燃料电池新型贱金属氧还原电催化剂的可控制备

Low temperature polymer electrolyte membrane fuel cells with high energy conversion efficiency and environmental benign has been developed very fast in the last several decades. The sluggish kinetics of oxygen reduction reaction (ORR) at the cathode, however, is one of the key roadblocks in hydrogen–oxygen (air) fuel cells. Currently, the noble metal Pt is predominantly used as the ORR catalyst in fuel cells. The replacement of the scarce and costly Pt by non-precious-metal catalysts is crucial for the large-scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation/reduction by metalloenzymes such as cytochrome c oxidase and multi-copper oxidase, in this research proposal various kinds of biomimetic model compounds (e.g. iron porphyrin, corrin, phthalocyanine, triazole-pyridine coordinated copper, cobalt and manganese compounds) will be designed to be covalently grafted to the surface of carbon-based materials (carbon nanotubes and graphenes), and their electrocatalytic ORR activity will be evaluated using various kinds of electrochemical methods. The catalyst ORR activity and stability will be tuned through varying the nature of the model compounds as well as the morphology of their immobilized carbon materials. The optimized catalyst will be finally applied to MEA test. The objective of this proposal is to prepare novel ORR non-precious-metal catalysts having high activity and stability without the need for high temperature pyrolysis treatment, thus enabling their activity can be modulated through well-defined structure modifications. This will provide the bio-inspired ORR catalysts as a potential alternative of Pt catalyst for application in fuel cell technology in future.

聚合物膜燃料电池（PEMFC）具有绿色高效零污染排放等优点，在未来电动汽车交通工具领域具有极大的潜在应用前景和商业价值。目前PEMFC广泛使用的催化剂是贵金属铂系催化剂。由于稀有金属铂自然储量少，价格昂贵，严重制约了PEMFC的大规模商业化生产。因而，开发新型的贱金属催化剂取代稀有金属铂具有重要现实意义。本项目集生物无机化学、纳米材料化学、电化学等学科交叉，设计新型仿生氧分子还原反应（ORR）催化剂的制备方法，达到仿生催化剂分子在碳基导电载体表面的单分子层修饰负载，实现ORR催化剂的可控制备；通过改变催化剂的分子结构和导电载体微观形貌来调控优化ORR催化性能，建立仿生催化剂分子结构与ORR催化性能的关系，并最终将其应用于燃料电池测试。该项目将改变燃料电池现有贱金属催化剂通过高温煅烧制备的通用方法，拓展仿生ORR催化剂在燃料电池中的应用，以期将来最终能完全替代贵金属Pt系催化剂。

燃料电池，尤其是质子交换膜燃料电池（PEMFC）技术发展活跃及其商业化的进展显著。因其不仅解决了传统的能源利用方式有两大弊病：能量利用效率低且环境污染严重，还具有比能量高、工作寿命长、应答速度快、操作温度低等优点。作为PEMFC阴极的必要反应，氧分子还原反应（ORR）的过电位高，严重制约了PEMFC的效率。因而，用廉价的高效非贵金属ORR催化剂材料取代目前广泛使用的铂基催化剂，是降低整个系统的成本所必要和必需的要求。. 我们旨在设计合成对ORR具有高电催化活性和稳定性的仿生过渡金属催化剂。仿生过渡金属催化剂也被认为是解决燃料电池问题最有希望的催化剂。现阶段，很多研究者都是将热处理过的这些有机过渡金属化合物负载在碳材料基底上并得到了较好的实验结果。然而，这不是真正意义上的仿生氧分子还原催化剂，且这些催化剂结构复杂，组分不明，导致对ORR的机理一直不是很清楚，对复合物的催化活性位点也不能确定。. 基于对血红素金属蛋白酶的模拟以及对其活性中心-卟啉类化合物对ORR催化机理有较明确的理解，我们设计了一种新型的金属卟啉作为催化剂活性中心,不经过热处理，直接共价交联到具有高导电性、高稳定性、高比表面积的碳基底材料的复合体系。与传统过渡金属ORR研究采取反复试错这种方式来优化催化剂性能相比，此类仿生过渡金属氧分子还原反应电催化剂以结构―性能可控的方式进行制备和优化，且具有以下优点：1. 复合物结构确定；2. 不进行热处理，不破坏过渡金属化合物的组成；3. 容易识别催化剂的活性位点；4. 在碳纳米管表面进行可控的单分子组装；5. 有助于氧分子还原反应的催化机理研究。我们所制备的仿生催化剂的催化活性和稳定性在酸、碱性环境中的表现都大大优于现有的商业贵金属铂碳催化剂，是目前氧还原贱金属催化剂中催化性能最佳的催化剂。