Bifunctional porphyrin-based metal-organic polymers for electrochemical water splitting

Electrochemical water splitting offers the potential for environmentally friendly hydrogen and oxygen gas generation. Here, we present the synthesis, characterization, and electrochemical analyses of four organic polymers where metalloporphyrins are the active center nodes. These materials were obtained from the polymerization reaction of poly(p-phenylene terephtalamide) (PPTA) with the respective amino-functionalized metalloporphyrins, where M = Fe, 1; Co, 2; Ni, 3; Cu, 4. Scanning and transmission electron microscopy images (SEM and TEM) show that these polymers exhibit a layer-type morphology, which is attributed to hydrogen bonding and π-π stacking between the metalloporphyrin nodes. The synthesized materials were characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), UV-Vis spectroscopy, and Fourier-transform infrared spectroscopy (FT-IR). Among the materials studied, the cobalt-based polymer, 2, demonstrates a bifunctional electrocatalytic activity for oxygen (OER) and hydrogen (HER) evolution reactions with overpotentials (η10) of 337 mV and 435 mV, respectively. The Fe, 1, and Ni, 2, polymers are less active for HER with maximum current densities (jmax) of 12.6 and 19.1 mA cm-2 and η10 678 mV, 644 mV. Polymer 2 achieves a jmax of 37.7 mA cm-2 for HER and 133 mA cm-2 for OER. The copper-based material, 4, on the other hand, shows selectivity towards HER with an overpotential (η) of 436 mV and a maximum current density (j) of 45.5 mA cm-2. The bifunctional electrocatalytic performance was tested in the overall water-splitting setup, where polymer 2 requires a cell voltage of 1.64 V at 10 mA cm-2. This work presents a novel approach to heterogenized molecular systems, providing materials with exceptional structural characteristics and enhanced electrocatalytic capabilities.

Photo/electro catalytic green hydrogen production promoted by Ga modified Co0.6Cu0.4Fe2O4 nano catalysts

The current work concentrates on the fabrication of Ga doped Co0.6Cu0.4Fe2O4 nanocatalysts via sol-gel auto-combustion (SGA) for the production of green and sustainable source of energy i.e., hydrogen through photocatalytic and electrocatalytic routes. Single-phased cubic crystal structure with Fd3m geometry was observed through XRD patterns. FESEM images show the aggregated and spherical shaped grains with distinct grain boundaries and average grain size of 1.04 and 1.39 μm for the Co0.6Cu0.4Fe2O4, and Co0.6Cu0.4Ga0.02Fe1.98O4 nanomaterials. Soft magnetic behaviour with a coercivity (Hc) and saturation magnetization (Ms) of 235.32-357.26 Oe and 54.65-61.11 emu/g was obtained for the produced nanomaterials. The estimation of photocatalytic nature for generating H2 was conducted using the sacrificial agents i.e., 0.128 M Na2S and 0.079 M Na2SO3. The analysis focused on measuring the maximum H2 generation was achieved by photocatalysts throughout three consecutive 4-h cycles. Out of all compositions, Co0.6Cu0.4Ga0.02Fe1.98O4 nanomaterial have the highest photocatalytic activity of 16.71 mmol gcat-1. However, the electrocatalytic behaviour of prepared Co0.6Cu0.4GaxFe2-xO4 (x = 0.00-0.03) electrocatalysts were determined for HER (Hydrogen evolution reaction) reaction. The overpotential values of Co0.6Cu0.4Fe2O4, Co0.6Cu0.4Ga0.01Fe1.99O4, Co0.6Cu0.4Ga0.02Fe1.98O4, and Co0.6Cu0.4Ga0.03Fe1.97O4 catalysts at 10 mA cm-2 were -0.81, -0.85, -1.03, and 1.21 V, correspondingly. Thus, at cathode current density of 10 mA/cm-2, an elevation in overpotential was noted, which indicates that the undoped Co0.6Cu0.4Fe2O4 (x = 0.00) electrocatalyst have remarkable electrocatalytic HER activity. Consequently, owing to photo/electro catalytic water splitting traits, the prepared catalysts are highly efficient for the green hydrogen generation.

High-Performance Hydrogen-Selective Pd-Ag Membranes Modified with Pd-Pt Nanoparticles for Use in Steam Reforming Membrane Reactors

A unique method for synthesizing a surface modifier for metallic hydrogen permeable membranes based on non-classic bimetallic pentagonally structured Pd-Pt nanoparticles was developed. It was found that nanoparticles had unique hollow structures. This significantly reduced the cost of their production due to the economical use of metal. According to the results of electrochemical studies, a synthesized bimetallic Pd-Pt/Pd-Ag modifier showed excellent catalytic activity (up to 60.72 mA cm-2), long-term stability, and resistance to COads poisoning in the alkaline oxidation reaction of methanol. The membrane with the pentagonally structured Pd-Pt/Pd-Ag modifier showed the highest hydrogen permeation flux density, up to 27.3 mmol s-1 m-2. The obtained hydrogen flux density was two times higher than that for membranes with a classic Pdblack/Pd-Ag modifier and an order of magnitude higher than that for an unmodified membrane. Since the rate of transcrystalline hydrogen transfer through a membrane increased, while the speed of transfer through defects remained unchanged, a one and a half times rise in selectivity of the developed Pd-Pt/Pd-Ag membranes was recorded, and it amounted to 3514. The achieved results were due to both the synergistic effect of the combination of Pd and Pt metals in the modifier composition and the large number of available catalytically active centers, which were present as a result of non-classic morphology with high-index facets. The specific faceting, defect structure, and unusual properties provide great opportunities for the application of nanoparticles in the areas of membrane reactors, electrocatalysis, and the petrochemical and hydrogen industries.

