Copper hexacyanoferrate as cathode material for hydrogen peroxide fuel cell

The current need for handheld electronic devices with high energy autonomy has amplified research into clean and mobile energy source developments. Among suitable and promising technologies for this application, fuel cells, FCs are highlighted because of their minimal emission of pollutants and high efficiency. One type of FCs that has yet to be studied is the hydrogen peroxide/direct hydrogen peroxide fuel cell (DPPFCs). The present work is dedicated to the development of DPPFCs of one compartment using copper hexacyanoferrates (CuHCFs) as cathodic material and a Ni grid as anodic material. CuHCFs containing Fe^II and/or Fe^III were synthesized, characterized and their electrocatalyst performances were compared in 0.1 mol L⁻¹ HCl and 0.5 mol L⁻¹ H₂O₂. The maximum power densities reached for the CuFe^II was 8.3 mW cm⁻² and for the CuFe^IIFe^III was 2.9 mW cm⁻². The CuHCFs cathode materials show promising results, standing out as innovative materials for such an application.     

Electronically tuned defective Prussian-blue on graphene for electrochemical water splitting

Exploiting high-performance and stable bifunctional electrocatalysts is highly desirable for water splitting applications to obtain large-scale renewable and clean fuels. Herein, a defective Prussian-blue (δ-PB or Fe^III_1.23[Fe^II_1.12(CN)₆]_0.87·δ_0.13) on graphene composite electrocatalyst was fabricated through a facile hydrolytic precipitation process, followed by a single-step carbonization treatment at 600 °C (denoted as δ-PB/G-600). The resultant optimized δ-PB/G-600 exhibits remarkable electrocatalytic water splitting in alkaline media, producing lower overpotentials of 189 and 105 mV at a current density of 10 mA cm^?2 for the oxygen evolution reaction and hydrogen evolution reaction, respectively. Most importantly, the δ-PB/G-600 shows remarkable durability for both reactions. The remarkable electrocatalysis was attributed to the abundant active sites and high electrical conductivity with a defective nature, which not only facilitate the electrolyte flux but also maintain the structural stability of δ-PB/G-600. Additionally, the high surface area confirms the facile mass transport and prompts the gaseous release of the composite.     

Synthesis and hydrogen adsorption properties of a new iron based porous metal-organic framework

A new metal-organic framework [Fe₃O(OOC-C₆H₄-COO)₃(H₂O)₃]Cl·(H₂O)_x was synthesized with a specific surface area of 2823 m²/g and a lattice parameter of 88.61 Å. Isostructural with MIL-101, this compound exhibits similar hydrogen adsorption properties, with maximum adsorption capacity of 5.1wt.% H at 77 K. The adsorption enthalpy of hydrogen for MIL-101 and ITIM-1 (MIL-101Fe) at zero coverage was calculated for a wide temperature range of 77 K ÷ 324 K, considering corrections for the variation of hydrogen gas entropy with the temperature. The resulted adsorption enthalpy is 9.4 kJ/mol for MIL-101, in excellent agreement with the value reported in literature from microcalorimetric measurements, and a value of 10.4 kJ/mol at zero coverage was obtained for ITIM-1 (MIL-101Fe).     

Designing of a novel Mn0.2Cd0.8S@ZnO heterostructure with Type-II charge transfer path for efficient photocatalytic hydrogen evolution reaction

The development of photocatalysts with efficient hydrogen evolution activity has been the goal for sustainable hydrogen production. In this work, heterojunction composite photocatalyst is formed by hydrothermal coupling of ZnO and Mn_0.2Cd_0.8S. Compared with pure ZnO and Mn_0.2Cd_0.8S, the composite photocatalyst has the ability to provide more abundant active sites and better photogenerated carriers separation efficiency. The optimized composite photocatalyst shows a 9.36-fold increase in hydrogen evolution activity (4297.99 μmol g^?1 h^?1) compared to Mn_0.2Cd_0.8S (459.31 μmol g^?1 h^?1) and exhibits excellent cycling stability. Density functional theory calculations identifies Type-II charge transfer path in the composite photocatalyst, achieving effective separation in space of photogenerated electrons from holes and suppressing recombination within the semiconductor. The results show that the construction of Type-II heterojunction in this work achieves a significant enhancement of the hydrogen evolution activity of the photocatalyst by constructing carrier transport channels at the contact interface of the heterojunction.     

