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Multiscale interfacial engineering of heterogeneous electrocatalysts: From structural design to mechanistic study
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In a typical heterogeneous electrocatalytic reaction, for the given active sites, the electronic structure plays a determining role in electron transfer between the active sites and reactant molecules, which impacts the reaction efficiency. Besides the electronic properties of the electrocatalysts, the reaction interface at which the charge transfer occurs plays an important role in the reaction kinetics. Moreover, the accessibility of the active sites to the reactant molecules also affects the reaction efficiency. However, a well-balanced effective strategy for electronic structure optimization that improves not only the activity but also stability and cost-effectiveness is needed. Besides, a robust model specifically tailored to investigate the kinetics of the electrocatalytic reaction is required to exclude the interference of thermodynamic factors. A feasible characterization technique for probing the complex interfacial process is also required.

 

To address these remaining challenges in the three aspects above, this thesis proposed the strategies to optimize the electrocatalytic reaction processes as follows:

 

(1) Tuning the electronic structure of the active sites by engineering coordination environment and introducing strain effect. Specifically, Ni single atom was constructed to engineer the coordination environment, and the electrocatalytic performance with the tuned electronic structure was examined towards hydrazine oxidation reaction. The strain effect was created by introducing Cu single atom to BiOCl substrate, and the optimized electronic structure was investigated;

(2) Optimizing the interfacial HER kinetics targeted by proposing a specific Pt model catalyst with a channel-opening modifier. The interfacial water structure was studied by in situ surface-enhanced Raman technique, and the role of this promoting modifier was elucidated by ab initio molecular dynamic simulation;

(3) Improving the local concentration of CO2 for electrochemical CO2 reduction reaction with a poly(ionic liquid) modifier, with Au as the model catalyst and the targeted characterization techniques.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University , 2024. , p. 71
Keywords [en]
heterogeneous electrocatalysis, electronic structure, coordination environment, single-atom catalysts, strain effect, hydrogen evolution reaction kinetics, charge transfer, electrochemical CO^2 reduction, local enrichment
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-225784ISBN: 978-91-8014-647-0 (print)ISBN: 978-91-8014-648-7 (electronic)OAI: oai:DiVA.org:su-225784DiVA, id: diva2:1830264
Public defence
2024-03-06, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2024-02-12 Created: 2024-01-22 Last updated: 2024-02-02Bibliographically approved
List of papers
1. Vacancy-Rich MXene-Immobilized Ni Single Atoms as a High-Performance Electrocatalyst for the Hydrazine Oxidation Reaction
Open this publication in new window or tab >>Vacancy-Rich MXene-Immobilized Ni Single Atoms as a High-Performance Electrocatalyst for the Hydrazine Oxidation Reaction
Show others...
2022 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 34, no 36, article id 2204388Article in journal (Refereed) Published
Abstract [en]

Single-atom catalysts (SACs), on account of their outstanding catalytic potential, are currently emerging as high-performance materials in the field of heterogeneous catalysis. Constructing a strong interaction between the single atom and its supporting matrix plays a pivotal role. Herein, Ti3C2Tx-MXene-supported Ni SACs are reported by using a self-reduction strategy via the assistance of rich Ti vacancies on the Ti3C2Tx MXene surface, which act as the trap and anchor sites for individual Ni atoms. The constructed Ni SACs supported by the Ti3C2Tx MXene (Ni SACs/Ti3C2Tx ) show an ultralow onset potential of −0.03 V (vs reversible hydrogen electrode (RHE)) and an exceptional operational stability toward the hydrazine oxidation reaction (HzOR). Density functional theory calculations suggest a strong coupling of the Ni single atoms and their surrounding C atoms, which optimizes the electronic density of states, increasing the adsorption energy and decreasing the reaction activation energy, thus boosting the electrochemical activity. The results presented here will encourage a wider pursuit of 2D-materials-supported SACs designed by a vacancy-trapping strategy. 