Recent Progress of 3D Printing of Polymer Electrolyte Membrane-Based Fuel Cells for Clean Energy Generation

This review summarizes recent advances in the application of 3D printing (additive manufacturing) for the fabrication of various components of hydrogen fuel cells with a polymer electrolyte membrane (HFC-PEMs). This type of fuel cell is an example of green renewable energy, but its active implementation into the real industry is fraught with a number of problems, including rapid degradation and low efficiency. The application of 3D printing is promising for improvement in HFC-PEM performance due to the possibility of creating complex geometric shapes, the exact location of components on the substrate, as well as the low-cost and simplicity of the process. This review examines the use of various 3D printing techniques, such as inkjet printing, fused deposition modeling (FDM) and stereolithography, for the production/modification of electrodes, gas diffusion and catalyst layers, as well as bipolar plates. In conclusion, the challenges and possible solutions of the identified drawbacks for further development in this field of research are discussed. It is expected that this review article will benefit both representatives of applied science interested in specific engineering solutions and fundamental science aimed at studying the processes occurring in the fuel cell.

Formic Acid Dehydrogenation through Ligand Design Strategy of Amidation in Half-Sandwich Ir Complexes

A series of Cp*Ir (Cp* = pentamethylcyclopentadienyl) complexes with amidated 8-aminoquinoline ligands were synthesized and tested for formic acid (FA) dehydrogenation. These complexes showed improved activities compared to pristine 8-anminquinoline (L1). Specially, amidation changed the outer coordination sphere of the complex (3) bearing N-8-quinolinylformamide (L3), and 3 was proved to be a proton-responsive catalyst. Our experimental results and DFT calculations demonstrated that the deprotonated carbanion in L3 could interact with a water molecule to stabilize the transition states and lower the reaction energy barrier, which improved the reaction activity. A turnover frequency of 206250 h-1 was achieved by 3 under optimized conditions. This study presents a method to develop new ligands and modify the existing ligands for efficient FA dehydrogenation.

Construction of ZnxCdyS with a 3D Hierarchical Structure for Enhanced Photocatalytic Hydrogen Production from Water Splitting

The ZnxCdyS has been proven to have unique photoelectric properties, but its synthesis method and photocatalytic water cracking performance need to be further improved. In this paper, Cd-MOF@ZIF-8 with a MOF-on-MOF (MOF = metal-organic framework) structure was prepared by a simple ion adsorption method. Then, a CdS/ZnxCdyS heterojunction with a 3D hierarchical structure was formed by solvothermal sulfidation. The prepared catalysts with different Zn/Cd ratios show an improved hydrogen production performance for photocatalytic water splitting, and the hydrogen evolution rate of Zn1Cd1S can reach up to 29.2 mmol·g-1·h-1. The excellent photocatalytic activity not only benefits from ZnxCdyS strong light conversion ability but also is closely related to the hierarchical structure and large specific surface area. A type II heterojunction also plays an important role in the spatial separation of photogenerated carriers. This paper provides a simple and feasible idea for the synthesis of a photocatalyst with a large specific surface area using a MOF-on-MOF synthesis strategy.

Electrochemical Properties and Structure of Membranes from Perfluorinated Copolymers Modified with Nanodiamonds

In this study, we aimed to design and research proton-conducting membranes based on Aquivion®-type material that had been modified with detonation nanodiamonds (particle size 4-5 nm, 0.25-5.0 wt. %). These nanodiamonds carried different functional groups (H, OH, COOH, F) that provided the hydrophilicity of the diamond surface with positive or negative potential, or that strengthened the hydrophobicity of the diamonds. These variations in diamond properties allowed us to find ways to improve the composite structure so as to achieve better ion conductivity. For this purpose, we prepared three series of membrane films by first casting solutions of perfluorinated Aquivion®-type copolymers with short side chains mixed with diamonds dispersed on solid substrates. Then, we removed the solvent and the membranes were structurally stabilized during thermal treatment and transformed into their final form with -SO3H ionic groups. We found that the diamonds with a hydrogen-saturated surface, with a positive charge in aqueous media, contributed to the increase in proton conductivity of membranes to a greater rate. Meanwhile, a more developed conducting diamond-copolymer interface was formed due to electrostatic attraction to the sulfonic acid groups of the copolymer than in the case of diamonds grafted with negatively charged carboxyls, similar to sulfonic groups of the copolymer. The modification of membranes with fluorinated diamonds led to a 5-fold decrease in the conductivity of the composite, even when only a fraction of diamonds of 1 wt. % were used, which was explained by the disruption in the connectivity of ion channels during the interaction of such diamonds mainly with fluorocarbon chains of the copolymer. We discussed the specifics of the mechanism of conductivity in composites with various diamonds in connection with structural data obtained in neutron scattering experiments on dry membranes, as well as ideas about the formation of cylindrical micelles with central ion channels and shells composed of hydrophobic copolymer chains. Finally, the characteristics of the network of ion channels in the composites were found depending on the type and amount of introduced diamonds, and correlations between the structure and conductivity of the membranes were established.

