Performance of CoNiO spinel oxide coating on AISI 430 stainless steel as interconnect for intermediate temperature solid oxide fuel cell

In order to decrease oxide growth kinetics, maintain suitable conductivity and prevent Cr-volatilization of AISI 430 stainless steels (430 SS) as the interconnect for intermediate temperature solid oxide fuel cells (SOFCs), a CoNiO spinel oxide protective coating has been successfully fabricated on the 430 SS specimen using a simple and cheap process with two steps: 1) electroplation of CoNi alloy layer and 2) pre-oxidation treatment to convert the CoNi alloy into spinel oxide. The CoNiO spinel layer on the 430 SS (CoNiO 430 SS) is dense and uniform with 8–10 μm thickness. And the CoNiO spinel oxide protective coating consists of a main face-centered-cubic (fcc) NiCo₂O₄ spinel phase and a minor fcc NiO phase. Compared with bare 430 SS, the oxidation resistance and the conductivity of the CoNiO 430 SS have been improved remarkably under simulated typical SOFC operating cathode conditions (at 800 °C in air). After an isothermal oxidation test at 800 °C, the area specific resistance (ASR) of CoNiO 430 SS is much lower and stable (0.1 Ω cm² for 100 h and 0.9 Ω cm² for 600 h) than that of bare 430 SS (1.2 Ω cm² for 100 h and 2.4 Ω cm² for 600 h). These performances of CoNiO 430 SS imply that it can be a promising candidate interconnect for solid oxide fuel cell.     

Tailoring a Pt–Ru catalyst for enhanced methanol electro-oxidation

A carbon-supported (1:1) Pt–Ru (Pt–Ru/C) alloy catalyst has been prepared in-house by the sulfito-complex route, and has been tailored to achieve enhanced activity towards methanol electro-oxidation by annealing it at varying temperatures in air. The catalyst samples annealed between 250 and 300 °C in air for 30 min exhibit superior catalytic activity towards methanol electro-oxidation in a solid-polymer-electrolyte direct methanol fuel cell (SPE-DMFCs) operating at 90 °C. Both the as-prepared and annealed Pt–Ru/C catalysts have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and cyclic voltammetry. It is conjectured that while annealing the Pt–Ru/C catalysts, both PtPt and PtRu bonds increase whereas the PtO bond shrinks. This is accompanied with a positive variation in Ru/Pt metal ratio suggesting the diffusion of Ru metal from the bulk catalyst to surface with an increase in oxidic ruthenium content. Such a treatment appears seminal for enhancing the electrochemical activity of Pt–Ru catalysts towards methanol oxidation.     

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.     

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.     

An experimental and mechanistic study on the laminar flame speed,Markstein length and flame chemistry of the butanol isomers

Laminar flame speeds and Markstein lengths for n-butanol, s-butanol, i-butanol and t-butanol at pressures from 1 to 5 atm were experimentally measured in a heated, dual-chamber vessel. Results at all pressures show that n-butanol has the highest flame speeds, followed by s-butanol and i-butanol, and then t-butanol. Results further show that the reduced Markstein length measured for n-butanol as compared to other isomers is a flame thickness effect, and that all four isomers have similar Markstein numbers, which is the appropriate nondimensional parameter to quantify flame stretch. Computation and flame chemistry analysis were performed using two recently published kinetic models on butanol isomers by Sarathy et al. and Ranzi et al., respectively. Comparison shows the former model satisfactorily agrees with the present results while agreement of the latter is less satisfactory. Based on reaction path analysis the major differences of the two models on fuel cracking pathway were identified. It is concluded that the primary reason for the lowered flame speed of s-butanol, i-butanol and t-butanol is that they crack into more branched intermediate species which are relatively stable, such as iso-butene, iso-propenol and acetone. This indicates that the general rule that fuel branching reduces flame speed for hydrocarbons can also be applied to alcohols, and that the fundamental reason for this generality is that in alcohols CO has similar bond energy to the CC bond while OH has similar bond energy to the CH bond.     

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.     

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.     

