中温H2S-空气燃料电池阴极催化剂的研究

Abstract Cathode catalysts comprising composite NiO, NiO-Pt, or LiNiO2 have been developed for electro- chemical oxidation of hydrogen sulfide in intermediate-temperature solid oxide fuel cells （ITSOFCs）. All catalysts exhibited good electrical conductivity and catalytic activity at operating temperature. Composite NiO catalysts were found to be more active and have lower over potential and higller current density than pure Pt although the electrical conductivity of NiO itself is lower than that of Pt. This problem has been overcome by either admixing as high as 10% （by mass）Ag powder into NiO_ cathode layer or using composite NiO c atalysts such as NiO-Pt and LiNiO2 catalysts. Composite catalysts like NiO with Ag, electrolyte and starch admixed, NiO-Pt, which was prepared from a mixture of NiO and Pt powders, by admixing electrolyte and starch, and LiNiO2, which is derived from the reaction of LiOH-H2O and NiO with electrolyte and starch admix_ed have been shown to be feasible and effective in an intermediate-temperature H2S-air fuel cell. A fuel cell using Li2SO4-based proton-conducting membrane as electrolyte, metal sulfides as anode catalysts, and composite NiO as cathode catalysts produced a maximum current density about 300mA·cm^-2 and maximum power density over 80 mW-cm-2 at 680℃.     

H2S燃料电池用质子传导膜及电池性能

研究了H2S燃料电池用的质子传导膜的制备及性能,考察了不同的Li2SO4与填充物Al2O3的匹配、微量元素B(H2BO3)的掺杂对膜及电池性能影响.研究了由H2S、(MoS2+NiS)/Li2SO4-Al2O3/pt、air构成的燃料电池在101.13kPa和600～700℃C时的电化学特性.在实验温度范围内,质子传导膜Li2SO4-Al2O3及整个电池系统在H2S气流下具有较好的化学稳定性.温度提高,质子传导膜的内阻减小,膜及电池性能变好.微量元素B的掺杂提高了膜的机械强度及膜的致密性,从而改善了电池的性能.在实验条件下,较适宜的B的掺杂量为2%～5%(质量百分数),较适宜的Li2SO4Al2O3(质量比)为(3～5)1,电池最大输出电流密度和功率密度在700℃时分别达到200mA.cm-2和55mW.cm-2.     

Pt-Co/C nanoparticles as electrocatalysts for oxygen reduction in H2SO4 and H2SO4/CH3OH electrolytes

The oxygen reduction reaction (ORR) was studied on carbon dispersed Pt and Pt-Co alloyed nanocatalysts with high contents of Co in H₂SO₄ and H₂SO₄/CH₃OH solutions. The characterization techniques considered were transmission electron microscopy (TEM), X-ray diffraction (XRD) and in situ X-ray absorption near edge structure (XANES). The electrochemical activity for the ORR was evaluated from steady state polarization measurements, which were carried out in an ultra thin layer rotating disk electrode. The results showed that with the increase of Co content, the nanoparticle size distributions become sharper and the mean particle diameters become smaller. XRD indicated low degree of alloy formation but significant phase segregation of Co was observed only for Pt-Co/C 1:3 and 1:5 (Pt:Co atomic ratios). The electrochemical measurements indicated that the four-electrons mechanism is mainly followed for the ORR on all materials and the electrocatalytic activities per gram of Pt is higher for the catalysts with higher Co contents. This was explained based on the XANES results which evidenced a decrease of the coverage of oxygenated Pt adsorbates due to the presence of Co. In the methanol-containing electrolyte, the Pt-Co/C 1:5 catalyst showed the highest performance. This was attributed to its low activity for the methanol oxidation due to the smaller probability for presenting three Pt neighboring Pt active sites.     

