1) on the surface and walls of track-etched nanochannel in polyethylene terephthalate (np-PET) membrane using a liquid-phase epitaxy (LPE) technique. The composite membrane (HKUST-1/np-PET) exhibits defect-free MOF growth continuity, strong attachment of MOF to the support, and a high degree of flexibility. The high flexibility and the strong confinement of the MOF in composite membrane results from (i) the flexible np-PET support, (ii) coordination attachment between HKUST-1 and the support, and (iii) the growth of HKUST-1 crystal in nanoconfined geometries. The MOF has a preferred growth orientation with a window size of 3.5 Å, resulting in a clear cut-off of CO2 from natural gas and olefins. The experimental results and DFT calculations show that the restricted diffusion of gases only takes place through the nanoporous MOF confined in the np-PET substrate. This research thereby provides a new perspective to grow other porous MOFs in artificially prepared nanochannels for the realization of continuous, flexible, and defect-free membranes for various applications.

An Ultrasensitive and Selective Metal-Organic Framework Chemosensor for Palladium Detection in Water.

A new europium-based metal-organic framework, termed KFUPM-3, was constructed using an allyloxy-functionalized linker. As a result of coordinative interactions between the allyloxy moieties and Pd2+, highly selective changes in both the absorption and emission spectra of KFUPM-3 were observed. Accordingly, KFUPM-3 was demonstrated to have an ultrasensitive Pd2+ detection limit (44 ppb), regenerative properties without loss in performance, detection of palladium in different oxidation states and in the presence of other competitor metal ions, and fully functional sensing capabilities over a wide pH range.

Electrocatalytic CO2 Reduction: From Homogeneous Catalysts to Heterogeneous-Based Reticular Chemistry.

CO2, emitted mainly from fossil fuel combustion, is one of the major greenhouse gases. CO2 could be converted into more valuable chemical feedstocks including CO, HCOOH, HCHO, CH3OH, or CH4. To reduce CO2, catalysts were designed and their unique characteristics were utilized based on types of reaction processes, including catalytic hydrogenation, complex metal hydrides, photocatalysis, biological reduction, and electrochemical reduction. Indeed, the electroreduction method has received much consideration lately due to the simple operation, as well as environmentally friendly procedures that need to be optimized by both of the catalysts and the electrochemical process. In the past few decades, we have witnessed an explosion in development in materials science-especially in regards to the porous crystalline materials based on the strong covalent bond of the organic linkers containing light elements (Covalent organic frameworks, COFs), as well as the hybrid materials that possess organic backbones and inorganic metal-oxo clusters (Metal-organic frameworks, MOFs). Owing to the large surface area and high active site density that belong to these tailorable structures, MOFs and COFs can be applied to many practical applications, such as gas storage and separation, drug release, sensing, and catalysis. Beyond those applications, which have been abundantly studied since the 1990s, CO2 reduction catalyzed by reticular and extended structures of MOFs or COFs has been more recently turned to the next step of state-of-the-art application. In this perspective, we highlight the achievement of homogeneous catalysts used for CO2 electrochemical conversion and contrast it with the advances in new porous catalyst-based reticular chemistry. We then discuss the role of new catalytic systems designed in light of reticular chemistry in the heterogeneous-catalyzed reduction of CO2.

Interconnected Hollow Cobalt Phosphide Grown on Carbon Nanotubes for Hydrogen Evolution Reaction.

Transition-metal phosphides are deemed as potential alternative to platinum for large-scale and sustainable electrocatalytic hydrogen production from water. In this study, facile preparation of interconnected hollow cobalt monophosphide (CoP) supported on carbon nanotubes is demonstrated and evaluated as a low-cost electrocatalyst for hydrogen evolution reaction. Hexamethylenetetramine is used as a structure-directing agent to guide the formation of interconnected cobalt oxide, which further grows into interconnected hollow CoP. Interconnected and hollow microstructural artifacts impart benign attributes, such as enhanced specific and electrochemically active surface area, low intrinsic charge transfer resistance, high interfacial charge transfer kinetics, and improved mass transport, to the electrocatalyst. As a result, the as-prepared electrode exhibits remarkable electrocatalytic performance, low onset (18 mV) and overpotential (η10 = 73 mV); small Tafel slope (54.6 mV dec-1); and high turnover frequency (0.58 s-1 at η = 73 mV). In addition, the electrode shows excellent electrochemical stability.

Tuning the Interplay between Selectivity and Permeability of ZIF-7 Mixed Matrix Membranes.

Nanoparticles of zeolitic imidazolate framework-7 (nZIF-7) were blended with poly(ether imide) (PEI) to fabricate a new mixed-matrix membrane (nZIF-7/PEI). nZIF-7 was chosen in order to demonstrate the power of postsynthetic modification (PSM) by linker exchange of benzimidazolate to benzotriazolate for tuning the permeability and selectivity properties of a resulting membrane (PSM-nZIF-7/PEI). These two new membranes were subjected to constant volume, variable pressure gas permeation measurements (H2, N2, O2, CH4, CO2, C2H6, and C3H8), in which unique gas separation behavior was observed when compared to the pure PEI membrane. Specifically, the nZIF-7/PEI membrane exhibited the highest selectivities for CO2/CH4, CO2/C2H6, and CO2/C3H8 gas pairs. Furthermore, PSM-nZIF-7/PEI membrane displayed the highest permeabilities, which resulted in H2/CH4, N2/CH4, and H2/CO2 permselectivities that are remarkably well-positioned on the Robeson upper bound curves, thus, indicating its potential applicability for use in practical gas purifications.