Synthetic fuels from 3-φ Fischer-Tropsch synthesis using syngas feed and novel nanometric catalysts synthesised by plasma

Nanometric carbon-supported catalysts based on cobalt and iron (Co/C, Fe/C and CoFe/C) were synthesised by plasma method for application in Fischer-Tropsch synthesis (FTS). FTS tests were conducted at reaction conditions (ca 533 K, 2 MPa) over the catalyst, in a feed stream of 60% mol fraction H₂ and 30% mol fraction CO at 1.0 cm³s⁻¹g⁻¹ of catalyst for 24 h. Prior to this, the catalysts were pre-treated at 673 K either in pure H₂ or CO flowing at 250 cm³ min⁻¹ for 24 h. Results showed that higher temperature promoted better CO conversion; up to 100% for the Co/C catalyst at 533 K. However, lower temperatures were more conducive for the selectivity of Co/C catalyst towards gasoline (C₄C₁₂) and diesel (C₁₃C₂₀) fractions, since production of undesired products such as CO₂ and CH₄ was prevalent at higher temperatures. At 493 K, the CoFe/C bimetallics were almost inert, but at 533 K, they showed improved CO conversion. When compared to the Co/C catalyst, Fe-containing catalysts suppressed both CO₂ and CH₄ production. Moderated H₂O production was witnessed in the CO-reduced catalysts, contrasting with catalysts pre-treated in H₂ gas. Catalyst characterisation by BET surface area, XRD analysis and microscopy (SEM & TEM) showed that plasma synthesis produces catalysts with consistency, having highly dispersed nanoparticle metal moieties, interspersed with various forms of metallic, carbidic and intermetallic CoFe species in the carbon matrix support.     

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.     

Aqueous phase reforming of polyols for hydrogen production using supported PtFe bimetallic catalysts

3-D cubic ordered mesoporous carbon (CMK-9) supported PtFe bimetallic catalysts with a range of PtFe compositions were applied to the aqueous phase reforming (APR) of polyols for hydrogen production. The catalytic performance with respect to the polyol and support used was also studied. The catalysts and supports were characterized via X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N₂ sorption, temperature programmed reduction (TPR), and CO chemisorption techniques. The polyols investigated include ethylene glycol (EG), glycerol, xylitol, and sorbitol. It was found that the addition of Fe to the Pt/CMK-9 catalyst significantly improved catalytic performance, with the optimum Pt:Fe ratio for APR activity being 1:3. It was also observed that, in the PtFe (1:3) system, the CMK-9 support demonstrated better catalytic performance than commercially available activated carbon or alumina. In addition, the catalytic activity of the PtFe/CMK-9 catalyst was successfully increased by both the effect of the water-gas shift reaction, promoted by Fe addition to Pt, and by the structural properties and nature of the CMK-9 support. Moreover, the PtFe (1:3)/CMK-9 catalyst showed efficient catalytic activity for different biomass derivatives (EG, glycerol, xylitol, and sorbitol), with the activity decreasing with increase in the number of carbon atoms.     

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.     

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.     

Influence of temperature on organic structure of biomass pyrolysis products

Biomass pyrolysis experiments were performed in a tubular reactor at different temperatures, the effects of which on organic structure of semi-char and tar had been investigated. Fourier-transform infrared (FTIR) analysis was conducted by a Nicolet 6700 FTIR spectrometer. The tar components at different temperatures were analyzed by GC/MS. It was observed that pyrolysis of biomass mainly occurs in the temperature range of 300–600 °C. A high temperature favored the production of gases. The yield of semi-char and the contained organic functional groups(CO, CC, C–H, C–O and OH) decreases significantly with the increasing final temperature. The tar yield passes through a maximum at about 500 °C. The organic functional groups in tar were stable but the transmittance of these groups decreased with the increasing final temperature.     

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.     

PtRh alloys on hybrid TiO2 – Carbon support as high efficiency catalyst for ethanol oxidation

High cost and poor stability of catalysts remain major obstacles for the commercialization of direct ethanol fuel cells (DEFCs). In this work, a Pt₉Rh/TiO₂C nanostructured catalyst is synthesized via an impregnation-reduction method followed by thermal annealing in N₂ at ambient pressure. X-ray powder diffraction (XRD) and scanning transmission electron microscopy (STEM) are used to characterize the corresponding physico-chemical properties of the as-prepared catalysts. The results reveal that PtRh nanoparticles are uniformly distributed on the TiO₂C hybrid support material. Cyclic voltammetry, linear scan voltammetry, CO-stripping voltammograms, chronoamperometry and chronopotentiometry methods are employed to investigate their catalytic performance for ethanol oxidation. The results show that the Pt₉Rh/TiO₂C produced a current density of 1039.5 mA mg_Pt^?1, which are 3.98, 8.31 and 2.43 times higher than Pt/TiO₂C, Pt/C and Pt₉Rh/C, respectively. Furthermore, the Pt₉Rh/TiO₂C also has greater resistance to CO-poisoning and displays better stability for ethanol oxidation than other catalysts. Pt₉Rh/TiO₂C therefore provides a promising material for ethanol oxidation in direct ethanol fuel cells.     

