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| Naji, M. |
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| Motta, Antonella |
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| Aletan, Dirar |
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| Mohamed, Tarek |
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| Ertürk, Emre |
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| Taccardi, Nicola |
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| Kononenko, Denys |
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| Petrov, R. H. | Madrid |
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| Alshaaer, Mazen | Brussels |
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| Bih, L. |
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| Casati, R. |
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| Muller, Hermance |
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| Kočí, Jan | Prague |
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| Šuljagić, Marija |
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| Kalteremidou, Kalliopi-Artemi | Brussels |
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| Azam, Siraj |
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| Ospanova, Alyiya |
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| Blanpain, Bart |
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| Ali, M. A. |
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| Popa, V. |
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| Rančić, M. |
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| Ollier, Nadège |
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| Azevedo, Nuno Monteiro |
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| Landes, Michael |
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| Rignanese, Gian-Marco |
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Alkhalifah, Mohammed A.
University of Bristol
in Cooperation with on an Cooperation-Score of 37%
Topics
Publications (4/4 displayed)
- 2024Activating Mn Sites by Ni Replacement in α-MnO2citations
- 2024Correlating molecular precursor interactions with device performance in solution-processed Cu2ZnSn(S,Se)4 thin-film solar cellscitations
- 2022Correlating Orbital Composition and Activity of LaMnxNi1-xO3 Nanostructures Towards Oxygen Electrocatalysiscitations
- 2022Correlating Orbital Composition and Activity of LaMnxNi1–xO3 Nanostructures toward Oxygen Electrocatalysiscitations
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article
Activating Mn Sites by Ni Replacement in α-MnO2
Abstract
Transition metal oxides are characterized by an acute structure and composition dependent electrocatalytic activity towards the oxygen evolution (OER) and oxygen reduction (ORR) reactions. For instance, Mn containing oxides are among the most active ORR catalysts, while Ni based compounds tend to show high activity towards the OER in alkaline solutions. In this study, we show that incorporation of Ni into α-MnO2, by adding Ni precursor into the Mn-containing hydrothermal solution, can generate distinctive sites with different electronic configuration and contrasting electrocatalytic activity. The structure and composition of the Ni modified Hollandite α-MnO2 phase were investigated by X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy (TEM-EDX), inductively coupled plasma – optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS). Our analysis suggests that Mn replacement by Ni into the α-MnO2 lattice (site A) occurs up to approximately 5 % of the total Mn content, while further increasing Ni content promotes the nucleation of separate Ni phases (site B). XAS and XRD shows that the introduction of sites A and B have negligible effect on the overall Mn oxidation state and bonding characteristics, while very subtle changes in the XPS spectra appears to suggest changes in the electronic configuration upon Ni incorporation into the α-MnO2 lattice. On the other hand, changes in the electronic structure promoted by site A have a significant impact in the pseudocapacitive responses obtained by cyclic voltammetry in KOH solution at pH 14, revealing the appearance of Mn 3d orbitals at the energy (potential) range relevant to the ORR. The evolution of Mn 3d upon Ni replacement significantly increases the catalytic activity of α-MnO2 towards the ORR. Interestingly, the formation of segregated Ni phases (site B) leads to a decrease in the ORR activity, while increasing OER rate.