High Spatial Resolution Electrochemical Microscopic Observation of Enhanced Charging under Bias at Active Sites of N-rGO

Abstract

Recent breakthrough reveals that the activation free energy decreases with the amount of the oxidative charge stored at the catalyst, which gives an insight into the role of chemistry vs bias in electrocatalysis. In this study, non-faradic and faradic currents from the total currents in the image of scanning electrochemical cell microscopy (SECCM) are isolated to realize the mapping of charge accumulation and electrochemical activity with a resolution of ∼135 nm. Enhanced charging under bias is observed at the active sites of N-doped graphene oxide (N-rGO) with high electrochemical activity in the hydrogen evolution reaction (HER), providing direct evidence to support the mechanism as mentioned above. This established electrochemical imaging method and the collected result could provide more effective information about the electrochemical mechanism of the HER performance, which is significant for the design of high HER catalysts.

Scanning Electrochemical Cell Microscopy Platform with Local Electrochemical Impedance Spectroscopy

“…As shown in Figure S8, for GO dissolved in pure water, the droplet gradually shrinks from the edge and more edges are exposed. 26 As shown in Figure S8a, more edge sites doped by N atoms can be verified by the higher conductivity. For GO dissolved in half water and half alcohol, this phenomenon does not arise, as shown in Figure S8b because of the small surface tension.…”

“…SECCM has been adopted to analyze the electrochemical activity of a material during the hydrogen evolution reaction. 26 The parameters of the equivalent circuit components were obtained by fitting the transient current. However, this transient current method is suitable only for simple equivalent circuits.…”

“…The width of the edge with high electrochemical activity is approximately 2 μm, which is approximately consistent with our previously reported result. 26 To calculate the contact diameter, the global C dl is normalized to match the local C dl . The global C dl of the ITO electrode is measured to be (∼0.35 F m −2 .…”

“…The N-rGO/ITO used in the imaging experiment was prepared according to a previously described method. 26 GO was prepared with a modified Hummers method, which involved dissolution into a 0.1 mg/L solution and dispersion into microsheets by ultrasound. The solution was dropped on an ITO substrate (20 × 10 × 1 mm) and subsequently dried under 80 °C.…”

“…The tip diameter was measured to be ∼150 nm (Figure S1, Supporting Information) by scanning electron microscopy (SEM, S-4800, Hitachi, Japan). The N-rGO/ITO used in the imaging experiment was prepared according to a previously described method . GO was prepared with a modified Hummers method, which involved dissolution into a 0.1 mg/L solution and dispersion into microsheets by ultrasound.…”