Highly dispersed metal nanoparticles on TiO2 acted as nano redox reactor and its synergistic catalysis on the hydrogen storage properties of magnesium hydride

In this paper, we have synthesized highly dispersed Co metal nanoparticles with the particle size about 5–10 nm on TiO₂ (25–50 nm) for the first time through an extremely facile solvothermal method. It is supposed that the synthesized Co/TiO₂ composite can combine the catalytic advantage of both Co and TiO₂, exhibiting the superior catalytic effect on the hydrogen de/absorption properties of MgH₂. The experimental data confirmed the above supposition and demonstrated that Co/TiO₂ additive highly enhances the hydrogen de/absorption kinetics of MgH₂ as compared to separate Co or TiO₂ additive. Specifically, the MgH₂Co/TiO₂ composite begins to desorb hydrogen at about 190 °C with a low apparent activation energy of 77 kJ/mol. Besides, the MgH₂Co/TiO₂ composite has a desorption peak temperature of 235.2 °C, which is 53.2, 94.2 and 132.2 °C lower than that of MgH₂TiO₂ (288.4 °C), MgH₂Co (329.4 °C) and ball-milled MgH₂ (367.4 °C). Moreover, MgH₂Co/TiO₂ composite also exhibits low temperature rehydrogenation properties, which can absorb 6.07, 5.56 and 4.24 wt% H₂ within 10 min at the temperature of 165, 130 and 100 °C, respectively. It is supposed that such excellent hydrogen desorption properties and low desorption energy barrier of MgH₂Co/TiO₂ composite are mainly ascribed to the novel synergistic catalytic effects of Co and TiO₂. Herein, we propose a novel catalytic mechanism and think that Co/TiO₂ acts as “nano redox reactor”, which can facilitate the dissociation and recombination process of hydrogen, thus reducing the reaction energy barrier and enhancing the de/rehydrogenation of MgH₂.     

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.     

MgCNi3 prepared by powder metallurgy for improved hydrogen storage properties of MgH2

With the depletion of global energies resources, improvement of hydrogen storage properties of materials like MgH₂ is of great interest for future efficient renewable resources. In this study, a novel antiperovskite MgCNi₃ was synthesized by powder metallurgy then introduced into Mg to fabricate MgMgCNi₃ composite. The hydrogen storage properties of the obtained MgMgCNi₃ composite were evaluated. MgMgCNi₃ showed a high capacity of hydrogen storage and fast kinetics of hydrogen uptake/release at relatively low temperatures. About 4.42 wt% H₂ was absorbed within 20 min at 423 K, and 4.81 wt% H₂ was reversibly released within 20 min at 593 K. By comparison, milled MgH₂ absorbed only 0.99 wt% H₂ and hardly underwent any hydrogen evolution under the same conditions. In addition, MgMgCNi₃ composite showed outstanding cycling stability, with hydrogen absorption capacity retention rates reaching 98% after ten cycles at 623 K. The characterization analyses revealed that MgCNi₃ and Mg formed Mg₂NiH₄ hydride and carbonaceous material during hydrogenation, where Mg₂NiH₄ induced dehydrogenation of MgH₂ and carbon played a dispersive role during the composite reaction. Both features synergistically benefited the hydrogen storage properties of MgH₂.     

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.     

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.     

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.     

Dry reforming of methane for hydrogen production over NiCo catalysts: Effect of NbZr promoters

Ni/Al₂O₃, NiCo/Al₂O₃MgO and NiCo/Al₂O₃MgO/NbZr nanocatalysts were prepared by the sol-gel technique with citric acid and tested in the dry reforming of methane (DRM). In this paper, the effects of Nb and Zr addition as promoters in Al₂O₃MgO supported catalysts on the physicochemical characteristics and the reaction performance in the DRM were investigated. The NbZr promoters are expected to enhance the activity and performance of the catalyst due to its high thermal stability and also improvement in the metal dispersion of the catalyst. The catalysts samples were characterized by FESEM, BET, XRD, TEM, H₂-TPR and CO₂-TPD techniques. FESEM results demonstrated that NiCo/Al₂O₃MgO/NbZr has more uniform and well-dispersion of metal than NiCo/Al₂O₃MgO. The BET results unravel that the addition of NbZr promoters increase the surface area of the synthesized catalyst due to the high surface area of the promoters. There is a formation of MgAl₂O₄ spinel-type solid solution proved by the XRD and CO₂-TPD analysis due to the interaction between alumina lattice and magnesium metal which has high resistance to carbon formation. The DRM reaction is performed in the tubular furnace reactor at 1073.15 K, 1 atm and a CH₄/CO₂ ratio of unity. The sol-gelled NiCo/Al₂O₃MgO/NbZr was found to be the most proper choice for DRM which illustrates much higher conversion (86.96% for CH₄ conversion and 87.84% for CO₂ conversion) compared to the other catalysts. This is due to the strong interaction between active metals and supports, resistance to coke formation and higher stability in DRM reaction.     

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.     

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.     

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.     

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.     

