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  • 1.
    Gilzad Kohan, Mojtaba
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solomon, Getachew
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    You, Shujie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yusupov, Khabib
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, Venezia, Mestre, 30172 Italy.
    Vertically aligned Co3O4 nanorods as a platform for inverted all‐oxide heterojunctions2021In: Nano Select, E-ISSN 2688-4011, Vol. 2, no 5, p. 967-978Article in journal (Refereed)
    Abstract [en]

    Direct stacking of n‐type and p‐type metal oxide (MOx) semiconductors is one of the appealing directions toward low cost and environmentally friendly photovoltaics (PVs). However, the main shortcoming, hindering the PV performance of MOx heterojunction devices is attributed to the tradeoff between light absorption and maximized carrier extraction in p‐type MOx. In this work, we demonstrate that the nanorod (NR) geometry of Co3O4 light absorber with a nearly ideal bandgap of ∼1.48 eV, can remove this hurdle through strong internal light trapping of adjacent one‐dimensional (1D) structure and enhanced carrier mobility. The inverted n‐on‐p configuration of the core‐shell 1D heterojunction, obtained by depositing a thin TiO2 n‐type layer, resulted in enlarged charge generation compared to the typical p‐on‐n counterpart device. Fine‐tuning of Co3O4 NRs length, permits PV investigation of the heterojunctions with respect to absorber layers thickness. The optimized Co3O4 NRs/TiO2 heterojunction (30 nm Co3O4 NR length) presented a record high open circuit photovoltage (Voc) of (0.52 ± 0.03) V under 1 sun irradiation. Impedance analysis of the heterojunctions, indicates formation of the p+‐p depletion. The presented work can highlight some vital venues to enhance photoconversion efficiency of the all‐oxide heterojunctions while introducing a pioneer contender as inverted (n‐on‐p) MOx heterojunction.

  • 2.
    Landström, Anton
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solomon, Getachew
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rotta Loria, Silvia
    Zavelani Rossi, Margherita
    Mezzi, Alessio
    Kaciulis, Saulius
    Protti, Stefano
    Mezzetti, Alberto
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chemisorption of 3-hydroxyflavone Onto TiO2 Nanoparticles: Optical and Charge Transfer PropertiesManuscript (preprint) (Other academic)
    Abstract [en]

    3-hydroxyflavone (3HF) is chemisorbed on TiO2 nanoparticle films with an Al2O3 interlayer through a facile dip coating process. The films are characterized with UV-Vis and IR absorption spectroscopy, fluorescence spectroscopy, energy-dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The 3HF adduct is shown to bond to the substrate through the carbonyl group, resulting in a bathochromic shift in its absorption spectra similar to that observed in 3HF-metal chelates. The emission spectrum is quenched in the case of adsorption on TiO2, but strongly enhanced in the case of Al2O3, with a quantum yield (9.3%) exceeding that of uncoordinated 3HF in acetonitrile.

  • 3.
    Shifa, Tofik Ahmed
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yusupov, Khabib
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solomon, Getachew
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gradone, Alessandro
    CNR-IMM Bologna Section, Via Piero Gobetti 101, 40129 Bologna, Italy; Chemistry Department “Giacomo Ciamician”, University of Bologna, Via Selmi 2, 40126 Bologna, Italy.
    Mazzaro, Raffaello
    CNR-IMM Bologna Section, Via Piero Gobetti 101, 40129 Bologna, Italy.
    Cattaruzza, Elti
    Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Mes-tre, 30172 Venezia, Italy.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Mes-tre, 30172 Venezia, Italy.
    In Situ-Generated Oxide in Sn-Doped Nickel Phosphide Enables Ultrafast Oxygen Evolution2021In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 11, no 8, p. 4520-4529Article in journal (Refereed)
    Abstract [en]

    Water splitting is considered one of the most promising approaches to power the globe without the risk of environmental pollution. The oxygen evolution reaction (OER) is even more challenging because the generation of only one oxygen molecule involves the transfer of four e and removal of four H+ ions from water. Thus, developing highly efficient catalysts to meet industrial requirements remains a focus of attention. Herein, the prominent role of Sn in accelerating the electron transfer kinetics of Ni5P4 nanosheets in OER is reported. The post catalytic survey elucidates that the electrochemically induced Ni–Sn oxides at the vicinity of phosphides are responsible for the observed catalytic activity, delivering current densities of 10, 30, and 100 mA cm–2 at overpotentials of only 173 ± 5.2, 200 ±7.4, and 310 ± 5.5 mV, respectively. The density functional theory calculation also supports the experimental findings from the basis of the difference observed in density of states at the Fermi level in the presence/absence of Sn. This work underscores the role of Sn in OER and opens a promising avenue toward practical implementation of hydrogen production through water splitting and other catalytic reactions. 

