Photovoltaic-assisted hydrogen generation (PH2ON) (completed)

• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Show all 9 contributors for this article] (2022). Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion. Small. ISSN 1613-6810. 18(29). doi: 10.1002/smll.202201106. Full text in Research Archive Show summary

  There is a growing need to control and tune nanoparticles (NPs) to increase their stability and effectiveness, especially for photo- and electrochemical energy conversion applications. Exsolved particles are well anchored and can be re-shaped without changing their initial location and structural arrangement. However, this usually involves lengthy treatments and use of toxic gases. Here, the galvanic replacement/deposition method is used, which is simpler, safer, and leads to a wealth of new hybrid nanostructures with a higher degree of tailorability. The produced NiAu bimetallic nanostructures supported on SrTiO3 display exceptional activity in plasmon-assisted photoelectrochemical (PEC) water oxidation reactions. In situ scanning transmission electron microscopy is used to visualize the structural evolution of the plasmonic bimetallic structures, while theoretical simulations provide mechanistic insight and correlate the surface plasmon resonance effects with structural features and enhanced PEC performance. The versatility of this concept in shifting catalytic modes to the hydrogen evolution reaction is demonstrated by preparing hybrid NiPt bimetallic NPs of low Pt loadings on highly reduced SrTiO3 supports. This powerful methodology enables the design of supported bimetallic nanomaterials with tunable morphology and catalytic functionalities through minimal engineering.

• Liu, Xin; Risbakk, Sanne; Carvalho, Patricia Almeida; Yang, Mingyi; Backe, Paul Hoff & Bjørås, Magnar [Show all 8 contributors for this article] (2022). Immobilization of FeFe-hydrogenase on black TiO2 nanotubes as biocathodes for the hydrogen evolution reaction. Electrochemistry communications. ISSN 1388-2481. 135. doi: 10.1016/j.elecom.2022.107221. Full text in Research Archive Show summary

  Hydrogenases are attractive biocatalysts for utilization in electrochemical devices as potential replacement for Pt in hydrogen evolving electrodes. In this work, we investigate the immobilization of ferredoxin tagged FeFe-hydrogenase (Fd-HydA1) on black TiO2 nanotubes (bTNTs), with uniform nanotube opening diameters of 140 nm. By utilizing an immunogold labelling method, we show that the enzymes attach on the top surface of the bTNTs film rather than on the inner nanotube walls, reflecting the difficulty to insert enzymes into high aspect-ratio nanomaterials for O2-shielding. Nevertheless, cyclic voltammetry demonstrates direct electron transfer between Fd-HydA1 and bTNTs for the hydrogen evolution reaction (HER) in neutral media. This work provides new insight towards design of new nanostructured electrodes for enzyme immobilization.

• Kang, Xiaolan; Chatzitakis, Athanasios; Aarholt, Thomas; Sun, Xinwei; Negri, Chiara & Norby, Truls (2022). Facet-engineered TiO<inf>2</inf>nanomaterials reveal the role of water-oxide interactions in surface protonic conduction. Journal of Materials Chemistry A. ISSN 2050-7488. 10(1), p. 218–227. doi: 10.1039/d1ta06075a. Full text in Research Archive Show summary

  Water adsorption and surface protonic conduction have been investigated at 25–400 °C in wet (H2O and D2O) atmospheres on nanocrystalline TiO2 hydrothermally grown to a predominance of different crystal facets. In situ Fourier transform infrared spectrometry shows that a portion of the water molecules in the first chemisorbed layer adsorbs dissociatively on the {001} and {100} surfaces, but molecularly on the {101} surface. The next layer of physisorbed molecular water is solid (ice)-like on the {001} and {100} surfaces, a fact that is attributed to relatively strong bonds to the surface terminating hydroxyls. On the other hand, it is looser, liquid-like on the {101} surface due to the lack of rigid hydroxyl groups to bond to. As relative humidity (RH) increases with decreasing temperature, additional water layers physisorb and eventually become liquid-like also on the {001} and {100} surfaces. The differences can be attributed to the different atomic arrangements and surface energies of the different crystal facets. Surface protonic conduction on {001} and {100} dominated samples exhibits high pre-exponentials, indicating a high concentration of sites for dissociative chemisorption, and high activation energies reflecting difficult proton migration in the rigid water layers on those surfaces. The surface protonic conduction on the {101} dominated sample reflects a lower coverage of dissociable water and lower activation enthalpies for protonic migration in the more loosely bonded water. This suggests that, more generally, surfaces with dissociative chemisorption may exhibit high surface protonic conductivity at the highest and lowest temperatures (corresponding to lowest and highest RH, respectively), while surfaces with molecular chemisorption may exhibit a relatively high conductivity (less deep minimum) at intermediate temperatures. H/D isotope effects show that the protonic conduction mechanism changes from Grotthuss to vehicle as the physisorbed water layers gain thickness and become liquid-like. The protonic conductivity decreased when the surface was terminated by more strongly bonded fluoride ions, believed to reflect that they block the sites for water adsorption.

