SOFC中干甲烷在Ni-ScSZ阳极上的氧化行为

以氧化钇稳定的氧化锆(YSZ)做电解质,氧化钪稳定的氧化锆(Ni-ScSZ)为阳极,研究了不同浓度干甲烷在固体氧化物燃料电池阳极上的氧化行为.改变甲烷浓度,利用色谱在线测量不同电流密度下阳极出口气体产生的种类与速率.通过氧的分析与反应发生时的电子数分析,研究了干甲烷在Ni-ScSZ阳极的氧化行为,并对比研究了相同浓度的干甲烷在Ni-YSZ阳极上的氧化行为.结果表明,在Ni-ScSZ阳极上,高浓度干甲烷与在Ni-YSZ阳极上类似,由甲烷裂解反应生成的碳发生氧化反应生成CO;低浓度干甲烷在电流密度较低的情况下,在1 000 ℃可发生CO氧化反应,生成CO2.在Ni-YSZ阳极上,低浓度干甲烷在较高电流密度下,在生成CO2的同时甲烷发生完全氧化反应.     

SOFC中低浓度干甲烷在Ni/YSZ阳极上的反应

固体氧化物燃料电池(SOFC)趋向于直接使用甲烷天然气为燃料,确定甲烷在固体氧化物燃料电池阳极发生的化学与电化学反应非常重要.以Ni/YSZ为阳极、YSZ板做电解质、LSM为阴极,用涂浆法制作电解质支撑的电池,研究低浓度干甲烷在固体氧化物燃料电池中的反应.改变甲烷浓度、电池工作温度、电解质厚度,用在线色谱测量不同电流密度下,阳极出口气体产生速率.根据阳极出口气体产生速率变化,分析干甲烷在阳极的反应变化.通过氧消耗计算和转移电子数的分析,说明甲烷在电池阳极发生不同类型的反应.电流密度小时,甲烷发生部分氧化反应.电流密度大时,发生氢氧化和CO氧化,部分甲烷发生总反应为完全氧化的反应.部分甲烷发生完全氧化反应的同时,部分甲烷仍发生部分氧化反应,但其反应速率随电流密度增加逐渐降低.甲烷浓度和试验温度增加,甲烷开始发生完全氧化的电流密度增加.     

SOFC中干甲烷流量对Ni-YSZ阳极上反应的影响

为为探讨SOFC中干甲烷流量对反应的影响,采用色谱在线检测阳极尾气,总结阳极尾气的变化规律,在此基础上,分析干甲烷在固体氧化物燃料电池Ni-YSZ阳极上的反应,寻找干甲烷流量与电流对电池阳极反应影响的数学关系。依据甲烷基元反应的活化能分析反应的途径,结果表明,随电流密度以及氧离子流量的增加,干甲烷与不同电流密度下的氧离子依次发生电化学反应。这些电化学反应分别是甲烷部分氧化反应生成CO、H2并产生电子,或生成CO、H2O、H2和产生电子的反应,或产生CO、H2O和产生电子的反应,或甲烷完全氧化的电化学反应。高流量甲烷只发生消耗氧离子最少的部分氧化反应,中流量甲烷发生前两个或前三个反应。依据法拉第第一定律及反应物之间的关系,确定甲烷的低、中、高流量的判定依据分别为:v(CH4)小于等于I/(4F),v(CH4)大于等于I/(4F)以及小于等于I/(2F),v(CH4)大于等于I/(2F)。     

操作条件对固体氧化物燃料电池阳极反应转变的影响

研究了不同电流密度下,甲烷浓度、反应温度对甲烷在SOFC中反应由部分氧化到完全氧化转变的规律;测量了不同电流密度下,阳极出口气体产生速率;确定了甲烷浓度和电池反应温度变化时甲烷电化学反应由部分氧化转变为完全氧化的电流密度门槛值,及该门槛值与甲烷浓度、电池操作温度的变化关系.结果说明甲烷开始发生完全氧化的电流密度门槛值与甲烷浓度成正比;甲烷浓度一定,温度升高,甲烷开始发生完全氧化的电流密度的门槛值也随之提高.     

