Integrated Process for Structuring and Functionalizing Ordered Mesoporous Silica to Achieve Superprotonic Conductivity

Abstract

Polyacid-functionalized inorganic mesoporous materials have attracted considerable interest as catalysts, permselective molecular sieves, or drug carriers. Despite the great interest, their synthesis into ordered mesostructures incorporating polyacids densely and homogeneously distributed in the mesopores is a challenge. Moreover, their properties as conductors for energy applications remain completely unexplored. Here, we report an efficient, one-shot environmentally friendly synthesis route to prepare ordered mesoporous silica functionalized with strong polyacids, which exhibits excellent proton conductivity. We used polyion electrostatic complex micelles as structure-directing, functionalizing, and pore-generating agents to obtain a material of remarkable textural and functional quality. It presents large and ordered mesopores hosting monodisperse polyacid chains corresponding to a dense and homogeneous functionalization of 1.2 mmol SO3H g SiO2 −1 and a function density of 1 SO 3 H per nm 3 of mesopore volume. Overcoming the performance-limiting inhomogeneities, we designed a superprotonic conductor, while the high value of the conductivity, 0.024 S cm −1 at 363 K/95% relative humidity, was maintained for at least 7 days.

Synthesis of Mesoporous Silica Using the Sol–Gel Approach: Adjusting Architecture and Composition for Novel Applications

“…The functionalization of polyacids is achieved through the sol–gel approach [ 93 , 94 ]. For example, Richard et al reported [ 95 ] the utilization of a robust polyacid with a precisely controlled length—namely, polystyrene sulfonic acid (PSS)—as the raw polyacid material, while they employed a complex consisting of polyacid-based dihydrophilic block copolymer (DHBC) and an oppositely charged polyelectrolyte as a co-template via the sol–gel process for the preparation of polyacid-functionalized mesoporous silica. The study revealed the successful formation of strong polyacid mesoporous silica (PIC/PSS).…”

“… ( a ) TEM image and ( b ) SEM image of the polyacid functionalized mesoporous silica (denoted MesoPIC-PSS). MesoPIC-PSS sorption isotherms of ( c ) nitrogen measured at 77 K and related pore size distribution and ( d ) water measured at 298 K. ( e ) The schematic illustration of the integrated process for structuring and functionalizing mesoporous silica to achieve super-protonic conductivity [ 95 ]. Copyright 2022, American Chemical Society.…”

Effects of the Polymer Amount and pH on Proton Transport in Mesopores

“…Géradin and coworkers [ 15 ] used an in situ mesopore functionalization approach [ 16 ] to integrate a polyion electrostatic complex consisting of a sulfonic acid‐bearing polyacid‐based double‐hydrophilic block copolymer and an oppositely charged polyelectrolyte for structure‐directing, functionalization, and mesopore generation of mesoporous silica. They achieved proton conductivities of up to 0.024 S cm −1 at 363 K/95% relative humidity with an environmentally friendly one‐shot synthesis procedure.…”