Understanding the Roles of Sulfur Dopants in Carbonaceous Electrocatalysts for the Oxygen Reduction Reaction: The Relationship between Catalytic Activity and Work Function

Abstract

We prepared a series of hollow sulfur-doped carbons with diverse S contents through the carbonization of microporous organic networks (MONs), which were synthesized through the Sonogashira coupling of thiophene moieties with different numbers of S atoms as building blocks. This preparation method enabled the doping level to be controlled without inducing any notable differences in textural and morphological characteristics, and these S-doped carbons did not show any notable differences in the chemical properties of carbon, regardless of the sulfur content. We used these well-controlled MON-derived carbons as a model to elucidate the role of sulfur dopants in the oxygen reduction reaction (ORR) and to investigate the relationship between the activities and work functions of carbonaceous catalysts. By excluding the effect of electrical properties of the S-doped carbon catalysts using conducting agents, we could successfully verify that increasing the number of dopants led to an enhancement in the ORR activities, and the high applicability of work function as the activity descriptor was also demonstrated. We believe that our experimental observations will provide a deeper understanding of carbonaceous electrocatalysts with p-block dopants, and the investigations performed in this study are also anticipated to serve as a rational guideline in designing carbonaceous catalysts for various electrochemical reactions. 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim