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Engineering inorganic nanostructured composites for boosting H2 and O2 evolution reactions
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0001-6039-1865
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydrogen is considered a promising energy source with zero emission of CO2; it can provide higher energy density compared to other sources of energy. The amount at which H2 is produced, and the method of production need further improvement for the advancement of hydrogen energy technologies. Water electrolysis using renewable energy sources such as electrical, solar, and wind energy is one of the alternative technologies that can produce pure H2. However, water electrolysis itself is not an easy process, it requires a highly active catalyst capable of converting water into hydrogen, and oxygen.

This Ph.D. dissertation mainly focuses on developing efficient, robust, and low-cost catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and Oxygen reduction reaction (ORR). The work describes different strategies for improving the performance of the catalyst, such as creating nanocomposite, Nobel metal decoration, core-shell structures, hierarchical nanostructure, and cocatalyst and protective layers, which are vital for improving the efficiency of the catalyst. Consequently :

Nanocomposites composed of Ag2S nanoparticle, MoS2, and reduced graphene oxide (RGO) flake, with a 0D/2D/2D interface were synthesized. Ag2S nanoparticles were homogeneously distributed and embedded in a layer of semi-crystalline MoS2 nanosheets. The ternary catalyst results in a superior performance due to the intimate contact created by the 2D-2D interface (MoS2/RGO) and due to the uniformly grown Ag2S nanoparticles, which provides the ease of hydrogen adsorption by modulating the electronic properties, and exposure of highly rich active sites

Nobel metal decorated (Ag-decorated vertically aligned MoS2 nanoflakes) were developed and investigated for OER and ORR. Results of this work revealed that, due to the presence of silver, the catalyst shows more than 1.5 times an increase in the roughness-normalized rate of OER. Based on the rate constant values obtained during the ORR test, Ag-MoS2 proceeds through a mixed 4 electron and a 2 + 2 serial route reduction mechanism, suggesting that the presence of silver decreases the electron transfer number and increases the peroxide yield. 

A core-shell structure of hydrous NiMoO4 micro rods conformally covered by Co3O4 nanoparticles was developed and employed as an OER catalyst, showing a remarkable catalytic activity towards OER with a record low overpotential of 120 mV at 10 mA/cm2. Here, the strong interactions between core (hydrated NiMoO4) and shell (Co3O4) help to tune the electronic properties by modifying the active sites densities of the surface.

A hierarchical nanostructure composed of NiMoO4 nanorods and MoS2 nanosheets was synthesized on interconnected nickel foam substrates. The as-prepared hierarchical structure exhibits excellent OER performance due to its numerous exposed active sites for adsorbing oxygen intermediates which are beneficial for promoting the enhancement of the OER catalytic performance

Cu2O photocathode protected by a very thin layer of TiO2 and an amorphous Vox were synthesized and used for HER, with aim of improving the photostability of Cu2O. Photooxidation of Cu2O nanowires are minimized by growing TiO2 protective layer and an amorphous VOx cocatalyst. After optimization of the overlayer and the cocatalyst, the photoelectrode exhibits a stable photocurrent density for an extended illumination time. 

Besides, advanced characterization tools were used for tracking ORR reaction intermediates and OER active sites. RRDE, Operando Raman, and synchrotron-based photoemission spectroscopy analysis were utilized together with Post OER characterization tools to reveal the reason behind the higher catalytic activity of the catalyst. 

