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.     

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.     

Carbon-supported phosphatized CuNi nanoparticle catalysts for hydrazine electrooxidation

Developing non-noble metal catalysts with high performance to reduce the cost of hydrazine fuel cells is urgent. Herein, in this study, a series of carbon-supported phosphatized CuNi catalysts (P-Cu_xNi_y/C) are designed for hydrazine oxidation reaction (HzOR) via high temperature phosphating process. Among them, the PCu₂Ni/C is found to be a promising candidate for hydrazine electrooxidation. Electrochemical measurement results indicate that the PCu₂Ni/C catalyst exhibits higher catalytic activity and stability for HzOR in comparison with PCuNi/C, PCuNi₂/C, Cu₂Ni/C, Cu/C and Ni/C catalysts. Additionally, HzOR kinetics are also investigated, and it proves that hydrazine electrooxidation on PCu₂Ni/C is a diffusion controlled irreversible process. Meanwhile, physical characterization reveals that the catalysts have doped phosphorus successfully. All results demonstrate that as-prepared PCu₂Ni/C catalyst is a promising electrocatalyst for direct hydrazine fuel cells.     

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.     

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.     

Sodium borohydride hydrolysis by using ceramic foam supported bimetallic and trimetallic catalysts

In this study, bimetallic and trimetallic catalysts with different contents on ceramic foam support were prepared in an integrated continuous system and performances of catalysts were investigated using a fixed bed reactor. Bimetallic copper-cobalt, lithium-cobalt, and platinum and palladium added bimetallic (trimetallic) catalysts were prepared and characterized by SEM for morphological structure analysis, BET for surface area measurements, and XRD and XPS for crystal structure analysis. In the hydrogen production tests carried out at different flow rates and temperatures, Pd included trimetallic catalysts performed slightly better than Pt added bimetallic catalysts. Although Pd catalysts have low activity than Pt catalysts according to literature, Pd catalyst prepared on ceramic foam had higher activity. In this work, PdLiCo and PdCuCo catalysts demonstrated highest hydrogen production rates (respectively 4.76 ml/min and 4.69 ml/min) as well as highest specific surface area (7.301 m²/g for PdLiCo, 11.821 m²/g for PdCuCo).     

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.     

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.     

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.     

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.     

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.     

High performance of the novel PdCeO2-NR/C (cerium oxide nanorods) nanocatalyst for the oxidation of C1, C2 and C3 organic molecules for fuel cells applications

Cerium oxide nanorods treated at 200 (CeO_2-NR2) and 400 °C (CeO_2-NR4) were used to synthesize of PdCeO_2-NR2/C and PdCeO_2-NR4/C nanocatalysts to promote the Methanol, Ethanol, Ethylene Glycol and Glycerol Oxidation Reactions (MOR, EOR, EGOR and GOR, respectively). The crystalline nanocatalysts had morphology of agglomerated Pd nanoparticles dispersed on Vulcan and on the nanorods as well. The polarization curves in 0.5 M KOH showed that the catalytic activity decreases in all reactions in the order PdCeO_2-NR4/C > PdCeO_2-NR2/C > Pd/C, which confirmed the synergetic effect of the nanorods on the catalytic behavior of Pd, particularly after heat treatment at 400 °C. The highest mass current density has been obtained from the EGOR (j_f = 6661 mA mg_Pd⁻¹) with the PdCeO_2-NR4/C nanocatalyst, which catalyzed the reaction with an onset potential (E_onset) of −0.26 V/SHE. Meanwhile, the EOR was promoted with the most negative E_onset (−0.40 V/SHE), delivering 5719 mA mg_Pd⁻¹, also using PdCeO_2-NR4/C. Therefore, considering electrocatalysis parameters for fuel cells applications, the oxidation of C₂H₆O₂ and C₂H₅OH showed advantages using PdCeO_2-NR4/C.     

