Application of Scanning Electrochemical Microscopy (SECM) to Study Electrocatalysis of Oxygen Reduction by MN4-Macrocyclic Complexes

Abstract

N4-macrocyclic complexes are among the most widely investigated molecular materials for the oxygen reduction reaction (ORR). These complexes are attractive because they inherently provide well-defined structural models for describing the ORR not only in nature, for example, in cytochrome c oxidases, but also for electrocatalysts of industrial importance. The development of more efficient N4-macrocyclic complexes as electrocatalysts for the ORR requires in-depth understanding of the most crucial properties that govern their functionality. This goal necessitates employing advanced techniques and methods to accurately probe electrocatalytic behavior. This chapter covers a brief introduction of scanning electrochemical microscopy (SECM) and discusses its application for evaluation of the electrocatalytic behavior of materials, with particular focus on the ORR. A general overview of the benefits of using SECM as an alternative or as a complimentary technique to rotating-ring disk electrode (RRDE) voltammetry in studying the kinetics of the ORR is provided, with examples of this application dedicated to catalysts derived from MN4-macrocyclic complexes. The chapter also covers examples of the application of SECM as a semi-combinatorial and high-throughput tool for catalyst screening and development, and the evaluation of electrocatalysts at temperatures of industrial relevance. Discussion of some recent developments of the application of SECM, or SECM coupled to other auxiliary techniques, in electrocatalysis, for example, in probing electrolysis of individual nanoparticles, and a forecast of its potential future applications in both fundamental and applied science are included at the end of this chapter.