• Touni, Aikaterini; Liu, Xin; Kang, Xiaolan; Papoulia, Chrysanthi; Pavlidou, Eleni & Lambropoulou, Dimitra [Show all 9 contributors for this article] (2022). Methanol Oxidation at Platinum Coated Black Titania Nanotubes and Titanium Felt Electrodes. Molecules. ISSN 1431-5157. 27(19), p. 1–15. doi: 10.3390/molecules27196382. Full text in Research Archive Show summary

  Optimized Pt-based methanol oxidation reaction (MOR) anodes are essential for commercial direct methanol fuel cells (DMFCs) and methanol electrolyzers for hydrogen production. High surface area Ti supports are known to increase Pt catalytic activity and utilization. Pt has been deposited on black titania nanotubes (bTNTs), Ti felts and, for comparison, Ti foils by a galvanic deposition process, whereby Pt(IV) from a chloroplatinate solution is spontaneously reduced to metallic Pt (at 65 °C) onto chemically reduced (by CaH2) TNTs (resulting in bTNTs), chemically etched (HCl + NaF) Ti felts and grinded Ti foils. All Pt/Ti-based electrodes prepared by this method showed enhanced intrinsic catalytic activity towards MOR when compared to Pt and other Pt/Ti-based catalysts. The very high/high mass specific activity of Pt/bTNTs (ca 700 mA mgPt−1 at the voltammetric peak of 5 mV s−1 in 0.5 M MeOH) and of Pt/Ti-felt (ca 60 mA mgPt−1, accordingly) make these electrodes good candidates for MOR anodes and/or reactive Gas Diffusion Layer Electrodes (GDLEs) in DMFCs and/or methanol electrolysis cells.

• Xu, Kaiqi; Chatzitakis, Athanasios Eleftherios; Backe, Paul Hoff; Ruan, Qiushi; Tang, Junwang & Rise, Frode [Show all 8 contributors for this article] (2021). In situ cofactor regeneration enables selective CO2 reduction in a stable and efficient enzymatic photoelectrochemical cell. Applied Catalysis B: Environmental. ISSN 0926-3373. 296. doi: 10.1016/j.apcatb.2021.120349. Full text in Research Archive Show summary

  Mimicking natural photosynthesis by direct photoelectrochemical (PEC) reduction of CO2 to chemicals and fuels requires complex cell assemblies with limitations in selectivity, efficiency, cost, and stability. Here, we present a breakthrough cathode utilizing an oxygen tolerant formate dehydrogenase enzyme derived from clostridium carboxidivorans and coupled to a novel and efficient in situ nicotinamide adenine dinucleotide (NAD+/NADH) regeneration mechanism through interfacial electrochemistry on g-C3N4 films. We demonstrate stable (20 h) aerobic PEC CO2-to-formate reduction at close to 100 % faradaic efficiency and unit selectivity in a bio-hybrid PEC cell of minimal engineering with optimized Ta3N5 nanotube photoanode powered by simulated sunlight with a solar to fuel efficiency of 0.063 %, approaching that of natural photosynthesis.

• Zhu, Junjie; Gudmundsdottir, Jonina Björg; Strandbakke, Ragnar; Both, Kevin Gregor; Aarholt, Thomas & Carvalho, Patricia Almeida [Show all 12 contributors for this article] (2021). Double Perovskite Cobaltites Integrated in a Monolithic and Noble Metal-Free Photoelectrochemical Device for Efficient Water Splitting. ACS Applied Materials & Interfaces. ISSN 1944-8244. 13(17), p. 20313–20325. doi: 10.1021/acsami.1c01900. Full text in Research Archive Show summary

  Water photoelectrolysis has the potential to produce renewable hydrogen fuel, therefore addressing the intermittent nature of sunlight. Herein, a monolithic, photovoltaic (PV)-assisted water electrolysis device of minimal engineering and of low (in the μg range) noble-metal-free catalysts loading is presented for unassisted water splitting in alkaline media. An efficient double perovskite cobaltite catalyst, originally developed for high-temperature proton-conducting ceramic electrolyzers, possesses high activity for the oxygen evolution reaction in alkaline media at room temperatures too. Ba1–xGd1–yLax+yCo2O6−δ (BGLC) is combined with a NiMo cathode, and a solar-to-hydrogen efficiency of 6.6% in 1.0 M NaOH, under 1 sun simulated illumination for 71 h, is demonstrated. This work highlights how readily available earth-abundant materials and established PV methods can achieve high performance and stable and monolithic photoelectrolysis devices with potential for full-scale applications.

