Athanasios Eleftherios Chatzitakis

• Andersen, Håkon; Xu, Kaiqi; Malyshkin, Dmitry; Strandbakke, Ragnar & Chatzitakis, Athanasios Eleftherios (2020). A highly efficient electrocatalyst based on double perovskite cobaltites with immense intrinsic catalytic activity for water oxidation. Chemical Communications.  ISSN 1359-7345.  56(7), s 1030- 1033 . doi: 10.1039/c9cc08765f
• Barakzehi, Marjan; Montazer, Majid; Sharif, Farhad; Norby, Truls Eivind & Chatzitakis, Athanasios Eleftherios (2020). MOF-modified polyester fabric coated with reduced graphene oxide/polypyrrole as electrode for flexible supercapacitors. Electrochimica Acta.  ISSN 0013-4686.  336, s 135743 . doi: 10.1016/j.electacta.2020.135743
• Getz, Marit Norderhaug; Chatzitakis, Athanasios Eleftherios; Liu, Xin; Almeida Carvalho, Patricia; Bjørheim, Tor Svendsen & Norby, Truls Eivind (2020). Voids in walls of mesoporous TiO2 anatase nanotubes by controlled formation and annihilation of protonated titanium vacancies. Materials Chemistry and Physics.  ISSN 0254-0584.  239 . doi: 10.1016/j.matchemphys.2019.121953 Show summary

  Amorphous TiO2 nanotubes (TNTs) grown anodically on Ti metal in aqueous electrolytes show a crystallization behaviour strongly dependent on the atmosphere used during annealing at high temperature. In wet oxidizing conditions, the amorphous TNTs walls transform into relatively large and well crystallized anatase-like domains permeated by prismatic voids. On the other hand, crystallization of the amorphous nanotubes under dry reducing conditions induces nanocrystalline aggregates that do not show prismatic voids and exhibit different electronic properties. Supported by density functional theory calculations, it is argued that the formation or absence of voids can be understood in terms of formation and condensation of protonated titanium vacancies. Tunable morphology through defect chemical engineering as such, enables TNTs with increased surface area and catalytic activity, which find potential application in supercapacitors, sensors, photocatalysis, photoelectrochemistry, and dye-sensitized solar cells.

• Getz, Marit Norderhaug; Chatzitakis, Athanasios Eleftherios; Liu, Xin; Almeida Carvalho, Patricia; Bjørheim, Tor Svendsen & Norby, Truls Eivind (2020). Voids in walls of mesoporous TiO2 anatase nanotubes by controlled formation and annihilation of protonated titanium vacancies. Materials Chemistry and Physics.  ISSN 0254-0584.  239 . doi: https://doi.org/10.1016/j.matchemphys.2019.121953 Show summary

  Amorphous TiO2 nanotubes (TNTs) grown anodically on Ti metal in aqueous electrolytes show a crystallization behaviour strongly dependent on the atmosphere used during annealing at high temperature. In wet oxidizing conditions, the amorphous TNTs walls transform into relatively large and well crystallized anatase-like domains permeated by prismatic voids. On the other hand, crystallization of the amorphous nanotubes under dry reducing conditions induces nanocrystalline aggregates that do not show prismatic voids and exhibit different electronic properties. Supported by density functional theory calculations, it is argued that the formation or absence of voids can be understood in terms of formation and condensation of protonated titanium vacancies. Tunable morphology through defect chemical engineering as such, enables TNTs with increased surface area and catalytic activity, which find potential application in supercapacitors, sensors, photocatalysis, photoelectrochemistry, and dye-sensitized solar cells.

• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Risbakk, Sanne; Yang, Mingyi; Backe, Paul Hoff; Grandcolas, Mathieu; Bjørås, Magnar & Norby, Truls Eivind (2020). High performance and toxicity assessment of Ta3N5 nanotubes for photoelectrochemical water splitting. Catalysis Today.  ISSN 0920-5861. . doi: 10.1016/j.cattod.2019.12.031 Full text in Research Archive. Show summary

  In this work, Co-based cocatalysts are electrodeposited on mesoporous Ta3N5 nanotubes. The electrodeposition time is varied and the optimized photoelectrode reaches a photocurrent density of 6.3 mA/cm2 at 1.23 V vs. SHE, under simulated solar illumination of 1 Sun, in 1 M NaOH. The best performing electrode, apart from the high photocurrent density, shows improved stability under intense photoelectrochemical water splitting conditions. The dual function of the cocatalyst to improve not only the photoelectrochemical performance, but also the stability, is highlighted. Moreover, we adopted a simple protocol to assess the toxicity of Co and Ta contained nanostructured materials (representing used photoelectrodes) employing the human cell line HeLa S3 as target cells.

• Barakezehi, Marjan; Montazer, Majid; Sharif, Farhad; Norby, Truls Eivind & Chatzitakis, Athanasios Eleftherios (2019). A textile-based wearable supercapacitor using reduced graphene oxide/polypyrrole composite. Electrochimica Acta.  ISSN 0013-4686.  305, s 187- 196 . doi: 10.1016/j.electacta.2019.03.058
• Chatzitakis, Athanasios Eleftherios & Longela, Simon Makusudi (2019). Electrochemical characterisation of bovine serum albumin adsorption on phenolic- coated nickel-titanium. Journal of Engineering Science and Technology Review.  ISSN 1791-9320.  12(2), s 1- 8 . doi: 10.25103/jestr.122.01
• Chatzitakis, Athanasios Eleftherios & Sartori, Sabrina (2019). Recent Advances in the Use of Black TiO2 for Production of Hydrogen and Other Solar Fuels. ChemPhysChem.  ISSN 1439-4235.  20(10), s 1272- 1281 . doi: 10.1002/cphc.201801094 Full text in Research Archive.
• Grandcolas, Mathieu; Wabende, Brian; Yang, Juan; Mei, Sen; Xu, Kaiqi; Norby, Truls Eivind & Chatzitakis, Athanasios Eleftherios (2019). Preparation of TiO2 rutile nanorods decorated with cobalt oxide nanoparticles for solar photoelectrochemical activity. Materials letters (General ed.).  ISSN 0167-577X.  247, s 1- 3 . doi: 10.1016/j.matlet.2019.03.087 Show summary

  The present paper investigates the preparation of titanium dioxide (TiO2) nanorods decorated with cobalt oxide (Co3O4) nanoparticles and its application as solar photoelectrocatalyst. TiO2 rutile nanorods have been prepared on conductive glass via a hydrothermal reaction in acidic media, shaped as squared rods with an average length of 1.7 µm and thicknesses between 50 and 120 nm. Co3O4 nanoparticles with an average diameter of 30 nm were synthesized using a simple precipitation method. Spin coating the nanoparticles on the TiO2 nanorods shows enhanced photocurrents under simulated solar light up to 1.3 mA/cm2 at 1.6 V vs. SHE.

• Liu, Xin; Almeida Carvalho, Patricia; Getz, Marit Norderhaug; Norby, Truls Eivind & Chatzitakis, Athanasios Eleftherios (2019). Black Anatase TiO2 Nanotubes with Tunable Orientation for High Performance Supercapacitors. Journal of Physical Chemistry C.  ISSN 1932-7447.  126(36), s 21391- 21940 . doi: 10.1021/acs.jpcc.9b05070 Show summary

  Black TiO2 is a versatile material that finds many applications in the field of photocatalysis but also in energy storage devices, such as supercapacitors. In this work, a new method is developed for the synthesis of black TiO2 in the form of nanotubes. Amorphous TiO2 nanotubes (TNTs) are annealed and reduced in the presence of CaH2, and by a simple manipulation, we are able to obtain control over the preferred crystal orientation. The reduced TNTs show high power and energy densities, as well as unprecedented stability under intensive charge/discharge cycling. The oriented reduced TNTs show metallic-like behavior with improved conductivity when compared to the polycrystalline analogue. This work contributes to the development of highly robust and efficient oxides for electrode material in supercapacitors.

