Nanoscale Imaging of Electrocatalytic Nanomaterials by High-resolution Scanning Electrochemical Microscopy

Author

Xiang Wang, The Graduate Center, City University of New YorkFollow

Date of Degree

2-2023

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Michael V. Mirkin

Committee Members

Dorthe M. Eisele

Hiroshi Matsui

Daniel Steingart

Michael V. Mirkin

Subject Categories

Analytical Chemistry | Chemistry | Materials Chemistry | Other Chemistry | Physical Chemistry

Keywords

scanning electrochemical microscopy

Abstract

Numerous insights of the structure–electrochemical activity relationship of nanocatalysts have been obtained by using macroscopic electrochemical measurements over the last several decades. However, signals measured by large electrodes are inevitably averaged out of many nanocatalysts, non-uniformed sizes, uneven morphologies, and multiple crystallographic facets. Over the last ten years, Scanning Electrochemical Microscopy (SECM) has advanced electrochemical measurements toward micro- to nanoscale level at a high spatial resolution. The advantages of using nanoelectrode in SECM include fast mass transfer of reactive species, dominated radial diffusion pattern, small double layer capacitance and small RC constant. In this thesis, high-resolution SECM is applied to image electrocatalytic nanomaterials, hoping to identify the differences of electrochemical properties between individual nanoelectrocatalysts as well as within single piece of nanoelectrocatalysts. Toward this goal, more reliable small-sized platinum nanoelectrodes were made in the first place. Non-destructive transmission electron microscope (TEM) was used to characterize and confirm the size of nanoelectrodes evaluated by electrochemical measurements. This part is included in chapter II. Structure-engineered two-dimensional (2D) electrocatalysts such as transition metal carbides (MXenes) (chapter Ⅲ) and MoS₂ (chapter IV) nanoflakes were studied by high-resolution SECM. Variation of electrochemical behavior among different individual MXenes nanoflakes was found; local distribution of electrochemical activities within single MoS₂ nanoflake was captured by high-resolution SECM.

Detailed insights of “local electrochemical properties--atomistic structure or defects” relation of electrocatalysts need high-resolution SECM to be correlated with atomic force microscopy (AFM) and TEM in situ or ex situ. In chapter Ⅴ, a methodology for correlative multi-tech SECM imaging was developed to map single TiO₂ nanorod for electrocatalysis on TEM grid.

Chapter VI presents SECM study of N-doped porous carbon with diatomic Ru-Ni sites for hydrogen oxidation reaction (HOR). The results confirmed that diatomic Ru-Ni single atom sites boosted the HOR performance of N-doped porous carbon. In chapter Ⅶ, chemically modified carbon nanoelectrodes for mediated oxidation/reduction of electroactive species were investigated based on bimolecular electron transfer between the dissolved electroactive species and a redox mediator attached to the surface of a carbon nanoelectrode. Tris(2,2'-bipyridine)ruthenium complex, Ru(bpy)₃, underwent reversible oxidation/reduction reactions at both positive and negative potentials and was used to prepare SECM nanoprobes for sensing analytes during electrocatalysis.

Recommended Citation

Wang, Xiang, "Nanoscale Imaging of Electrocatalytic Nanomaterials by High-resolution Scanning Electrochemical Microscopy" (2023). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/5232