煤基合成气甲烷化反应过程的热力学计算与分析

建立了煤基合成气甲烷化反应过程基于吉布斯自由能最小法的热力学计算模型。考察了温度、压力对CO,CO_2单独及同时甲烷化反应的影响,探讨了原料气脱碳处理后,CO_2摩尔分数对CO转化率、CH_4选择性、CH_4产率及积炭的影响。结果表明,低温高压有利于甲烷化反应。在多数情况下CO转化率要高于CO_2,尤其是温度低于600℃时,CO甲烷反应比CO_2更容易发生;随着温度进一步升高,CO_2转化率明显上升,而CO转化率迅速下降。另外,当原料气中CO_2摩尔分数低于2.44%时对积炭无影响,对CH_4的选择性和产率降幅小于10%,在脱碳工艺中可以不予脱除。     

铱-钽氧化物涂层阳极氧化再生酸性蚀刻液

采用Ir-Ta氧化物涂层阳极(DSA)和直流电解法研究了酸性蚀刻液的阳极氧化再生回用过程.酸性蚀刻液在Ir-Ta氧化物涂层阳极的氧化再生过程中发生浓差极化,电极反应速率为Cu+离子扩散传质所控制,极限电流密度与Cu+离子浓度和温度成正比,采用小于或等于极限电流密度的电流密度进行阳极氧化时不析出氯气.酸性蚀刻液阳极氧化再生的电流密度小,槽电压低,电解能耗少,电流效率可达到100%.阳极氧化再生后酸性蚀刻液的蚀刻能力与双氧水再生的相近,完全可以替代双氧水再生.     

垃圾填埋气部分氧化重整制合成气的热力学分析

采用吉布斯自由能最小法对垃圾填埋气(简化为甲烷与二氧化碳混合物)部分氧化重整制合成气进行了热力学分析,得出了生成适于费托反应的合成气组分的最适反应条件。结果显示:当反应温度大于1 073 K时,CH_4转化率大于99%,反应生成的气体中CH_4的含量小于0.25%。分别提高反应温度和O_2/CH_4摩尔比均有助于抑制积炭的生成。反应生成的气体中,H_2和CO分别达到最大值时,所对应的反应条件的范围不同,但在特定条件下它们有所重叠。填埋气组分CO_2/CH_4摩尔比分别为0.5,0.7,0.9时,通过等高线法得到了生成适于费托反应的合成气组分所需的最适反应条件,而CO_2/CH_4摩尔比为1.1时,无法获得相应的最适反应条件。     

铱-钽氧化物涂层阳极氧化再生酸性蚀刻液

采用Ir–Ta氧化物涂层阳极(DSA)和直流电解法研究了酸性蚀刻液的阳极氧化再生回用过程。酸性蚀刻液在Ir–Ta氧化物涂层阳极的氧化再生过程中发生浓差极化,电极反应速率为Cu+离子扩散传质所控制,极限电流密度与Cu+离子浓度和温度成正比,采用小于或等于极限电流密度的电流密度进行阳极氧化时不析出氯气。酸性蚀刻液阳极氧化再生的电流密度小,槽电压低,电解能耗少,电流效率可达到100%。阳极氧化再生后酸性蚀刻液的蚀刻能力与双氧水再生的相近,完全可以替代双氧水再生。     

Ba_(0.9)Co_(0.7)Fe_(0.2)Nb_(0.1)O_(3–δ)–Gd_(0.1)Ce_(0.9)O_(2–δ)双相复合透氧膜的氧渗透性能

通过干压成型制备了Ba_(0.9)Co_(0.7)Fe_(0.2)Nb_(0.1)O_(3–δ)–Gd_(0.1)Ce_(0.9)O_(2–δ)(BCFN–GDC)双相复合透氧膜。研究了GDC掺入量对氧渗透性能的影响。结果表明:70%BCFN–30%GDC透氧膜的氧渗透速率最高。对70%BCFN–30%GDC透氧膜进行100 h稳定性测试,其透氧量稳定在0.33 mL/(cm~2·min),稳定性良好。进一步将70%BCFN–30%GDC透氧膜用于甲烷部分氧化重整(POM)研究,在900℃、(18 mL/min He+2 mL/min CH_4)的混合气吹扫下,100 h的稳定性测试过程中,CH_4转化率、CO选择性以及透氧量最终分别达到60%、84%和1.7 mL/(cm~2·min),并有缓慢增长的趋势。研究表明:70%BCFN–30%GDC透氧膜具有良好的透氧性能,在POM膜反应器方面具有重要的应用价值。     

