Visualizing Water Reduction with Diazonium Grafting on a Glassy Carbon Electrode Surface in a Water-in-Salt Electrolyte.

Aqueous batteries are regaining interest, thanks to the extended working stability voltage window in a highly concentrated electrolyte, namely the water-in-salt electrolyte. A solid-electrolyte interphase (SEI) forms on the negative electrode to prevent water access to the electrode surface. However, we further reported that the formed SEI layer was not uniform on the surface of the glassy carbon electrode. The SEI after passivation will also show degradation during the remaining time of open-circuit voltage (OCV); hence, it calls for a more stable passivation layer to cover the electrode surface. Here, a surface modification was successfully achieved via artificial diazonium grafting using monomers, such as poly(ethylene glycol), α-methoxy, ω-allyloxy (PEG), and allyl glycidyl cyclocarbonate (AGC), on glassy carbon. Physical and electrochemical measurements indicated that the hydrophobic layer composed of PEG or AGC species was well grafted on the electrode surface. The grafted hydrophobic coatings could protect the electrode surface from the water molecules in the bulk electrolyte and then suppress the free water decomposition (from LSV) but still migrating lithium ions. Furthermore, multiple cycles of CV with one-hour resting OCV identified the good stability of the hydrophobic grafting layer, which is a highlight compared with our precious work. These findings relying on the diazonium grafting design may offer a new strategy to construct a stable artificial SEI layer that can well protect the electrode surface from the free water molecule.

Local Degradation of PEDOT:PSS on Silicon Nanostructures Using Scanning Electrochemical Microscopy.

Conducting polymers show attractive characteristics as electrode materials for micro-electrochemical energy storage (MEES). However, there is a lack of characterization techniques to study conjugated/conducting polymer-based nanostructured electrodes. Here, scanning electrochemical microscopy (SECM) is introduced as a new technique for in situ characterization and acceleration of degradation processes of conducting polymers. Electrodes of PEDOT:PSS on flat silicon, silicon nanowires (SiNWs) and silicon nanotrees (SiNTrs) are analyzed by SECM in feedback mode with approach curves and chronoamperometry. The innovative degradation method using SECM reduces the time required to locally degrade polymer samples to a few thousand seconds, which is significantly shorter than the time usually required for such studies. The degradation rate is modeled using Comsol Multiphysics. The model provides an understanding of the phenomena that occur during degradation of the polymer electrode and describes them using a mathematical constant A0 and a time constant τ.