  • 4.
    Solomon, Getachew
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Engineering inorganic nanostructured composites for boosting H2 and O2 evolution reactions2022Doctoral 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.

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  • 5.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gilzad Kohan, Mojtaba
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mazzaro, Raffaello
    Istituto di Microelettronica e Microsistemi-CNR (CNR, IMM), Via Piero Gobetti 101, Bologna, 40129 Italy; Department of Physics and Astronomy, University of Bologna, Via Berti Pichat 6/2, Bologna, 40129 Italy.
    Jugovac, Matteo
    Elettra Sincrotrone Trieste, SS 14 Km 163,5, Trieste, 34149 Italy.
    Moras, Paolo
    Istituto di Struttura della Materia-CNR (ISM-CNR), SS 14, Km 163.5, Trieste, 34149 Italy.
    Morandi, Vittorio
    Istituto di Microelettronica e Microsistemi-CNR (CNR, IMM), Via Piero Gobetti 101, Bologna, 40129 Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, Bologna, 30172 Italy.
    MoS2 Nanosheets Uniformly Anchored on NiMoO4 Nanorods, a Highly Active Hierarchical Nanostructure Catalyst for Oxygen Evolution Reaction and Pseudo-Capacitors2023In: Advanced sustainable systems, E-ISSN 2366-7486, Vol. 7, no 2, article id 2200410Article in journal (Refereed)
    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.

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  • 6.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gilzad Kohan, Mojtaba
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vagin, Mikhail
    Department of Science and Technology, Laboratory of Organic Electronics, Linköping University, SE-601 74 Norrköping, Sweden.
    Rigoni, Federica
    Department of Molecular Sciences and Nanosystems, Ca’Foscari University of Venice, Via Torino 155, 30172 Venezia Mestre, Italy.
    Mazzaro, Raffaello
    CNR-Institute of Microelectronics and Microsystem (IMM), Section of Bologna Via Piero Gobetti 101, Bologna 40129, Italy.
    Natile, Marta Maria
    Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE), National Research Council (CNR) and Department of Chemical Sciences, University of Padova, Via Francesco Marzolo, 1, 35131 Padova PD, Italy.
    You, Shujie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Morandi, Vittorio
    CNR-Institute of Microelectronics and Microsystem (IMM), Section of Bologna Via Piero Gobetti 101, Bologna 40129, Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’Foscari University of Venice, Via Torino 155, 30172 Venezia Mestre, Italy.
    Decorating vertically aligned MoS2 nanoflakes with silver nanoparticles for inducing a bifunctional electrocatalyst towards oxygen evolution and oxygen reduction reaction2021In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 81, article id 105664Article in journal (Refereed)
    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

  • 7.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kohan, Mojtaba Gilzad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Landström, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, via Torino 155, 30170 Venezia Mestre, Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Semiconducting metal oxides empowered by graphene and its derivatives: Progresses and critical perspective on selected functional applications2020In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 128, no 18, article id 180905Article, review/survey (Refereed)
    Abstract [en]

    This Perspective presents and discusses the most recent advancements in the field of exploitation of hybrid nanostructured composites consisting of semiconducting metal oxides and graphene and its derivatives (graphene oxide, reduced graphene oxide, graphene quantum dots, and carbon nanotubes) in specific fields of applications, namely, photovoltaics, water splitting, photocatalysis, and supercapacitors. These hybrid materials have received remarkable attention over the last decade thanks to claimed outstanding functional optoelectronic properties, especially as for (photogenerated) charge carriers storage and transport, allowing the promotion of useful reactions and enhancement of the efficiency of several processes based on charge exchange. In situ and ex situ synthetic strategies have been applied in order to optimize the contact between the two partners and efforts have as well been devoted to investigate the best amount of carbon material to insert in the semiconductor scaffold. We provide the reader with an overview of the research carried out in the last decade, together with a critical analysis of the claimed benefits provided by the carbon materials, also highlighting the current questions waiting for the scientific community to provide an answer to.

