Computer-aided prediction of structure and hydrogen storage properties of tetrakis(4-aminophenyl)silsesquioxane based covalent-organic frameworks

With the aid of computer simulation, we have designed four covalent-organic frameworks based on tetrakis(4-aminophenyl)silsesquioxane (taps-COFs) and their hydrogen storage properties were predicted with grand canonical Monte Carlo (GCMC) simulation. The structural parameters and physical properties were investigated after the geometrical optimization. The accessible surface for H₂ molecule (5564.68–6754.78 m²/g) were estimated using the numerical Monte Carlo integration and the pore volume (4.06–10.74 cm³/g) was evaluated by the amounts of the containable nonadsorbing helium molecules at low pressures and room temperature. GCMC simulation reveals that at 77 K, tapsCOF1 has the highest gravimetric H₂ adsorption capacity of 51.43 wt% and tapsCOF3 possesses the highest volumetric H₂ adsorption capacity of 58.51 g/L. Excitedly, at room temperature of 298 K, the gravimetric hydrogen adsorption capacities of tapsCOF1 (8.58 wt%) and tapsCOF2 (8.20 wt%) have exceeded the target (5.5 wt%) of onboard hydrogen storage system for 2025 set by the U.S Department of Energy.     

Hydrogen evolution in the dehydrogenation of methylcyclohexane over Pt/CeMgAlO catalysts derived from their layered double hydroxides

Pt/CeMgAl layered double hydroxides with different Ce contents were prepared by one-step co-precipitation method, which underwent calcination and reduction with hydrogen and were finally converted into Pt/CeMgAlO catalysts. These catalysts were tested in the dehydrogenation of methylcyclohexane (MCH) into toluene to produce hydrogen. The addition of CeO₂ promoted the dispersion of Pt and decreased the Pt particle size. During the dehydrogenation reaction, toluene was the only liquid product and its selectivity was higher than 99.9%. MCH conversion increased with the reaction temperature rising. The conversion and hydrogen evolution rate on Pt/Ce₁₄MgAlO350 reached up to 98.5% and 1358.6 mmol/g_Pt/min at 350 °C. Moreover, Pt/CeMgAlO catalysts exhibited no acidity and presented a high anti-coking ability and good stability. These results suggest that Pt/CeMgAlO catalysts have potential industrial application for hydrogen energy utilization.     

The preparation and performance of a novel spherical spider web-like structure RuNi / Ni foam catalyst for NaBH4 methanolysis

In this work, a spherical spider web-like structure RuNi/Ni foam catalyst was prepared for hydrogen evaluation from sodium borohydride (NaBH₄) by a combination of electroless plating and electroplating. Microstructure, surface morphology, surface area and elemental composition of the RuNi/Ni foam catalyst were analyzed by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM-EDS and X-ray Photoelectron Spectroscopy (XPS), Brunauere-Emmette-Teller method (BET, AS-1C-VP), respectively. The influences of RuNi with different molar ratios, NaOH concentration, NaBH₄ concentration, and solution temperature on the hydrogen production rate were investigated in this paper. The results showed that the RuNi metals were arrayed densely and uniformly on the surface of Ni foam. The average hydrogen production rate is 360 mL min ⁻¹ g⁻¹ in 20 wt % of NaBH₄, 1 wt% of NaOH at 30 °C in the presence of the RuNi/Ni foam catalysts. The calculated activation energy was 39.96 kJ mol⁻¹ for hydrogen production from sodium borohydride using the RuNi/Ni foam catalyst.     

Effect of iron content on the hydrogen production kinetics of electroless-deposited CoNiFeP alloy catalysts from the hydrolysis of sodium borohydride,and a study of its feasibility in a new hydrolysis using magnesium and calcium borohydrides