Oxygen reduction at Pt and Pt70Ni30 in H2SO4/CH3OH solution

The electrochemical oxygen reduction reaction (ORR) was studied at Pt and Pt alloyed with 30 atom% Ni in 1 M H₂SO₄ and in 1 M H₂SO₄/0.5 M CH₃OH by means of rotating disc electrode. In pure sulphuric acid, the overpotential of ORR at 1 mA cm⁻² is about 80 mV lower at Pt₇₀Ni₃₀ than at pure Pt. It was found that in methanol containing electrolyte solution the onset potential for oxygen reduction at PtNi is shifted to more positive potentials and the alloy catalyst has an 11 times higher limiting current density for oxygen reduction than Pt. Thus, PtNi as cathode catalyst should have a higher methanol tolerance for fuel cell applications. On the other hand, no significant differences in the methanol oxidation on both electrodes was found using cycling voltammetry, especially regarding the onset potential for methanol oxidation. During all the measurements no significant electrochemical activity loss was observed at Pt_0.7Ni_0.3. Ex-situ XPS investigations before and after the electrochemical experiments have revealed Pt enrichment in the first surface layers of the PtNi.     

金属硫化物作为阳极材料对H2S固体氧化物燃料电池性能研究

Two anode catalysts with Pt, MoS2 and composite metal sulfides (MoS2 NiS), are investigated for electrochemical oxidation of hydrogen sulfide in solid oxide fuel cell (SOFC) at temperatures 750-850℃. The catalysts comprising MoS2 and MoS2 NiS exhibited good electrical conductivity and catalytic activity. MoS2 and composite catalysts were found to be more active than Pt, a widely used catalyst for high temperature H2S/O2 fuel cell at 750-850℃. However, MoS2 itself sublimes above 450℃. In contrast, composite catalysts containing both Mo and transition metal (Ni) are shown to be stable and effective in promoting the oxidation of H2S in SOFC up to 850℃. However, electric contact is poor between the platinum current collecting layer and the composite metal sulfide layer, so that the cell performance becomes worse. This problem is overcome by adding conductive Ag powder into the anode layer (forming MoS2 NiS Ag anode material) to increase anode electrical conductance instead of applying a thin laver of platinum on the top of anode.     

Electrochemical behavior of LiCoO2 in a saturated aqueous Li2SO4 solution

The electrochemical behavior of a commercial LiCoO₂ with spherical shape in a saturated Li₂SO₄ aqueous solution was investigated with cyclic voltammetry and electrochemical impedance spectroscopy. Three redox couples at E_SCE = 0.87/0.71, 0.95/0.90 and 1.06/1.01 V corresponding to those found at ELi/Li⁺=4.08/3.83, 4.13/4.03 and 4.21/4.14 V in organic electrolyte solutions were observed. The diffusion coefficient of lithium ions is 1.649 × 10⁻¹⁰ cm² s⁻¹, close to the value in organic electrolyte solutions. The results indicate that the intercalation and deintercalation behavior of lithium ions in the Li₂SO₄ solution is similar to that in the organic electrolyte solutions. However, due to the higher ionic conductivity of the aqueous solution, current response and reversibility of redox behavior in the aqueous solution are better than in the organic electrolyte solutions, suggesting that the aqueous solution is favorable for high rate capability. The charge transfer resistance, the exchange current and the capacitance of the double layer vary with the charge voltage during the deintercalation process. At the peak of the oxidation (0.87 V), the charge transfer resistance is the lowest. These fundamental results provide a good base for exploring new safe power sources for large scale energy storage.     

钙钛矿阳极固体氧化物燃料电池在CO–CO2燃料下的性能和稳定性

以原位析出纳米Co–Fe颗粒的La_0.4Sr_0.6Co_0.2Fe_0.7Nb_0.1O_3–δ(LSCFN)钙钛矿为阳极,考察了直接使用CO–CO₂燃料时的阳极结构演变、单电池电化学性能和稳定性。结果表明:在CO燃料中,ABO₃钙钛矿结构LSCFN转变为A₂BO₄层状钙钛矿结构;在CO中引入少量CO₂后,LSCFN则以单钙钛矿结构为主,并有效抑制了碳沉积。单电池在CO燃料下的最大功率密度可达0.6 W/cm²(850℃),并在n(CO):n(CO₂)=5:1(摩尔比)燃料下运行超过100 h。     

生物滴滤塔处理VOCs和H2S混合废气的工程实例

在浙江某化工厂建立了处理生产车间VOCs和自备污水站H2S混合废气的生物滴滤塔（BTF）。BTF经过12d完成启动。在启动之后的调试期间,混合废气中VOCs的质量浓度为200～400mg／m3,H2s的质量浓度为80-150mg／m3,BTF对VOCs和H2S的去除率均分别能保持在86％和96％左右。VOCs和H2s均达标排放。     

