基于阻隔型策略的燃料电池阳极抗CO毒化电催化剂的表面构筑与性能调控

Increasing CO tolerance of anode catalysts enables fuel cells to use low-cost reformed hydrogen, which is significant to reduce fuel cost. Traditional methods for increasing the CO tolerance are based on introducing second element into Pt or changing catalyst supports to weaken CO adsorption or promote CO stripping through bifunctional mechanism. However, such methods can not satisfy the requirement of fuel cells yet, due to the strong adsorption of CO, and low working potential of hydrogen oxidation in fuel cells. Herein, we propose a new strategy to increase CO tolerance. On basis of the difference in molecular size of H2 and CO, we try to construct a size-selective blocking layer on noble metal catalyst surface. CO can be blocked by this layer, but small-sized H2 can still pass through it, and access to active sites. This strategy has a potential to overcome the bottleneck of increasing CO tolerance: very strong adsorption of CO on noble metal surface. We will fabricate two blocking layers based on organic molecule adsorption and inorganic metal oxide thin film. As for organic molecule adsorption, the Å-scale space between organic molecule and surface unoccupied active sites is formed, which is accessible for H2, but not for CO. As for metal oxide coating, Å-scale micropores are formed through oxygen defect induced by partially reduction of metal oxide, which may be also accessible for H2, but not for CO. To understand the anti-CO poisoning mechanism at molecular level, we will characterize carefully the interfacial structure of metal/blocking layer and CO adsorption behavior by a series of electrochemical in-situ spectroscopic method and TEM technology. This project has a potential to yield a new design principle for next-generation fuel cell anode catalysts with high CO tolerance.

提高燃料电池阳极催化剂抗CO毒化性能，有望使用廉价的重整氢气为燃料，大幅降低燃料成本。传统抗毒化方法是改变贵金属催化剂组成或载体，削弱CO吸附强度，或者通过双功能机制促进CO氧化。然而，CO在贵金属表面吸附能力很强，H2氧化工作电位低导致CO氧化速度很慢，这使得现有方法的抗CO毒化性能满足不了燃料电池要求。本项目根据H2与CO分子尺寸的差异，提出“在催化剂表面构筑尺寸选择性阻隔层，H2能通过，而CO被拦截，以提高催化剂抗CO毒化”的新策略，有望通过阻止CO接触到活性位来克服“CO吸附能力强”这个难题。本项目拟在贵金属表面构筑有机分子吸附层和无机氧化物两种阻隔层，利用有机分子与表面形成的微小反应空间或氧化物中氧缺陷引入的埃级别孔隙来实现阻隔CO而让H2通过。结合多种电化学原位谱学和电镜技术表征催化剂表界面结构和CO吸附行为，揭示抗毒化机制。本项目有望为燃料电池抗CO毒化催化剂设计提供新思路。

提高燃料电池阳极催化剂抗CO毒化性能，有望使用成本低廉但含CO的重整氢气作为燃料，大幅降低燃料成本。由于CO很强烈吸附在铂表面，使得具有实用价值的抗毒化催化剂研制极具挑战。传统抗毒化方法是改变贵金属催化剂组成或载体，削弱CO吸附强度，或者通过双功能机制促进CO氧化。然而，CO在贵金属表面吸附能力很强，H2氧化工作电位低导致CO氧化速度很慢，这使得现有方法的抗CO毒化性能满足不了燃料电池要求。本项目中我们发展了一种基于“阻隔层”的抗毒化催化剂设计新策略，利用H2与CO在分子尺寸和扩散传输速率上的差异，在贵金属催化剂表面构筑纳米级厚度的阻隔层，其允许H2通过，但又能阻隔CO接触到活性位，从而提高催化剂的抗CO毒化性能。我们着重研究了Ru@RuO2/TiO2、PtRu@RuO2/C和PtRu@MoO2/C等系列基于氧化物阻隔层的抗毒化催化剂，发现其抗CO毒化性能比传统抗毒化PtRu/C催化剂提高1-2个数量级。所制备的Ru@RuO2/TiO2可以在含1%CO/H2稳定工作50h，活性保持率94%，最高可耐受15%CO的毒化；通过商业PtRu/C热氧化诱导Ru偏析而制得的PtRu@RuO2/C可以在几乎不损失氢气氧化活性的基础上将抗CO毒化性能提高1个数量级以上，在燃料电池中可以耐受100ppm CO的毒化，具有良好的应用前景。结合CO吸附和氧化动力学、电化学原位红外谱学和分子动力学模拟，证实抗毒化性能不是基于促进CO氧化的双功能机制，而是通过氧化物促进界面水吸附从而阻碍CO吸附的新机制，从而为新型抗CO毒化催化剂设计提供新方向。本项目研究成果在J Am Chem Soc, ACS Catal等期刊上发表标注论文16篇论文，培养毕业4名博士生和2名硕士生，申请发明专利1项。