Abstract
Amorphous molybdenum sulfide (a-MoSx) is a promising candidate to replace noble metals as electrocatalysts for the hydrogen evolution reaction (HER) in electrochemical water splitting. So far, understanding of the activity of a-MoSx in relation to its physical (e.g., porosity) and chemical (e.g., Mo/S bonding environments) properties has mostly been derived from bulk electrochemical measurements, which provide limited information about electrode materials that possess microscopic structural heterogeneities. To overcome this limitation, herein, scanning electrochemical cell microscopy (SECCM) has been deployed to characterize the microscopic electrochemical activity of a-MoSx thin films (ca. 200 nm thickness), which possess a significant three-dimensional structure (i.e., intrinsic porosity) when produced by electrodeposition. A novel two-step SECCM protocol is designed to quantitatively determine spatially resolved electrochemical activity and electrochemical surface area (ECSA) within a single, high-throughput measurement. It is shown for the first time that although the highest surface area (e.g., most porous) regions of the a-MoSx film possess the highest total activity (measured by the electrochemical current), they do not possess the highest specific activity (measured by the ECSA-normalized current density). Instead, the areas of highest specific activity are localized at/around circular structures, coined “pockmarks”, which are tens to hundreds of micrometers in size and ubiquitous to a-MoSx films produced by electrodeposition. By coupling this technique with structural and elemental composition analysis techniques (scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy) and correlating ECSA with activity and specific activity across SECCM scans, this work furthers the understanding of structure-activity relations in a-MoSx and highlights the importance of local measurements for the systematic and rational design of thin film catalyst materials.
Original language | English |
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Pages (from-to) | 33620-33632 |
Number of pages | 13 |
Journal | ACS Applied Materials and Interfaces |
Volume | 16 |
Issue number | 26 |
Early online date | 18 Jun 2024 |
DOIs | |
Publication status | Published - 3 Jul 2024 |
Funding
This work has been supported by the University of Bath and Monash University, both of which are thanked for the provision of a joint Bath\u2013Monash Global PhD studentship to T.R.H.L. M.K. is the recipient of an Australian Research Council (ARC) Discovery Early Career Researcher award (DECRA, project: DE220101105) funded by the Australian Government. C.L.B. is the recipient of an Australian Research Council (ARC) Discovery Early Career Researcher Award (DECRA, project: DE200101076) funded by the Australian Government. The authors acknowledge the use of the instruments and scientific and technical assistance at the Monash Centre for Electron Microscopy (MCEM), a Node of Microscopy Australia.
Funders | Funder number |
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Australian Research Council | DE220101105 |
Australian Government | DE200101076 |
Keywords
- electrocatalysis
- HER
- hydrogen evolution reaction
- molybdenum disulfide
- MoS
- scanning electrochemical cell microscopy
- SECCM
ASJC Scopus subject areas
- General Materials Science