一种高活性耐硫甲烷化催化剂的反应性能

本文报道了一种多组分钼系耐硫甲烷化催化剂的反应性能。考察了反应温度、压力、空速和原料气组成对活性的影响,结果表明,此催化剂具有活性高、稳定性好和对原料气中硫浓度适应性强等特点。在压力2.0MPa、空速1000h~(-1)、入口温度380℃的反应条件下,CO 转化率约达95％,甲烷选择性约为75％。CO 转化率与原料气中 H_2S 浓度呈X_(co)∞[H_2S]~(0.05)关系。     

SOFC中不同浓度干甲烷在Ni-YSZ阳极上的反应

引言 天然气是适于固体氧化物燃料电池(SOFC)应用的燃料之一,天然气中主要成分是甲烷.甲烷通过全氧化或部分氧化[1-4]反应,在发电的同时,生成适于发电或其他用途的富含H2、CO的气体.     

Effect of methane concentration on reaction behavior in direct-methane solid oxide fuel cells with (Ce,Gd)O2−x-impregnated FeCr layer for fuel processing

A solid oxide fuel cell (SOFC) with a Ni-yttria-stabilized zirconia anode of 1 cm² area was set up with a porous disk of gadolinia-doped ceria-impregnated FeCr as a gas diffusion layer (GDL) under direct-methane feeding. In this setup of SOFC plus GDL, the tests at 800 °C and ambient pressure show that the current density, the methane conversion rate, the product formation rates, and the CO₂ selectivity increased with increasing methane concentration. The major reaction in the GDL is CO₂ reforming of methane to produce the syngas (CO plus H₂). The anodic electrochemical oxidation of CO from GDL results in an overall rate of CO₂ formation being much larger than that of CO formation. There is a synergy between the rate of reaction in the GDL and that over the anode.     

Oxidation of methane on a Au + SrFeO3−δ//YSZ electrode characterised by mass spectroscopy and 18O2 pulses

A solid state electrochemical reactor is described in which reactants can be oxidised at high temperatures over an anode/catalyst using co-fed oxygen gas as well as electrochemically supplied oxygen. The setup permits injection of isotopic pulses in the reactant streams. The composition and isotopic distribution in the products are recorded with a quadrupole mass spectrometer. The use of the system is exemplified by oxidation of methane over a Au + SrFeO_3?δ//YSZ anode at 800–850°C. Pulses of ¹⁸O₂ in the stream of co-fed O₂ were used to study the reactivity and products of gaseous oxygen as distinguished from the electrochemically supplied oxygen. The results indicate that the anode used supports oxygen pumping, but is only moderately active for methane oxidation. The products are mainly CO and CO₂. The content of ¹⁸O in the products is low, indicating that methane oxidation takes place by ¹⁶O-rich lattice oxygen. In comparison, a reference Au//YSZ electrode was found to be a slower anode for oxygen pumping, but a better catalyst for the reaction between CH₄ and gaseous O₂, seemingly involving adsorbed oxygen.     

Redox Tolerance of Thin and Thick Ni/YSZ Anodes of Electrolyte‐Supported Single‐Chamber Solid Oxide Fuel Cells under Methane Oxidation Conditions

Redox tolerance of 50 and 500 μm thick Ni/YSZ (yttria‐stabilized zirconia) anodes supported on YSZ electrolytes were studied under single‐chamber solid oxide fuel cell conditions. Open circuit voltage, electrochemical impedance spectra, and discharge curves of the cells were measured under different methane/oxygen ratios at 700 °C. For the cell with the thin anode, a significant degradation accompanying oscillatory behaviors was observed, whereas the cell based on the thick anode was much more stable under the same conditions. In situ local anode resistance (R_s) results indicated that the Ni/NiO redox cycling was responsible for the oscillatory behaviors, and the cell degradation was primarily caused by the Ni reoxidation. Reoxidation of the thick anode took place at a low methane/oxygen ratio, but the anode can be recovered to its original state by switching to a methane‐rich environment. On the contrary, the thin anode was unable to be regenerated after the oxidation. Microstructure damage of the anode was attributed to its irreversible degradation.     