  • 8.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Landström, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mazzaro, Raffaello
    Istituto di Microelettronica e Microsistemi-CNR (CNR, IMM), Via Piero Gobetti 101, Bologna, 95121 Italy.
    Jugovac, Matteo
    Istituto di Struttura della Materia-CNR (ISM-CNR), SS 14 Km 163,5, Trieste, 34149 Italy.
    Moras, Paolo
    Istituto di Struttura della Materia-CNR (ISM-CNR), SS 14 Km 163,5, Trieste, 34149 Italy.
    Cattaruzza, Elti
    Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, 30172 Italy.
    Morandi, Vittorio
    Istituto di Microelettronica e Microsistemi-CNR (CNR, IMM), Via Piero Gobetti 101, Bologna, 95121 Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, Venezia Mestre, 30172 Italy.
    NiMoO4@Co3O4 Core–Shell Nanorods: In Situ Catalyst Reconstruction toward High Efficiency Oxygen Evolution Reaction2021In: Advanced Energy Materials, ISSN 1614-6832, E-ISSN 1614-6840, Vol. 11, no 32, article id 2101324Article in journal (Refereed)
    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.

  • 9.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Landström, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rotta Loria, Silvia
    Dipartimento di Fisica, Politecnico di Milano, piazza L. da Vinci 32, 20133 Milano, Italy.
    Bolli, Eleonora
    Institute for the Study of Nanostructured Materials, ISMN-CNR, 00015 Monterotondo Stazione, Roma, Italy.
    Mezzetti, Alberto
    Laboratoire de Réactivité de Surface (LRS), Sorbonne Université, CNRS, 4 Place Jussieu, Paris 75005, France.
    Facibeni, Anna
    Dipartimento di Energia, Politecnico di Milano, via G. Ponzio 34/3, 20133 Milano, Italy; IFN-CNR, piazza L. da Vinci 32, 20133 Milano, Italy.
    Cattarin, Sandro
    Istituto di Chimica della Materia Condensata e di Tecnologie per l'Energia, ICMATE-CNR, C.so Stati Uniti 4, 35127, Padova, Italy.
    Mezzi, Alessio
    Institute for the Study of Nanostructured Materials, ISMN-CNR, 00015 Monterotondo Stazione, Roma, Italy.
    Protti, Stefano
    Photogreen Lab, Department of Chemistry, University of Pavia, Viale Taramelli 10, 27100 Pavia, Italy.
    Kaciulis, Saulius
    Institute for the Study of Nanostructured Materials, ISMN-CNR, 00015 Monterotondo Stazione, Roma, Italy.
    Zavelani-Rossi, Margherita
    Dipartimento di Energia, Politecnico di Milano, via G. Ponzio 34/3, 20133 Milano, Italy; IFN-CNR, piazza L. da Vinci 32, 20133 Milano, Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tunable physics through coordination chemistry: formation on oxide surface of Ti and Al chelates with 3-hydroxyflavone capable of electron injection and light emission2022In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 51, no 48, p. 18489-18501Article in journal (Refereed)
    Abstract [en]

    The optoelectronic features of 3-hydroxyflavone (3HF) self-assembled on the surface of an n-type semiconducting metal oxide (TiO2) and an insulator (Al2O3) are herein investigated. 3HF molecules use the coordinatively unsaturated metal ions present on the oxide surface to form metal complexes, which exhibit different behaviors upon light irradiation, depending on the nature of the metal ion. Specifically, we show that the photoluminescence of the surface species can be modulated according to the chemical properties of the complex (i.e. the binding metal ion), resulting in solid-state emitters in a high quantum yield (about 15%). Furthermore, photoinduced charge injection can be promoted or inhibited, providing a multifunctional hybrid system.