Design and operation performance of the plate-heat transfer type hydrogen production reactor for bio-methanol reforming

In this paper, the plate-heat transfer type bio-methanol steam reforming reactor for hydrogen fuel cell vehicles and its operation performance was studied. The structure of the plate-heat transfer type for bio-methanol reforming has been designed and optimized with the application parameters of hydrogen production capacity, hydrogen production rate, bio-methanol conversion rate, volume limitation. Results showed the catalyst particle size has little influence when it less than 0.85 mm; However, when the catalyst loading was 20 g and the feed rate of bio-methanol solution was 1.5 mL/min, the effect of reforming bio-methanol was the best. At this time, the specific hydrogen production was 64.062 mL/gcat.min, the hydrogen production rate was 21.354 mL/s, the bio-methanol conversion rate was 82.25%. This paper can provide scientific reference for further research and development of high-efficiency and low-cost bio-methanol reforming hydrogen production equipment.

Approaches to the Modification of Perfluorosulfonic Acid Membranes

Polymer ion-exchange membranes are featured in a variety of modern technologies including separation, concentration and purification of gases and liquids, chemical and electrochemical synthesis, and hydrogen power generation. In addition to transport properties, the strength, elasticity, and chemical stability of such materials are important characteristics for practical applications. Perfluorosulfonic acid (PFSA) membranes are characterized by an optimal combination of these properties. Today, one of the most well-known practical applications of PFSA membranes is the development of fuel cells. Some disadvantages of PFSA membranes, such as low conductivity at low humidity and high temperature limit their application. The approaches to optimization of properties are modification of commercial PFSA membranes and polymers by incorporation of different additive or pretreatment. This review summarizes the approaches to their modification, which will allow the creation of materials with a different set of functional properties, differing in ion transport (first of all proton conductivity) and selectivity, based on commercially available samples. These approaches include the use of different treatment techniques as well as the creation of hybrid materials containing dopant nanoparticles. Modification of the intrapore space of the membrane was shown to be a way of targeting the key functional properties of the membranes.

Improving PFSA Membranes Using Sulfonated Nanodiamonds

Aquivion®-type perfluorosulfonic acid membranes with a polytetrafluoroethylene backbone and short side chains with sulfonic acid groups at the ends have great prospects for operating in hydrogen fuel cells. To improve the conducting properties of membranes, various types of nanofillers can be used. We prepared compositional Aquivion®-type membranes with embedded detonation nanodiamond particles. Nanodiamonds were chemically modified with sulfonic acid groups to increase the entire amount of ionogenic groups involved in the proton conductivity mechanism in compositional membranes. We demonstrated the rise of proton conductivity at 0.5-2 wt.% of sulfonated nanodiamonds in membranes, which was accompanied by good mechanical properties. The basic structural elements, conducting channels in membranes, were not destroyed in the presence of nanodiamonds, as follows from small-angle neutron scattering data. The prepared compositional membranes can be used in hydrogen fuel cells to achieve improved performance.

Perfluorosulfonic Acid Membranes with Short and Long Side Chains and Their Use in Sensors for the Determination of Markers of Viral Diseases in Saliva

The development of accessible express methods to determine markers of viral diseases in saliva is currently an actual problem. Novel cross-sensitive sensors based on Donnan potential with bio-comparable perfluorosulfonic acid membranes for the determination of salivary viral markers (N-acetyl-L-methionine, L-carnitine, and L-lysine) were proposed. Membranes were formed by casting from dispersions of Nafion or Aquivion in N-methyl-2-pyrollidone or in a mixture of isopropyl alcohol and water. The influence of the polymer equivalent weight and the nature of dispersing liquid on water uptake, ion conductivity, and slope of Donnan potential for the membranes in H+ and Na+ form was investigated. The varying of the sorption and transport properties of perfluorosulfonic acid membranes provided a change in the distribution of the sensor sensitivity to N-acetyl-L-methionine, L-carnitine, and L-lysine ions, which was necessary for multisensory system development. The simultaneous determination of three analytes, and the group analysis of them in artificial saliva solutions, was performed. The errors of N-acetyl-L-methionine and L-carnitine determination were 4-12 and 3-11%, respectively. The determination of L-lysine was complicated by its interaction with Ca2+ ions. The error of the group analysis was no greater than 9%. The reverse character of the viral markers' sorption by the membranes provided long-term sensor operation.