Synthesis gas production in methane conversion using the P|yttria-stabilized zirconia|Ag electrochemical membrane system

The electrochemical membrane reactor of YSZ (yttria-stabilized zirconia) solid electrolyte coated with Pd and Ag as anode and cathode, respectively, has been applied to the partial oxidation of methane to synthesis gas (CO + H₂). The Pd|YSZ|Ag catalytic system has shown a remarkable activity for CO production at 773 K, and the selectivity to CO was quite high (96.3%) under oxygen pumping condition at 5 mA. The H₂ production strongly depended on the oxidation state of the Pd anode surface. Namely, the H₂ treatment of the Pd anode at 773 K for 1 h drastically reduced the rate of H₂ production, while air treatment enhanced the H₂ production rate. From the results of the partial oxidation of CH₄ with molecular oxygen, it is considered that the reaction site of the electrochemical oxidation of CH₄ to synthesis gas was the Pd–YSZ–gas-phase boundary (triple-phase boundary). In addition, it is found that the oxygen species pumped electrochemically over the Pd surface demonstrated similar activity to adsorbed oxygen over Pd, PdO_ad, for the selective oxidation of CH₄ to CO, when the Pd supported on YSZ was used as a fixed-bed catalyst for CH₄ oxidation with the adsorbed oxygen. The difference with respect to the H₂ formation between the electrochemical membrane system and the fixed-bed catalyst reactor results from differences in the average particle size of Pd and the way of the oxygen supply to the Pd surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamic Behavior of a PEM Fuel Cell During Electrochemical CO Oxidation on a PtRu Anode

The dynamic behaviour of a single PEM fuel cell (PEMFC) with a PtRu/C anode catalyst using CO containing H₂ as anode feed was investigated at ambient temperature. The autonomous oscillations of the cell potential were observed during the galvanostatic operation with hydrogen anode feed containing CO up to 1000 ppm. The oscillations were ascribed to the coupling of the adsorption of CO (the poisoning step) and the subsequent electrochemical oxidation of CO (the regeneration step) on the anode catalyst. The oscillations were dependent on the CO concentration of the feed gas and the applied current density. Furthermore, it was found that with CO containing feed gas, the time average power output was remarkably higher under potential oscillatory conditions in the galvanostatic mode than during potentiostatic operation. Accompanying these self-sustained potential oscillations, oscillation patterns of the anode outlet CO concentration were also detected at low current density (<100 mA/cm²). The online measurements of the anode outlet CO concentrations revealed that CO in the anode CO/H₂ feed was partially electrochemically removed during galvanostatic operation. More than 90% CO conversion was obtained at the current densities above 125 mA/cm² with low feed flow rates (100–200 mL/min).     

Improved electrochemical CO removal via potential oscillations in serially connected PEM fuel cells with PtRu anodes

The polarization performance of two PEM fuel cells (with anode PtRu/C catalyst) connected either in parallel or serial, was compared to the performance of a single PEM fuel cell in galvanostatic operation using CO-free H₂ or 200 ppm CO-containing H₂ stream as anode feed at ambient temperature. Spontaneous potential oscillations were observed experimentally for the coupled configuration with two cells connected in serial or parallel using CO-containing H₂ feed at various current densities applied. The potential oscillations are ascribed by the dynamic CO adsorption and subsequent electrochemical CO oxidation on the anode. The measured anode outlet CO concentration was found to decrease with the order: single cell > parallel cells > serial cells at various current densities and anodic flow rates. The low anode outlet CO concentration (<10 ppm) at high current densities applied showed that CO in the anode feed was removed efficiently by the electrochemical CO oxidation occurring on the PtRu anode. The anode outlet CO concentration decreased as follows: a single cell > the parallel cells > the serial cells at broad range of current densities and anodic flow rates. The highest CO conversion and the highest average power output at equal hydrogen recovery degree were obtained with serially coupled fuel cells.     

天然气内重整和外重整下SOFC多场耦合三维模拟分析

内重整（IR）和外重整（ER）是固体氧化物燃料电池（SOFC）以天然气（NG）为燃料时的两种工作方式,不同重整方式下的电池性能、效率也不尽相同。借助有限元分析软件COMSOL Multiphysics^? 5.2,以天然气为燃料,建立了电池组成为Ni-YSZ//YSZ//LSCF-GDC的ER-SOFC和IR-SOFC两种三维单电池模型。模拟结果表明：相同条件下,IR-SOFC具有比ER-SOFC更高的功率密度、燃料利用率和能量利用率;阳极重整反应主要发生在靠近燃料入口的区域内;H₂和CO含量在IR-SOFC中先升高后降低,在ER-SOFC中则一直降低;IR-SOFC的温度变化更剧烈,燃料入口处温度梯度最大;越靠近集流体的区域,电解质表面的离子电流密度越大;ER-SOFC阳极不会发生热力学上的积炭现象,对于IR-SOFC,CH₄热分解反应是整个阳极发生积炭的主要原因,其在燃料入口处的积炭活性高达270。