• Sun, Xinwei; Simonsen, Stian Christopher; Norby, Truls Eivind & Chatzitakis, Athanasios Eleftherios (2019). Composite Membranes for High Temperature PEM Fuel Cells and Electrolysers: A Critical Review. Membranes.  ISSN 2077-0375.  9(7) . doi: 10.3390/membranes9070083
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Jensen, Ingvild Julie Thue; Grandcolas, Mathieu & Norby, Truls Eivind (2019). Ta3N5/Co(OH)x composites as photocatalysts for photoelectrochemical water splitting. Photochemical and Photobiological Sciences.  ISSN 1474-905X.  18(4), s 837- 844 . doi: 10.1039/c8pp00312b Full text in Research Archive.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Vøllestad, Einar; Ruan, Qiushi; Tang, Junwang & Norby, Truls Eivind (2019). Hydrogen from wet air and sunlight in a tandem photoelectrochemical cell. International journal of hydrogen energy.  ISSN 0360-3199.  44(2), s 587- 593 . doi: 10.1016/j.ijhydene.2018.11.030 Full text in Research Archive.
• Fleischer, Christian; Chatzitakis, Athanasios Eleftherios & Norby, Truls Eivind (2018). Intrinsic photoelectrocatalytic activity in oriented, photonic TiO2 nanotubes. Materials Science in Semiconductor Processing.  ISSN 1369-8001.  88, s 186- 191 . doi: 10.1016/j.mssp.2018.08.009 Show summary

  In this work, we grow oriented photonic TiO2 nanotubes (TNTs) with a well-established anodization method and their intrinsic catalytic and electronic properties are studied by means of (photo)electrochemical methods. The oriented photonic TNTs are assessed by the RctCdl (ΩF) product, which is a measure of the intrinsic photoelectrocatalytic activity (IPA) of the material. The RctCdl product decouples any surface area effects and it can be applied at any potential and accompanied reaction without knowing the actual electrochemically active surface area (EASA). Moreover, electrochemical impedance spectroscopy (EIS) is used in order to investigate the frequency dispersion in the single frequency Mott-Schottky (MS) measurement. The choice of frequency and the frequency dispersion in MS measurements in nanostructured and of high surface area semiconductors are rarely addressed and can result in erroneous values of two important parameters, i.e. flat band position and donor or acceptor densities. This work provides further insights into important electrochemical aspects and catalytic properties of high surface area nanomaterials for photoelectrochemical applications.

• Sun, Xinwei; Xu, Kaiqi; Fleischer, Christian; Liu, Xin; Grandcolas, Mathieu; Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Norby, Truls Eivind & Chatzitakis, Athanasios Eleftherios (2018). Earth-abundant electrocatalysts in proton exchange membrane electrolyzers. Catalysts.  ISSN 2073-4344.  8:657(12), s 1- 41 . doi: 10.3390/catal8120657 Full text in Research Archive. Show summary

  In order to adopt water electrolyzers as a main hydrogen production system, it is critical to develop inexpensive and earth-abundant catalysts. Currently, both half-reactions in water splitting depend heavily on noble metal catalysts. This review discusses the proton exchange membrane (PEM) water electrolysis (WE) and the progress in replacing the noble-metal catalysts with earth-abundant ones. The efforts within this field for the discovery of efficient and stable earth-abundant catalysts (EACs) have increased exponentially the last few years. The development of EACs for the oxygen evolution reaction (OER) in acidic media is particularly important, as the only stable and efficient catalysts until now are noble-metal oxides, such as IrOx and RuOx. On the hydrogen evolution reaction (HER) side, there is significant progress on EACs under acidic conditions, but there are very few reports of these EACs employed in full PEM WE cells. These two main issues are reviewed, and we conclude with prospects for innovation in EACs for the OER in acidic environments, as well as with a critical assessment of the few full PEM WE cells assembled with EACs.

