Automated Redox Titrations via Interdigitated Electrode Arrays: Application to the Mediated Electron Transfer Interrogation of Charge and Rate on Electrodeposited Polymers

Mediated electron
transfer (MET) plays a crucial role in energy
storage and conversion technologies such as redox targeting flow batteries
(RTFBs), yet its experimental investigation often requires labor-intensive
and low-throughput setups. To address this, we developed a microfabricated
interdigitated electrode array (IDA) platform that enables automated,
high-throughput electrochemical redox titration measurement to be
performed to study the MET process. Our redox titration method enables
simultaneous measurement of the charge capacity and rate of MET processes
on a material or surface. Automated redox titration (ART) facilitates
systematic investigation of the MET process across a broad parameter
space, exemplified through the study of polypyrrole (PPy) and a pyrene-4,5,9,10-tetrone
azo group-based polymer (PTAP), both redox-active polymers relevant
to various energy storage applications. Using PPy as a model material,
500 redox titration measurements were conducted within 50 h, varying
the electrode gap widths, polymer charging potentials, voltammetric
scan rates, and electrolyte concentrations. Finite-element simulations
confirmed the electrochemical responses and elucidated the kinetics
of the MET reactions. Our automated methodology was further tested
with PTAP, revealing a surprising charging potential dependence on
the rate of MET. The automation, flexibility, and scalability of our
redox titration platform pave the way not only for advanced studies
of MET processes relevant to RTFBs, but also with implications in
the understanding of next-generation energy storage materials, molecular
electrocatalysis, and biosensing.