Modeling the anodic half-cell of a low-temperature coal fuel cell.
Modeling the anodic half-cell of a low-temperature coal fuel cell.
复制标题
对低温煤燃料电池的阳极半电池进行建模。
DOI：
10.1002/anie.200501192
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Whitesides,GeorgeM
中科院分区：
文献类型：
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作者：
Weibel,DouglasB;Boulatov,Roman;Lee,Andrew;Ferrigno,Rosaria;Whitesides,GeorgeM
5m H2SO4，1008C。该反应的最大速率常数为 8·10±4 cm·s±1，[1] 比之前报道的速率常数大 15–160 倍。[2, 3] 我们在煤燃料电池原型的阳极室中使用了该反应，该电池在 1008C 和大气压下运行，以 VO2+ 作为模型氧化剂。该电池产生的最大电流（功率）密度为每升电解质和煤浆液 5 A (0.6 W)，在我们进行实验的规模 (19 mL) 下产生 100 mA (11 mW)。开发直接利用煤炭氧化发电的工艺的尝试可以追溯到 19 世纪末。[4]最近关于煤动力燃料电池的研究受到两个事实的推动：1) 全球煤炭储量大大超过其他化石燃料，[5] 和 2) 在燃料电池中直接将煤炭转化为电力而不是在涡轮机中产生蒸汽的环境效益被认为是显着的。[6]碳的电化学氧化具有很大的活化能（26 kcal mol-1），[7]并且在室温下仅在过电势大于 1 V 时才能以可检测的速率进行。已使用两种策略来克服煤燃料电池中碳氧化的固有缓慢动力学。一种策略是在高温（> 6008C）下以电化学方式氧化碳质燃料（例如石墨）——最近关于煤燃料电池的大部分研究都是基于这种方法。[2, 7–9] 熔融碳酸盐通常用作高温电池中的电解质；还使用了熔融氢氧化物、硼酸盐和硅酸盐以及固体氧化物。最先进的直接碳空气燃料电池示例之一，在 6308°C 下运行 500 小时，使用熔融 KOH/NaOH 作为电解质，石墨阳极也用作燃料，Fe-Ti 合金作为阴极，O2 被还原。该电池产生的电流和功率密度分别为 30 ALà1（阳极 270 mA cm-2）和 2.5 WL-1（阳极 0.12 W cm-2）。[10]此类电池的高工作温度往往会导致腐蚀，特别是在有氧存在的情况下。[10]这些电池的其他技术问题包括：1) 熔盐的高电阻率（高达 100 Ωcm）；[11] 2) 通过与 CO2 反应产生 CO 来消耗碳；[7] 和 3) 电池中的灰分和其他未氧化的成分会堵塞电池。 [9]烟煤等碳燃料的高电阻率和较差的机械稳定性使得它们作为煤燃料电池中的自耗阳极不切实际——在熔融电解质中使用煤浆需要剧烈搅拌。 [6]泽切维奇等人。认为由于这些问题，高温煤燃料电池无法实用。[10]克服煤直接电化学氧化缓慢动力学的另一种策略是基于观察到几种过渡金属离子，包括 FeIII、SnIV、CuII 和 CeIV，氧化煤浆的活化能为 7-16 kcalmolÀ1，这明显低于煤直接电氧化的活化能。 [12, 13] 尽管已经研究了过渡金属离子存在下煤浆的电解广泛地，[2,3,12,13]我们不知道任何使用二次氧化还原电对（例如，FeIII/FeII）的燃煤燃料电池。这种类型的电池（其中金属离子会被煤还原并在阳极以电化学方式重新氧化）已被认为是不切实际的，因为
5m H2SO4 at 1008C. The reaction proceeds with a maximum rate constant of 8 10À4 cm sÀ1,[1] which is 15–160 times greater than those reported previously.[2, 3] We used this reaction in the anode compartment of a prototype of a coal fuel cell that operated at 1008C and at atmospheric pressure with VO2+ as the model oxidant. The cell produced a maximum current (power) density of 5 A (0.6 W) per liter of a slurry of electrolyte and coal, and 100 mA (11 mW) at the scale at which we carried out experiments (19 mL). Attempts to develop a process for generating electricity directly from the oxidation of coal date back to the late 19th century.[4] Recent work on coal-powered fuel cells has been motivated by two facts: 1) the worldwide reserves of coal significantly exceed those of other fossil fuels,[5] and 2) the environmental benefits of converting coal into electricity directly in a fuel cell rather than by generating steam in turbines have been perceived as significant.[6] The oxidation of carbon electrochemically has a large activation energy (26 kcal molÀ1),[7] and proceeds at room temperature at detectable rates only at an overpotential of greater than 1 V. Two strategies have been used to overcome the intrinsically slow kinetics of the oxidation of carbon in a coal fuel cell. One strategy is to oxidize a carbonaceous fuel (eg, graphite) electrochemically at high temperatures (> 6008C)—the majority of recent research on coal fuel cells has been based on this approach.[2, 7–9] Molten carbonates are typically used as electrolytes in high-temperature cells; molten hydroxides, borates and silicates, and solid oxides have also been used. One of the most advanced examples of a direct carbon–air fuel cell operated at 6308C for 500h with molten KOH/NaOH as the electrolyte, a graphite anode that also served as the fuel, and a Fe–Ti alloy as the cathode at which O2 was reduced. The cell produced current and power densities of 30 ALà1 (270 mA cmÀ2 of anode) and 2.5 WLÀ1 (0.12 W cmÀ2 of anode), respectively.[10] The high operating temperature of this class of cells tends to result in their corrosion, particularly in the presence of oxygen.[10] Other technical problems with these cells include: 1) the high resistivity of molten salts (up to 100 Ωcm);[11] 2) the consumption of carbon by reaction with CO2 to produce CO;[7] and 3) the clogging of cells by ash and other components of the fuel that are not oxidized.[9] The high resistivity and poor mechanical stability of carbon fuels such as bituminous coal make them impractical as consumable anodes in coal fuel cells—the use of coal slurries in molten electrolytes requires vigorous stirring.[6] Zecevic et al. have argued that high-temperature coal fuel cells cannot be made practical because of these problems.[10] An alternative strategy for overcoming the slow kinetics of the direct electrochemical oxidation of coal is based on the observation that several transition-metal ions, including FeIII, SnIV, CuII, and CeIV, oxidize coal slurries with an activation energy of 7–16 kcalmolÀ1, which is significantly lower than that for the direct electrooxidation of coal.[12, 13] Although the electrolysis of coal slurries in the presence of transition-metal ions has been studied extensively,[2, 3, 12, 13] we are not aware of any coal-powered fuel cells that use a secondary redox couple (eg, FeIII/FeII). This type of cell—in which metal ions would be reduced by the coal and reoxidized at the anode electrochemically—has been considered impractical because of the