Quantifying defects in carbon nanotubes undergoing prolonged electrochemical cycling with Raman phase map

Abstract

Electrically conducting graphitic carbon materials are ubiquitous constituents of electrocatalysts and electrochemical energy storage materials. During electrolysis and electrochemical charge-discharge cycles, the carbon matrix is subjected to chemical stress due to drastic changes in the redox environment, the formation of reactive intermediate species and to steric strain caused by intercalation of counter ions. These factors trigger the formation of defects in the graphitic lattice, leading to scattering the charge carriers, thereby reducing the carrier mobility. It is of utmost importance to reliably monitor the graphitic lattice to maintain the integrity of the material and recognize the nature of defects. We have applied statistical Raman measurement technique in conjunction with Raman phase map and Raman ellipse to monitor and quantify the formation of point and line defects in functionalized carbon nanotubes. We also demonstrate how the Raman ellipse in combination with ID/ID′ is a new and powerful analytical tool which can serve to deduce the correct defect generation process in a graphitic lattice exposed to stress during electrochemical cycling. Thus, a deep mechanical insight by “simple” optical spectroscopy can be captured through our proposed Raman phase map analysis.