CO电催化氧化的形核表面层模型与非线性谱学分析

A thorough understanding of the CO electro-catalytic oxidation mechanism and its proper mathematical description are the keys for the system diagnostics and control as well as the electro-catalyst selection and optimization for fuel cells. In this study, a nucleation–surface layer (N&SL) model is put forward for the CO electro-catalytic oxidation to solve a dilemma confronted by the Langmuir-Hinshelwood mechanism with respects to simulations of the electrode kinetics and arguments for the temporal-spatial distribution of the adsorbents. The core assumption of the N&SL model is an active layer, that contains CO and H2O, exists on the electrode surface. The CO and H2O are supposed to react with adsorbents OHads and COads via an Eley-Rideal mechanism, respectively. Above dilemma is then successfully solved by the OHads mobility independent kinetics of the N&SL model. By means of simulation, the role of the OHads nucleation and its oxidation will be emphatically analyzed for the CO electro-catalytic oxidation processes. The nonlinearity of the N&SL model will be simulated using a new nonlinear spectroscopy method – total harmonic distortion (THD) spectroscopy. To support the N&SL mechanism, existence of the active layer will be examined experimentally. Moreover, with the help of comparisons to the simulation, CO striping cyclic voltammetry and THD response of the CO electro-catalytic oxidation will be characterized experimentally to verify the reliability of the N&SL model. Therefore, results from this study can promote the application of nonlinear spectroscopy methods in the research of the electrode kinetics.

在燃料电池领域，对CO电催化氧化机理的深入认识及正确表述，已成为实现系统诊断与控制及优选电催化材料的关键。本项目针对CO氧化的Langmuir-Hinshelwood机理在模拟电极过程与解释表面吸附物时空分布中面临的两难，提出形核表面层（N&SL）模型。该模型的核心是假设电极表面存在活性分子层，其中的CO和H2O分别与表面吸附物OHads和COads发生Eley-Rideal型反应。由于电极动力学与OHads的表面流动性无关，合理解释了上述的两难。拟通过数值模拟，考察OHads的形核模式与氧化过程在CO氧化中的贡献，并运用新的非线性谱学方法——总谐波失真（THD）谱描述N&SL模型的非线性特征。通过实验研究，探明活性分子层存在的可能性，并对CO在系列铂电极表面的溶出伏安及THD谱进行表征，最终经与模拟结果比较，验证N&SL机理的可靠性。研究结果可推动非线性谱学方法在电极动力学研究中的应用。

在燃料电池领域，对CO电催化氧化机理的深入认识及正确表述，是实现燃料电池系统诊断与控制以及优选电催化材料的关键。本项目针对CO氧化的Langmuir-Hinshelwood（LH）机理在模拟电极过程与解释表面吸附物时空分布中面临的两难，提出CO氧化的形核表面层（N&SL）模型；并采用新一代的电化学谱学分析方法——总谐波失真（THD）谱考察电极过程的非线性特征，通过对比THD谱的数值模拟结果和实验表征结果来识别CO电催化氧化机理。研究结果表明：相比于基于均匀场近似与基于形核增长理论的LH机理，由N&SL机理描述的CO氧化THD谱的数值模拟结果与实验结果更为接近，证实了CO氧化N&SL机理模型的可行性。为进一步拓展THD谱在电化学领域中的应用，同样应用数值模拟与实验比较研究了COads作为中间产物的甲醇氧化动力学的线性与非线性频率响应。研究结果表明：在PtRu/C表面，甲醇氧化的Karauman-Fremkin/Termkin机理更接近真实，且THD谱对于Ru流失的诊断具有突出优势。项目研究中，Pt表面水的电化学解离被发现同是CO和甲醇电催化氧化的速率控制步骤。为深入理解这一基元反应，我们提出了电化学析氢反应（HER）的“离子氛”模型以量化碱金属离子与电催化材料对HER的协同作用机制；并基于该反应机制研究开发出面向碱性介质应用的高活性Ni-Mo-N-C电极与有序中孔碳载铱泡沫镍（Ir-OMC–Ni）电极。与此同时，研究方向进一步拓展至CO2电催化还原，本项目在电极制备、电解池设计与电化学系统研发等方面取得的成果在未来能源转化、环境治理等方面应用优势明显。

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