Fuel processor integrated H2S catalytic partial oxidation technology for sulfur removal in fuel cell power plants

H₂S catalytic partial oxidation technology with an activated carbon catalyst was found to be a promising method for the removal of hydrogen sulfide from fuel cell hydrocarbon feedstocks. Three different fuel cell feedstocks were considered for analysis: sour natural gas, sour effluent from a liquid middle distillate fuel processor and a Texaco O₂-blown coal-derived synthesis gas. The H₂S catalytic partial oxidation reaction, its integratability into fuel cell power plants with different hydrocarbon feedstocks and its salient features are discussed. Experimental results indicate that H₂S concentration can be removed down to the part-per-million level in these plants. Additionally, a power law rate expression was developed and reaction kinetics compared to prior literature. The activation energy for this reaction was determined to be 34.4 kJ/g mol with the reaction being first order in H₂S and 0.3 order in O₂.     

直接NaBH4/H2O2燃料电池的研究进展

直接NaBH₄/H₂O₂燃料电池是一种燃料和氧化剂均为液体的新型燃料电池,它直接以NaBH₄溶液为阳极燃料,H₂O₂ 为阴极氧化剂。该燃料电池有很高的输出电压、能量转化效率和能量密度,并且反应中能产生8个电子。本文对硼氢化钠电氧化材料、过氧化氢电还原材料,以及直接NaBH₄/H₂O₂燃料电池的性能进行了综述。     

N-Positive ion activated rapid addition and mitochondrial targeting ratiometric fluorescent probes for in vivo cell H2S imaging

Heterocyclic compound quinoline and its derivatives exist in natural compounds and have a broad spectrum of biological activity.They play an important role in the design of new structural entities for medical applications.Similarly,indoles and their derivatives are found widely in nature.Amino acids,alkaloids and auxin are all derivatives of indoles,as are dyes,and their condensation with aldehydes makes it easy to construct reaction sites for nucleophilic addition agents.In this work,we combine these two groups organically to construct a rapid response site(within 30 s)for H₂S,and at the same time,a ratiometric fluorescence response is presented throughout the process of H₂S detection.As such,the lower detection limit can reach 55.7 nmol/L for H₂S.In addition,cell imaging shows that this probe can be used for the mitochondrial targeted detection of endogenous and exogenous H₂S.Finally,this probe application was verified by imaging H₂S in nude mice.     

Low-temperature H2S removal from gas streams with SBA-15 supported ZnO nanoparticles

Mesoporous silica SBA-15 with zinc oxide (ZnO) nanoparticles was prepared via incipient wetness impregnation and ultrasonic method, followed by in situ activation at 523 K. The mesoporous materials obtained were characterized by ICP, XRD, FTIR, nitrogen adsorption, TEM and XPS. The prepared materials showed a superior ability to remove H₂S down to parts per billion (ppb) from gas stream at lower temperature (298 K), and the highest H₂S breakthrough capacity, 436 mg S/g adsorbent, was observed for SBA-15 with 3.04 wt% zinc loading. The enhancement of H₂S removal capacity was attributed to the integration of the high surface area of the mesoporous material and the promising desulphurization properties of ZnO nanoparticles. It was believed that ZnO-modified SBA-15 is a promising adsorbent for H₂S cleaning at ambient conditions, which will extend the application of the mesoporous materials to the environmental protection area.     

添加Li_2O对YSZ电解质性能影响

8%（摩尔分数,下同）Y2O3稳定的ZrO2（8YSZ）是固体氧化物燃料电池（SOFC）中最常用的电解质材料,本文研究了在8YSZ基体中加入n%Li2O（n=0,0.25,0.50,1.00,1.50,1.70,2.00,2.50,3.00）后（记为n%Li2OYSZ）对其晶相结构、晶格常数、烧结性能、微观形貌、电导率及其作为SOFC电解质性能的影响。结果表明,Li2O中的Li＋可以固溶到YSZ的晶格内使其晶格常数减小;Li2O的加入量n〈1.70时,瓷体在烧结过程中不会发生相变。加入少量的Li2O（n=0.25,0.50）可以提高YSZ的致密度和电导率,0.25%Li2OYSZ和0.50%Li2OYSZ样品800℃的电导率分别高达0.030 2 S/cm和0.027 6 S/cm,分别是纯YSZ的1.35和1.24倍;当Li2O含量n≥1.00时,相同条件下烧结体致密度随Li2O加入量的增大而逐渐减小;当n≥1.70时,样品在烧结过程中虽然出现相变,但在高于1400℃可以烧结致密,并得到纯立方相YSZ。将1250℃烧结制得的0.25%Li2OYSZ和0.50%Li2OYSZ作为SOFC电解质的单电池,800℃时的开路电压高于1.0V,说明YSZ中没有出现电子电导,具有比纯YSZ为电解质的单电池更高的性能输出,表现出了良好的应用前景。     

