Researcher:
Usman, Emre

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Master Student

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Emre

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Usman

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Usman, Emre

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2021 - 20223

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Researcher Of Publications: search.filters.isAuthorOfPublication.f58461e5-140f-43f9-a4a6-f23af5c774c2

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Now showing 1 - 3 of 3
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    Hybrid cufe-cofe Prussian blue catalysts on BIVO4 for enhanced charge separation and injection for photoelectrochemical water oxidation
    (American Chemical Society (ACS), 2022) Vishlaghi, Mahsa Barzgar; Akbari, Sina Sadigh; Karadas, Ferdi; Department of Chemistry; N/A; N/A; Kaya, Sarp; Usman, Emre; Barzgarvishlaghi, Mahsa; Faculty Member; Master Student; PhD Student; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 116541; N/A; N/A
    The utilization of cocatalysts on the photoelectrode surface is a feasible strategy to achieve a high photocurrent density in the photoelectrochemical water oxidation process. The catalysts can enhance the activity by improving the reaction kinetics, retarding charge carrier recombination, or accumulating charge carriers. In this work, we have utilized a CuFe-CoFe Prussian blue (PB) catalyst layer on the BiVO4 photoanode surface to enhance its water oxidation activity. The hybrid catalyst, in which the semiprecious cobalt ions are partially substituted with earth-abundant copper ions, exhibits 56% higher photocurrent density than the CoFe PB-modified BiVO4. We show that photogenerated hole accumulation is present in the CuFe PB layer, which results in higher charge extraction from the BiVO4 surface. The CoFe PB layer on top of the CuFe one facilitates the charge transfer due to its catalytic activity toward the oxygen evolution reaction (OER).
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    Modifying the electron-trapping process at the BiVO4 surface states via the TiO2 overlayer for enhanced water oxidation
    (Amer Chemical Soc, 2021) N/A; N/A; N/A; N/A; Department of Chemistry; Usman, Emre; Barzgarvishlaghi, Mahsa; Kahraman, Abdullah; Solati, Navid; Kaya, Sarp; Master Student; PhD Student; PhD Student; Researcher; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 116541
    BiVO4 is one of the most promising photoanode candidates to achieve high-efficiency water splitting. However, overwhelming charge recombination at the interface limits its water oxidation activity. In this study, we show that the water oxidation activity of the BiVO4 photoanode is significantly boosted by the TiO2 overlayer prepared by atomic layer deposition. With a TiO2 overlayer of an optimized thickness, the photocurrent at 1.23 VRHE increased from 0.64 to 1.1 mA-cm(-2) under front illumination corresponding to 72% enhancement. We attribute this substantial improvement to enhanced charge separation and suppression of surface recombination due to surface-state passivation. We provide direct evidence via transient photocurrent measurements that the TiO2 overlayer significantly decreases the photogenerated electron-trapping process at the BiVO4 surface. Electron-trapping passivation leads to enhanced electron photoconductivity, which results in higher photocurrent enhancement under front illumination rather than back illumination. This feature can be particularly useful for wireless tandem devices for water splitting as the higher band gap photoanodes are typically utilized with front illumination in such configurations. Even though the electron-trapping process is eliminated completely at higher TiO2 overlayer thicknesses, the charge-transfer resistance at the surface also increases significantly, resulting in a diminished photocurrent. We demonstrate that the ultrathin TiO2 overlayer can be used to fine tune the surface properties of BiVO4 and may be used for similar purposes for other photoelectrode systems and other photoelectrocatalytic reactions.
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    The significance of the local structure of cobalt-based catalysts on the photoelectrochemical water oxidation activity of BiVO4
    (Pergamon-Elsevier Science Ltd, 2021) Harfouche, Messaoud; Ogasawara, Hirohito; N/A; N/A; N/A; N/A; N/A; N/A; N/A; Department of Chemistry; Barzgarvishlaghi, Mahsa; Kahraman, Abdullah; Apaydın, Sinem; Usman, Emre; Aksoy, Dilan; Balkan, Timuçin; Munir, Shamsa; Kaya, Sarp; PhD Student; PhD Student; Master Student; Master Student; PhD Student; Other; Researcher; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; N/A; College of Sciences; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; N/A; N/A; N/A; N/A; N/A; N/A; 116541
    The local structures of the water oxidation catalysts play an important role in reaction kinetics and the performance of the photoanodes. In this study, we deposited cobalt-based catalysts on nanoporous BiVO4 with controlled thicknesses by atomic layer deposition (ALD). Despite the similar oxidation states of cobalt in all depositions, different water oxidation activities in neutral pH conditions were observed. A dramatic photocurrent raise, lowered kinetic overpotential, and smaller charge transfer resistance across the photoanode/electrolyte interface were achieved when a uniform ultrathin Co(OH)(2) layer was formed on BiVO4. Photocurrent density for water oxidation showed a 95% enhancement at 0.6 V vs. RHE when the catalyst was in the form of Co(OH)(2), while an 80% increase was obtained for CoO. Ideal coordination of Co(OH)(2) on hydroxylated BiVO4 surface assists the charge transfer between the electrolyte and BiVO4 without increasing surface recombination. The results of this study emphasize the importance of controlling the local structure of the catalysts in the performance of the water splitting photoanodes.