PEM燃料电池电极硫中毒分析
Analysis of Sulfur Poisoning on a PEM Fuel Cell Electrode
摘要：
在功能性PEM燃料电池中量化了由于硫吸附和随后的电化学氧化而导致的Pt对氢氧化反应（HOR）的不可逆失活程度。在70 °C下，连续的硫化氢（H2S）暴露和电化学氧化实验表明，在PEM燃料电池的开路电势下，每单层硫吸附多达6%的总Pt位点失活，随后将其去除。当燃料电池在有限负载下操作时，当电极暴露于H2S时，这种失活的程度高得多，并且取决于局部过电位和暴露的持续时间。不管这种失活，在恢复后电极上获得的H2/O2极化曲线不显示性能损失，这表明这种性能曲线不能单独用于评估由于硫中毒而导致的恢复程度。提出了H_2S在Pt阳极上的吸附和电氧化机理。H2S以两种不同的硫物种和中间氧化电位解离吸附在Pt上，经历电氧化成硫，然后变成二氧化硫（SO2）。这一机制通过Pt上的氢脱附和硫电氧化之间的电荷平衡得到了验证。硫氧化的点火电位随着温度的升高而降低，这与更快的电氧化动力学相结合，导致在更高的温度下更容易去除吸附的硫。此外，发现吸附电位影响暴露于H2S的电极的硫覆盖。作为暗示，暴露于H2S污染的燃料的PEM燃料电池阳极的局部电势应保持低于硫氧化的平衡电势，以防止Pt位点的不可逆损失。
英文摘要：
The extent of irreversible deactivation of Pt towards hydrogen oxidation reaction (HOR) due to sulfur adsorption and subsequent electrochemical oxidation is quantified in a functional PEM fuel cell. At 70 °C, sequential hydrogen sulfide (H2S) exposure and electrochemical oxidation experiments indicate that as much as 6% of total Pt sites are deactivated per monolayer sulfur adsorption at open circuit potential of a PEM fuel cell followed by its removal. The extent of such deactivation is much higher when the electrode is exposed to H2S when the fuel cell is operating at a finite load, and is dependent on the local overpotential and the duration of exposure. Regardless of this deactivation, the H2/O2 polarization curves obtained on post-recovery electrodes do not show performance losses suggesting that such performance curves alone cannot be used to assess the extent of recovery due to sulfur poisoning. A concise mechanism for the adsorption and electro-oxidation of H2S on Pt anode is presented. H2S dissociatively adsorbs onto Pt as two different sulfur species and at intermediate oxidation potentials, undergoes electro-oxidation to sulfur and then to sulfur dioxide (SO2). This mechanism is validated by charge balances between hydrogen desorption and sulfur electro-oxidation on Pt. The ignition potential for sulfur oxidation decreases with increase in temperature, which coupled with faster electro-oxidation kinetics result in the easier removal of adsorbed sulfur at higher temperatures. Furthermore, the adsorption potential is found to influence sulfur coverage of an electrode exposed to H2S. As an implication, the local potential of a PEM fuel cell anode exposed to H2S contaminated fuel should be kept below the equilibrium potential for sulfur oxidation to prevent irreversible loss of Pt sites.
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