Analysis of adsorption equilibrium of hydrogen on graphene sheets

The adsorption equilibrium of hydrogen on graphene sheets (GS) was studied based on a sample of GS with S_BET = 300 m²/g at the temperatures of 77.15 K–293.15 K and the pressures of 0 MPa–6 MPa. In the meantime, the adsorptions (Excess adsorption measurements) of hydrogen on granular coconut shell SAC-02 activated carbon (S_BET = 2074 m²/g) and carbon nanofiber (CNFs, S_BET = 205 m²/g) were investigated at the pressures of 0–8 MPa and the temperature of 77.15 K. The outcomes from experiments were used to determine the parameters in Toth equation by way of Non-linear fit. The absolute adsorption amounts of hydrogen on the GS, which were calculated from the equation, were used to calculate the isosteric heat of hydrogen adsorption by use of adsorption isosteres.     

Modeling and interpretations by the statistical physics formalism of hydrogen adsorption isotherm on LaNi4.75Fe0.25

Three theoretical expressions for the adsorption isotherms of hydrogen on LaNi_4.75Fe_0.25 alloy at 303 K and 313 K have been established. Our objective in this modeling is to select the adequate model that presents a high correlation with the experimental curves. The establishment of these new expressions is based on statistical physics formalism. This method has allowed the estimation of physicochemical parameters in the theoretical model. The parameters intervening in the adsorption process have been deduced directly from experimental adsorption isotherms by numerical simulation. We will mainly introduce four parameters affecting the adsorption process, namely; the density of hydrogen receptor sites N_M, the number of molecules per site and the hydrogen adsorption energy. Then we apply the model to calculate thermodynamics functions which govern the adsorption mechanism such as entropy, free enthalpy and internal energy.     

A highly stable of tungsten doped Pr0.6Sr0.4Fe0.9W0.1O3-δ electrode for symmetric solid oxide fuel cells

In this work, a single perovskite Pr_0.6Sr_0.4Fe_0.9W_0.1O_3-δ (PSFW) for the electrode of SSOFCs is designed and successfully synthesized. The PSFW exhibits excellent structure stability in both reducing and oxidizing atmospheres and thermal compatibility with La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM) electrolyte. The area specific polarization resistances (ASRs) of PSFW under oxidizing and reducing atmospheres are only 0.086 and 0.215 Ω cm² at 800 °C, respectively. The symmetric electrode shows excellent electro-catalytic activity toward oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) and the corresponding impedance spectra under different hydrogen and oxygen partial pressures are further explored by distribution of relaxation times (DRT), which reveals that rate-limiting steps of HOR and ORR are the hydrogen adsorption/diffusion and oxygen diffusion, respectively. A LSGM electrolyte-supported cell with PSFW as symmetric electrodes displays the outstanding power density, considerable stability and reversibility, proving that the PSFW is a promising electrode material for symmetric solid oxide fuel cells.     

Ni(OH)2 modified Mn0.5Cd0.5S with efficient photocatalytic H2 evolution activity under visible-light

Developing high-efficiency photocatalysts for water decomposition is one of the major challenges in converting solar energy to chemical energy. In this paper, Ni(OH)₂ modified Mn_0.5Cd_0.5S solid solution without the use of precious metals is successfully synthesized via hydrothermal method followed by precipitation, the photocatalytic activity for hydrogen evolution and stability of composite samples present significant improvement with respect to the pristine Mn_0.5Cd_0.5S. These improvements are attributed to that Mn_0.5Cd_0.5S CB potential (−0.7 V vs. NHE) is more negative than the potential of Ni²⁺/Ni (−0.23 V vs. NHE), which promotes the transfer of photo-generated electrons from Mn_0.5Cd_0.5S CB to Ni(OH)₂ for H₂ production as well as partial reduction of Ni²⁺ to Ni⁰, leaving VB holes to oxidize the sacrificial reagents. The metal Ni atoms with conductivity and Ni(OH)₂ nanoparticles not only boost the segregation and transfer of photo-induced carriers but also act as water-reduction promoter, thereby promoting the photocatalytic activity for hydrogen release. A novel visible light responsive Mn_xCd_1-xS-based photocatalytic material promising for practical applications is provided in this subject.     