The Effect of Divinylbenzene on the Structure and Properties of Polyethylene Films with Related Radiation Chemical Grafted Polystyrene and Sulfocationite Membranes

In the present work, the effect of divinylbenzene (DVB) on the kinetics of post-radiation chemical graft polymerization styrene (St) on polyethylene (PE) film and its structural and morphological features were investigated. It has been found that the dependence of the degree of polystyrene (PS) grafting on the DVB concentration in the solution is extreme. An increase in the rate of graft polymerization at low concentrations of DVB in the solution is associated with a decrease in the mobility of the growing chains of PS. A decrease in the rate of graft polymerization at high concentrations of DVB is associated with a decrease in the rate of diffusion of St and iron(II) ions in the cross-linked network structure of macromolecules of graft PS. A comparative analysis of the IR transmission and multiple attenuated total internal reflection spectra of the films with graft PS shows that graft polymerization of St in the presence of DVB leads to the enrichment of the film surface layers in PS. These results have been confirmed by the data on the distribution of sulfur in these films after sulfonation. The micrographs of the surface of the grafted films show the formation of cross-linked local microphases of PS with fixed interfaces.

AI for Nanomaterials Development in Clean Energy and Carbon Capture, Utilization and Storage (CCUS)

Zero-carbon energy and negative emission technologies are crucial for achieving a carbon neutral future, and nanomaterials have played critical roles in advancing such technologies. More recently, due to the explosive growth in data, the adoption and exploitation of artificial intelligence (AI) as part of the materials research framework have had a tremendous impact on the development of nanomaterials. AI has enabled revolutionary next-generation paradigms to significantly accelerate all stages of material discovery and facilitate the exploration of the enormous design space. In this review, we summarize recent advancements of AI applications in nanomaterials discovery, with a special emphasis on the selected applications of AI and nanotechnology for the net-zero emission future including the development of solar cells, hydrogen energy, battery materials for renewable energy, and CO₂ capture and conversion materials for carbon capture, utilization and storage (CCUS) technologies. In addition, we discuss the limitations and challenges of current AI applications in this area by identifying the gaps that exist in current development. Finally, we present the prospect for future research directions in order to facilitate the large-scale applications of artificial intelligence for advancements in nanomaterials.

Mitigation of Physical Aging of Polymeric Membrane Materials for Gas Separation: A Review

The first commercial hollow fiber and flat sheet gas separation membranes were produced in the late 1970s from the glassy polymers polysulfone and poly(vinyltrimethyl silane), respectively, and the first industrial application was hydrogen recovery from ammonia purge gas in the ammonia synthesis loop. Membranes based on glassy polymers (polysulfone, cellulose acetate, polyimides, substituted polycarbonate, and poly(phenylene oxide)) are currently used in various industrial processes, such as hydrogen purification, nitrogen production, and natural gas treatment. However, the glassy polymers are in a non-equilibrium state; therefore, these polymers undergo a process of physical aging, which is accompanied by the spontaneous reduction of free volume and gas permeability over time. The high free volume glassy polymers, such as poly(1-trimethylgermyl-1-propyne), polymers of intrinsic microporosity PIMs, and fluoropolymers Teflon^® AF and Hyflon^® AD, undergo significant physical aging. Herein, we outline the latest progress in the field of increasing durability and mitigating the physical aging of glassy polymer membrane materials and thin-film composite membranes for gas separation. Special attention is paid to such approaches as the addition of porous nanoparticles (via mixed matrix membranes), polymer crosslinking, and a combination of crosslinking and addition of nanoparticles.

Alumina supported copper oxide nanoparticles (CuO/Al2O3) as high-performance electrocatalysts for hydrazine oxidation reaction

Direct hydrazine liquid fuel cell (DHFC) is perceived as effectual energy generating mean owing to high conversion efficiency and energy density. However, the development of well-designed, cost effective and high performance electrocatalysts is the paramount to establish DHFCs as efficient energy generating technology. Herein, gamma alumina supported copper oxide nanocatalysts (CuO/Al₂O₃) are synthesized via impregnation method and investigated for their electrocatalytic potential towards hydrazine oxidation reaction. CuO with different weight percentages i.e., 4%, 8%, 12%, 16% and 20% are impregnated on gamma alumina support. X-ray diffraction analysis revealed the cubic crystal structure and nanosized particles of the prepared metal oxides. Transmission electron microscopy also referred to the cubic morphology and nanoparticle formation. Electrochemical oxidation potential of the CuO/Al₂O₃ nanoparticles is explored via cyclic voltammetry as the analytical tool. Optimization of conditions and electrocatalytic studies shown that 16% CuO/Al₂O₃ presented the best electronic properties towards N₂H₂ oxidation reaction. BET analysis ascertained the high surface area (131.2546 m² g¹) and large pore diameter (0.279605 cm³ g^-1) for 16% CuO/Al₂O₃. Nanoparticle formation, high porosity and enlarged surface area of the proposed catalysts resulted in significant oxidation current output (600 μA), high current density (8.2 mA cm^-2) and low charge transfer resistance (3.7 kΩ). Electrooxidation of hydrazine on such an affordable and novel electrocatalyst opens a gateway to further explore the metal oxide impregnated alumina materials for different electrochemical applications.