The effect of Fe content in electroless-deposited CoNi-Fe_x-P alloy catalysts (x = 5.5–11.8 at.%) from the hydrolysis of NaBH₄ is investigated in alkaline sodium borohydride solution. The electroless-deposited CoNiFe_5.5-P and CoNiFe_7.6-P alloy catalysts are composed of flake-like micron particles; however, with an increase in Fe content to 11.8 at.%, the flake-like morphology is changed to a spherical shape and the crystal structure of the electroless-deposited CoNiFeP catalyst is transformed from FCC to BCC. Among all the CoNi-Fe_x-P alloy catalysts, the CoNi-Fe_x-P (x = 7.6 at.%) catalyst has the highest hydrogen production rate of 1128 ml min⁻¹ g⁻¹_catalyst in alkaline solution containing 1 wt% NaOH + 10 wt% NaBH₄ at 303 K. For the optimized catalyst, the activation energy of the hydrolysis of NaBH₄ is calculated to be 54.26 kJ mol⁻¹. Additionally, in this work, we report a new hydrolysis using Mg(BH₄)₂ and Ca(BH₄)₂. As a result, the Mg(BH₄)₂ is stored unstably in an alkaline solution, whereas the Ca(BH₄)₂ is stored stably. When optimizing the hydrogen production kinetics from the hydrolysis of Ca(BH₄)₂, the rate is 784 ml min⁻¹ g⁻¹_catalyst in 10 wt% NaOH + 3 wt% Ca(BH₄)₂ solution.     

Electrodeposited nickel–iron–carbon–molybdenum film as efficient bifunctional electrocatalyst for overall water splitting in alkaline solution

Designing and synthesizing of efficient and inexpensive bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is one of the current research topics. In this study, NiFeCMo film in nickel mesh substrate is prepared by one-step direct-current electrodeposition method. The obtained NiFeCMo film shows the excellent electrocatalytic activity, which only requires overpotentials of 254 mV for HER and 256 mV for OER to drive current density of 10 mA cm⁻², with corresponding Tafel slopes of 163.9 and 60.3 mV·dec⁻¹ in 30% KOH medium, respectively. Moreover, NiFeCMo film only needs a low cell voltage of 1.61 V to drive current density of 10 mA cm⁻² in an alkaline electrolyzer. Such remarkably HER and OER properties of NiFeCMo alloy is attributed to the increased effective electrochemically active surface area and the synergy effect among Ni, Fe, C and Mo.     

Electrodeposition of NiMoCu coatings from roasted nickel matte in deep eutectic solvent for hydrogen evolution reaction

It is attractive to design and develop a low-cost and environment friendly material preparation route for the catalysts used in alkaline hydrogen evolution reaction. Mineral reconstruction in chlorination roasting and electrodeposition in deep eutectic solvent have been combined in this work. The electrodeposition of NiMoCu coatings from roasted nickel matte precursor in choline chloride (ChCl)-urea deep eutectic solvent (DES) has been investigated. Cyclic voltammetry (CV) implies that the electrodeposition process of NiMoCu coatings in ChCl-urea DES consists of a one-step reaction of Ni(II), a two-step reaction of Cu(II) and Ni/Mo inductive co-deposition. The hydrogen evolution performance parameters of deposited NiMoCu coatings have been systematically studied in alkaline solution by linear sweep voltammetry (LSV), and the electrochemical surface area (ECSA) has been tested by CV. The hydrogen evolution kinetics of deposited NiMoCu coatings has been further investigated by electrochemical impedance spectroscopy (EIS). Owing to its high electrochemical surface area, the NiMoCu coating deposited on Ni foam at −1.2 V can deliver a current density of 10 mA cm⁻² at an overpotential of 93 mV in 1 M KOH. It is suggested that NiMoCu coating can be a promising candidate for water splitting in alkaline solution.     

Trimetallic nanoparticles: Synthesis,characterization and catalytic degradation of formic acid for hydrogen generation

PdAgFe, FePdAg and FeAgPd trimetallic nanoparticles were synthesized by seedless and step-wise simultaneous chemical reduction of Fe³⁺, Ag⁺ and Pd²⁺ by using hydrazine in presence of cetyltrimethylammonium bromide and used as a catalyst for the degradation of formic acid. The effects of nanoparticle composition, presence of sodium format (promoter), [catalyst], [formic acid] and temperature play key roles in the hydrogen generation. The Ba(OH)₂ trap experiment and water displacement technique were used to determine the generation of CO₂ and H₂, respectively. The decomposition of formic acid followed complex-order kinetics with respect to [formic acid]. It was found that FeAgPd showed a maximum catalytic activity (turn over frequency) of 75 mol H₂ per mol catalyst per h. The activation energy (E_a = 51.6 kJ/mol), activation enthalpy (ΔH = 48.9 kJ/mol) and activation entropy (ΔS = −151.0 JK^-1 mol⁻¹) were determined and discussed for the catalytic reaction. The reusability of the FeAgPd at 50 °C shows an efficient degree of activity for six consecutive catalytic cycles.     

