In Situ Raman Spectroelectrochemical Doping of Monolayer Graphene at Micro-Scale

Abstract

The chemical vapor deposited (CVD) graphene with large monolayer coverage is preferred for applications over the mechanical cleavage of graphite. Large-area graphene has a lot of potential in electrochemical applications, e.g., as electrodes for supercapacitors, smart windows etc. However, in contrast to the almost perfect cleaved graphene, the CVD samples are more heterogeneous and contain many defects and topographic features originating from the transfer process, all of which may influence the properties of the material. Therefore, it is important to study the electrochemical doping of graphene with such a lateral resolution that enables the assessment of the influence of the local structure on the electrochemical performance. The recently developed micro-droplet in-situ Raman spectroelectrochemical technique was used to provide insights into localized structural changes as a function of electrochemical doping as well asother parasitic redox reactions at small area (few hundreds μm2) of the 1L CVD graphene. In all cases, we observed an extensive shift of the G peak with the disappearance of 2D peak and appearance of defects at higher potentials. The Raman frequency of the G peak was shifted by up to ⁓30 cm-1 for hole doping with all monovalent (LiCl, LiClO4,) divalent (Zn ClO4) and multivalent (AlCl3, Al(ClO4)3, Al(NO3)3) electrolyte salts. In addition, the onset potential of the defect formation and the initial doping state (the latter assessed from the G/2D frequency analysis) were studied. Keywords:CVD Graphene, electrochemical doping, concentrated electrolytes,