Tailoring the Nanostructure of Colloidal Imprinted Carbons for Their Application in Electrochemical Devices
Authors: Atwa Marwa , O’Connell David , Li Xiaoan , Karan Kunal , Birss Viola 
Published: February 2020

Mesoporous colloid imprinted carbons (CIC) have many promising properties for use in various applications, including as catalyst supports in fuel cells, and in supercapacitors, batteries, sensors, and for water deionization. For example, in our past work, we have shown that Pt-loaded CICs exhibit very good activity for oxygen reduction in proton exchange membrane fuel cells (PEMFCs) [1, 2].

The CICs are typically prepared by imprinting a mesophase pitch powder with a colloidal silica template, carbonizing the imprinted pitch, and then removing the silica template [3-5]. The CICs are distinguished by their ordered spherical pores, having uniform diameters on the nanometer scale. The diameter of these CIC pores can be tuned during the synthesis by using silica colloids of controlled particle sizes (e.g., from several to hundreds of nanometers). This allows a wide variety of ordered pore sizes to be produced and studied. However, constrictions present between each spherical pore may limit ion transport. Theoretical calculations suggest that these pore “necks” are ca. 25-50% of the diameter of the corresponding spherical pores. The relatively small diameter of these pore necks can potentially hinder transport from one region to another, thus influencing the performance of CIC-based electrochemical devices when mass transport is limiting.

In our work, we are focusing on how CIC nanostructuring, including controlling the pore neck size, influences electrochemical performance. Here, we report a novel approach to tuning the pore neck size, using a silica precursor to modify the colloidal silica templates prior to imprinting with mesophase pitch. By adjusting the concentration of the silica precursor solution, we can improve the accessibility of each spherical pore within the CICs.

To characterize the modified CICs, nitrogen adsorption/desorption isotherms were collected to determine the surface area and pore size distribution, while FE-SEM was used to verify the size of the nanopores, particularly the diameter of the pore necks. Cyclic voltammetry and electrochemical impedance spectroscopy were then used to investigate the effect of pore neck size on mass transport through the CIC particles.

References:

[1] D. Banham, F. Feng, T. Fürstenhaupt, K. Pei, S. Ye, V. Birss, Novel Mesoporous Carbon Supports for PEMFC Catalysts, Catalysts, 5 (2015) 1046.

[2] K. Pei, D. Banham, F. Feng, T. Fürstenhaupt, S. Ye, V. Birss, Oxygen reduction activity dependence on the mesoporous structure of imprinted carbon supports, Electrochemistry Communications, 12 (2010) 1666-1669.

[3] B. Fang, J.H. Kim, J.S. Yu, Colloid-imprinted carbon with superb nanostructure as an efficient cathode electrocatalyst support in proton exchange membrane fuel cell, Electrochemistry Communications, 10 (2008) 659-662.

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[5] Z. Li, M. Jaroniec, Colloidal imprinting: A novel approach to the synthesis of mesoporous carbons [2], Journal of the American Chemical Society, 123 (2001) 9208-9209.