Correlation between Nafion Morphology in Various Dispersion Liquids and Properties of the Cast Membranes

Nafion is a perfluorosulfonic acid polymer that is most commonly used in proton-exchange membrane fuel cells. The processes of pretreatment and formation of such membranes strongly affect their properties. In this work, dispersions of Nafion in various ionic forms and dispersing liquids (ethylene glycol, N,N-dimethylformamide, N-methyl-2-pyrrolidone and isopropyl alcohol-water mixtures in different ratios) were obtained and studied. Membranes fabricated by casting of the various dispersions were also studied. The effect of the nature of the dispersing liquid and the counterion on the properties of Nafion dispersions, the morphology of the polymer in the dispersions and the characteristics of the membranes obtained from them has been shown. Based on the overall results, it can be concluded that the use of perfluorosulfonic acid dispersions in aprotic polar solvents is advisable for obtaining membranes by the casting procedure. This is because it provides optimal polymer morphology in the dispersion, which leads to the formation of films with good selectivity, mechanical and transport properties. The performed investigations show the relationship between the composition of dispersions, the morphology of the polymer and the properties of the membranes formed from them by the casting procedure.

Dependence of the Atomic Structure of Solid Solutions in the Pd-Cu System Ordered According to the B2 Type on the Composition

Owing to exceptionally high selectivity, membranes based on palladium alloys are widely used for obtaining high-purity hydrogen. An important issue for providing high hydrogen permeability of the membranes is to form the required phase composition. The structural organization of the solid solutions consisting of Cu–36.4 at .% Pd and Cu–50 at .% Pd were studied by X-ray diffraction (XRD), electron diffraction (ED), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDXS). It was found that the former composition can be ordered in the temperature range of 300–400 °C and in the heating (up to 800 °C)–cooling cycle. In the presence of excess Cu atoms (27.2%), this structure can be represented by CsCl type structural units (β-phase) and distributed body center cubic (BCC) copper structural units in the corresponding concentration dose. The formation of a single crystal ordered phase within the mosaic blocks of the disordered phase was established. Experimental evidence was obtained for the separation of the α-phase solid solution in the elemental composition; the very low rate of ordering inherent in this system was attributed to this effect. The hydrogen permeability of a foil of the equiatomic composition was described.

Polystyrene-Based Single-Ion Conducting Polymer Electrolyte for Lithium Metal Batteries

Lithium metal batteries are one of the more promising replacements for lithium-ion batteries owing to their ability to reach high energy densities. The main problem limiting their commercial application is the formation of dendrites, which significantly reduces their durability and renders the batteries unsafe. In the present work, we used a single-ion conducting gel polymer electrolyte based on a poly(ethylene-ran-butylene)-block-polystyrene (SEBS) block copolymer, which was functionalized with benzenesulfonylimide anions and plasticized by a mixture of ethylene carbonate and dimethylacetamide (SSEBS-Ph-EC-DMA), with a solvent uptake of 160% (~12 solvent molecules per one functional group of the membrane). The SSEBS-Ph-EC-DMA electrolyte exhibits an ionic conductivity of 0.6 mSm∙cm−1 at 25 °C and appears to be a cationic conductor (TLi+ = 0.72). SSEBS-Ph-EC-DMA is electrochemically stable up to 4.1 V. Symmetrical Li|Li cells; further, with regard to SSEBS-Ph-EC-DMA membrane electrolytes, it showed a good performance (~0.10 V at first cycles and <0.23 V after 700 h of cycling at ±0.1 mA∙cm−2 and ±0.05 mAh∙cm−2). The LiFePO4|SSEBS-Ph-EC-DMA|Li battery showed discharge capacity values of 100 mAh∙g−1 and a 100% Coulomb efficiency, at a cycling rate of 0.1C.

Synthesis and Study of Palladium Mono- and Bimetallic (with Ag and Pt) Nanoparticles in Catalytic and Membrane Hydrogen Processes

A controlled strategy for the electrochemical synthesis of mono- and bimetallic nanoparticles with a unique and complex morphology has been developed. The investigation of the effect of changing the surfactant concentration and current density regulating the medium pH has revealed the fundamental patterns of nanoparticle growth. The developed method has allowed to synthesis of nanoparticles with a controlled pentabranched structure for the monometallic palladium as well as for favorable combinations of metals-Pd-Ag and Pd-Pt. The obtained nanoparticles were investigated in alkaline methanol oxidation. The results demonstrated quite high catalytic activity up to 83.51 mA cm^-2 and long-term stability, which are caused by the increase in electrochemically active surface area by increasing the active center's number. This was made possible due to the creation of unusual nanoparticle morphology, namely the presence of high-energy high-index facets. The developed nanoparticles were also studied as a modifying coating for hydrogen-permeable membranes in the processes of hydrogen transport. The membranes coated with the nanoparticles demonstrated sufficiently high hydrogen flux up to 11.33 mmol s^-1 m^-2 and high H₂/N₂ selectivity up to 2254. Such results can be explained by the obvious acceleration of surface processes through the application of the developed nanoparticles. The novel synthesis strategy can potentially be extended to other metal nanoparticle systems. Thus it can be an effective way to solve relevant problems of design of controlled synthetic methods allowing the nanoparticle morphology tuning according to the required functional properties.

