The Influence of Monolayer and Multilayer Diazonium Functionalities on the Electrochemical Oxidation of Nanoporous Carbons

Abstract

High surface area carbon powders are used in many electrochemical applications, e.g., fuel cells, supercapacitors, and batteries. However, despite their advantages, they are susceptible to oxidation and carbon corrosion when exposed to oxidizing potentials. Our goal has been to use diazonium chemistry to attach surface groups to block corrosion-susceptible sites and alter wettability. In prior work, mesoporous colloid imprinted carbons (CICs) with pores of 12–50 nm and still smaller pore necks hindered access of the diazonium precursors and limit mass transport in electrochemical applications. Here, CIC-85 powders (85 nm pores) were modified with -PhF5 or PhSO3H groups to engender hydrophobicity or hydrophilicity, respectively. Both groups decrease corrosion-induced surface roughening of the CIC-85 by ∼50% in 0.5 M sulfuric acid. The -PhF5 group decreases irreversible oxidation of carbon to CO2 by a factor of ∼9, while the -PhSO3H group protects the CIC-85 surface by ∼4 times. An analogous free-standing, binder-free 85 nm pore size carbon sheet, exhibiting similar oxidation behavior, was examined by XPS, showing that surface functionalities are fully retained after corrosion. This work offers novel insights on the role, impact, and fate of diazonium-attached surface groups in protecting carbon surfaces during accelerated stress testing in sulfuric acid.