Proton conductivity and chemical stability of Li2SO4 based electrolyte in a H2S–air fuel cell

Proton conductivity of Li₂SO₄-Al₂O₃ (LA) based electrolyte was determined under non-reducing dynamic conditions using current interruption technique. The performance of LA as electrolyte has been examined at 600 °C in a H₂S fuel cell with MoS₂-NiS as anode catalyst and NiO as cathode catalyst. XRD and XPS results show that Li₂SO₄ is not stable when heated in pure H₂S as it is reduced to Li₂S by hydrogen produced in equilibrium amounts from the thermal decomposition of H₂S. In contrast, under dynamic operation in a H₂S fuel cell the concentration of H₂ is much lower, the reduction reaction does not occur and, surprisingly, Li₂SO₄ is a chemically stable electrolyte.     

Use of electropolymerized films of macrocyclic compounds in direct methanol fuel cell components

Electropolymerized Co(III) and Ru(II)(CO)(2-aminophenyl)porphyrins (poly[Co(III)] and poly[Ru(II)]) were used as catalysts in a direct methanol fuel cell for the reduction of oxygen at the cathode and the oxidation of methanol at the anode, respectively. Although the half-wave potentials for oxygen reduction are +0.3 and +0.55 V when using poly[Co(III)]/C and Pt/C, respectively, as catalysts, higher limiting currents can be obtained with the non-noble metal catalyst. Moreover, the macrocyclic catalyst is 10-fold less prone to methanol poisoning than the one based on Pt. The H₂O₂ yields obtained during oxygen reduction, as measured by the RRDE technique, were 1.9, 4.1 and 2.3% for poly[Co(III)]/C, Pt/C and for a commercial heat-treated Co(III)porphyrin. Methanol oxidation with a catalyst consisting of Pt and poly[Ru(II)] was characterized by a higher limiting current (i_L=13 mA/cm², E_1/2=+0.6 V) than that obtained with a commercial Pt-Ru catalyst (i_L=4 mA/cm², E_1/2=+0.5 V) although the same Pt content was used in the two cases (1 mg/cm²). Experiments conducted in a fuel cell configuration confirmed the half-cell results and indicated that better distribution of the catalysts in the porous structure of the electrodes and reduction of methanol crossover through the membrane are necessary in order to improve the performance of the cell.     

A proton-conducting solid state H2S-O2 fuel cell. 1. anode catalysts, and operation at atmospheric pressure and 20–90°C

A stable solid state H₂S--O₂ fuel cell has been developed and operated at 1 atm and 20-90°C. A series of anode catalysts has been examined using Nafion^® as a common proton conducting membrane; those containing Pd and Pt were found to be effective using H₂ or H₂S as the anode feed gas, but MoS₂--C catalysts were effective for use of H₂S but not for H₂. The highest potential attained using H₂S and Pd/C catalyst was 722 mV (theory: 1140 mV). When H₂S was used as anode feed the potential decreased up to 35% over 24 h as sulfur was deposited on the anode. The efficiency of the cell increased with temperature up to 90°C.     

New insight into effect of potential on degradation of Fe-N-C catalyst for ORR

In recent years, Fe-N-C catalyst is particularly attractive due to its high oxygen reduction reaction (ORR) activity and low cost for proton exchange membrane fuel cells (PEMFCs). However, the durability problems still pose challenge to the application of Fe-N-C catalyst. Although considerable work has been done to investigate the degradation mechanisms of Fe-N-C catalyst, most of them are simply focused on the active-site decay, the carbon oxidation, and the demetalation problems. In fact, the 2e⁻ pathway in the ORR process of Fe-N-C catalyst would result in the formation of H₂O₂, which is proved to be a key degradation source. In this paper, a new insight into the effect of potential on degradation of Fe-N-C catalyst was provided by quantifying the H₂O₂ intermediate. In this case, stability tests were conducted by the potential-static method in O₂ saturated 0.1 mol/L HClO₄. During the tests, H₂O₂ was quantified by rotating ring disk electrode (RRDE). The results show that compared with the loading voltage of 0.4 V, 0.8 V, and 1.0 V, the catalysts being kept at 0.6 V exhibit a highest H₂O₂ yield. It is found that it is the combined effect of electrochemical oxidation and chemical oxidation (by aggressive radicals like H₂O₂/radicals) that triggered the highest H₂O₂ release rate, with the latter as the major cause.     