In summary, the presented outcomes can significantly contribute to the fundamental insight towards improving the efficiency of HER, OER, and ORR catalyst, by offering a clear and in-depth understanding of the preparation and characterization of cheap and efficient catalysts.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords [en]
Hydrogen evolution(HER), Oxygen evolution reaction (OER), Oxygen reduction reaction (ORR), Water splitting, Electrocatalyst, Atomic layer deposition, Core-shell structure
National Category
Materials Chemistry Composite Science and Engineering
Research subject
Experimental Physics
Identifiers
URN: urn:nbn:se:ltu:diva-88432ISBN: 978-91-8048-007-9 (print)ISBN: 978-91-8048-008-6 (electronic)OAI: oai:DiVA.org:ltu-88432DiVA, id: diva2:1627738
Public defence
2022-04-05, E632, Laboratorievägen 14, Luleå, 14:00 (English)
Opponent
Supervisors
Available from: 2022-01-17 Created: 2022-01-14 Last updated: 2022-03-02Bibliographically approved
List of papers
1. Ag2S/MoS2 Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution Reaction
Open this publication in new window or tab >>Ag2S/MoS2 Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution Reaction
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2019 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 25, p. 22380-22389Article in journal (Refereed) Published
Abstract [en]

Hydrogen evolution reaction through electrolysis holds great potential as a clean, renewable, and sustainable energy source. Platinum-based catalysts are the most efficient to catalyze and convert water into molecular hydrogen; however, their large-scale application is prevented by scarcity and cost of Pt. In this work, we propose a new ternary composite of Ag2S, MoS2, and reduced graphene oxide (RGO) flakes via a one-pot synthesis. The RGO support assists the growth of two-dimensional MoS2 nanosheets partially covered by silver sulfides as revealed by high-resolution transmission electron microscopy. Compared with the bare MoS2 and MoS2/RGO, the Ag2S/MoS2 anchored on the RGO surface (the ternary system Ag2S/MoS2/RGO) demonstrated a high catalytic activity toward hydrogen evolution reaction (HER). Its superior electrochemical activity toward HER is evidenced by the positively shifted (−190 mV vs reversible hydrogen electrode (RHE)) overpotential at a current density of −10 mA/cm2 and a small Tafel slope (56 mV/dec) compared with a bare and binary system. The Ag2S/MoS2/RGO ternary catalyst at an overpotential of −200 mV demonstrated a turnover frequency equal to 0.38 s–1. Electrochemical impedance spectroscopy was applied to understand the charge-transfer resistance; the ternary sample shows a very small charge-transfer resistance (98 Ω) at −155 mV vs RHE. Such a large improvement can be attributed to the synergistic effect resulting from the enhanced active site density of both sulfides and to the improved electrical conductivity at the interfaces between MoS2 and Ag2S. This ternary catalyst opens up further optimization strategies to design a stable and cheap catalyst for hydrogen evolution reaction, which holds great promise for the development of a clean energy landscape.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
electrocatalyst, hydrogen evolution, silver sulfide, molybdenum sulfide, reduced graphene oxide
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-75551 (URN)10.1021/acsami.9b05086 (DOI)000473251100036 ()31145582 (PubMedID)2-s2.0-85068008830 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-16 (johcin)

Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2022-01-14Bibliographically approved
2. Decorating vertically aligned MoS2 nanoflakes with silver nanoparticles for inducing a bifunctional electrocatalyst towards oxygen evolution and oxygen reduction reaction
Open this publication in new window or tab >>Decorating vertically aligned MoS2 nanoflakes with silver nanoparticles for inducing a bifunctional electrocatalyst towards oxygen evolution and oxygen reduction reaction
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2021 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 81, article id 105664Article in journal (Refereed) Published
Abstract [en]

Catalysts capable of improving the performance of oxygen evolution reaction (OER) and oxygen reduction reactions (ORR) are essential for the advancement of renewable energy technologies. Herein, Ag-decorated vertically aligned MoS2 nanoflakes are developed via magnetron co-sputtering and investigated as electrocatalyst towards OER and ORR. Due to the presence of silver, the catalyst shows more than 1.5 times an increase in the roughness-normalized rate of OER, featuring a very low Tafel slope (58.6 mv dec−1), thus suggesting that the catalyst surface favors the thermodynamics of hydroxyl radical (OH•) adsorption with the deprotonation steps being the rate-determining steps. The improved performance is attributed to the strong interactions between OOH intermediates and the Ag surface which reduces the activation energy. Rotating ring disk electrode (RRDE) analysis shows that the net disk currents on the Ag-MoS2 sample are two times higher at 0.65 V compared to MoS2, demonstrating the co-catalysis effect of silver doping. Based on the rate constant values, Ag-MoS2 proceeds through a mixed 4 electron and a 2 + 2 serial route reduction mechanism, in which the ionized hydrogen peroxide is formed as a mobile intermediate. The presence of silver decreases the electron transfer number and increases the peroxide yield due to the interplay of a 2 + 2 electron reduction pathway. A 2.5–6 times faster conversion rate of peroxide to OH- observed due to the presence of silver, indicating its effective cocatalyst nature. This strategy can help in designing a highly active bifunctional catalyst that has great potential as a viable alternative to precious-metal-based catalysts.Graphica