Hydrogen adsorption and interactions in self-reducing shell hosted palladium nanoparticles on magnetite support

The nanoparticles (NP), consisting of hydrazine grafted organo-silica with PdNPs embedded shell on the Fe₃O₄ core, were prepared to study the adsorption and interactions of hydrogen in PdNPs and their support matrix. This material is expected to find the applications in the hydrogen technology including catalysis. The PdNPs were formed spontaneously in the organo-silica shell on magnetite nanoparticles by the reduction of Pd²⁺ ions with grafted hydrazine in the organo-silica shell. Thus formed NPs, termed as Fe₃O₄-GTEOS@PdNPs, were also thermally treated at 1033 K in Ar atmosphere to convert organic components to carbon. The chemical composition, physical structure, and magnetic properties were studied by high resolution transmission electron microscopy, X-rays diffraction, Mössbauer spectroscopy and X-ray photoelectron spectroscopy for the characterizations of physical, chemical and magnetic changes occurred in the Fe₃O₄-GTEOS@PdNPs after hydrogen adsorption-desorption at varying temperatures with respect to that in unused one. The hydrogen adsorption pressure-composition (PC) isotherms in Fe₃O₄-GTEOS@PdNPs followed the expected trend from 173 to 303 K as expected from PdNPs. However, thermally treated Fe₃O₄-GTEOS@PdNPs were found to adsorb lower amount of hydrogen due to oxidation of Pd⁰ to PdO and morphological changes during heating in Ar atmosphere. The comparison of n_H/n_Pd value (0.49) obtained for the PdNPs in Fe₃O₄-GTEOS@PdNPs with the values those reported in the literature for different Pd materials showed the decrease in n_H/n_Pd value with decrease in the size of Pd particles. This was attributed to stronger Pd–H bond in a nanoscale palladium, which prevented hydrogen transfer to interior matrix as compared to bigger Pd particles. The hydrogen adsorption PC isotherm at 373 K in Fe₃O₄-GTEOS@PdNPs could not be obtained as the unknown chemical reaction happened in the sample during the experiment. The considerably higher H₂ consumption in the Fe₃O₄-GTEOS@PdNPs occurred at 373 K than that expected from the hydrogen adsorption in the PdNPs alone.     

Photocatalytic hydrogen evolution over Pt/Cd0.5Zn0.5S from saltwater using glucose as electron donor: An investigation of the influence of electrolyte NaCl

Surface property of Cd_0.5Zn_0.5S in basic aqueous solution was characterized by X-ray photoelectron spectroscope (XPS). The surface S species at Cd_0.5Zn_0.5S under basic condition is substituted by O species. The surface adsorption performance of glucose and NaCl was characterized by adsorption experiment and electrophoretic analysis. Glucose is adsorbed on Cd_0.5Zn_0.5S via two modes. Na⁺ can be also adsorbed on Cd_0.5Zn_0.5S. The effect of electrolyte NaCl on photocatalytic hydrogen evolution over Pt/Cd_0.5Zn_0.5S using glucose as an electron donor has been investigated under visible light irradiation. NaCl can promote markedly the photocatalytic hydrogen evolution, which is very important to practical application. The photocatalytic activity for hydrogen evolution from 3.0 mol L⁻¹ NaCl saltwater increases by 77% compared to that from pure water. A possible mechanism was discussed.     