Activity and corrosion of tungsten carbide recombination electrodes during lead/acid battery operation

The oxidation of the tungsten carbide (WC) catalyst in recombination electrodes partially immersed in H₂SO₄ solution was investigated when the electrodes operated in an atmosphere of oxygen and hydrogen. It has been established that after a long operation period (400 h) 60 to 70% of the catalysts, depending on the initial active surface of WC, may be oxidized to WO_x, whereby the rate of recombination decreases about three times. It is assumed that the oxidation of WC is due to the H₂O₂ formed as an intermediate product of the recombination of hydrogen and oxygen. Silver accelerates the decomposition of H₂O₂ and hence the use of a WC—Ag mixture as catalyst in the recombination electrodes reduces strongly the carbide corrosion.     

A tubular direct methanol fuel cell with Ti mesh anode

A novel tubular cell structure for a direct methanol fuel cell (DMFC) is proposed based on a tubular Ti mesh and a Ti mesh anode. A dip coating method has been developed to fabricate the cell. The characterization of the tubular MEA has been analyzed by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), half cell and single cell testing. The tubular DMFC single cell comprises: a Ti mesh, a cathode diffusion layer and catalyst layer, a Nafion recast membrane and a PtRuO_x/Ti anode. Half cell tests show that the optimum catalyst loading, Ru/(Ru + Pt) atomic ratio and the Nafion loading of a PtRuO_x/Ti mesh anode are: 4 mg cm⁻², 38% and 0.6 mg cm⁻², respectively. Single cell tests show that the Nafion loading of the recast Nafion membrane and the concentration of the methanol in the electrolyte have a major influence on cell performance.     

A study of cathode catalysis for the aluminium/hydrogen peroxide semi-fuel cell

The characterization and use of a Pd and Ir catalyst combination on a C substrate in an Al/H₂O₂ semi-fuel cell is described. The Pd–Ir combination outperforms Pd alone or Ir alone on the same substrate. Scanning electron microscopy (SEM) and energy dispersive spectrophotometry (EDS) were used to establish the location of Pd, Ir and O in clusters on the cathode substrate surface. X-ray photoelectron spectroscopy (XPS) binding energy measurements indicate that Pd is in the metallic state and the Ir is in the +3 state. A configuration consisting of an Ir(III) oxide (Ir₂O₃) core and a Pd shell is proposed. The electrochemical, corrosion, direct and decomposition reactions which take place during cell discharge were evaluated. Improved initial and long term performance, at low current densities, of the Al/H₂O₂ semi-fuel cell incorporating a Pd–Ir on C cathode relative to a similarly catalyzed Ni substrate and a baseline silver foil catalyst is demonstrated.     

Characterization and evaluation of Pt-Ru catalyst supported on multi-walled carbon nanotubes by electrochemical impedance

In this work the authors present the results of a systematic characterization and evaluation of the carbon nanotube supported Pt-Ru (Pt-Ru/CNT) for its use as methanol oxidation catalyst. Its activity was compared with that of Pt and Pt-Ru catalysts supported on Vulcan and synthesized from carbonyl precursors, and another commercial Pt-Ru catalyst. The cyclic voltammetry, CO stripping and electrochemical impedance techniques were employed to determine the electrocatalytic activity of the catalysts. The electrochemical studies were performed in 0.5 M H₂SO₄ containing different concentrations of methanol (0.05–1 M). The results showed a noticeable influence of the catalyst support (CNT) on the performance of the catalyst for CO oxidation. The electrochemical impedance studies allowed us to separate the different steps in the methanol oxidation reaction and to control these steps or reactions by varying the applied potential and the methanol concentration. At low methanol concentration and potentials the de-hydrogenation of methanol predominated. But, at high potential and methanol concentrations, the CO oxidation predominated. These results allowed us to clearly describe at what potential and concentration ranges the bi-functional effect of Ru becomes evident. Our results indicated that the CO oxidation occurs both on Pt and Ru. Compared to other catalysts, Pt-Ru supported on carbon nanotubes showed superior catalytic activity for CO and methanol oxidation.     