Sonochemical-driven ultrafast facile synthesis of SnO2 nanoparticles: Growth mechanism structural electrical and hydrogen gas sensing properties.

Synthesis of SnO2 nanoparticles have been successfully accomplished moderately at lower temperature by facile, rapid, efficient and mild ultrasonic irradiation method. The as-grown SnO2 nanoparticles are investigated by various characterization techniques in terms of structural, optical, electrical and gas sensing properties. XRD investigation has shown that the SnO2 nanoparticles materials exhibit single rutile crystal phase with high crystallinity. FESEM studies showed uniform and monodisperse morphology of SnO2 nanoparticles. The chemical composition of SnO2 was systematically studied by EDX measurements. Additional confirmation of three Raman shifts (432, 630, 772cm-1) indicated the characteristic properties of the rutile phase of the as-grown SnO2 nanoparticles. The optical properties of SnO2 nanoparticles were examined by DRS, and the electronic band gap of SnO2 nanoparticles were around 3.6eV. Electrical properties of the SnO2 nanoparticles measured at various temperatures have shown the semiconducting properties. Surface area and pore size of synthesized nanoparticles were analyzed from BET. It has been revealed that SnO2 nanoparticles have surface area is 47.8574m2/g and the pore size is 10.5nm. Moreover, hydrogen gas sensor made of SnO2 nanoparticles showed good sensitivity and faster response for the hydrogen gas. This method is template-less and surfactant-free which circumvents rigorous reaction work-up for the former removal, reaction temperature and reaction time compared to hydrothermal synthesis and pertinent to many other oxide materials.

Sonochemical Assisted Solvothermal Synthesis of Gallium Oxynitride Nanosheets and their Solar-Driven Photoelectrochemical Water-Splitting Applications.

Gallium oxynitride (GaON) nanosheets for photoelectrochemical (PEC) analysis are synthesized via direct solvothermal approach. Their FE-SEM revealed nanosheets morphology of GaON prepared at a reaction time of 24 hours at 180 °C. The elemental composition and mapping of Ga, O and N are carried out through electron dispersive X-ray spectroscopy (EDX). The cubic structure of GaON nanosheets is elucidated by X-ray diffraction (XRD)analysis. The X-ray Photoelectron Spectroscopy (XPS) further confirms Ga, O and N in their respective ratios and states. The optical properties of GaON nanosheets are evaluated via UV-Visible, Photoluminescence (PL) and Raman spectroscopy's. The band gap energy of ~1.9 eV is calculated from both absorption and diffused reflectance spectroscopy's which showed stronger p-d repulsions in the Ga (3d) and N (2p) orbitals. This effect and chemical nitridation caused upward shift of valence band and band gap reduction. The GaON nanosheets are investigated for PEC studies in a standard three electrode system under 1 Sun irradiation in 0.5 M Na2SO4. The photocurrent generation, oxidation and reduction reactions during the measurements are observed by Chronoampereometry, linear sweep Voltametry (LSV) and Cyclic Voltametry (CV) respectively. Henceforward, these GaON nanosheets can be used as potential photocatalyts for solar water splitting.

Fluorescein-N-Methylimidazole Conjugate as Cu(2+) Sensor in Mixed Aqueous Media Through Electron Transfer.

A new highly selective, chromogenic, and fluorogenic Cu(2+) chemosensor, fluorescein-N-methylimidazole conjugate 1, and another fluorescein-N-imidazole conjugate 2 were synthesized and investigated by UV-visible and fluorescence spectroscopy. The sensing of Cu(2+) quenches the emission band of 1 at λmax = 525 nm, with an association constant (K a = 1.0 x 10(7) M(-1)) and a stoichiometry of 1:1 in a buffered H2O: MeOH solution (4:1, pH = 7.4). The Cu(2+) detection limit for chemosensor 1 is 37 nM. The presence of the N-methyl group in 1 increased the Cu(2+) binding selectivity, resulting in a stronger binding constant and a broader pH working range (pH 5-10) in comparison to 2. The fluorescence in 1 and 2 is caused by electron transfer phenomenon from the imidazole nitrogen to fluorescein, which is readily inhibited by Cu(2+) binding.

Enhanced photoelectrochemical and photocatalytic activity of WO3-surface modified TiO2 thin film.

Development of nanostructured photocatalysts for harnessing solar energy in energy-efficient and environmentally benign way remains an important area of research. Pure and WO3-surface modified thin films of TiO2 were prepared by magnetron sputtering on indium tin oxide glass, and photoelectrochemical and photocatalytic activities of these films were studied. TiO2 particles were <50 nm, while deposited WO3 particles were <20 nm in size. An enhancement in the photocurrent was observed when the TiO2 surface was modified WO3 nanoparticles. Effect of potential, WO3 amount, and radiations of different wavelengths on the photoelectrochemical activity of TiO2 electrodes was investigated. Photocatalytic activity of TiO2 and WO3-modified TiO2 for the decolorization of methyl orange was tested. Graphical abstractWO3-surface modified TiO2 film showing better photocatalytic and photoelectrocatalytic activity.