Pt nanoparticles supported on a novel electrospun polyvinyl alcohol-CuOCo3O4/chitosan based on Sesbania sesban plant as an electrocatalyst for direct methanol fuel cells

Here, novel polyvinyl alcohol (PVA) nanofibers with incorporated CuO and Co₃O₄ nanoparticles (PVA-CuOCo₃O₄) were synthesized through a conventional single-nozzle electrospinning technique and characterized by atomic force microscopy (AFM), energy dispersive X-ray analysis (EDX), fourier-transform infrared spectroscopy (FT-IR), elemental analysis, transmission electron microscopy (TEM), differential thermal analysis (DTA), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Novel Pt/polyvinyl alcohol-CuOCo₃O₄/chitosan (Pt/PVA-CuOCo₃O₄/CH) catalyst was successfully prepared. EDX, TEM, and FT-IR spectroscopy techniques were used to characterize the prepared catalysts. The electrocatalytic activity of Pt/PVA-CuOCo₃O₄/CH catalyst was investigated for methanol electrooxidation through cyclic voltammetry, chronoamperometry, CO stripping voltammetry, and electrochemical impedance spectroscopy techniques. The effects of some experimental factors for methanol electrooxidation were studied on the prepared catalysts and the optimum conditions were determined. Pt/PVA-CuOCo₃O₄/CH catalyst had extraordinary electrocatalytic activity for methanol electrooxidation. It exhibited better stability, higher electrochemically active surface area, and better antipoisoning effect than Pt/PVA-CuOCo₃O₄ and Pt/PVA/CH catalysts indicating that Pt/PVA-CuOCo₃O₄/CH could be a promising catalyst for direct methanol fuel cell (DMFC) applications. A real DMFC was designed, assembled and tested with Pt/PVA-CuOCo₃O₄/CH as anodic 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.     

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.     

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 production of γ-valerolactone from furfural using Zr-graphitic carbon nitride/H-β composite

In order to efficiently produce γ-valerolactone (GVL) from furfural, a Zr-graphitic carbon nitride/H-β composite (ZrCN/H-β) had been simply prepared via an impregnation-calcination protocol. The morphology and structure, elemental information, and total acid and base properties of the ZrCN/H-β and related catalysts (H-β, CN/H-β, and Zr/H-β) were determined by SEM, TEM, X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD-NH₃, CO₂) characterizations. The effects of reaction temperature and time, and the furfural dosage on GVL production as well as the recyclability of ZrCN/H-β were investigated. With a catalyst/furfural dosage of 0.1/0.22 g, the ZrCN/H-β produced a remarkable 76.5% of GVL yield at 160 °C in 18 h using isopropanol as the solvent. The results of NH₃, CO₂-TPD experiments indicated that the simultaneous introduction of Zr species and carbon nitride onto H-β formed new types of acid and base, which should be responsible for the high efficient conversion of furfural to GVL. Additionally, the recyclability of ZrCN/H-β was reasonable.     

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.     

Enhanced photocatalytic hydrogen evolution of CdWO4 through polar organic molecule modification

In this work, a polar molecule 4-mercaptobenzoic acid (4-MBA) is anchored on the surface of CdWO₄ by forming CdS and WS bond. Photocatalytic hydrogen evolution is significantly enhanced (about 3.41 times) after the modification. The reason is due to the modification of 4-MBA, which results in a polar surface and built-in electric field. The polar surface is confirmed by the steady state and time-resolved PL spectra, V_oc and SHG results.     

Catalytic activities of non-noble metal catalysts (CuB,FeB, and NiB) with C.Vulgaris microalgal strain support modified by using phosphoric acid for hydrogen generation from sodium borohydride methanolysis

In this study, a novel microalgae based support material was developed and applied. The Chlorella Vulgaris microalgal strain was modified by treating the algal biomass with phosphoric acid for proton binding process (CVMS-H₃PO₄). Ultimately, the CVMS-H₃PO₄-metal (CuB, NiB, or FeB) catalysts were used as highly efficient solid catalysts to produce hydrogen from the methanolysis of NaBH₄. Once the superior metal was identified, the NaBH₄ concentration, metal percentage in the supported-catalyst, catalyst amount, and temperature effect on the methanolysis reaction was thoroughly investigated. The maximum hydrogen production rate for the CVMS-H₃PO₄ supported-catalyst was obtained with the use of 20% Cu metal at 30 °C and it was found to be 6500 mL/min/g_cat. In addition, the maximum hydrogen production rate for the CVMS-H₃PO₄ supported-catalyst was attained with the use of 20% Cu metal at 60 °C and it was found to be 21176 mL/min/g_cat. Also, the activation energy was determined as 23.79 kJ/mol. The re-usability studies of the microalgal strain supported-CuB catalyst were performed and it was found that there was no decrease in % conversion for this catalyst. XRD, FTIR, SEM, and ICP-MS analysis were carried out to characterize CVMS-H₃PO₄CuB catalyst thoroughly.