纤维素温和条件下一步水热法制备甲烷的研究

生物质发酵法制备甲烷存在甲烷收率低、CO₂含量高等问题。本研究以纤维素为原料,在温和条件下采用水热催化转化的方法制备甲烷。对一系列催化剂进行了考察,发现Ru/C对该反应的催化活性最高。采用Ru/C催化剂进一步考察了一系列反应条件,结果表明,升高反应温度、延长反应时间、增加催化剂用量以及提高氢气初始压力对甲烷的生成具有促进作用。在1 MPa H₂、220℃、12 h反应条件下,甲烷碳摩尔收率最高,达88%,反应过程中无CO₂产生。采用TEM、BET、XRD和FT-IR等对催化剂进行了表征,结果表明,Ru/C催化剂的高催化活性可能与催化剂本身比表面积大、钌粒子颗粒小且分散均匀的特性有关。本研究采用的催化转化方法具有甲烷收率高、CO₂排放量小（<5%）、反应条件更为温和等特点。     

Investigation of lithium intercalation materials with organic solvents and molten salts as electrolytes at temperatures between 60 and 175 °C

Lithium intercalation in TiS₂ and vanadium oxides (V₂O₅, V₂O₄, V₂O₃) has been investigated in two kinds of electrolytes: (i) molten chloroaluminates (butylpyridinium chloride-AlCl₃-LiCl) at 60 °C, and LiAlCl₄-LiCl (saturated) at 175 °C; and (ii) dimethylsulfone (DMSO₂) + LiClO₄ or LiAsF₆ at 130 – 150 °C. The intercalation process has been studied by cyclic voltammetry, galvanostatic discharge/charge and open-circuit voltage measurements.

In chloroaluminates, TiS₂ appears to be stable in both media, with a one-step intercalation at 0.40 V (60 °C) or 0.65 V (175 °C) (versus Al reference). V₂O₅ can only be cycled at a low temperature (60 °C) and two steps are observed at 1 V and 0.45 V.

In DMSO₂, V₂O₅ intercalates 2.5 Li⁺ per unit V₂O₅, with four steps, as observed in propylene carbonate (PC).

OCV measurements at different intercalation steps indicate that the effect of temperature increases the kinetics of the processes.

A comparison of the OCV variations with Li⁺ concentration in DMSO₂ and PC suggests that the intercalation process differs in both solvents. The difference can be correlated with changes in the Li⁺ solvation effects of the solvents.     

Ti4O7 supported IrOx for anode reversal tolerance in proton exchange membrane fuel cell

Fuel starvation can occur and cause damage to the cell when proton exchange membrane fuel cells operate under complex working conditions. In this case, carbon corrosion occurs. Oxygen evolution reaction (OER) catalysts can alleviate carbon corrosion by introducing water electrolysis at a lower potential at the anode in fuel shortage. The mixture of hydrogen oxidation reaction (HOR) and unsupported OER catalyst not only reduces the electrolysis efficiency, but also influences the initial performance of the fuel cell. Herein, Ti₄O₇ supported IrO_x is synthesized by utilizing the surfactant-assistant method and serves as reversal tolerant components in the anode. When the cell reverse time is less than 100 min, the cell voltage of the MEA added with IrO_x/Ti₄O₇ has almost no attenuation. Besides, the MEA has a longer reversal time (530 min) than IrO_x (75 min), showing an excellent reversal tolerance. The results of electron microscopy spectroscopy show that IrO_x particles have a good dispersity on the surface of Ti₄O₇ and IrO_x/Ti₄O₇ particles are uniformly dispersed on the anode catalytic layer. After the stability test, the Ti₄O₇ support has little decay, demonstrating a high electrochemical stability. IrO_x/Ti₄O₇ with a high dispersity has a great potential to the application on the reversal tolerance anode of the fuel cell.     

A screen-printed Ce0.8Sm0.2O1.9 film solid oxide fuel cell with a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode

Screen-printing technology was developed to fabricate Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte films onto porous NiO–SDC green anode substrates. After sintering at 1400 °C for 4 h, a gas-tight SDC film with a thickness of 12 μm was obtained. A novel cathode material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ was subsequently applied onto the sintered SDC electrolyte film also by screen-printing and sintered at 970 °C for 3 h to get a single cell. A fuel cell of Ni–SDC/SDC (12 μm)/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ provides the maximum power densities of 1280, 1080, 670, 370, 180 and 73 mW cm⁻² at 650, 600, 555, 505, 455 and 405 °C, respectively, using hydrogen as fuel and stationary air as oxidant. When dry methane was used as fuel, the maximum power densities are 876, 568, 346 and 114 mW cm⁻² at 650, 600, 555 and 505 °C, respectively. The present fuel cell shows excellent performance at lowered temperatures.     