Fabrication and optical property improvement of gasochromic switchable mirror based on Pd/MgNb2O5 thin film

Recently, the application of magnesium-based gasochromic switchable mirror has been baffled by the low optical dynamic range due to the insufficient conversion between Mg and MgH₂. Based on the excellent catalytic property of Nb₂O₅ for the magnesium-hydrogen reaction, we fabricated fluorocarbon (FC)/Pd/MgNb₂O₅ switchable films via magnetron sputtering and low-temperature inductively coupled plasma chemical vapor deposition technologies in this study, and the optical performance and microstructure of the films were investigated. The results show that the FC/Pd/Mg-3 mol% Nb₂O₅ film exhibits the higher dynamic ranges of the luminous (49.4%) and solar transmittance (54.7%), compared with most of reported Mg-based alloys and MgTiO₂ systems. The addition of Nb₂O₅ and covering a FC layer on the Pd/Mg film could effectively accelerate the switching response and improve such optical properties as transmittance at transparent state and dynamic range. The microstructural analysis reveals that the Nb₂O₅ and appropriate amount of ternary MgNbO phase in the Mg-based layer are supposed to facilitate rapid and sufficient hydrogen absorption and desorption. Furthermore, the high-valence Nb ions scattering around Mg atoms may act as a transfer station for catalyzing the reversible reaction between Mg and H. The excellent optical modulation performance and enhanced hydrophobicity of the FC/Pd/MgNb₂O₅ films signify an application prospect for gasochromic switchable mirror.     

A continuous valence band through NO orbital hybridization in NTiO2 and its induced full visible-light absorption for photocatalytic hydrogen production

Photocatalytic hydrogen production represents an effective approach for solar energy conversion, which can greatly ease the current energy crisis. Herein, we report a successful NO orbital hybridization in N-doped TiO₂ nanotube, the absorption wavelength is greatly red-shifted to visible light (from 400 to 800 nm) with large absorbance. The doping N element can partially replace the oxygen sites in TiO₂ lattice to form NTiN bonds. The hybridization effect of N 2p and O 2p makes a continuous valence band and the position up-shift from 1.99 to 1.67 eV, the band gap is subsequently narrowed from 3.21 to 2.77 eV for 1.85-NTiO₂ nanotube, which has been confirmed by ultraviolet–visible diffuse reflectance spectra and X-ray photoelectron spectroscopy valence band spectra. Benefiting from the enhanced visible light absorption ability and ultrathin shell feature, 1.85-NTiO₂ nanotube exhibits exciting photocatalytic hydrogen evolution performance with a rate of 10870 μmol h⁻¹ g⁻¹ under the selected visible light irradiation (λ > 400 nm). This work demonstrates an alternative strategy for tuning visible light absorption ability by doping for wide-band-gap semiconductors in photocatalysts design, and the philosophy can also be extended to other photocatalytic systems.     

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.     

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.     

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.     

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.     

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.     

CoMoB nanoparticles supported on foam Ni as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane solution

We report on CoMoB nanoparticles supported on foam Ni as catalysts for hydrogen generation from hydrolysis of ammonia borane (NH₃BH₃) solution. The CoMoB/foam Ni catalysts with different molar ratios of Co²⁺and MoO₄²⁻ were synthesized via the electroless-deposition technique at ambient temperature. In order to analyze the phase composition, chemical composition, microstructure, and electron bonding structure of the as-prepared samples, powder X–ray diffraction (XRD), inductively coupled plasma-mass spectroscopy (ICP-MS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used. The results showed that CoMoB nanoparticles were variously dispersed on the surface of the foam Ni and the catalytic activity correlated with the molar ratio of Co²⁺ and MoO₄²⁻. The highest hydrogen generation rate was 5331.0 mL min⁻¹ g_cat⁻¹ at 298 K, and the activation energy was calculated to be 45.5 kJ mol⁻¹ toward the hydrolysis of NH₃BH₃ solution. The better catalytic activity was largely attributed to the smaller particle size, higher surface roughness and the novel three-dimensional cone-like architectures of the obtained samples. The kinetic results show that the hydrolysis of NH₃BH₃ is a first-order reaction in catalyst concentration. In addition, the reusability experiment exhibited that the catalytic activity was reduced after 5 cycles and the reason of the decay was also investigated.     

Ruthenium catalyst supported on Ba modified ZrO2 for ammonia decomposition to COx-free hydrogen

The Ba modified ZrO₂ materials were prepared and loaded Ru nanoparticles for ammonia decomposition to CO_x-free hydrogen reaction. The catalytic activity of Ru supported on BaZrO₂ derived from sol-gel process (Ru/BaZrO₂) is found to be several times of those for Ru/ZrO₂ without any promoter and RuBa/ZrO₂ catalysts prepared by conventional immersion method at the identical conditions. It is found that the formation of BaZrO₃ phase in BaZrO₂ can enhance the electron-donating ability of the support and Ru nanoparticles dispersion. Therefore, mobile electrons would be transferred from BaZrO₃ to the surface Ru particles, facilitating the recombinative desorption of N over Ru particles, leading to the increase of activity for ammonia decomposition sufficiently. Additionally, the suitable size of spherical Ru particles with average size of 2.4 nm for the formation of active sites are also responsible factors for the higher activity of this catalyst. The catalytic performance of Ru/BaZrO₂ catalyst can also be further improved by introducing of K and Cs promoters, and the apparent activation energies over Ru/BaZrO₂ of 94.1 kJ/mol decrease to 70.7 kJ/mol and 64.2 kJ/mol for K and Cs promoted Ru/BaZrO₂, respectively.