Localized Charge Transfer in Two-Dimensional Molybdenum Trioxide

Abstract

Molybdenum trioxide is an interesting inorganic system in which the empty 4d states have potential to hold extra electrons and therefore can change states from insulating opaque (MoO) to colored semimetallic (HMoO). Here, we characterize the local electrogeneration and charge transfer of the synthetic layered two-dimensional 2D MoO-II (a polymorph of MoO and analogous to α-MoO) in response to two different redox couples, i.e., [Ru(NH)] and [Fe(CN)] by scanning electrochemical microscopy (SECM). We identify the reduction of [Ru(NH)] to [Ru(NH)] at the microelectrode that leads to the reduction of MoO-II to conducting blue-colored molybdenum bronze HMoO It is recognized that the dominant conduction of the charges occurred preferentially at the edges active sites of the sheets, as edges of the sheets are found to be more conducting. This yields positive feedback current when approaching the microelectrode toward 2D MoO-II-coated electrode. In contrast, the [Fe(CN)], which is reduced from [Fe(CN)], is found unfavorable to reduce MoO-II due to its higher redox potential, thus showing a negative feedback current. The charge transfer on MoO-II is further studied as a function of applied potential. The results shed light on the charge transfer behavior on the surface of MoO-II coatings and opens the possibility of locally tuning of their oxidation states.

Scanning Gel Electrochemical Microscopy for Topography and Electrochemical Imaging

“…Later, the developments involved using nonelectrochemical signals (e.g., shear force − and atomic force microscopy (AFM) − ) to independently determine the probe–sample distance for SECM and SICM, which allowed topography of the sample to be analyzed separately from the electrochemical activity. SECM and SICM, as well as their combination with other techniques, have been well developed as powerful methodologies for measuring kinetics of heterogeneous charge transfer on electrodes, − analyzing the biological activity of proteins and living cells, − evaluating localized corrosion behavior of metals, − and patterning/etching various materials. ,− …”

NIR-II responsive PEGylated MoO2 nanocrystals with LSPR for efficient photothermal and photodynamic performance enhancement

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Investigation of Charge Transfer Kinetics at Carbon/Hydroquinone Interfaces for Redox-Active-Electrolyte Supercapacitors

“…By fitting the approach curve data ( I T vs L ) to the analytical approximate expression, the normalized rate constant (κ) was extracted (SI). Finally, the effective heterogeneous charge transfer rate constant ( k eff ) was determined by using the equation (κ = k eff r T / D ) ,− where r T is the radius of employed UME (= 12.5 μm), and D is the diffusion coefficient of HQ (= 0.73 × 10 –5 cm 2 s –1 ) . As a result, we obtained k eff values of 1.2 × 10 –2 and 1.3 × 10 –2 cm s –1 for SWNTs and RGOs, respectively.…”