Microalgae-derived hydrogen production towards low carbon emissions via large-scale outdoor systems

Hydrogen as a clean fuel is receiving attention because it generates only water and a small amount of nitrogen oxide upon combustion. Biohydrogen production using microalgae is considered to be a highly promising carbon-neutral technology because it can secure renewable energy while efficiently reducing CO2 emissions. However, previous studies have mainly focused on improving the biological performance of microalgae; these approaches have struggled to achieve breakthroughs in commercialization because they do not heavily consider the complexity of the entire production process with microalgae, including large-scale cultivation, biomass harvest, and biomass storage. This work presents an in-depth analysis of the state-of-the-art technologies focused on large-scale cultivation systems with efficient downstream processes. Considering the individual processes of biohydrogen production, strategies are discussed to minimize carbon emissions and improve productivity simultaneously. A comprehensive understanding of microalgae-derived biohydrogen production suggests future directions for realizing environmental and economic sustainability.

Effect of Organo-Silanes Structure on the Properties of Silane-Crosslinked Membranes Based on Cardo Polybenzimidazole PBI-O-PhT

Polybenzimidazoles (PBI) doped with phosphoric acid (PA) are promising electrolytes for medium temperature fuel cells. Their significant disadvantage is a partial or complete loss of mechanical properties and an increase in hydrogen permeability at elevated temperatures. Covalent silanol crosslinking is one possible way to stabilize PBI membranes in the presence of PA. Three organo-substituted silanes, namely (3-Bromopropyl)trimethoxysilane (SiBr), trimethoxy [2-(7-oxabicyclo [4.1.0]hept-3-yl)ethyl]silane (Si-biC) and (3-Glycidyloxypropyl)trimethoxysilane (KH 560), were used as covalent crosslinkers of PBI-O-PhT in order to determine the effect of the silane structure and crosslinking degree on membrane properties. The crosslinking degree was 1-50%. All crosslinked membranes were characterized by impedance and IR-spectroscopy. The mechanical properties, morphology, stability and hydrogen permeability of the membranes were determined. In the case of silanes with linear substituents (SiBr, KH 560), a denser structure is formed, which is characterized by greater oxidative stability and lower hydrogen permeability in comparison to the silane with a bulk group. All the crosslinked membranes have a higher mechanical strength compared with the initial PBI-O-PhT membrane both before and after doping with PA. Despite the hardening of the polymer matrix of the membranes, their proton conductivity changes insignificantly. It was shown that cross-linked membranes can be used in fuel cells.

Structural and Electrotransport Properties of Perfluorinated Sulfocationic Membranes Modified by Silica and Zirconium Hydrophosphate

A correlation between changes in structural and electrotransport properties of membranes after modification by silica and zirconium hydrophosphate was established. The total water volume, volume fraction of the free water in the membrane and the volume fraction of the water having high binding energy were considered as structural characteristics, which were found from the curves of water distribution on the water binding energy and the effective pore radii. The conductivity, diffusion and electroosmotic permeabilities were investigated as electrotransport properties. The influence of the modifier type on the current flow paths in the membrane was analyzed within the framework of the extended three-wire model. It has been established that the treatment of membranes with alcohol before the intercalation of a modifier leads to the appearance of cavities with an effective size of more than 100 nm filled with free water with the binding energy less than 10 J/mol. It is accompanied with an increase in the diffusion permeability of hybrid membranes by approximately 3-6 times in NaCl and HCl solutions, which limits the application of such materials in proton exchange membrane fuel cells. The different conditions of modification of perfluorinated membranes with similar properties by the dopant with same type allow for the preparation of the hybrid materials for various applications such as electrodialysis concentration or electric current generation devices.

Membranes Based on Polyvinylidene Fluoride and Radiation-Grafted Sulfonated Polystyrene and Their Performance in Proton-Exchange Membrane Fuel Cells

Proton-exchange membranes based on gamma-irradiated films of PVDF and radiation-grafted sulfonated polystyrene with an ion-exchange capacity of 1.8 meq/g and crosslinking degrees of 0 and 3% were synthesized. A solvent-free, environmentally friendly method of styrene grafting from its aqueous emulsion, with a styrene content of only 5 vol.% was used. Energy dispersive X-ray mapping analysis showed that the grafted sulfonated polystyrene is uniformly distributed throughout the membrane thickness. The obtained materials had a proton conductivity up to 132 mS/cm at 80 °C and a hydrogen permeability of up to 5.2 cm²/s at 30 °C, which significantly exceeded similar values for Nafion^®-212 membranes. The resulting membranes exhibited a H₂/O₂ fuel cell peak power density of up to 0.4 W/cm² at 65 °C. Accelerated stability tests showed that adding a crosslinking agent could significantly increase the stability of the membranes in the fuel cells. The thermal properties and crystallinity of the membranes were investigated through differential scanning calorimetry and X-ray powder diffraction methods. The conductivity, water uptake, and mechanical properties of the membranes (stress–strain curves) were also characterized.

