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Using density functional theory (DFT) calculations, we investigated the electrochemical reduction of CO 2 and the competing H 2 evolution reaction on ligand-protected Au 25 nanoclusters (NCs) of different charge states, Au 25 (SR) 18 q ( q = −1, 0, +1). Our results showed that regardless of charge state, CO 2 electroreduction over Au 25 (SR) 18 q NCs was not feasible because of the extreme endothermicity to stabilize the carboxyl (COOH) intermediate. When we accounted for the removal of a ligand (both –SR and –R) from Au 25 (SR) 18 q under electrochemical conditions, surprisingly we found that this is a thermodynamically feasible process at the experimentally applied potentials with the generated surface sites becoming active centers for electrocatalysis. In every case, the negatively charged NCs, losing a ligand from their surface during electrochemical conditions, were found to significantly stabilize the COOH intermediate, resulting in dramatically enhanced CO 2 reduction. The generated sites for CO 2 reduction were also found to be active for H 2 evolution, which agrees with experimental observations that these two processes compete. Interestingly, we found that the removal of an –R ligand from the negatively charged NC, resulted in a catalyst that was both active and selective for CO 2 reduction. This work highlights the importance of both the overall charge state and generation of catalytically active surface sites on ligand-protected NCs, while elucidating the CO 2 electroreduction mechanisms. Overall, our work rationalizes a series of experimental observations and demonstrates pathways to convert a very stable and catalytically inactive NC to an active electrocatalyst.
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Redox Reactions at Colloidal Semiconductor Nanocrystal Surfaces
The adaptation of colloidal semiconductor nanocrystals (NCs) in applications like displays, photovoltaics, and photocatalysis relies primarily on the core electronic structure of NC materials that give rise to desirable optoelectronic properties like broad absorption and size-tunable emission. However, reduction or oxidation events at localized NC surface sites can greatly affect sample stability and device efficiencies by contributing to NC degradation and carrier trapping. Understanding the local composition, structure, and electrochemical potentials of redox-active NC surface sites continues to present a challenge. In this perspective, we discuss how NC surface reduction, oxidation, and electrostatics contribute to NC electronic properties that include photoluminescence quenching or brightening and shifts in NC band edge potentials, among others. Recent efforts toward combining spectroscopic, electrochemical, and computational methods to characterize redox-active surface sites and trap states are highlighted, including developing methods in the field and future opportunities.
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- Award ID(s):
- 2154948
- PAR ID:
- 10410283
- Date Published:
- Journal Name:
- Chemistry of Materials
- ISSN:
- 0897-4756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.chemmater.3c00481