Hydrogen storage properties of nanostructured 2MgH2Co powders: The effect of high-pressure compression

In this study, MgH₂ and Co powders were mechanically milled in the molar ratio 2:1 and compressed to hard-packed cylindrical pellets. The microstructure, phase changes, and hydrogen storage properties of the mechanically milled 2MgH₂Co powder and the 2MgH₂Co compressed pellet were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and synchronous thermal (DSC/TG) analyses. Dehydrogenation of the 2MgH₂Co compressed pellet is mainly due to the decomposition of Mg₂CoH₅ while it is the dehydriding of MgH₂ for the milled 2MgH₂Co powder. Pressure composition absorption isotherms of the 2MgH₂Co powder and 2MgH₂Co compressed pellet show two and three plateaus, respectively, corresponding to the formation of Mg₆Co₂H₁₁ and Mg₂CoH₅ hydride phases. For the compressed 2MgH₂Co pellet, enthalpies of formation/decomposition were measured to be −58.11±7.69 kJ/mol H₂/55.70±3.34 kJ/mol H₂ for Mg₂CoH₅ and -81.89±10.39 kJ/mol H₂/74.47±5.27 kJ/mol H₂ for Mg₆Co₂H₁₁. In contrast, hydrogenation/dehydrogenation enthalpies of Mg₂CoH₅ and Mg₆Co₂H₁₁ mechanically milled 2MgH₂Co powder were −73.98±10.1 kJ/mol H₂/71.67±1.38 kJ/mol H₂ and -96.86±8.73 kJ/mol H₂/89.95±10.81 kJ/mol H₂, respectively. Fast hydrogenation was observed in the dehydrided 2MgH₂Co compressed pellet with about 2.75 wt% absorbed in less than 1 min at 300 °C and a maximum hydrogen storage capacity of 4.43 wt% (2.32 wt% for the 2MgH₂Co powder) was achieved. The hydrogen absorption activation energy of the 2MgH₂Co compressed pellet (64.34 kJ-mol⁻¹ H₂) is lower than the mechanically milled 2MgH₂Co powder (73.74 kJ-mol⁻¹ H₂). The results show that mechanical milling followed by high-pressure compression is an efficient method for the synthesis of Mg-based complex hydrides with superior hydrogen sorption properties.     

Ultra-thin phosphate glass exhibiting high proton conductivity at intermediate temperatures

Ultra-thin proton-conducting phosphate glass was fabricated by press-forming at high temperature. The glass was evaluated for its ohmic loss reduction when installed as an electrolyte in intermediate-temperature fuel cells. The 36HO_1/24NbO_5/22BaO4LaO_3/24GeO₂1BO_3/249PO_5/2 glass (36H-glass) was prepared by alkali-proton substitution. Herein, 3–4 mg of 36H-glass was placed onto a 50 μm-thick stainless steel or Pd support and then sandwiched by a glassy carbon plate, whereupon a 600 kg load was applied at temperatures varying as 333–391 °C. Ultra-thin 36H-glass with a thickness of 16 μm was successfully obtained without degradation of proton conductivity. A fuel cell incorporating the Pd-supported ultra-thin 36H-glass was successfully operated at 300 °C, and the ohmic loss of the fuel cell was reduced down to 2.7 Ω cm² from the previous reported value of several tens of Ω·cm².     

Flame synthesis of nitrogen,boron co-doped carbon as efficient electrocatalyst for oxygen reduction reaction

The flame synthesis provides a simple low-cost method to produce novel carbon materials. In this study, N, B co-doped carbon (NBC) materials have been prepared by flame synthesis. Among many as-prepared samples, the NBC catalyst which prepared under carbonization temperature of 1000 °C for 3 h with acetonitrile/acetone precursor of 1:1 exhibits the best catalytic activity and stability, as well as good resistance to methanol interference for oxygen reduction reaction (ORR), with half-wave potential being almost nearly to Pt/C, and a quasi-four-electron transfer process. This study would provide an economic, environmental feasible and scalable approach for fabricating novel heteroatom co-doped carbon materials for ORR applications.     