Reduction of NiAl2O4 containing catalysts for steam methane reforming reaction

Reducibility of a NiAl₂O₄ containing catalyst was studied. On a measurement of NiAl₂O₄ concentration in a catalyst, a peak area ratio of NiAl₂O₄ in XRD analysis was verified to express the NiAl₂O₄ concentration. The reducibility of NiAl₂O₄ was confirmed to be dependent on the calcining temperature to form NiAl₂O₄, not dependent on the calcining time. The catalyst containing NiAl₂O₄ was ascertained to be reduced under convenient conditions to actual plant operations; H₂/N₂ = 30/70 at 1023K for 1 h + steam/CH₄ = 6 at 1023K for 17 h.     

Synthesis and characterization of osmium carbonyl cluster compounds with molecular oxygen electroreduction capacity

A transition metal cluster electrocatalyst based on Os_x(CO)_n was synthesized by pyrolysis of Os₃(CO)₁₂ in 1,2-Dichlorobenzene (b.p.≈180°C) under inert atmosphere (N₂). The electrocatalytic parameters of the oxygen reduction reaction (ORR) for an Os_x(CO)_n catalyst were studied with a rotating disk electrode in 0.5 MH₂SO₄ electrolyte. The diffusion coefficient and solubility of O₂ in 0.5 MH₂SO₄ were calculated. Koutecky–Levich analysis of the linear voltamperometry data showed that the reaction follows first-order kinetics and the value of the Koutecky–Levich slope indicates a multielectron charge transfer during the ORR. The value of the Tafel slope obtained from the mass transfer corrected Tafel plots is 131 mV/decade. The performance of the catalyst in a H₂/O₂ PEM fuel cell cathode was evaluated and found to be nearly as good as that of Pt.     

Effects of ZrO2-promoter on catalytic performance of CuZnAlO catalysts for production of hydrogen by steam reforming of methanol

When ZrO₂-promoter was added to CuZnAlO catalyst, its methanol conversion H₂ yield and H₂ selectivity improved greatly during production of hydrogen by methanol steam reforming. Using COPZr-2 catalyst that expressed best catalytic performance as an example, the optimized reaction conditions were first confirmed. Then the 150 h stability test of COPZr-2 catalyst showed that the catalyst had good stability: methanol conversion and H₂ yield were kept at 88% and 83%, respectively; and outlet H₂ and CO content were >63% and 0.20–0.31%, respectively. A series of techniques, such as SEM, XRD, XPS, were used to characterize the catalysts with or without ZrO₂-promoter. SEM and XRD results show that ZrO₂-promoter can improve the dispersion of CuO and Cu crystallites. XPS results show that ZrO₂-promoter can lower Al content on the surface of catalyst in effect, and weaken the interaction between CuO and Al₂O₃ so as to avoid the generation of CuAl₂O₄ spinel-type compound.     

Thermochemical hydrogen production from a two-step solar-driven water-splitting cycle based on cerium oxides

A new thermochemical cycle for H₂ production based on CeO₂/Ce₂O₃ oxides has been successfully demonstrated. It consists of two chemical steps: (1) reduction, 2CeO₂ → Ce₂O₃ + 0.5O₂; (2) hydrolysis, Ce₂O₃ + H₂O → 2CeO₂ + H₂. The thermal reduction of Ce(IV) to Ce(III) (endothermic step) is performed in a solar reactor featuring a controlled inert atmosphere. The feasibility of this first step has been demonstrated and the operating conditions have been defined (T = 2000 °C, P = 100–200 mbar). The hydrogen generation step (water-splitting with Ce(III) oxide) is studied in a fixed bed reactor and the reaction is complete with a fast kinetic in the studied temperature range 400–600 °C. The recovered Ce(IV) oxide is then recycled in first step. In this process, water is the only material input and heat is the only energy input. The only outputs are hydrogen and oxygen, and these two gases are obtained in different steps avoiding a high temperature energy consuming gas-phase separation. Furthermore, pure hydrogen is produced (it is not contaminated by carbon products like CO, CO₂), thus it can be used directly in fuel cells. The results have shown that the cerium oxide two-step thermochemical cycle is a promising process for hydrogen production.     

