Nanoengineering of Pore Neck Size within Ordered Nanoporous Carbon Powders: Improving Ion Transport Rates for Clean Energy Applications

Abstract

While the use of high surface area, porous carbon powders as an electrode material and/or catalyst support is pervasive in many electrochemical applications, it is known that this can lead to transport limitations through and around the particles that can, in turn, lower the achievable power densities. Here, we use a family of colloid imprinted carbon (CIC) powders to create a nanoporous structure with primary pores of either 50 or 85 nm in diameter and with each pore connected 3-dimensionally to its neighbors via 12 smaller necks (21 and 28 nm, respectively), with the objective being to examine the CIC mass transport properties during electrochemical polarization. In this study, a novel approach was used to controllably increase only the pore neck size of CIC-50 and CIC-85 by up to 6 and 4 nm, respectively, thus increasing their cross-sectional areas by factors of 1.7 and 1.4, respectively. At the same time, the overall ordered porous structure, primary pore size, specific area, and elemental composition all remained essentially unchanged. Impedance spectroscopy confirmed it is the pore necks that fully control the ionic transport resistance through the CICs during electrochemistry, with the resistance lowered proportionally when the neck radius (i.e., cross-sectional area) is increased. This work has important ramifications for the application of porous electrode materials in fuel cells, batteries, capacitors, and other advanced energy and environment devices, showing that the size of the smallest channels and pores through which ions flow must be kept large enough to minimize the mass transport resistance, while also maintaining a maximum surface area.