Increased interface effects of PtFe alloy/CeO2/C with PtFe selective loading on CeO2 for superior performance in direct methanol fuel cell

Here, a simple two-step solvothermal approach has been employed to synthesize PtFe alloy (or Pt)/CeO₂/C with PtFe (or Pt) selective loading on CeO₂ nanoparticles. In addition, the selective loading of PtFe alloy or Pt nanoparticles on the surface of CeO₂ is achieved under weak alkaline environment, which is mainly attributed to the opposite electrostatic force between H⁺ enriched on the surface of CeO₂ particles and OH⁻ covered with carbon supporters. As-prepared PtFe alloy (or Pt)/CeO₂/C catalysts with two-stage loading structures show more excellent electro-catalytic efficiency for methanol oxidation as well as duration compared with commercial Pt/C and PtCeO₂/C with random loading structure. Further, single-cell assembly based on Pt₃Fe/CeO₂/C as the anode catalyst exhibits a maximum power density of 31.1 mW cm⁻², which is 1.95 times that of an analogous cell based on the commercial Pt/C. These improved performances with considerable low Pt content (<0.3 mg cm⁻²) are mainly ascribed to the abundant three phase interfaces (PtCeO₂ carbon) induced by the selective and efficient dispersion of Pt nanoparticles on ceria.     

One-pot synthesis of PdZnO/C by microwave sintering method as an efficient electro catalyst for ethanol oxidation reaction

The PdZnO/C catalytic material for ethanol oxidation reaction is prepared by microwave heating-glycol reduction method. PdZnO is well polymerized and dispersed on XC72. The results demonstrate that PdZnO/C has better electro catalytic activity and stability for ethanol oxidation reaction than Pd/C at room temperature. ZnO/C shows no catalysis for ethanol oxidation. The oxidation peak potential of PdZnO/C electrode is shifted negatively to 0.21 V. The current density of PdZnO/C electrode is 145 mA cm⁻², while that of the Pd/C electrode is 60 mA cm⁻². Moreover, single cell discharge test shows that discharge voltage of the PdZnO/C electrode reaches to 0.41 V at 30 mA cm⁻². In summary, ZnO as a co-catalyst significantly improves the activity of PdZnO/C catalyst for ethanol oxidation reaction.     

A novel AlBiOCl composite for hydrogen generation from water

In this paper, a novel AlBiOCl material has been prepared by milling Al powder and BiOCl firstly. Experimental results show that BiOCl-doped can prevent an inert alumina film forming on the surface of Al particles and induce the rapid hydrogen generation as well as high conversion rate. SEM, XRD, EDS, TEM, XPS and calorimetric techniques are used for the mechanism analysis of the samples. The results demonstrate the fresh surface of Al, AlCl₃, Bi and Bi₂O₃ are produced in situ under ball milling Al and BiOCl, which play an important role in hydrolysis reaction of Al. The hydrogen yield of Al-15 wt% BiOCl rises to 1058.1 mL g⁻¹ in about 5 min, corresponding to the high conversion yield of 91.6% at room temperature. After doping additives (such as LiH, Bi or AlCl₃), hydrogen generation performances of AlBiOCl-additive are further improved. For example, the conversion yield and maximum hydrogen generation rate (MHGR) of AlBiOClLiH can increase to 94.9% and 3178.5 mL g⁻¹ min⁻¹, respectively. Therefore, the proposed materials in this paper are expected to serve as a hydrogen generation material for the fuel cells.     

