Simultaneous Observation of Faradaic and Tunneling Current at a Flat Surface Using Tunneling-Current-Based Constant-Distance Scanning Electrochemical Microscopy with a Platinum Nanoelectrode

• Main Authors: Hiroshi YAMADA, Nobutaka YAMANAKA, Kenji YASUNAGA
• Format: Article
• Language: English
• Published: The Electrochemical Society of Japan 2021-05-01
• Series: Electrochemistry
• Subjects: secm; stm; nanoelectrode; nanoparticle
• Online Access: https://www.jstage.jst.go.jp/article/electrochemistry/89/3/89_21-00013/_pdf/-char/en

A conical-shaped Pt nanoelectrode whose tip apex features an effective electrode area was fabricated and used as a probe for scanning electrochemical microscopy (SECM). Nanoelectrodes were prepared by electroplating Pt in porous pyrolyzed polydimethylsiloxane filled into the tip of a quartz nanopipette. The current–distance curves were obtained by acquiring raw (without a low-pass filter) and low-pass-filtered (10 Hz) current simultaneously while a tip approached a flat Pt substrate. The raw-current approach curve showed the transition from faradaic feedback current to electron tunneling between the tip of the probe and the substrate. Alternatively, in the low-pass-filtered approach curve, a faradaic current with an improved signal-to-noise ratio was obtained without a transient increase of the tunneling current. From scanning electron microscopy observations, voltammograms, approach-curve measurements, and digital simulations of the response of a nanoelectrode, we deduced that only the apex of the conical-shaped electrode exhibited electrochemical activity and acted as an effective electrode. The constant-distance SECM imaging of an Au-sputtered polycarbonate membrane with sub-micrometer pores and Pt nanoparticles deposited on a highly oriented pyrolytic graphite (HOPG) was successfully demonstrated using the tunneling-current-based standing approach mode.