ZnS/Cd1-xZnxS composite photocatalyst synthesized with excessive strong alkali solution as a hydrothermal solvent: The chemical equilibrium theory of the synthesis process and its influence on photocatalytic performance

The ZnS/Cd_1-xZn_xS composite photocatalyst was successfully synthesized using a hydrothermal solvent by adding excess hydroxide ions. The ZnS/Cd_1-xZn_xS composite photocatalyst showed excellent photocatalytic activity for hydrogen production with a hydrogen evolution rate of 21.8 mmol/g⁻¹ h⁻¹, which is the highest photocatalytic activity reported to date among visible-light-driven photocatalysts without loading cocatalysts. According to the theoretical calculation and analysis of the chemical equilibrium in the synthesis process, the synthesized Cd_1-xZn_xS solid solution contained a certain amount of ZnS. A certain amount of ZnS was also contained in the synthesized Cd_1-xZn_xS solid solution based on experimental results, thus demonstrating the validity of the theoretical calculation. Experimental results showed that the key factor affecting the photocatalytic activity of hydrogen production for the ZnS/Cd_1-xZn_xS composite photocatalyst was not the heterojunction formed between ZnS and Cd_1-xZn_xS but rather the stacking fault structures in the Cd_1-xZn_xS solid solution. However, more stacking fault structures could be formed in the Cd_1-xZn_xS solid solution due to the presence of ZnS.     

Fe supported on ceria as effective catalyst for the heterogeneous photo-oxidation of basic orange 2 in aqueous solution with sunlight

Fe^III supported on ceria as an effective catalyst for oxidation was prepared and used for the degradation of basic orange 2 azo textile dye (BO2). BO2 was chosen as a model pollutant and the catalytic oxidation was carried out in a batch reactor using hydrogen peroxide as the oxidant at pH 3. The influent factors on BO2 oxidation, such as catalyst dosage, H₂O₂ concentration, and BO2 concentration were studied by considering the BO2 conversion and chemical oxygen demand (COD) removal. The Fe^III-ceria catalyst showed a high catalytic activity for the oxidation of BO2 in aqueous solution. It was observed that the solution became colorless after 5 h of oxidation and over 90% COD removal was achieved with all the Fe^III-ceria catalysts used under dark conditions in the catalytic oxidation system. The catalytic removal of BO2 during BO2 oxidation was improved under solar radiation, which notably increased the BO2 degradation rate. Consecutive BO2 oxidation cycles carried out with the same Fe^III-ceria catalyst and untreated fresh dyestuff solution showed that the catalyst had good stability and good degradation performance, thus evidencing the possibility of being used in continuous processes. This study showed that the Fe^III-ceria catalytic oxidation process is an efficient method for the treatment of BO2 aqueous solutions.     

In situ observation of H2 dissociation on the ZnO (0001) surface under high pressure of hydrogen using ambient-pressure XPS

The interaction of H₂ molecules with a ZnO (0001) single crystal surface has been studied over a wide pressure (10^?6–0.25 Torr) and temperature (300–600 K) range using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). ZnO is well-known for interstitial hydrogen and hydrogen atoms in ZnO are believed to be incorporated by the dissociative adsorption of H₂ molecules in the atmosphere and their subsequent diffusion into the bulk. The dissociative adsorption of H₂ has been investigated at elevated pressures because H₂ molecules are not dissociated on the ZnO single crystal surface under ultrahigh vacuum (UHV) conditions. When the pressure is increased to several mTorr, the dissociative adsorption of H₂ takes place to form OH bonds on the surface. At 0.25 Torr, the ZnO surface is saturated with H atoms and the coverage is estimated to be 1.1 × 10¹⁵ atoms/cm² at 300 K. At higher surface temperatures, the equilibrium between the dissociative adsorption of gas-phase H₂ molecules and the associative desorption of surface H atoms is established. While maintaining the equilibrium, the surface has been monitored successfully in situ by utilizing AP-XPS.     