Effect of LiCe(BH4)3Cl with a high Li ion conductivity on the hydrogen storage properties of LiMgNH system

The effect of LiCe(BH₄)₃Cl on the hydrogen storage properties of Mg(NH₂)₂2LiH system was studied systematically, which has a high Li ion conductivity. The hydrogen desorption temperatures for LiMgNH system shift to lower temperatures by 0.05LiCe(BH₄)₃Cl doping with the onset temperature of dehydrogenation decreasing by 40 °C and the peak temperature decreasing by 30 °C. The Mg(NH₂)₂2LiH–0.03LiCe(BH₄)₃Cl composite exhibits an improved comprehensive hydrogen storage properties, which can reversibly store about 5.0 wt% hydrogen at 160 °C, and released hydrogen as much as 8.6 times faster than that of the Mg(NH₂)₂2LiH composite at 160 °C. The results indicated that the LiCe(BH₄)₃Cl-containing sample exhibited much better cycling properties than that of Mg(NH₂)₂2LiH sample. XRD and FTIR results show that the structure of LiCe(BH₄)₃Cl does not change before and after hydrogen absorption/desorption, indicating it plays the catalytic effect. The hydrogen desorption activation energy of Mg(NH₂)₂2LiH doped with 0.03LiCe(BH₄)₃Cl was reduced by 37.5%. The rate-controlling step of desorption shifted from the diffusion to the chemical reaction by the addition of LiCe(BH₄)₃Cl, indicating that the diffusion rates of small ions like H⁺, Li⁺ and Mg²⁺ in LiMgNH system are significantly enhanced, which could be well explained by the improved ionic conductivity of LiCe(BH₄)₃Cl doped sample.     

High-performance FeCoP alloy catalysts by electroless deposition for overall water splitting

At present, it is difficult for electrocatalytic electrode materials with high-Performance to be prepared at low cost and large area under mild conditions. Therefore, we adopt a facile electroless plating method to deposit the FeCoP alloys on the nickel foam (NF) with different areas of 1 cm², 4 cm², 8 cm² and 16 cm². The FeCoP/NF catalysts exhibit extraordinary catalytic activity for the oxygen evolution reaction (OER) in alkaline media and are comparable to the state-of-the-art IrO₂ in 1.0 M KOH, capable of yielding a current density of 10 mA cm⁻² at an overpotential of only 250 mV. Furthermore, the FeCoP/NF catalysts show efficient activity towards the hydrogen evolution reaction (HER) with an overpotential of 163 mV at j = 10 mA cm⁻² as well. Remarkably, when used as both the anode and cathode, a low potential of 1.68 V (vs. RHE) is required to reach the current density of j = 10 mA cm⁻², making the FeCoP/NF alloys as an active bifunctional electrocatalyst for overall water splitting. The FeCoP/NF alloy catalysts with high catalytic activity, facile preparation and low cost would provide a new pathway for the design and large-scale application of high-performance bifunctional catalysts for electrochemical water splitting.     

Hydrogen permeation and stability in ultra-thin PdRu supported membranes

In this paper, we report the performance of supported PdRu membranes for possible applications to hydrogen purification and/or production. For this purpose, we fabricated three ultra-thin α-alumina-supported membranes by combined plating techniques: a PdAg membrane (3 μm-thick ca.) and two PdRu (1.8 μm-thick ca.). The former is set as a benchmark for comparison. The membranes were characterised using different methodologies: permeation tests, thermal treatment and SEM analysis. Preliminary leakage tests performed with nitrogen has revealed that the two PdRu membranes, namely PdRu#1 and PdRu#2, show a non-ideal (non-infinite) selectivity, which is relatively low for the former (around 830 at 400 °C) and sufficiently high for the latter (2645 at 400 °C). This indicates a relevant presence of defects in the PdRu#2 membrane, differently from what observed for the PdAg and PdRu#1 ones. The permeation tests show that the hydrogen permeating flux is stable up to around 550 °C, with an apparently unusual behaviour at higher temperatures (600 °C), where we observe a slightly decrease of hydrogen flux with an increase of the nitrogen one. Moreover, a peculiar bubble-shaped structure is observed in the metal layer of all membranes after usage by means of SEM image analysis. This is explained by considering the effect of the Pd-alloy grain surface energy, which tends to minimise the exposed surface area of the grain interface by creating sphere-like bubble in the lattice, similar to what occurs for soap bubbles in water. The above-mentioned decrease in hydrogen flux at 600 °C is explained to be caused by the bubble formation, which pushes the alloy deeper in the support pores.     

