Structural effects on the enhancement of ORR activity on Pt single-crystal electrodes modified with alkylamines

Enhanced oxygen reduction reaction on caffeine-modified platinum single-crystal electrodes

Enhancing the activity of the oxygen reduction reaction (ORR) is crucial for fuel cell development, and hydrophobic species are known to increase the ORR activity. This paper reports that caffeine enhanced the specific ORR activity of Pt(111) 11-fold compared to that without caffeine in a 0.1 M HClO4 aqueous solution. Moreover, caffeine increased the ORR activity of Pt(110) 2.5-fold; however, the activity of Pt(100) was unaffected. The infrared (IR) band of PtOH (blocking species of the ORR) decreased for all the surfaces. Caffeine was adsorbed with its molecular plane perpendicular to the Pt(111) and Pt(110) surfaces and tilted relative to the Pt(100) surface. Thus, the effects of caffeine on the ORR activity can be rationalized by a decrease in PtOH coverage and the difference in adsorption geometry of caffeine.

Introduction of Surface Modifiers on the Pt-Based Electrocatalysts to Promote the Oxygen Reduction Reaction Process

The design of Pt-based electrocatalysts with high efficiency towards acid oxygen reduction reactions is the priority to promote the development and application of proton exchange membrane fuel cells. Considering that the Pt atoms on the surfaces of the electrocatalysts face the problems of interference of non-active species (such as OH_ad, OOH_ad, CO, etc.), high resistance of mass transfer at the liquid-solid interfaces, and easy corrosion when working in harsh acid. Researchers have modified the surfaces' local environment of the electrocatalysts by introducing surface modifiers such as silicon or carbon layers, amine molecules, and ionic liquids on the surfaces of electrocatalysts, which show significant performance improvement. In this review, we summarized the research progress of surface modified Pt-based electrocatalysts, focusing on the surface modification strategies and their mechanisms. In addition, the development prospects of surface modification strategies of Pt-based electrocatalysts and the limitations of current research are pointed out.

An Integrated Single-Electrode Method Reveals the Template Roles of Atomic Steps: Disturb Interfacial Water Networks and Thus Affect the Reactivity of Electrocatalysts

A method enabling the accurate and precise correlation between structures and properties is critical to the development of efficient electrocatalysts. To this end, we developed an integrated single-electrode method (ISM) that intimately couples electrochemical rotating disk electrodes, in situ/operando X-ray absorption fine structures, and aberration-corrected transmission electron microscopy on identical electrodes. This all-in-one method allows for the one-to-one, in situ/operando, and atomic-scale correlation between structures of electrocatalysts with their electrochemical reactivities, distinct from common methods that adopt multisamples separately for electrochemical and physical characterizations. Because the atomic step is one of the most fundamentally structural elements in electrocatalysts, we demonstrated the feasibility of ISM by exploring the roles of atomic steps in the reactivity of electrocatalysts. In situ and atomic-scale evidence shows that low-coordinated atomic steps not only generate reactive species at low potentials and strengthen surface contraction but also act as templates to disturb interfacial water networks and thus affect the reactivity of electrocatalysts. This template role interprets the long-standing puzzle regarding why high-index facets are active for the oxygen reduction reaction in acidic media. The ISM as a fundamentally new method for workflows should aid the study of many other electrocatalysts regarding their nature of active sites and operative mechanisms.