Hydrogen isotope effect of nanoporous palladium

Materials used in hydrogen isotopes separation are crucial in modern hydrogen energy field. In this article, a promising material nanoporous palladium was prepared and its relative properties were studied. Nanoporous palladium with pore scale of about 5 nm was fabricated by free dealloying corrosion. Its kinetic and PCT curves of hydrogen/deuterium adsorption at room temperature were tested using a Sievert-type volumetric apparatus. Microstructures were observed with Scanning Electron Microscopy and Atomic Force Microscopy. Crystalline structure was characterized with X-Ray Diffractometer before and after deuterium adsorption. Comparative experiments with spongy palladium that is commonly used in relative industry were also carried out. According to the results, nanoporous palladium shows faster hydrogen/deuterium adsorption rate than spongy palladium, which is due to its nanoporous structure that supplies a large amount of specific surface area. PCT curves of hydrogen/deuterium adsorption in nanoporous palladium among 298–338 K were tested and plateau pressures at different temperatures were obtained. Deuterium/hydrogen isotopes separation factors were calculated using plateau pressures above and were plotted with temperature. It's found that nanoporous palladium shows larger hydrogen isotope separation factors compared with spongy palladium at temperatures no higher than 323 K. These findings illustrate that nanoporous palladium would be an ideal material for hydrogen isotopes separation applications.     

Phosphorus-doped Fe3O4 nanoflowers grown on 3D porous graphene for robust pH-Universal hydrogen evolution reaction

It is extremely necessary to develop highly efficient and low-cost non-noble metal electrocatalysts for hydrogen evolution reaction (HER) under a pH-universal condition in the realm of sustainable energy. Herein, we have successfully prepared phosphorus doped Fe₃O₄ nanoflowers on three-dimensional porous graphene (denoted as P–Fe₃O₄@3DG) via a simple hydrothermal and low-temperature phosphating reaction. The P–Fe₃O₄@3DG hybrid composite not only demonstrates superior performance for HER in 1.0 M KOH with low overpotential (123 mV at 10 mA/cm²), small Tafel slope (65 mV/dec), and outstanding durability exceeding 50 h, but also exhibits satisfying performances under neutral and acidic medium as well. The 3D graphene foam with large porosity, high conductivity, and robust skeleton conduces to more active sites, and faster electron and ion transportation. The phosphorus dopant provides low Gibbs free energy and ability of binging H⁺. The synergistic effect of 3DG substrate and P–Fe₃O₄ active material both accelerates the catalytic activity of Fe-based hybrid composite for HER.     

Spatially and temporally heterothermic kinetic model of hydrogen absorption and desorption in metals with heat transport

Numerical modelling of hydrogen transport is effective for designing and optimizing various energy systems, including hydrogen storage devices, fuel cells, and nuclear fusion reactors. In the present study, we propose and demonstrate a spatiotemporally heterothermic, autonomous kinetic model of hydrogen absorption and desorption in metals for precise simulations. Our bidirectional transport model comprises elementary mass transfer processes of surface adsorption and desorption, subsurface transport, and bulk diffusion. Also implemented are heat generation and conduction stemming from the absorption enthalpy, to determine the evolution of temperature distribution in the metal body, as well as the hydrogen concentration profile. Simulations by our transport model reproduce experimental hydrogen absorption and desorption curves for various temperature levels and metal scales with a single identical set of numerical equations and kinetic parameters, to thus verify the validity of the model.     

Hydrogen adsorption simulations in isomorphous borohydride and imidazolate frameworks: Evaluations using interpolation

We simulate hydrogen adsorption on two topologically identical crystalline solids using the grand canonical Monte Carlo (GCMC) method. One solid is the γ - magnesium borohydride, γ-Mg(BH₄)₂, the first borohydride crystal with a permanent porosity. The other solid is ZIF-72, Zn(dcIm)₂, a zinc imidazolate framework synthesized with dichloroimidazole (dcIm) ligands. Both solids maintain narrow sized pore networks, capable of storing molecular hydrogen. We introduce an interpolation scheme for the temperature dependence of adsorption isotherms. The interpolation employs a special control function based on the adsorption enthalpy. We compare the hydrogen capacities of the two samples at variable temperatures and pressures and attribute the discrepancies to the implicit surface texture and size of the confinements. Notably, the porous Mg(BH₄)₂ can physically adsorb 3.44 wt% H₂ at cryogenic temperatures that is cumulative to the already high content of 14.9 wt% of atomic hydrogen bound on the boron atoms. This content makes the γ-Mg(BH₄)₂ one of the most hydrogen rich solids reported to date.     