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Oxygen evolution reaction (OER), Oxygen reduction reaction (ORR), Electrocatalys, tBifunctional catalyst, Magnetron co-sputtering
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-82322 (URN)10.1016/j.nanoen.2020.105664 (DOI)000620327900002 ()2-s2.0-85098781620 (Scopus ID)
Funder
Vinnova, 2015-01513Knut and Alice Wallenberg FoundationEU, Horizon 2020, 654002, 785219The Kempe FoundationsLuleå University of TechnologySwedish Research Council, 2019-05577
Note

Validerad;2021;Nivå 2;2021-01-12 (alebob);

Finansiär: MIUR-PON TARANTO (ARS01_00637)

Available from: 2021-01-12 Created: 2021-01-12 Last updated: 2022-01-14Bibliographically approved
3. NiMoO4@Co3O4 Core–Shell Nanorods: In Situ Catalyst Reconstruction toward High Efficiency Oxygen Evolution Reaction
Open this publication in new window or tab >>NiMoO4@Co3O4 Core–Shell Nanorods: In Situ Catalyst Reconstruction toward High Efficiency Oxygen Evolution Reaction
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2021 (English)In: Advanced Energy Materials, ISSN 1614-6832, E-ISSN 1614-6840, Vol. 11, no 32, article id 2101324Article in journal (Refereed) Published
Abstract [en]

The sluggish kinetics of the oxygen evolution reaction (OER) is the bottleneck for the practical exploitation of water splitting. Here, the potential of a core–shell structure of hydrous NiMoO4 microrods conformally covered by Co3O4 nanoparticles via atomic layer depositions is demonstrated. In situ Raman and synchrotron-based photoemission spectroscopy analysis confirms the leaching out of Mo facilitates the catalyst reconstruction, and it is one of the centers of active sites responsible for higher catalytic activity. Post OER characterization indicates that the leaching of Mo from the crystal structure, induces the surface of the catalyst to become porous and rougher, hence facilitating the penetration of the electrolyte. The presence of Co3O4 improves the onset potential of the hydrated catalyst due to its higher conductivity, confirmed by the shift in the Fermi level of the heterostructure. In particular NiMoO4@Co3O4 shows a record low overpotential of 120 mV at a current density of 10 mA cm−2, sustaining a remarkable performance operating at a constant current density of 10, 50, and 100 mA cm−2 with negligible decay. Presented outcomes can significantly contribute to the practical use of the water-splitting process, by offering a clear and in-depth understanding of the preparation of a robust and efficient catalyst for water-splitting.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2021
National Category
Physical Chemistry
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-86472 (URN)10.1002/aenm.202101324 (DOI)000673277700001 ()2-s2.0-85110046238 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationEU, Horizon 2020, 654002The Kempe FoundationsVinnova, 2015-01513EU, Horizon 2020, 20205170
Note

Validerad;2021;Nivå 2;2021-09-01 (johcin);

Finansiärer:Swedish foundation consolidator fellowship; Luleå University of Technology laboratory fund program; EUROFEL-ROADMAP ESFRI

