6. Highly Ordered Macroporous Electrodes

In recent years, the field of highly ordered macroporous thin films coated onto solid electrode surfaces has received increasing attention, on the one hand, due to interesting fundamental questions, and, on the other hand, because of a large variety of potential applications of such designer structures, ranging from electrocatalysis to biosensors and energy storage/conversion. This chapter describes the synthesis, the characterization, and the features of such organized layers, with a special emphasis on an increasingly sophisticated and rational design, which is possible when using colloidal crystal structures as templates. Some possible applications of such modified electrodes are also highlighted in the last section of the chapter, illustrating their beneficial effects in various domains, going eventually far beyond pure electrochemical aspects.

In this chapter, we present the elaboration of highly-ordered macroporous electrodes using colloidal crystal templating. A structure is considered as macroporous, when the pore size exceeds 50 nm; pores with 2–50 nm are considered as mesopores, whereas pores smaller than 2 nm are termed microporous. Several techniques allowing the self-assembly of microspheres into colloidal crystal templates will be discussed in Sect. 6.1.1. After giving an overview in Sect. 6.1.2 over existing methods to infiltrate colloidal templates, Sects. 6.1.3 and 6.1.4 will focus on the controlled electrodeposition of metals and conducting polymers (CPs) into colloidal templates, and the electrochemical characterization of the resulting macroporous electrodes. Section 6.2 illustrates an approach to fabricate macroporous electrodes with complex pore architectures, including gradient pore structures. Assembly of colloidal microspheres into complex colloidal crystal architectures in a layer-by-layer deposition process using the Langmuir–Blodgett technique followed by infiltration of the template by electrochemical deposition enabled us to obtain this objective. In Sect. 6.3, we focus on miniaturized macroporous gold electrodes with a cylindrical geometry and their utility with respect to the electrocatalytic reduction of oxygen. The broad field of applications, in which macroporous electrodes can be used for, is presented in Sect. 6.4.