Cu2O/CuS/ZnS Nanocomposite Boosts Blue LED-Light-Driven Photocatalytic Hydrogen Evolution

In the present work, we described the synthesis and characterization of the ternary Cu2O/CuS/ZnS nanocomposite using a facile two-step wet chemical method for blue LED-light-induced photocatalytic hydrogen production. The concentrations of the ZnS precursor and reaction time were essential in controlling the photocatalytic hydrogen production efficiency of the Cu2O/CuS/ZnS nanocomposite under blue LED light irradiation. The optimized Cu2O/CuS/ZnS nanocomposite exhibited a maximum photocatalytic hydrogen evolution rate of 1109 µmolh−1g−1, which was remarkably higher than Cu2O nanostructures. Through the cycle stability it can be observed that the hydrogen production rate of the Cu2O/CuS/ZnS nanocomposite decreased after 4 cycles (1 cycle = 3 h), but it remained at 82.2% of the initial performance under blue LED light irradiation. These reasons are mainly attributed to the introduction of CuS and ZnS to construct a rationally coupled reaction system, which enables the synergistic utilization of photogenerated carriers and the increased absorption of visible light for boosting blue LED-light-driven photocatalytic hydrogen evolution.

New Generation of Compositional Aquivion®-Type Membranes with Nanodiamonds for Hydrogen Fuel Cells: Design and Performance

Compositional proton-conducting membranes based on perfluorinated Aquivion^®-type copolymers modified by detonation nanodiamonds (DND) with positively charged surfaces were prepared to improve the performance of hydrogen fuel cells. Small-angle neutron scattering (SANS) experiments demonstrated the fine structure in such membranes filled with DND (0-5 wt.%), where the conducting channels typical for Aquivion^® membranes are mostly preserved while DND particles (4-5 nm in size) decorated the polymer domains on a submicron scale, according to scanning electron microscopy (SEM) data. With the increase in DND content (0, 0.5, and 2.6 wt.%) the thermogravimetric analysis, potentiometry, potentiodynamic, and potentiotatic curves showed a stabilizing effect of the DNDs on the operational characteristics of the membranes. Membrane-electrode assemblies (MEA), working in the O₂/H₂ system with the membranes of different compositions, demonstrated improved functional properties of the modified membranes, such as larger operational stability, lower proton resistance, and higher current densities at elevated temperatures in the extended temperature range (22-120 °C) compared to pure membranes without additives.

The synthesis of CoS/MnCo2O4-MnO2 nanocomposites for supercapacitors and energy-saving H2 production

In this study, CoS/MnCo₂O₄-MnO₂ (CMM) nanocomposites were synthesized by hydrothermal and then electrochemical deposition. Their electrochemical properties were systematically investigated for supercapacitors and energy-saving H₂ production. As an electrode material for supercapacitor, CMM demonstrates a specific capacitance of 2320F g^-1 at 1 A/g, and maintains a specific capacitance of 1216F g^-1 at 10 A/g. It also shows 72.8 % capacitance retention after 8000 cycles. The aqueous asymmetric supercapacitor exhibited high energy storage capacity (887.86F g^-1 specific capacitance at a current density of 1 A/g), good rate performance and cycling stability. Besides, CMM shows outstanding urea oxidation reaction(UOR) and glycol oxidation reaction (MOR) performances for H₂ production. Compared to oxygen evolution reaction (OER) (1.635 V) at 20 mA cm^-2, the potentials were reduced by 213 mV for UOR and 233 mV for MOR, respectively. Therefore, this study shows the promising practical applications of CMM nanocomposites for energy storage and energy-saving H₂ production.

Performance Prediction of High-Speed Hydrogen Gas-Lubricated Herringbone Grooved Journal Bearing

The liquefaction of hydrogen is considered to be a crucial process in the large-scale utilization of hydrogen energy. In hydrogen liquefaction, hydrogen turbo-expander is a key refrigerating machine for high liquefaction efficiency. Performance of the turbo-expander is directly affected by the hydrogen gas bearings. To obtain a deep understanding of the performance characteristics of hydrogen gas bearings, the static and dynamic characteristics of herringbone grooved journal bearings under hydrogen and other lubricating gases were numerically calculated and compared. The bearing load capacity and critical mass of hydrogen gas bearings were slightly lower than those of helium-, air- and nitrogen-lubricated bearings. To improve the performance of the hydrogen gas bearings used in high-speed turbo-machinery, the influence of working conditions was analyzed. It is found that the load capacity of hydrogen gas bearings can be improved by increasing the ambient pressure, reducing the gas film clearance, and raising the bearing eccentricity ratio. Meanwhile, the critical mass increases, and the bearing dynamic stability is enhanced.

