Long-Range Electrification of an Air/Electrolyte Interface and Probing Potential of Zero Charge by Conductive Amplitude-Modulated Atomic Force Microscopy

The structure of an electrical double layer (EDL) at the interface of electrode/electrolyte or air/electrode/electrolyte is a fundamental aspect, however not fully understood. The potential of zero charge (PZC) is one of the clues to dictate the EDL, where the excess charge on the electrode surface is zero. Here, a nanoscale configuration of immersion method was proposed by integrating an electrochemical system into conductive atomic force spectroscopy under the amplitude modulation (AM) mode and agarose gel as the solid-liquid electrolyte. The PZC of boron-doped diamond was determined to be at 0.2 V (vs Ag/AgCl). By AM spectroscopy, the capacitive force shows remote electrification without direct electrode/electrolyte contact, which is dependent on the population of ions at the air/electrolyte interface. The surface potential by alignment of water is also evaluated. Prospectively, our study could benefit applications such as PZC measurement and non-electrode electrochemical processes at the air/electrolyte interface.