• Chatzitakis, Athanasios Eleftherios; Grandcolas, Mathieu; Xu, Kaiqi; Mei, Sen; Yang, Juan; Jensen, Ingvild Julie Thue; Simon, Christian & Norby, Truls Eivind (2017). Assessing the photoelectrochemical properties of C, N, F codoped TiO2 nanotubes of different lengths. Catalysis Today.  ISSN 0920-5861.  287, s 161- 168 . doi: 10.1016/j.cattod.2016.11.040 Full text in Research Archive. Show summary

  The aim of this work has been the photoelectrochemical (PEC) study of nanostructured photoanodes based on TiO2. Highly ordered and well adhered TiO2 nanotubes (TNTs) of different lengths (∼2–20 μm) were prepared in a two-step process in ethylene glycol solutions containing fluorides, and detailed XPS analysis showed that they have become co-doped with C, N and F. PEC measurements revealed that increasing surface area is not followed by increase in the photoconversion efficiency, but rather that an optimal balance between electroactive surface area (ESA) and charge carrier concentration exists. TNTs of around 10 μm show the optimum incident photon-to-current efficiency (IPCE) of ∼33% and an overall photoconversion efficiency of ∼6.3% under UV illumination of 4 mW cm−2 light intensity. Finally, Mott-Schottky analysis revealed significant frequency dispersion of the estimated space charge layer capacitance, which renders the accurate estimation of the flatband position and charge carrier concentration unreliable. On the other hand, more realistic charge carrier concentrations can be obtained by normalizing the capacitance per ESA.

• Longela, Simon M & Chatzitakis, Athanasios Eleftherios (2017). In vitro corrosion behaviour of phenolic coated nickel-titanium surfaces. Biosurface and Biotribology.  ISSN 2405-4518. . doi: 10.1016/j.bsbt.2017.10.002
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios & Norby, Truls (2017). Solid-state photoelectrochemical cell with TiO2 nanotubes for water splitting. Photochemical and Photobiological Sciences.  ISSN 1474-905X.  16(1), s 10- 16 . doi: 10.1039/c6pp00217j Full text in Research Archive.

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• Liu, Xin; Risbakk, Sanne; Almeida Carvalho, Patricia; Yang, Mingyi; Backe, Paul Hoff; Bjorås, Magnar; Norby, Truls Eivind & Chatzitakis, Athanasios Eleftherios (2020). Hydrogenase-assisted catalysis on titania electrode oxides. Show summary

  The widespread use of fuel cells and water splitting devices for energy generation and storage is limited by the dependence on noble metal catalysts. There is thus a tremendous need for the development of efficient electrocatalysts based on Earth-abundant elements. Nature inspired hydrogenases (HydA) are metallo-enzymes that catalyze the reversible reaction of H2 to protons and electrons. Hydrogenases containing Fe at the active sites, known as [FeFe]-HydA, show activities comparable to that of Pt. This work addresses a new class of electrodes for [FeFe]-HydA attachment and bio-assisted catalysis based on TiO2 nanotubes. The conducting oxide material provides suitable electronic conduction and hydrophilicity, while the nanostructure ensures tunability (tube length, crystal orientation and pore diameter) and high surface area for HydA attachment. In this work, electron microscopy is used to characterize the bio-electrodes. Based on the experimental findings, density functional theory (DFT) calculations are used to probe the catalytic reaction sites on the HydA and address the interaction between enzymes and TiO2. The novel bioelectrode will be employed in a system of artificial photosynthesis and generation of solar fuels by simultaneous water splitting and CO2 capture and utilization.

• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Backe, Paul Hoff; Ruan, Qiushi; Tang, Junwang; Bjørås, Magnar; Rise, Frode & Norby, Truls Eivind (2020). The use of NMR to assess the activity of formate dehydrogenase biocatalysts for CO2 utilization.
• Chatzitakis, Athanasios Eleftherios (2019). Artificial Photosynthesis: Mimicking nature for a sustainable energy future.
• Chatzitakis, Athanasios Eleftherios (2019). Can we make fuel in the future from… simply air?.
• Chatzitakis, Athanasios Eleftherios (2019). Prospects of photoelectrochemical water electrolysis and the production of solar fuels.
• Liu, Xin; Chatzitakis, Athanasios Eleftherios; Almeida Carvalho, Patricia; Risbakk, Sanne; Yang, Mingyi; Backe, Paul Hoff & Norby, Truls Eivind (2019). Enzyme-assisted Catalysis on Titania Electrodes.
• Sun, Xinwei; Chatzitakis, Athanasios Eleftherios & Norby, Truls Eivind (2019). Composite membranes for high temperature PEM fuel cells and electrolysers. Show summary

  Polymer electrolyte membrane(PEM) fuel cells and electrolysers offer efficient use and production of H2 for emission-free transport and sustainable energy systems. In order to reduce the cost,complexity,flooding,catalyst poisoning and degradation,operation above 80°C and at lower relative humidities(RH) is preferable. Acid doped polybenzimidazole(PBI),sulfonated polyetheretherketone(SPEEK) and their composites are being investigated for high temperature and low RH operation with sufficient conductivities. We take a critical view and a surface protonic approach to gain fundamental insight.

• Sun, Xinwei; Chatzitakis, Athanasios Eleftherios & Norby, Truls Eivind (2019). Polymer-ceramic composite membranes for intermediate temperature PEM fuel cells.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Norby, Truls Eivind & Bjørheim, Tor Svendsen (2019). Ta3N5 nanotubes loaded with Co(OH)x/Co-Pi-high photocurrent densities and improved photocorrosion resistance.
• Xu, Kaiqi; Grandcolas, Mathieu; Yang, Juan; Mei, Sen; Chatzitakis, Athanasios Eleftherios & Norby, Truls Eivind (2019). Photoelectrochemical water splitting on Ta3N5 nanotubes for H2 production.
• Chatzitakis, Athanasios Eleftherios; Simonsen, Stian; Fontaine, Marie Laure; Thomassen, Magnus & Norby, Truls Eivind (2018). Conductivity of polymer-ceramic composite membranes at high T and p(H2O) using a novel PEEK sample holder.
• Fontaine, Marie-Laure; Chatzitakis, Athanasios Eleftherios; Vøllestad, Einar; Thomassen, Magnus & Norby, Truls Eivind (2018). Principles of proton conduction in polymer-ceramic composite membranes for PEM applications.
• Grandcolas, Mathieu; Wabende, Brian; Yang, Juan; Mei, Sen; Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios & Norby, Truls Eivind (2018). TiO2 Nanorods Decorated With Cobalt oxide as Photoanodes for a Bio-Hybrid PEC Cell.
• Sun, Xinwei; Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios & Norby, Truls Eivind (2018). Can hydroxyl radicals travel far? Gas phase transport and detection after photocatalytic generation at TiO2 nanorods.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Bjørheim, Tor Svendsen & Norby, Truls Eivind (2018). Surface modification of Ta3N5 nanotubes as photocatalyst for photoelectrochemical water splitting.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Norby, Truls Eivind; Grandcolas, Mathieu; Yang, Juan & Mei, Sen (2018). Ta3N5 / Co(OH)x composite as the photocatalyst for photoelectrochemical water splitting.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Vøllestad, Einar; Ruan, Qiushi; Tang, Junwang & Norby, Truls Eivind (2018). Solid-state photoelectrochemical cell for wet air electrolysis and hydrogen production.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Vøllestad, Einar; Ruan, Qiushi; Tang, Junwang & Norby, Truls Eivind (2018). Solid-state tandem photoelectrochemical cell for wet air electrolysis and hydrogen production.
• Chatzitakis, Athanasios Eleftherios (2017). (Photo)electrochemical applications of TiO2 nanotubes.
• Chatzitakis, Athanasios Eleftherios; Xu, Kaiqi & Norby, Truls Eivind (2017). TiO2 nanotubes as photoanode electrodes in solid-state photoelectrochemical cells.
• Fleischer, Christian; Chatzitakis, Athanasios Eleftherios; Grandcolas, Mathieu; Mei, Sen & Norby, Truls Eivind (2017). Solid-state photoelectrochemical water splitting: Application and properties of TiO2 nanotubes..
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Bjørheim, Tor Svendsen & Norby, Truls Eivind (2017). Fuels from the sun, sea and air-by solid-state photoelectrochemical cell.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Bjørheim, Tor Svendsen & Norby, Truls Eivind (2017). Tantalum oxynitride for photoelectrochemical water splitting.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Norby, Truls Eivind; Mei, Sen; Juan, Yang; Grandcolas, Mathieu & Simen, Christian (2017). Solid-state photoelectrochemical Cell with Tantalum Nitride Nanotubes as Photoanode.
• Yang, Juan; Mei, Sen; Grandcolas, Mathieu; Simon, Christian; Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Norby, Truls Eivind; Yang, Mingyi; Backe, Paul Hoff & Bjørås, Magnar (2017). Synthesis of Nanosized Cobalt Oxides and Application in a Bio-hybrid Photoelectrochemical Cell for CO2 Utilization. Show summary

