Interfacial electrical double layer in electrocatalytic reactions: Fundamentals, characterizations and applications

Abstract

The interfacial electrical double layer (EDL) is the interfacial space filled with a complex and dynamic reaction network formed by catalyst's surface atoms, reactants, intermediates, products, solvent molecules, ions, and other components. EDL has a profound impact on electrocatalytic reactions, affecting both the thermodynamics and kinetics of these processes. Manipulating the composition and structure of the EDL microenvironment sets an additional level of tuning toward the electrocatalysis, to the traditional catalyst optimization. It resembles the delicate manipulation of the environment around the active sites by protein scaffold in enzymes. However, the rational optimization of the EDL demands a deep understanding of its structure and dynamics. Problems lie in the complexities of interfacial EDL, which include complicated multi-body interactions, few molecular-level characterization techniques, and scarce EDL modification strategies.

In this tutorial, we delve into the intricacies of the interfacial EDL in electrocatalytic reactions and seek to provide those who are new to this field a thorough summary of the theory, characterization, history, recent progress within the regime of EDL for electrocatalysis. We begin by discussing the theoretical models that describe the structure and properties of EDL, including 4 classical EDL models, their applications in electrocatalytic analysis and modifications, and relevant calculation modulation methods. These models are arranged chronologically, such that a historical summary of how the EDL theory evolves from simple models to complicated details is provided. We then provide an overview of cutting-edge techniques in electrochemical measurement methods, in situ spectroscopic characterization techniques, and scanning probe microscopy methods. Specifically, we aim to summarize the advantages and disadvantages of each technique, with an emphasis on their capability of probing the EDL region. The summary table can provide junior students with a quick overview and a useful tool for selecting the appropriate techniques toward addressing the EDL properties for electrocatalysis. Furthermore, by combining the theory and characterization techniques, we list several pivotal studies from the past five years emphasizing the “electrode side interfacial modification” approach and the “solution side interfacial modification” approach, toward modulating the EDL to optimize the electrocatalytic properties. These examples not only show the recent progress in this field and offer fundamental details about how researchers in this field address the problems from the aspect of EDL. With these combined theory, characterization and research samples, we hope that the newcomers can gain interest in this field, sense the enormous opportunities and understand the general principles of EDL toward electrocatalysis.