Keywords
electronic density of states, hydrazine oxidation reaction, Ni single-atom electrocatalysts, Ti vacancies, Ti3C2Tx MXene
National Category
Materials Engineering Chemical Sciences
Identifiers
urn:nbn:se:su:diva-209778 (URN)10.1002/adma.202204388 (DOI)000837009000001 ()35839429 (PubMedID)2-s2.0-85135530791 (Scopus ID)
Available from: 2022-09-30 Created: 2022-09-30 Last updated: 2024-01-22Bibliographically approved
2. Singly Dispersed Copper Atoms with Compressive Residual Strain for Superior Photocatalytic Diluted CO2 Reduction
Open this publication in new window or tab >>Singly Dispersed Copper Atoms with Compressive Residual Strain for Superior Photocatalytic Diluted CO2 Reduction
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Solar-driven diluted CO2 reduction is an alternative way to realize carbon neutrality, although promoting the photo-reactivity and selectivity in low CO2 contents remains a great challenge. Herein, an atomically dispersed Cu catalyst in a compressive strained BiOCl substrate (Cu1-BOC-CRS) is identified as a promising photocatalyst for diluted CO2 reduction reaction, capable of producing CO without any sacrificial agents or sensitizers. The single Cu atoms and the local surface strain facilitate CO2 adsorption, resulting in impressive CO formation rates of 122 and 99 μmol g-1 h-1 respectively under pure and diluted CO2 conditions. Experimental investigations revealed that the occupation of single Cu atoms in the BiOCl extends the light absorbance and charge transfer, which in turn integrates the surface CO2 capture and conversion. Moreover, the compressive strain provides an extra low-energy route towards CO2-to-CO conversion, offering valuable insights for the future design of highly efficient photocatalysts for diluted CO2 reduction.

Keywords
Single atomic Cu, Strain, Diluted CO2 reduction, Photocatalysis, Energy conversion
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-225775 (URN)
Available from: 2024-01-22 Created: 2024-01-22 Last updated: 2024-02-26Bibliographically approved
3. Engineering interfacial hydrogen-bond network via cage-enabled soft confinement of Pt for facilitated hydrogen evolution kinetics
Open this publication in new window or tab >>Engineering interfacial hydrogen-bond network via cage-enabled soft confinement of Pt for facilitated hydrogen evolution kinetics
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The sluggish HER kinetics under alkaline conditions largely limit the development of alkaline water electrolysis. Decades of efforts have been reported to elucidate the origin of the pH dependence of HER kinetics and facilitate the alkaline HER kinetics. Apart from the widely concerned thermodynamic factors, the electrode process also depends unignorably on the kinetics of the electrochemical interface. Herein, we presented the facilitated HER kinetics by introducing porous amine cage-enabled confinement to Ptcatalyst to engineer the interface between the Pt surface and the aqueous electrolyte. In situ electrochemical surface-enhanced Raman spectra (SERS) measurements and ab initio molecular dynamics (AIMD) simulation jointly unveiled the fundamental interfacial interaction between water and cage that its -NH- moiety largely reduces the rigidity of the net of interfacial water H-bonds at negative HER potentials, which makes the net flexible enough to reorganize for better charge transfer. Our in-depth investigation pinpointed that the -NH- moiety acted as a proton pump and generated hydroxide transfer by forming and breaking H-bonds with interfacial water, refreshing the reactive water layer on the Pt surface. Our results address the crucial role of controllable interfacial kinetics during electrocatalytic reactions, and our strategy of establishing a soft-confining interfacial regulator offers a promising roadmap for manipulating electrocatalytic interfacial kinetics.

Keywords
Hydrogen evolution kinetics, porous organic cage, charge transfer, in situ Raman, ab initio molecular dynamics
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-225776 (URN)
Funder
Knut and Alice Wallenberg Foundation, KAW 2022.0194Stockholm University, SU FV-2.1.1-005
Available from: 2024-01-22 Created: 2024-01-22 Last updated: 2024-02-26Bibliographically approved
4. CO2-philic poly(ionic liquid)-assisted local enrichment strategy for enhancedelectrochemical CO2 reduction
Open this publication in new window or tab >>CO2-philic poly(ionic liquid)-assisted local enrichment strategy for enhancedelectrochemical CO2 reduction
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Electrochemical CO2 reduction reaction (ECO2RR) to produce valuable chemicals and fuels is a promising way to make use of excessive CO2 as one of the major green-house gases debatably responsible for climate change. The chemically inert feature of CO2 molecules makes the first-step elementary reaction with one electron reduction challenging in thermodynamics, leading to a high overpotential for this step and the overall ECO2RR as well. Herein, we reported the successful fabrication of CO2-philic PIL-modified Au model catalyst with enhanced ECO2RR performance by a local CO2 enrichment strategy. The modified gas diffusion electrode exhibited ~ 100% Faradaic efficiency for CO2-to-CO conversion (FECO) in a wide potential window of -0.2 ~ -1.0 V (versus reversible hydrogen electrode. RHE) with pure CO2 feeding, and notablymaintained the FECO > 90% even at a low CO2 concentration of 20 % vol..

Keywords
electrochemical CO2 reduction, poly(ionic liquid), local environment, low-concentration CO2
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-225779 (URN)
Available from: 2024-01-22 Created: 2024-01-22 Last updated: 2024-02-26Bibliographically approved

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