Reduction of hydrogen peroxide production at anode of proton exchange membrane fuel cell under open-circuit conditions using ruthenium–carbon catalyst

This study examines the effect of hydrogen peroxide (H₂O₂) on the open-circuit voltage (OCV) of a proton exchange membrane fuel cell (PEMFC) and the reduction of H₂O₂ in the membrane using a ruthenium/carbon catalyst (Ru/C) at the anode. Each cathode and anode potential of the PEMFC in the presence of H₂O₂ is examined by constructing a half-cell using 1.0 M H₂SO₄ solution as an electrolyte and Ag/AgCl as the reference electrode. H₂O₂ is added to the H₂SO₄ solution and the half-cell potential is measured at each H₂O₂ concentration. The cathode potential is affected by the H₂O₂ concentration while the anode potential remains stable. A Ru catalyst is used to reduce the level of H₂O₂ formation through O₂ cross-over at the interface of a membrane and the anode. The Ru catalyst is known to produce less H₂O₂ through oxygen reduction at the anode of PEMFC than a Pt catalyst. A Ru/C layer is placed between the Nafion^® 112 membrane and anode catalyst layer and the cell voltage under open-circuit condition is measured. A single cell is constructed to compare the OCV of the Pt/C only anode with that of the Ru/C-layered anode. The level of hydrogen cross-over and the OCV are determined after operation at a current density of 1 A cm⁻² for 10 h and stabilization at open-circuit for 1 h to obtain an equilibrium state in the cell. Although there is an increase in the OCV of the cell with the Ru/C layer at the anode, excessive addition of Ru/C has an adverse effect on cell performance.     

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.     

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.     

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.     

A highly active catalyst, Ni/Ce–ZrO2/θ-Al2O3, for on-site H2 generation by steam methane reforming: pretreatment effect

The steam treatment effect has been investigated over the doubly impregnated catalyst, Ni/Ce–ZrO₂/θ-Al₂O₃, in steam methane reforming (SMR). The catalyst was remarkably deactivated by steam treatment but reversibly regenerated by H₂-reduction. XRD results showed that the steam treatment resulted in the formation of NiAl₂O₄ which is inactive for SMR but it was reversibly converted to Ni by the reduction. The reversible oxidation-reduction of Ni state was also evidenced by XPS and it was observed that the formation of NiAl₂O₄ is more favorable at higher temperature. It is most likely that the alumina support is only partially covered with Ce–ZrO₂ and most Ni directly interacts with θ-Al₂O₃ which would probably make easy formation of NiAl₂O₄ in the presence of steam alone. The results imply that, during the start-up procedure in SMR, too high concentration of steam could deactivate seriously Al₂O₃ supported Ni catalysts.     

Mo2C/Al2O3的制备及其催化二甲醚水蒸气重整性能研究

通过浸渍沉淀法结合程序升温碳化法制备了Mo₂C/Al₂O₃复合催化剂,并应用于二甲醚水蒸气重整催化体系的研究。考察了二甲醚水解催化载体、水解功能组分Al₂O₃与重整功能组分Mo₂C的比例、反应物浓度对复合催化剂活性的影响。结果表明,β-Mo₂C与γ-Al₂O₃载体以Mo/Al = 1/1耦合后能够高效催化二甲醚重整制氢,其最佳进料水醚比为5,最适反应温度为400℃。     

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.     

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.     

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.     

Optimization of the magnesium-solution phase catholyte semi-fuel cell for long duration testing

A magnesium semi-fuel cell (Mg-SFC) was investigated as an energetic electrochemical system for low rate, long endurance undersea vehicle applications. This electrochemical system uses a Mg anode, a sea water electrolyte, a Nafion membrane, a carbon paper cathode catalyzed with Pd and Ir, and a catholyte of hydrogen peroxide in a sea water/acid electrolyte. Unique to the approach described here is the use of a magnesium anode together with the introduction of the catholyte in solution with the sea water, thus operating as a semi-fuel cell as opposed to a battery. Five critical operating parameters were optimized using a Taguchi matrix experimental design. Using these optimized conditions, high voltage and high efficiencies were obtained during long duration tests.     

Effect of Bi2O3 content on characteristics of Bi2O3–GDC systems for direct methane oxidation

Ceramic systems of Bi₂O₃ and gadolinia-doped ceria (GDC) solid mixture were prepared as catalysts for direct methane oxidation. These systems were characterized by temperature-programmed reduction using hydrogen and carbon monoxide, temperature-programmed reaction of methane, fixed-temperature direct methane oxidation, and X-ray diffraction analysis. Adding Bi₂O₃ to GDC promotes both hydrogen and CO oxidation activities, because of the presence of surface Bi₂O₃ and the high content of mobile oxygen in Bi₂O₃. The reactivity of CO with surface lattice oxygen is enhanced to a higher extent than that of H₂, and this enhanced extent shows a maximum in Bi₂O₃ content. Such a maximum also exists for the catalytic activity of direct methane oxidation. A synergistic effect occurs due to a combination of the high methane reactivity of GDC and the high content of mobile oxygen in Bi₂O₃. The CO₂ selectivity of direct methane oxidation can be modulated by varying the Bi₂O₃ content. The mixing of Bi₂O₃ with GDC also increases the self-de-coking capability of the catalyst during direct methane oxidation, which stabilizes the activity.     

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.     

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...     