Three-demensional NiCoNiCo2O4/NF as an efficient electrode for hydrogen evolution reaction

At present, there is an urgent need for plentiful non-noble metal catalyst to substitute for valuableness platinum based metal catalyst in electrochemical water splitting. Here, we fabricated a three-demensional (3D) NiCoNiCo₂O₄ nanosheets electrocatalyst that directly grew on Ni foam firstly and then were reduced in 0.1 mol dm⁻³ sodium borohydride solution. This electrode exhibited high activity in 1.0 mol dm⁻³ KOH solution with an onset potential of ∼40 mV and a tafel slope of 77 mV dec⁻¹. Furthermore, the NiCoNiCo₂O₄/NF electrode showed a splendid durability during long-playing electrochemical test. Our work may provide an inexpensive, easy-to-obtain and excellent catalyst candidate for future electrolytic water research and industry studies that may involve hydrogen applications in the future.     

Exploration of Ti substitution in AB2-type YZrFe based hydrogen storage alloys

To improve the hydrogen storage properties of YZrFe alloys, the alloying with Ti was carried out to obtain Y_0.7Zr_(0.3-x)Ti_xFe₂ (x = 0.03, 0.09, 0.1, 0.2) alloys by different processes. It was expected that Ti would substitute Zr and decrease the lattice constant of YFe₂-based C15 Laves phase. All YZrTiFe quaternary alloys consist of the main Y(Zr)Fe₂ phase and the minor YFe₃ phase. Despite the large solubility of Ti in Zr or Zr in Y, the Ti incorporation into YZrFe alloys results in the inhomogeneity of Y and the segregation of Ti, and thus decreases the hydrogen storage capacity. Only the alloy Y_0.7Zr_0.27Ti_0.03Fe₂ containing very few Ti shows the substitution of Ti to Zr and the resultant improvement in the dehydriding equilibrium pressure.     

Theoretical study on the effect of an O vacancy on the hydrogen storage properties of the LaFeO3 (010) surface

Based on first-principles calculations, we investigated the hydrogen adsorption dissociation on the LaFeO₃ (010) surface with an O vacancy. It was confirmed that H₂ molecules have four kinds of adsorption modes on LaFeO₃ (010) surfaces with an O vacancy. First, H atoms are adsorbed on O atoms to form an OH group. Second, H atoms are adsorbed on Fe atoms to form FeH bonds. Third, two H atoms are adsorbed on the same O atom to form H₂O. Fourth, two H atoms are adsorbed on the same Fe atom and it is a new type of adsorption, which does not exist in the ideal surface. The main channel of dissociative adsorption is the fourth adsorption mode of OH and FeH, where the H atoms adsorbed on the surface of Fe can be easily diffused into O atoms. Charge population analysis showed that increasing the O vacancy enhanced the interaction between FeH. In the system containing O vacancies adsorbed H atoms in the top of Fe to diffuse to the top of O need to overcome the energy barrier decreased from 0.968 eV to 0.794 eV. So the existence of an O vacancy enhances the hydrogen absorption properties of Fe atoms in LaFeO₃.     

Biomass-derived porous carbon supported CoCoO yolk-shell nanoparticles as enhanced multifunctional electrocatalysts

Developing highly efficient, durable and low-cost electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in energy conversion and storage is still required, urgent and challenging. Herein, a novel structure of biomass-derived nitrogen-doped porous carbon supported yolk-shell CoCoO nanoparticles (yolk-shell CoCoO/BC) was successfully prepared via a facile impregnation strategy. The pyrolysis temperature and heating rate of Co²⁺/BC composite are two key factors in the formation of the yolk-shell structure. The synthesized yolk-shell CoCoO/BC exhibits excellent electrochemical activity and stability as multifunctional electrocatalysts. The yolk-shell CoCoO/C with a positive onset potential (0.91 V vs. RHE) and half-wave potential (0.82 V vs. RHE) exhibits an effective 4-electron transfer path and excellent methanol tolerance in alkaline electrolyte for ORR. Moreover, a low cell potential (η₁₀ = 1.77 V vs. RHE at the current density of 10 mA cm⁻²) for overall water splitting can be reached. The synergistic catalytic effects between BC support and yolk-shell CoCoO nanoparticles should be responsible for the excellent performance for ORR, OER and HER. This work opens up a way to the facile fabrication of carbon supported yolk-shell nanostructures with high-performance in electrocatalytic applications for ORR, OER and HER.