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  • 10.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lecca, Marco
    Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE) National Research Council (CNR) and Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, Padova 35131, Italy.
    Bisetto, Matteo
    Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE) National Research Council (CNR) and Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, Padova 35131, Italy.
    Gilzad Kohan, Mojtaba
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Natile, Marta Maria
    Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE) National Research Council (CNR) and Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, Padova 35131, Italy.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Molecular Sciences and Nanosystems, Ca' Foscari University of Venice, Via Torino 155, Venezia Mestre 30172, Italy.
    Engineering Cu2O Nanowire Surfaces for Photoelectrochemical Hydrogen Evolution Reaction2023In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 6, no 2, p. 832-840Article in journal (Refereed)
    Abstract [en]

    Cu2O is a narrow band gap material serving as an important candidate for photoelectrochemical hydrogen evolution reaction. However, the main challenge that hinders its practical exploitation is its poor photostability, due to its oxidation into CuO by photoexcited holes. Here, we thoroughly minimize the photo-oxidation of Cu2O nanowires by growing a thin layer of the TiO2 protective layer and an amorphous layer of the VOx cocatalyst using magnetron sputtering and atomic layer deposition, respectively. After optimization of the protective and the cocatalyst layers, the photoelectrode exhibits a current density of −2.46 mA/cm2 under simulated sunlight (100 mW/cm2) at 0.3 V versus reversible hydrogen electrode, and its performance is stable for an extended illumination time. The chemical stability and the good performance of the engineered photoelectrode demonstrate the potential of using earth-abundant materials as a light-harvesting device for solar hydrogen production.

  • 11.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lecca, Marco
    Istituto di Chimica della Materia Condensata e Tecnologie per l’Energia, Consiglio Nazionale delle Ricerche (ICMATE-CNR) and Dipartimento di Scienze Chimiche, Universitàdi Padova, 35131 Padova, Italy.
    Gilzad Kohan, Mojtaba
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Natile, Marta Maria
    Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE), National Research Council (CNR) and Department of Chemical Sciences, University of Padova, Via Francesco Marzolo, 1, 35131 Padova PD, Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Improving the photostability of Cu2O photoelectrode using TiO2 protection layer and amorphous V2 O5 cocatalystManuscript (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.

  • 12.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mazzaro, Raffaello
    CNR-Institute of Microelectronics and Microsystem (IMM), Section of Bologna Via Piero Gobetti 101, 40129 Bologna, Italy.
    Morandi, Vittorio
    CNR-Institute of Microelectronics and Microsystem (IMM), Section of Bologna Via Piero Gobetti 101, 40129 Bologna, Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microwave-Assisted vs. Conventional Hydrothermal Synthesis of MoS2 Nanosheets: Application towards Hydrogen Evolution Reaction2020In: Crystals, ISSN 2073-4352, Vol. 10, no 11, article id 1040Article in journal (Refereed)
    Abstract [en]

    Molybdenum sulfide (MoS2) has emerged as a promising catalyst for hydrogen evolution applications. The synthesis method mainly employed is a conventional hydrothermal method. This method requires a longer time compared to other methods such as microwave synthesis methods. There is a lack of comparison of the two synthesis methods in terms of crystal morphology and its electrochemical activities. In this work, MoS2 nanosheets are synthesized using both hydrothermal (HT-MoS2) and advanced microwave methods (MW-MoS2), their crystal morphology, and catalytical efficiency towards hydrogen evolution reaction (HER) were compared. MoS2 nanosheet is obtained using microwave-assisted synthesis in a very short time (30 min) compared to the 24 h hydrothermal synthesis method. Both methods produce thin and aggregated nanosheets. However, the nanosheets synthesized by the microwave method have a less crumpled structure and smoother edges compared to the hydrothermal method. The as-prepared nanosheets are tested and used as a catalyst for hydrogen evolution results in nearly similar electrocatalytic performance. Experimental results showed that: HT-MoS2 displays a current density of 10 mA/cm2 at overpotential (−280 mV) compared to MW-MoS2 which requires −320 mV to produce a similar current density, suggesting that the HT-MoS2 more active towards hydrogen evolutions reaction.

  • 13.
    Solomon, Getachew
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mazzaro, Raffaello
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    You, Shujie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Natile, Marta Maria
    CNR-Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE), Department of Chemical Sciences, University of Padova, Padova , Italy.
    Morandi, Vittorio
    CNR-Institute of Microelectronics and Microsystem (IMM), Bologna, Italy.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ag2S/MoS2 Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution Reaction2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 25, p. 22380-22389Article in journal (Refereed)
    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.

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