RII Track 4: Isolating the Role of Metal Centers in the Capacitive Behavior of Porous Framework Electrodes

Electrodes exist in many of our pockets and briefcases (e.g., at either pole of a lithium-ion battery). These are typically based on a conductive material like graphite that has the designed property of “storing” or absorbing a large number of ions (e.g., lithium ions) in the dense bulk “in between” the tightly spaced rows of atoms that make up its structure.

Recently, it has been shown that ultrafast transport of these ions (leading to rapid charging and discharging of the energy storage device) can be achieved in novel materials with built-in molecular channels or pores referred to as metal-organic frameworks (MOFs), if they are suitably conductive - a nontrivial task for the materials chemist to design. Our project aims to compare such conductive MOFs with a class of metal-free carbon frameworks synthesized in Montana, known as zeolite-templated carbons (ZTCs), providing a logical middle ground between graphite (nonporous carbon) and MOFs (porous, metal-containing materials).

This comparison can be used to isolate the role of the metal atoms present in the MOFs’ structures, in order to determine whether and how they play a role in rapid ion storage in porous framework electrodes.

A collaborative effort will be forged between the Stadie Research Group at Montana State University (MSU) and the Dincă Research Group at the Massachusetts Institute of Technology (MIT) aimed at bridging the scientific gap between MOFs and ZTCs. These two classes of open, porous framework solids of bottom-up designable structure and chemistry, have both been deployed in capacitive energy storage devices such as supercapacitors and hybrid batteries, but investigations of their electrochemical properties have been disjointed.

The lack of crystalline structure or a realistic atomistic model have hindered fundamental studies of ZTCs despite their excellent energy storage properties. On the other hand, more is known about charge transport, ion mobility, and capacitive energy storage in MOFs, but these materials have so far fallen short of porous carbons in their promise for applications.

A common language and set of metrics founded on an atomistic physical chemical perspective are direly needed to effectively combine the insights gained from each body of research. Our plan is to bring newly developed, realistic structural models and several samples of pristine ZTCs to the Dincă laboratory to carry out combined experimental and theoretical investigations of electrical conductivity and related electrochemical properties of porous framework solids.

A primary goal of this work will be to ascertain the mechanism of charge transport within the metal-free carbon framework of ZTCs, and subsequently tailor new MOFs and ZTCs with both high electrical conductivity and ion storage capacity. These studies will shed new insight into the rational design of capacitive electrode materials for next-generation energy storage applications.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.