Quantifying charge transfer to nanostructures: Polyaniline nanotubes

Abstract

The nano-impact method is used to quantify electrolytic doping levels of single polyaniline nanotubes in aqueous sulphuric acid solution. Even at extreme potentials only partial (≤18%) doping of the tubes is observed. Comparisons are made with the doping of ensembles of tubes where the levels of charge transfer appears even less. The implications for practical applications are assessed.

Nitrite‐Enhanced Charge Transfer to and from Single Polyaniline Nanotubes

“…From the magnification inset of curve a, some small and clear spikes in the current transients were observed, which is consistent with the reduction of the conductive “half‐oxidized” emeraldine PANI observed in the cyclic voltammograms. The average charge from a total of 406 spikes in 58 scans is found to be 37±4.2 pC at −0.2 V, which is much less than the expected charge of an individual PANI nanotube of 171±112 pC (assuming 2‐electron transfer from the initial emeraldine to fully reduced state leucoemeraldine, detailed calculation was shown in the Experimental Section) . In particular, the charge transferred becomes less and less when applying a more negative potential.…”

“…However, during the application in electrical devices, the specific charge and doping extent of PANI and utilization efficacy in PANI nanomaterials has rarely been taken into consideration. In a previous study, we found that the doping level of PANI ensembles across the electrode can be only 6 %, whilst that of individual PANI tubes is 17 %, by comparison with the theoretical expected charge per PANI tube assuming 2‐electron doping from the intermediate conductive state Em salt form to Leuco form as shown in Scheme , which indicates the material utilization efficacy is tiny . In the study, upon impact at the electrode surface, single PANI tubes are partially and locally converted from the conducting emeraldine form to non‐conducting states (leucoemeraldine or pernigraniline).…”

“…The as‐prepared PANI nanotube exists in its conducting Em salt state . Cyclic voltammetry was carried out (Figure ).…”

“…in which, D =1.6×10 −5 cm 2 s −1 (diffusion coefficient of nitrite in aqueous solution), n is the number of electrons transferred per nitrite molecules during reduction on the nanotube, where n =1, r 0 (0.2±0.02 μm) and l (2.9±1.9 μm) represent, respectively, the radius and length of one single PANI nanotube, which were measured by SEM previously . Assuming the duration time of spikes of 10 ms, I m is then calculated to be 1.2 nA .…”

“…In the study, upon impact at the electrode surface, single PANI tubes are partially and locally converted from the conducting emeraldine form to non‐conducting states (leucoemeraldine or pernigraniline). This change in conductivity due to the altered oxidation state hence inhibits further electron transfer to the distant materials of the single tube . Therefore, it is of importance to develop an effective way in order to enhance the oxidation and improve the doping level of PANI nanomaterials in exploring the application of PANI electronic devices.…”