Platinum-Containing Nanoparticles on N-Doped Carbon Supports as an Advanced Electrocatalyst for the Oxygen Reduction Reaction

New highly active electrocatalysts were obtained by depositing bimetallic Pt-Cu nanoparticles on the surface of an N-doped carbon support. The structural–morphological characteristics and electrochemical behavior of the catalysts were studied. Using current stress testing protocols, their resistance to degradation was assessed in comparison with that of a commercial Pt/C material. A combined approach to catalyst synthesis that consists in alloying platinum with copper and doping the support makes it possible to obtain catalysts with a uniform distribution of bimetallic nanoparticles on the carbon surface. The obtained catalysts exhibit high activity and durability.

Layered Oxygen-Deficient Double Perovskites as Promising Cathode Materials for Solid Oxide Fuel Cells

Development of new functional materials with improved characteristics for solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) is one of the most important tasks of modern materials science. High electrocatalytic activity in oxygen reduction reactions (ORR), chemical and thermomechanical compatibility with solid electrolytes, as well as stability at elevated temperatures are the most important requirements for cathode materials utilized in SOFCs. Layered oxygen-deficient double perovskites possess the complex of the above-mentioned properties, being one of the most promising cathode materials operating at intermediate temperatures. The present review summarizes the data available in the literature concerning crystal structure, thermal, electrotransport-related, and other functional properties (including electrochemical performance in ORR) of these materials. The main emphasis is placed on the state-of-art approaches to improving the functional characteristics of these complex oxides.

Methanol Steam Reforming on Bimetallic Catalysts Based on In and Nb Doped Titania or Zirconia: A Support Effect

Methanol steam reforming (MSR) is considered an effective method for hydrogen storage and to generate high-quality hydrogen for fuel cells. In this work, a comprehensive investigation of the methanol steam reforming process using a bimetallic Pt–Rh and Cu–Ni based on different oxide supports is presented. Highly dispersed titania and zirconia doped with indium and niobium ions were synthesized by sol–gel method. The effect of the nature and quantity of the dopant cation (In, Nb) on the catalytic performance of titania supported metal catalysts was investigated. The conclusions obtained show a significant effect of both the metal alloy and the oxide support nature on the activity and selectivity of the methanol steam reforming process. Pt–Rh alloy catalyst shows higher hydrogen yield, but its selectivity in the MSR process is lower than for the catalysts containing the Cu0.8-Ni0.2 alloy. Heterovalent indium doping of titania leads to the catalytic activity increase. It was suggested that this is due to the defects formation in the oxygen TiO2 sublattice. On the contrary, the use of niobium oxide as a dopant decreases the catalyst activity in the methanol steam reforming process but leads to the selectivity increase in the studied process.

Gram-Scale Synthesis of CoO/C as Base for PtCo/C High-Performance Catalysts for the Oxygen Reduction Reaction

The composition, structure, catalytic activity in the ORR and stability of PtCo/C materials, obtained in two stages and compared with commercial Pt/C analogs, were studied. At the first stage of the synthesis performed by electrodeposition of cobalt on a carbon support, a CoOx/C composite containing 8% and 25 wt% cobalt oxide was successfully obtained. In the second step, PtCoOx/C catalysts of Pt1.56Co and Pt1.12Co composition containing 14 and 30 wt% Pt, respectively, were synthesized based on the previously obtained composites. According to the results of the composition and structure analysis of the obtained PtCoOx/C catalysts by X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) methods, the formation of small bimetallic nanoparticles on the carbon support surface has been proved. The resulting catalysts demonstrated up to two times higher specific catalytic activity in the ORR and high stability compared to commercial Pt/C analogs.

Nafion/Surface Modified Ceria Hybrid Membranes for Fuel Cell Application

Low chemical durability of proton exchange membranes is one the main factors limiting their lifetime in fuel cells. Ceria nanoparticles are the most common free radical scavengers. In this work, hybrid membranes based on Nafion-117 membrane and sulfonic or phosphoric acid functionalized ceria synthesized from various precursors were prepared by the in situ method for the first time. Ceria introduction led to a slight decrease in conductivity of hybrid membranes in contact with water. At the same time, conductivity of membranes containing sulfonic acid modified ceria exceeded that of the pristine Nafion-117 membrane at 30% relative humidity (RH). Hydrogen permeability decreased for composite membranes with ceria synthesized from cerium (III) nitrate, which correlates with their water uptake. In hydrogen-air fuel cells, membrane electrode assembly fabricated with the hybrid membrane containing ceria synthesized from cerium (IV) sulfate exhibited a peak power density of 433 mW/cm² at a current density of 1080 mA/cm², while operating at 60 °C and 70% RH. It was 1.5 times higher than for the pristine Nafion-117 membrane (287 mW/cm² at a current density of 714 mA/cm²).