Effects of ball milling time on the microstructure and hydrogen storage performances of Ti21.7Y0.3Fe16Mn3Cr alloy

TiFe alloy can store hydrogen at room temperature and low hydrogen pressure, and its theoretical hydrogen storage capacity is up to 1.8 wt%. However, TiFe alloy needs to be activated at high pressure (5 MPa hydrogen) and high temperature (673–723 K), which limits the practical application of TiFe alloy. The as-cast Ti_21.7Y_0.3Fe₁₆Mn₃Cr alloy was milled for 0, 0.5, 0.75, 1, and 3 h to study the effects of ball milling on phase structures and hydrogen storage performances. Emphasis was focused on the activation process of as-milled alloys at different temperatures, including the activation process at 483, 443, and 403 K. The results show that the alloys were consisted of TiFe phase, and [Fe, Cr] solid solution. The nanocrystalline boundary produced by milling and the phase boundary provided by the second phase provide a large number of channels for hydrogen diffusion and promote the improvement of hydrogen storage performances. The time required for activation process of as-milled alloys was significantly reduced, and the activation time of as-milled (0.75 h) was only 4 min, and its enthalpy variation for hydrogen absorption and desorption was 22.943 and 26.215 kJ mol⁻¹ H₂, respectively.     

Hydrogen permeation and diffusion in densified MOF-5 pellets

The metal-organic framework Zn₄O (BDC)₃ (BDC = 1,4-bezene dicarboxlate), also known as MOF-5, has demonstrated considerable adsorption of hydrogen, up to 7 excess wt.% at 77 K. Consequently, it has attracted significant attention for vehicular hydrogen storage applications. To improve the volumetric hydrogen density and thermal conductivity of MOF-5, prior studies have examined the hydrogen storage capacities of dense MOF-5 pellets and the impact of thermally conductive additives such as expanded natural graphite (ENG). However, the performance of a storage system based on densified MOF-5 powders will also hinge upon the rate of hydrogen mass transport through the storage medium. In this study, we further characterize MOF-5 compacts by measuring their hydrogen transport properties as a function of pellet density (ρ = 0.3–0.5 g cm⁻³) and the presence/absence of ENG additions. More specifically, the Darcy permeability and diffusivity of hydrogen in pellets of neat MOF-5, and composite pellets consisting of MOF-5 with 5 and 10 wt.% ENG additions, have been measured at ambient (296 K) and liquid nitrogen (77 K) temperatures. The experimental data suggest that the H₂ transport in densified MOF-5 is strongly related to the MOF-5 pellet density ρ.     

Water sorption studies on ZnSO4-zeolite composite as potential thermochemical heat storage materials

ZnSO₄·7H₂O is modified by impregnation method with zeolite matrices (13X-zeolite and LTA-zeolite) to improve its hydration performance. Water sorption ability of composites was carried out in a constant temperature and humidity environment. Composite of ZnSO₄/13X-zeolite showed highest water sorption (0.26 g/g) at 75% relative humidity under 45°C air temperature, which is double than pure ZnSO₄·7H₂O. This is due to larger surface area (491 m² g^-1) and pore volume (0.31 cm³). Furthermore, both hydration rate and adsorption mass depends on relative humidity and hydration temperature. However, if the air temperature and the relative humidity are higher than 45°C and 75% RH, the hydration ability of the composite material is significantly reduced. Besides, X-ray measurements of composite (ZnSO₄/13X) revealed that sorption/desorption process, crystallinity and phase of partially hydrated ZnSO₄ remain the same, which enhance the adsorption mass and enthalpy during the hydration process.