Hydrogen production from steam and autothermal reforming of LPG over high surface area ceria

Steam and autothermal reforming reactions of LPG (propane/butane) over high surface area CeO₂ (CeO₂ (HSA)) synthesized by a surfactant-assisted approach were studied under solid oxide fuel cell (SOFC) operating conditions. The catalyst provides significantly higher reforming reactivity and excellent resistance toward carbon deposition compared to the conventional Ni/Al₂O₃. These benefits of CeO₂ are due to the redox property of this material. During the reforming process, the gas–solid reactions between the hydrocarbons present in the system (i.e. C₄H₁₀, C₃H₈, C₂H₆, C₂H₄, and CH₄) and the lattice oxygen (O_O^x) take place on the ceria surface. The reactions of these adsorbed surface hydrocarbons with the lattice oxygen (C_nH_m + O_O^x → nCO + m/2(H₂) + V_O + 2e′) can produce synthesis gas (CO and H₂) and also prevent the formation of carbon species from hydrocarbons decomposition reactions (C_nH_m ⇔ nC + 2mH₂). Afterwards, the lattice oxygen (O_O^x) can be regenerated by reaction with the steam present in the system (H₂O + V_O + 2e′ ⇔ O_O^x + H₂). It should be noted that V_O denotes as an oxygen vacancy with an effective charge 2⁺.At 900 °C, the main products from steam reforming over CeO₂ (HSA) were H₂, CO, CO₂, and CH₄ with a small amount of C₂H₄. The addition of oxygen in autothermal reforming was found to reduce the degree of carbon deposition and improve product selectivities by completely eliminating C₂H₄ formation. The major consideration in the autothermal reforming operation is the O₂/LPG (O/C molar ratio) ratio, as the presence of a too high oxygen concentration could oxidize the hydrogen and carbon monoxide produced from the steam reforming. A suitable O/C molar ratio for autothermal reforming of CeO₂ (HSA) was 0.6.     

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.     

Structural dependence of photocatalytic hydrogen production over La/Cr co-doped perovskite compound ATiO3 (A = Ca,Sr and Ba)

The crystal structure of a photocatalyst generally plays a pivotal role in its electronic structure and catalytic properties. In this work, we synthesized a series of La/Cr co-doped perovskite compounds ATiO₃ (M = Ca, Sr and Ba) via a hydrothermal method. Their optical properties and photocatalytic activities were systematically explored from the viewpoint of their dependence on structural variations, i.e. impact of bond length and bond angles. Our results show that although La/Cr co-doping helps to improve the visible light absorption and photocatalytic activity of these wide band gap semiconductors, their light absorbance and catalytic performance are strongly governed by the TiO bond length and TiOTi bond angle. A long TiO bond and deviation of TiOTi bond angle away from 180° deteriorate the visible light absorption and photocatalytic activity. The best photocatalytic activity belongs to Sr_0.9La_0.1Ti_0.9Cr_0.1O₃ with an average hydrogen production rate ～2.88 μmol/h under visible light illumination (λ ≥ 400 nm), corresponding to apparent quantum efficiency ～ 0.07%. This study highlights an effective way in tailoring the light absorption and photocatalytic properties of perovskite compounds by modifying cations in the A site.     

Thin-film rechargeable lithium batteries

Thin-film rechargeable batteries with a lithium metal anode, an amorphous inorganic electrolyte, and cathodes of amorphous V₂O₅ and crystalline and amorphous Li_xMn₂O₄ have been fabricated and characterized. The performance of the thin-film cells was evaluated at different current densities and, in the case of LiV₅, at several temperatures. Electrical measurements show that the current density of the thin-film cells is limited by the lithium-ion mobility in the cathodes. The resistance of LiLi_xMn₂O₄ cells with crystalline cathodes is about two orders of magnitude lower than that of LiV₅ cells with amorphous cathodes.