Surface Functionalization of Electrode Materials with Aryl-Diazonium Salts: Influence on Electronic Structure and Electrochemical Reactivity

Abstract

The development of efficient and abundant materials for the conversion and storage of renewably generated electricity is the lynchpin for enabling the global transition to a sustainable and cyclical economic model. In this work I explore two promising systems to meet this need; nickel phosphide as a hydrogen evolution electrocatalyst and sulfur cathodes for next-generation rechargeable lithium-ion batteries. Both earth abundant alternative chemistries promise to challenge current state-of-the-art materials, which rely on scarce and expensive metals. However, much work is still needed to tune the electrochemical properties of these materials before their true potential can be realized. Electrochemical activity is dictated by a delicate balance of a material’s internal electronic structure and the way in which its surface atoms interact with the external environment, namely the electrolyte and active material substrates. Herein, I show how functional surface chemistry can address both aspects through the installation of substituted aryl functional groups on the electrode surface via reduction of aryl diazonium salts. The functionalization of nickel phosphide nanocrystals with an array of substituted aryl groups of varying electron donating and withdrawing character showcases how the internal electronic structure of a material can be tuned to improve its catalytic activity. Then, the way in which rationally designed surface functional groups can offer new reaction pathways for dynamic conversion electrode reactions is showcased through the installation of thiophenol groups in a sulfur/carbon composite electrode. Though there is still much work to be done in the development of novel material systems for these critical electrochemical applications, I hope that this work can serve as a case study in the utility that surface chemistry can have in altering the intrinsic properties and reactivity of earth abundant materials.