Electrocatalyst materials for fuel cells based on the polyoxometalates—K7 or H7[(P2W17O61)Fe(H2O)] and Na12 or H12[(P2W15O56)2Fe4(H2O)2]

Free acids of the iron substituted heteropoly acids (HPA), H₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (HFe1) and H₁₈[(P₂W₁₅O₅₆)₂Fe^III₂(H₂O)₂] (HFe2) were prepared from the salts K₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (KFe1) and Na₁₂[(P₂W₁₅O₅₆)₂Fe^III₄(H₂O)₂] (NaFe4), respectively. The iron-substituted HPA were adsorbed on to XC-72 carbon based GDLs to form HPA doped GDEs after water washing with HPA loadings of ca. 1 μmol. The HPA was detected throughout the GDL by EDX. Solution electrochemistry of the free acids are reported for the first time in sulfate buffer, pH 1-3. The hydrogen oxidation reaction was catalyzed by KFe1 at 0.33 V, with an exchange current density of 38 mA/cm². Moderate activity for the oxygen reduction reaction was observed for the iron substituted HPA, which was dramatically improved by selectively removing oxygen atoms from the HPA by cycling the fuel cell cathode under N₂ followed by reoxidation to give a restructured oxide catalyst. The nanostructured oxide achieved an OCV of 0.7 V with a Tafel slope of 115 mV/decade. Cycling the same catalysts in oxygen resulted in an improved catalyst/ionomer/carbon configuration with a slightly higher Tafel slope, 128 mV/decade but a respectable current density of 100 mA/cm² at 0.2 V.     

High temperature proton exchange membrane fuel cell using a sulfonated membrane obtained via H2SO4 treatment of PEEK-WC

A method for the sulfonation of PEEK-WC, a glassy poly(ether ether ketone) with sulphuric acid is presented. Depending on the reaction time, polymers with ion exchange capacity (IEC) from 0.30 to 0.76 meq_H⁺/g are obtained, as determined by titration with NaOH solutions. The thermal properties of the polymers were studied by differential scanning calorimetry, showing that the glass transition temperature increases with increasing degree of sulfonation, from 224 °C for pure PEEK-WC to 246 °C for the polymer having an IEC of 0.76 meq_H⁺/g. The sulfonated polymers were used to prepare proton exchange membranes for possible application in fuel cells. Dense membranes were prepared by solvent evaporation, using DMA as the solvent. The transport properties of the membranes were determined in terms of water uptake and permeability for hydrogen and oxygen. Electrochemical characterization was performed by measuring cell voltage and power density curves as a function of current density at different working temperatures and the results were compared with those of a commercial Nafion membrane. A power density of 284 mW/cm² was obtained for S-PEEK-WC membrane at 120 °C in H₂/air fuel cell, slightly above the corresponding value found for Nafion.     

Electrochemical studies with a Cu-5wt.%Ni alloy in 0.5 M H2SO4

The electrochemical behavior of the annealed Cu-5wt.%Ni alloy in 0.5 M H₂SO₄ was studied by means of open-circuit potential (E_OCP) measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and quasi-stationary linear potential sweep. The hydrodynamics of the system was also studied. This material is constituted by a single α₁ phase. The anodic behavior of a Cu-Ni alloy in H₂SO₄ consists fundamentally on the electrodissolution of Cu, its main component, and the formation of a sulfur-containing passive layer. The presence of Ni decreases the rate of Cu oxidation, mostly at high positive potentials. The impedance spectra, obtained for the unrotating electrode, can be interpreted in terms of a simple charge-transfer reaction across a surface layer. When the electrode is rotated, the occurrence of an inductive loop evidenced the existence of an adsorbed layer. All the resistance estimated from the proposed equivalent circuits diminished with the electrode rotation rate, emphasizing the influence of ion transport in the overall electrode process. The system presented two anodic Tafel slopes: 40 mV dec⁻¹ for E<255 mV and 67 mV dec⁻¹ for E>275 mV. A Tafel slope of 40 mV dec⁻¹ evidences that copper dissolution can be interpreted in terms of the mechanism proposed by Mattsson and Bockris. The second Tafel suggests that at potentials more positive than 275 mV, copper dissolves according to a mechanism that considers the disproportionation of adsorbed Cu(I) species.     

Safety evaluation of rechargeable cells with lithium metal anodes and amorphous V2O5 cathodes

Rechargeable cells with lithium metal anodes have a very large theoretical energy density and are a promising cell system. However, rechargeable lithium metal cells are not yet currently commercially available. One of the biggest problems with the cells is the poor safety aspect resulting from the high chemical reactivity of lithium. We have been studying a cell system consisting of an amorphous (a-)V2O5P2O5 (95:5 in molar ratio) cathode, a lithium (Li) metal anode and an organic electrolyte in fabricating an AA-size prototype. In this paper, we report recent progress on our rechargeable lithium metal cell focusing on its safety.     

Oxygen reduction mechanism on copper in a 0.5 M H2SO4

The mechanism of the oxygen reduction reaction (ORR) in a naturally aerated stagnant 0.5 M H₂SO₄ was studied using electrochemical methods. The cathodic polarization curve showed three different regions; electrochemical impedance spectroscopy (EIS) measurement was used accordingly. The EIS data were analyzed, and the mechanism for the ORR was proposed consequently. The three regions include a limiting current density region with the main transfer of 4e⁻ controlled by diffusion (−0.50 V < E < −0.40 V), a combined kinetic-diffusion region (−0.40 V < E < −0.20 V) with an additional 2e⁻ transfer due to the adsorption of the anions, and a hump phenomenon region (−0.20 V < E < −0.05 V), in which the chemical redox between the anodic intermediate and the cathodic intermediate , together with the electrochemical reaction, synergistically results in the acceleration of the ORR. Therefore, a coupled electrochemical/chemical process (the EC mechanism) in the hump phenomenon region was proposed, and a good agreement was found between the experimental and fitted results. The EC mechanism was confirmed by the deaerated experiments.     

Effect of temperature on the reaction of H2S with a coke

The effect of temperature on reaction of H₂S with carbon structures of a coke were studied in a fixed-bed quartz tube reactor coupled with two parallel detectors, flame photometric detector (FPD) and mass spectrum (MS). The uptake of H₂S with the coke matrix was studied through a sulfur uptake/temperature programmed desorption process (SU/TPD) and a temperature programmed oxidation process (TPO). The results show that the sulfur imbibed by a demineralized coke at elevated temperatures is very stable, which can only be decomposed and released to gas phase under combustion conditions. The chemical imbibition of sulfur takes place at an elevated temperature. At relatively lower temperatures, H₂S was adsorbed physically by the sample and then transformed to stable sulfur species. At higher temperatures, the chemical reactions between H₂S and DM-Coke led to the formation of more stable sulfur-containing forms and consequently increased H₂S uptake ability. This is essence of the temperature effect on the uptake of H₂S by a de-mineralized coke. The irregular behavior with the temperature was caused by the different interactions.     

Sustainable H2 production from ethanol steam reforming over a macro-mesoporous Ni/Mg-Al-O catalytic monolith

A macro-meso-porous monolithic Ni-based catalyst was prepared via an impregnation route using polystyrene foam as the template and then used in the steam reforming of ethanol to produce a H₂-rich gas. The Ni/Mg-Al catalyst has a hierarchically macro-meso-porous structure as indicated by photographs and scanning electron microscopy (SEM). The surface area of the catalyst was 230 m²?g^-1 and the Ni dispersion was 5.62%. Compared to the pelletized sample that was prepared without a template, the macro-meso-porous Ni/Mg-Al monolith exhibited superior reactivity in terms of H₂ production and also had lower CH₄ yields at 700oC and 800oC. Furthermore, the monolithic catalyst maintained excellent activity and H₂ selectivity after 100-h on-stream at 700^oC, as well as good resistance to coking and metal sintering.