Role of hydrous ruthenium oxide in Pt-Ru direct methanol fuel cell anode electrocatalysts: The importance of mixed electron/proton conductivity
Role of hydrous ruthenium oxide in Pt-Ru direct methanol fuel cell anode electrocatalysts: The importance of mixed electron/proton conductivity
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DOI：
10.1021/la9807863
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发表时间：
1999-02-02
期刊：
影响因子：
3.9
通讯作者：
Long, JW
中科院分区：
文献类型：
--
作者：
Rolison, DR;Hagans, PL;Long, JW
Pt-Ru是直接甲醇燃料电池（dmfc）中甲醇氧化的理想阳极催化剂。基于其x射线衍射图，纳米级Pt-Ru黑被认为是双金属合金。我们的体积和表面分析表明，尽管实际的Pt-Ru黑色具有与合金分配一致的衍射图案，但它们主要是Pt金属和Ru氧化物加上一些Pt氧化物和少量Ru金属的混合物。接收Pt-Ru电催化剂的热重分析和x射线光电子能谱分析表明，DMFC材料含有大量的水合氧化钌（RuOxHy）。纳米级Pt-Ru黑色的潜在错误识别出现，因为RuOxH是无定形的，不能通过x射线衍射识别。含水氧化钌是质子和电子的混合导体，天然表达钌- oh形态。这些性质在甲醇氧化机制中至关重要，特别是Ru-OH是直接甲醇氧化双功能机制的关键组成部分，因为它是氧转移物质，可以氧化解离Pt表面的c =O碎片。dmfc的催化剂和膜电极组件不应在或暴露于150℃以下的温度下加工，因为这样的条件会有害地降低含水氧化钌的质子电导率，从而影响电催化剂中Ru组分解离水的能力。通过对实际纳米级Pt-Ru电催化剂的真实性质的分析理解，我们现在可以建议，在这些催化剂中，有水氧化钌，而不是金属钌或无水氧化钌是首选的钌形态。
Pt-Ru is the favored anode catalyst for the oxidation of methanol in direct methanol fuel cells (DMFCs). The nanoscale Pt-Ru blacks are accepted to be bimetallic alloys as based on their X-ray diffraction patterns. Our bulk and surface analyses show that although practical Pt-Ru blacks have diffraction patterns consistent with an alloy assignment, they are primarily a mix of Pt metal and Ru oxides plus some Pt oxides and only small amounts of Ru metal. Thermogravimetric analysis and X-ray photoelectron spectroscopy of as-received Pt-Ru electrocatalysts indicate that DMFC materials contain substantial amounts of hydrous ruthenium oxide (RuOxHy). A potential misidentification of nanoscale Pt-Ru blacks arises because RuOxH is amorphous and cannot be discerned by X-ray diffraction. Hydrous ruthenium oxide is a mixed proton and electron conductor and innately expresses Ru-OH speciation. These properties are of key importance in the mechanism of methanol oxidation, in particular, Ru-OH is a critical component of the bifunctional mechanism proposed for direct methanol oxidation in that it is the oxygen-transfer species that oxidatively dissociates -C=O fragments from the Pt surface. The catalysts and membrane-electrode assemblies of DMFCs should not be processed at or exposed to temperatures > 150 degrees C, as such conditions deleteriously lower the proton conductivity of hydrous ruthenium oxide and thus affect the ability of the Ru component of the electrocatalyst to dissociate water. With this analytical understanding of the true nature of practical nanoscale Pt-Ru electrocatalysts, we can now recommend that hydrous ruthenium oxide, rather than Ru metal or anhydrous RuO2, is the preferred Ru speciation in these catalysts.