Scanning electrochemical potential microscopy (SECPM) has been introduced by C. Li et al. (Veeco Inst. Inc.). It was designed mainly to probe the potential profile across the electric double layer by approaching a probe towards charged surface immersed in electrolyte solution. In addition, SECPM offers the possibility to map surface potential of an electrode/electrolyte interface.

Hurth et al. reported their EDL potential profile measurements with the SECPM, and concluded that the data did not fit the classical Gouy-Chapmann-Stern (GCS) model. They suggested the need for a theoretical model to explain the measurement process and the effect of the EDL’s overlap on the probed potential. Recently, Baier et al. published their results, which concern the surface potential mapping for a single enzyme adsorbed on an electrode. They showed the high spatial resolution which can be reached with SECPM. This can have an interesting advantage comparing to the electrochemical scanning tunneling microscopy (EC-STM) in imaging non-conductive samples.

To our knowledge, a comprehensive theory of SECPM has not been developed, and experimentally this technique to probe the electric double layer is hardly applied yet. We believe that a computational method will help addressing this need for thorough theoretical model. Our motivation is to gain a deeper understanding of the measurement mechanism. The effects of the metallic protrusion of the probe, its open circuit potential (OCP), and the EDLs overlap on the probed potential are studied. A clear Debye screening effect was observed when varying the OCP of the probe. We observed steeper potential profiles for high OCPs due essentially to the electrostatic screening. The dependence on the metallic apex shape was also noticed.

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