Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States.
Department of Materials Science and Engineering , University of Illinois at Urbana-Champaign , 1304 West Green Street , Urbana , Illinois 61801 , United States.
ACS Nano. 2018 Mar 27;12(3):2980-2990. doi: 10.1021/acsnano.8b00702. Epub 2018 Feb 21.
The electronic properties and extreme thinness of graphene make it an attractive platform for exploring electrochemical interactions across dissimilar environments. Here, we report on the systematic tuning of the electrocatalytic activity toward the oxygen reduction reaction (ORR) via heterostructures formed by graphene modified with a metal underlayer and an adlayer consisting of a molecular catalyst. Systematic voltammetric testing and electrochemical imaging of patterned electrodes allowed us to confidently probe modifications on the ORR mechanisms and overpotential. We found that the surface configuration largely determined the ORR mechanism, with adlayers of porphyrin molecular catalysts displaying a higher activity for the 2e pathway than the bare basal plane of graphene. Surprisingly, however, the underlayer material contributed substantially to lower the activation potential for the ORR in the order Pt > Au > SiO , strongly suggesting the involvement of the solution-excluded metal on the reaction. Computational investigations suggest that ORR enhancements originate from permeation of metal d-subshell electrons through the graphene layer. In addition, these physically impermeable but electronically transparent electrodes displayed tolerance to cyanide poisoning and stability toward long-term cycling, highlighting graphene as an effective protection layer of noble metal while enabling electrochemical interactions. This work has implications in the mechanistic understanding of 2D materials and core-shell-type heterostructures for electrocatalytic reactions.
石墨烯的电子性质和极薄的厚度使其成为探索不同环境之间电化学相互作用的理想平台。在这里，我们通过在金属底层和包含分子催化剂的覆盖层修饰的石墨烯上形成的异质结构，报告了对氧还原反应（ORR）的电催化活性的系统调节。系统的电势测试和图案化电极的电化学成像使我们能够有信心地探测 ORR 机制和过电势的修饰。我们发现表面结构在很大程度上决定了 ORR 机制，与石墨烯的裸露基面相比，卟啉分子催化剂的覆盖层显示出更高的 2e 途径活性。然而，令人惊讶的是，底层材料对 ORR 的活化势的降低有很大贡献，顺序为 Pt > Au > SiO ，强烈表明反应中排除溶液的金属的参与。计算研究表明，ORR 增强源于金属 d 壳层电子通过石墨烯层的渗透。此外，这些物理不可渗透但电子透明的电极对氰化物中毒具有耐受性，并且在长期循环中稳定，突出了石墨烯作为在保护贵金属的同时实现电化学相互作用的有效保护层。这项工作对于二维材料和核壳型异质结构的电催化反应的机理理解具有重要意义。