Effect of Co content on performance of LiAl1/3−xCoxNi1/3Mn1/3O2 compounds for lithium-ion batteries

Layered LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ (0  x  1/3) compounds were studied via the combination of computational and experimental approach. The calculated voltage curve of LiNi_1/3Al_1/3Mn_1/3O₂ compound is presented, indicating it is of great potential for a cathode material of lithium-ion batteries. Unfortunately, it was found that the LiNi_1/3Al_1/3Mn_1/3O₂ compound without impurity phase could not be synthesized via a sol–gel process. To obtain a layered compound without impurity phase, partial of Al is replaced by Co in LiNi_1/3Al_1/3Mn_1/3O₂ compound in this study. Layered LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ (0  x  1/3) compounds were synthesized via sol–gel reaction at 900 °C under a oxygen stream. Single phase of the LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ in 1/6  x  1/3 region could be prepared successfully. The discharge capacity and conductivity increased with an increase in the Co-substitution content. The enhancement of the conductivity and phase purity by the introduction of Co content shows profound influence on the performance of the LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ compounds.     

Porous nickel MCFC cathode coated by potentiostatically deposited cobalt oxide: II. Structural and morphological behavior in molten carbonate

Cobalt oxide was deposited on porous nickel by an electrodeposition technique as precursor of a novel MCFC cathode. The behavior of this cathode in molten (Li_0.52Na_0.48)₂CO₃ eutectics at 650 °C under an atmosphere of CO₂:air (30:70) was studied before and after 50 h of exposure by different techniques. Before the exposure, the deposit of cobalt corresponded to a Co₃O₄ thin layer of. This crystalline structure was identified by XRD and Raman spectroscopy. After its exposure in the eutectic melt a loss of cobalt was observed by XRD, Raman spectroscopy, XPS, EDS and ICP-AES. The change in the Co₃O₄ structure into lithium–cobalt–nickel oxide (LiCo_1−yNi_yO₂) was observed by Raman spectroscopy. The SEM micrographs for Co₃O₄-coated porous nickel showed different angular shapes with respect to porous Ni. The nickel solubility for the coated porous nickel, measured by ICP-AES, decreased with respect to uncoated nickel. The Co₃O₄-coated porous nickel cathode showed, after its immersion in the molten carbonate melt, a similar porosity but a higher pore size. LiCo_1−yNi_yO₂-coated NiO offers interesting features which combine the properties of nickel, lithium and cobalt in molten carbonate. This could be a promising novel MCFC cathode material.     

Preparation of LiNi0.80Co0.15Al0.05O2 cathode material via Li-rich method

本文采用共沉淀法制备球形Ni_0.80Co_0.15Al_0.05(OH)_2.05前驱体,经预氧化后,采用富锂配比在氧气和空气气氛下烧结合成LiNi_0.80Co_0.15Al_0.05O₂正极材料.用X射线衍射,扫描电镜和恒电流充放电测试等方法对该材料的结构,形貌及电化学性能进行表征.结果表明:当锂配比为1.15时,氧气和空气中烧结合成的LiNi_0.80Co_0.15Al_0.05O₂正极材料的形貌,结构和电化学性能相当.富锂配比方法可在空气气氛下制备出电化学性能优异的LiNi_0.80Co_0.15Al_0.05O₂正极材料.0.1 C放电克比容量在200 mA·h/g以上,首次效率在87%左右;1 C放电克比容量在168 mA·h/g以上;800周循环容量保持率在80%以上.     

Selective removal of CO from hydrogen-rich stream over CuO/CexSn1−xO2–Al2O3 catalysts

The solid solutions of Ce_xSn_1−xO₂ incorporated with alumina to form Ce_xSn_1−xO₂–Al₂O₃ mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/Ce_xSn_1−xO₂–Al₂O₃ catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al₂O₃ increased the dispersion of Ce_xSn_1−xO₂, but did not change their main structures and did not weaken their redox properties. Doping Sn⁴⁺ into CeO₂ increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/Ce_xSn_1−xO₂–Al₂O₃ catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn⁴⁺ exceeded 0.5. Incorporating appropriate amounts of Sn⁴⁺ and Al₂O₃ could obtain good candidates 7%CuO/Ce_xSn_1−xO₂–Al₂O₃(20%), 1–x=0.1–0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al₂O₃.     

Electrocatalysis for dioxygen reduction by a μ-oxo decavanadium complex in alkaline medium and its application to a cathode catalyst in air batteries

The redox behavior of a decavanadium complex [(V=O)₁₀(μ₂-O)₉(μ₃-O)₃(C₅H₇O₂)₆] (1) was studied using cyclic voltammetry under acidic and basic conditions. The reduction potential of V(V) was found at less positive potentials for higher pH electrolyte solutions. The oxygen reduction at complex 1 immobilized on a modified electrode was examined using cyclic voltammetry and rotating ring-disk electrode techniques in the 1 M KOH solutions. On the basis of measurements using a rotating disk electrode (RDE), the complex 1 was found to be highly active for the direct four-electron reduction of dioxygen at −0.2 V versus saturated calomel electrode (SCE). The complex 1 as a reduction catalyst of O₂ with a high selectivity was demonstrated using rotating ring-disk voltammograms in alkaline solutions. The application of complex 1 as an oxygen reduction catalyst at the cathode of zinc–air cell was also examined. The zinc–air cell with the modified electrode showed a stable discharge potential at approximately 1 V with discharge capacity of 80 mAh g⁻¹ which was about five times larger than that obtained with the commonly used manganese dioxide catalyst.     

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.