Pyrolytic Carbon Films with Tunable Electronic Structure and Surface Functionality: A Planar Stand-in for Electroanalysis of Energy-Relevant Reactions

Abstract

Nanostructured carbons are critical components within many of the electrodes used for energy-storage and –conversion systems, where they can provide pathways for electron conduction to enable high-rate operation, act as supports for other active materials (e.g., electrocatalytic metals and oxides), and contribute to the mechanical properties of the electrode. Yet often overlooked when selecting a particular carbon is the nature of electronic/chemical/physical interactions at the junction of carbon with nanoscale phases that impart desired storage or electrocatalytic functionality. Our own research with otherwise high-performing carbon-based electrode architectures suggests that sub-optimal interface design ultimately hinders energy and power capability. In order to address fundamental questions regarding interfacial processes, we step back from the complex structure of practical carbon-containing electrodes to a planar electrode configuration designed to mimic those same interfaces. For example, pyrolytic carbon (pyC) films prepared by chemical vapor deposition are planar analogs of the disordered carbon blacks used in many battery and fuel-cell electrodes, and thus serve as an electroanalytical substrate on which we deposit charge-storing metal oxides (e.g., MnO2), electroactive polymers, and metal colloids [1]. We use classical electroanalytical methods to determine fundamental properties such as electron-transfer rate constants and impedance-derived response times, absent the complexities imposed by 3D electrodes. By moving to 2D model surfaces we are also able to interrogate interfacial processes by scanning probe microscopy, including in situ monitoring of conductivity and surface morphology under potential/current control. Lessons learned from these model 2D interfaces are readily applied to the redesign of practical 3D electrode structures to improve next-generation electrochemical capacitors and batteries. [1] J. F. Parker, G. E. Kamm, A. D. McGovern, P. A. DeSario, D. R. Rolison, and J. W. Long, Languir, 33 (2017) 9415–9425.