  CO2 capture and utilization (CCU) can alleviate the disastrous effects of greenhouse gas (GHG) emissions form the use of fossil fuels. The use of CO2 emission as feedstock for direct conversion into valuable chemicals has attracted increasing research interest worldwide. A number of approaches, such as chemical, electrochemical, photochemical and biological routes have used CO2 as a sustainable carbon resource for the production of chemicals. In the present CO2BioPEC project, a novel hybrid photoelectrochemical concept, based on solar energy and formate dehydrogenase biocatalyst is applied, as illustrated in Figure 1 (left). This multidisciplinary project aims at demonstrating a bio-hybrid photoelectrochemical cell, in which solar energy is efficiently captured and utilized to convert CO2 into energy-rich compounds, using formate dehydrogenase enzymes as biocatalysts. Cobalt oxide is a low-cost material with a band gap that can absorb visible light. It is also a promising co-catalyst that has been widely used for oxygen evolution route. In the present work, nanosized cobalt oxide was synthesized and used as a co-catalyst on the photoanode. The results showed that the formation of cobalt oxides (Co3O4, CoOOH and Co(OH)2) is strongly dependent on the temperature and reaction time. The photochemical efficiency will be further investigated by impregnating nanosized cobalt oxides onto Ta3N4 /TaON nanotubes.

• Chatzitakis, Athanasios Eleftherios; Grandcolas, Mathieu; Xu, Kaiqi; Mei, Sen; Yang, Juan; Simon, Christian & Norby, Truls (2016). Assessing the photoelectrocatalytic activity of C, N, F codoped TiO2 nanotubes of different lengths for oxygen evolution.
• Fleischer, Christian; Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios & Norby, Truls Eivind (2016). Development of high surface area TiO2 photo-electrodes and the significance of solid-state proton conductor in water splitting photoelectrochemical cell..
• Grandcolas, Mathieu; Sahoo, Prangya Parimita; Foss, Carl Erik Lie; Xing, Wen; Polfus, Jonathan M.; Sunde, Svein; Chatzitakis, Athanasios Eleftherios & Norby, Truls (2016). Novel photoelectrocatalytic concepts for conversion of nitrogen to fuels and chemicals.
• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios & Norby, Truls (2016). An All-Solid-State Photoelectrochemical Cell for Water Splitting.
• Chatzitakis, Athanasios Eleftherios & Norby, Truls (2015). Solar hydrogen production.
• Chatzitakis, Athanasios Eleftherios & Norby, Truls (2015). Solid electrolytes for photoelectrochemical cells.
• Chatzitakis, Athanasios Eleftherios; Xu, Kaiqi; Boye, Ole; Backe, Paul Hoff; Bjorås, Magnar; Dalhus, Bjørn; Grandcolas, Mathieu; Mei, Sen; Simon, Christian; Tilset, Bente Gilbu; Yang, Juan; Yang, Mingyi & Norby, Truls (2015). Solar based H2 generation in a novel photoelectrochemical-enzymatic hybrid cell.

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