Available from: 2021-07-27 Created: 2021-07-27 Last updated: 2022-01-14Bibliographically approved
4. MoS2 Nanosheets Uniformly Anchored on NiMoO4 Nanorods, a Highly Active Hierarchical Nanostructure Catalyst for Oxygen Evolution Reaction and Pseudo-Capacitors
Open this publication in new window or tab >>MoS2 Nanosheets Uniformly Anchored on NiMoO4 Nanorods, a Highly Active Hierarchical Nanostructure Catalyst for Oxygen Evolution Reaction and Pseudo-Capacitors
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2023 (English)In: Advanced sustainable systems, E-ISSN 2366-7486, Vol. 7, no 2, article id 2200410Article in journal (Refereed) Published
Abstract [en]

Hierarchical nanostructures have attracted considerable research attention due to their applications in the catalysis field. Herein, we design a versatile hierarchical nanostructure composed of NiMoO4 nanorods surrounded by active MoS2 nanosheets on an interconnected nickel foam substrate. The as-prepared nanostructure exhibits excellent oxygen evolution reaction performance, producing a current density of 10 mA cm−2 at an overpotential of 90 mV, in comparison with 220 mV necessary to reach a similar current density for NiMoO4. This behavior originates from the structural/morphological properties of the MoS2 nanosheets, which present numerous surface-active sites and allow good contact with the electrolyte. Besides, the structures can effectively store charges, due to their unique branched network providing accessible active surface area, which facilitates intermediates adsorptions. Particularly, NiMoO4/MoS2 shows a charge capacity of 358 mAhg−1 at a current of 0.5 A g−1 (230 mAhg−1 for NiMoO4), thus suggesting promising applications for charge-storing devices.

Place, publisher, year, edition, pages
John Wiley & Sons, 2023
Keywords
electrocatalysts, hierarchical nanostructures, hydrous catalysts, magnetron sputtering, oxygen evolution reaction, pseudo capacitors, water splitting
National Category
Energy Engineering Materials Chemistry
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-88421 (URN)10.1002/adsu.202200410 (DOI)000894620200001 ()2-s2.0-85144090100 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationEU, Horizon 2020, 654002Luleå University of TechnologyThe Kempe Foundations
Note

Validerad;2023;Nivå 2;2023-03-03 (hanlid);

Funder: European Commission Graphene Flagship Core3 (881603); EUROFEL-ROADMAP ESFRI;

This article has previously appeared as a manuscript in a thesis.

Available from: 2021-12-15 Created: 2021-12-15 Last updated: 2024-03-27Bibliographically approved
5. Improving the photostability of Cu2O photoelectrode using TiO2 protection layer and amorphous V2 O5 cocatalyst
Open this publication in new window or tab >>Improving the photostability of Cu2O photoelectrode using TiO2 protection layer and amorphous V2 O5 cocatalyst
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(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

Hydrogen fuel generation using solar energy is one of the sustainable and environmentally friendly methods. Here we utilize a Cu2O-based photocathode protected by a very thin layer of TiO2 and an amorphous VOx for the hydrogen evolution reaction (HER).  Cu2O photoelectrode has a favorable energy band position for HER. However, the main challenges that hinder its application are its poor photostability, due to its oxidation into CuO by photoexcited holes. Here we carefully minimize the photooxidation of Cu2O nanowires by growing a thin (40 nm) TiO2 protective layer and an amorphous VOx cocatalyst using magnetron sputtering and atomic layer deposition (ALD) respectively. After optimization of the overlayer and the cocatalyst, the photoelectrode exhibits a current density of -2.46 mA/cm2 under light at 0.3V vs RHE and its performance is stable for an extended illumination time. Moreover, the chemical stability of the photoelectrode improved, suggesting that the method demonstrates the potential of using earth-abundant Cu2O based materials as a light-harvesting device for solar hydrogen production.

National Category
Energy Engineering
Research subject
Renewable energy (AERI)
Identifiers
urn:nbn:se:ltu:diva-88430 (URN)
Available from: 2021-12-15 Created: 2021-12-15 Last updated: 2022-01-14

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