Two-step steam pretreatment of softwood by dilute H2SO4 impregnation for ethanol production

Fuel ethanol can be produced from softwood through hydrolysis in an enzymatic process. Prior to enzymatic hydrolysis of the softwood, pretreatment is necessary. In this study two-step steam pretreatment by dilute H₂SO₄ impregnation to improve the overall sugar and ethanol yield has been investigated. The first pretreatment step was performed under conditions of low severity (180°C, 10 min, 0.5% H₂SO₄) to optimise the amount of hydrolysed hemicellulose. In the second step the washed solid material from the first pretreatment step was impregnated again with H₂SO₄ and pretreated under conditions of higher severity to hydrolyse a portion of the cellulose, and to make the cellulose more accessible to enzymatic attack. A wide range of conditions was used to determine the most favourable combination. The temperatures investigated were between 180°C and 220°C, the residence times were 2, 5 and 10 min and the concentrations of H₂SO₄ were 1% and 2%.

The effects of pretreatment were assessed by both enzymatic hydrolysis of the solids and with simultaneous saccharification and fermentation (SSF) of the whole slurry, after the second pretreatment step. For each set of pretreatment conditions the liquid fraction was fermented to determine any inhibiting effects. The ethanol yield using the SSF configuration reached 65% of the theoretical value while the sugar yield using the SHF configuration reached 77%. Maximum yields were obtained when the second pretreatment step was performed at 200°C for 2 min with 2% H₂SO₄. This form of two-step steam pretreatment is a promising method of increasing the overall yield in the wood-to-ethanol process.     

Electrochemistry of poly(vinylferrocene) modified electrodes in aqueous acidic media

A cyclic voltammetric study of the electrochemistry and chemical stability of the poly(vinylferrocene) (PVFc) redox couple, coated on a gold substrate, in aqueous solutions of H₂SO₄, HClO₄ and HCl was carried out. It was found that the anodic peak potential (E_pa) did not depend on the acid concentration in the range (1.0 × 10⁻² to 1.0 × 10⁻⁷ mol L⁻¹). However, the E_pa values shifted linearly to less positive potentials when investigated in more concentrated acid solutions in the range 1–5 mol L⁻¹. The slope of the E_pa versus acid concentration graph was found to be in the order H₂SO₄ > HCl > HClO₄. In this regard PVFc behaved very similar to 1,1′-bis(11-mercaptoundecyl)ferrocene (Fc(C₁₁SH)₂) except for its chemical stability. In H₂SO₄ media the PVFc was found to be much less stable than 1,1′-Fc(C₁₁SH)₂. The dependence of E_pa on acid concentration could be used to monitor state of charge of lead-acid batteries. However, for this application Fc(C₁₁SH)₂ would be a better choice because of its superior chemical stability.     

Synthesis and characterization of PtRuMo/C nanoparticle electrocatalyst for direct ethanol fuel cell

This research aims at enhancement of the performance of anodic catalysts for the direct ethanol fuel cell (DEFC). Two distinct DEFC nanoparticle electrocatalysts, PtRuMo/C and PtRu/C, were prepared and characterized, and one glassy carbon working electrode for each was employed to evaluate the catalytic performance. The cyclic-voltammetric, chronoamperometric, and amperometric current–time measurements were done in the solution 0.5 mol L⁻¹ CH₃CH₂OH and 0.5 mol L⁻¹ H₂SO₄. The composition, particle sizes, lattice parameters, morphology, and the oxidation states of the metals on nanoparticle catalyst surfaces were determined by energy dispersive analysis of X-ray (EDAX), X-ray diffraction (XRD), transmission electron micrographs (TEM) and X-ray photoelectron spectrometer (XPS), respectively. The results of XRD analysis showed that both PtRuMo/C and PtRu/C had a face-centered cubic (fcc) structure with smaller lattice parameters than that of pure platinum. The typical particle sizes were only about 2.5 nm. Both electrodes showed essentially the same onset potential as shown in the CV for ethanol electrooxidation. Despite their comparable active specific areas, PtRuMo/C was superior to PtRu/C in respect of the catalytic activity, durability and CO-tolerance. The effect of Mo in the PtRuMo/C nanoparticle catalyst was illustrated with a bifunctional mechanism, hydrogen-spillover effect and the modification on the Pt electronic states.     

Ni-Co双金属催化剂上沼气重整制氢宏观动力学

用传统湿式浸渍法制备La2O3掺杂的商业γ-Al2O3负载的沼气重整催化剂Ni-Co/La2O3-γ-Al2O3,通过对NiCo双金属催化剂上沼气重整制氢在常压下的宏观动力学分析,得出该催化剂上CH4与CO2消耗、H2与CO生成时的表观反应速率方程.通过改变进料中CH4与CO2的分压,求出各物质的反应分级数,确定总反应...