• Kang, Xiaolan; Berberidou, Chrysanthi; Galeckas, Augustinas; Bazioti, Kalliopi; Sagstuen, Einar & Norby, Truls Eivind [Show all 8 contributors for this article] (2021). Visible Light Driven Photocatalytic Decolorization and Disinfection of Water Employing Reduced TiO2 Nanopowders. Catalysts. 11(2). doi: 10.3390/catal11020228. Full text in Research Archive Show summary

  Defect-engineering of TiO2 can have a major impact on its photocatalytic properties for the degradation of persisting and non-biodegradable pollutants. Herein, a series of intrinsic and extrinsic defects are induced by post annealing of crystalline TiO2 under different reducing atmospheres. A detailed optoelectronic characterization sheds light on the key characteristics of the defect-engineered TiO2 nanopowders that are linked to the photocatalytic performance of the prepared photocatalysts. The photodegradation of a model dye, malachite green, as well as the inactivation of bacterial endospores of the Geobacillus stearothermophilus species were studied in the presence of the developed catalysts under visible light illumination. Our results indicate that a combination of certain defects is necessary for the improvement of the photocatalytic process for water purification and disinfection under visible light.

• Kang, Xiaolan; Chaperman, Larissa; Galeckas, Augustinas; Ammar, Souad; Mammeri, Fayna & Norby, Truls [Show all 7 contributors for this article] (2021). Water Vapor Photoelectrolysis in a Solid-State Photoelectrochemical Cell with TiO2 Nanotubes Loaded with CdS and CdSe Nanoparticles. ACS Applied Materials & Interfaces. ISSN 1944-8244. 13(39), p. 46875–46885. doi: 10.1021/acsami.1c13047. Full text in Research Archive Show summary

  In this study, polyol-made CdS and CdSe crystalline nanoparticles (NPs) are loaded by impregnation on TiO2 nanotube arrays (TNTAs) for solar-simulated light-driven photoelectrochemical (PEC) water vapor splitting. For the first time, we introduce a safe way to utilize toxic, yet efficient photocatalysts by integration in solid-state PEC (SSPEC) cells. The enabling features of SSPEC cells are the surface protonic conduction mechanism on TiO2 and the use of polymeric electrolytes, such as Nafion instead of liquid ones, for operation with gaseous reactants, like water vapor from ambient humidity. Herein, we studied the effects of both the operating conditions in gaseous ambient atmospheres and the surface modifications of TNTAs-based photoanodes with well-crystallized CdS and CdSe NPs. We showed 3.6 and 2.5 times increase in the photocurrent density of defective TNTAs modified with CdS and CdSe, respectively, compared to the pristine TNTAs. Electrochemical impedance spectroscopy and structural characterizations attributed the improved performance to the higher conductivity induced by intrinsic defects as well as to the enhanced electron/hole separation at the TiO2/CdS heterojunction under gaseous operating conditions. The SSPEC cells were evaluated by cycling between high relative humidity (RH) (80%) and low RH levels (40%), providing direct evidence of the effect of RH and, in turn, adsorbed water, on the cell performance. Online mass spectrometry indicated the corresponding difference in the H2 production rate. In addition, a complete restoration of the SSPEC cell performance from low to high RH levels was also achieved. The presented system can be employed in off-grid, water depleted, and air-polluted areas for the production of hydrogen from renewable energy and provides a solution for the safe use of toxic, yet efficient photocatalysts.

• Touni, Aikaterini; Liu, Xin; Kang, Xiaolan; Carvalho, Patricia Almeida; Diplas, Spyridon & Both, Kevin Gregor [Show all 8 contributors for this article] (2021). Galvanic Deposition of Pt Nanoparticles on Black TiO2 Nanotubes for Hydrogen Evolving Cathodes. ChemSusChem. ISSN 1864-5631. 14(22), p. 4993–5003. doi: 10.1002/cssc.202101559. Full text in Research Archive Show summary

  A galvanic deposition method for the in-situ formation of Pt nanoparticles (NPs) on top and inner surfaces of high-aspect-ratio black TiO2-nanotube electrodes (bTNTs) for true utilization of their total surface area has been developed. Density functional theory calculations indicated that the deposition of Pt NPs was favored on bTNTs with a preferred [004] orientation and a deposition mechanism occurring via oxygen vacancies, where electrons were localized. High-resolution transmission electron microscopy images revealed a graded deposition of Pt NPs with an average diameter of around 2.5 nm along the complete nanotube axis (length/pore diameter of 130 : 1). Hydrogen evolution reaction (HER) studies in acidic electrolytes showed comparable results to bulk Pt (per geometric area) and Pt/C commercial catalysts (per mg of Pt). The presented novel HER cathodes of minimal engineering and low noble metal loadings (μg cm−2 range) achieved low Tafel slopes (30–34 mV dec−1) and high stability in acidic conditions. This study provides important insights for the in-situ formation and deposition of NPs in high-aspect-ratio structures for energy applications.

• 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), p. 1030–1033. doi: 10.1039/c9cc08765f. Full text in Research Archive

View all works in NVA

• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Show all 9 contributors for this article] (2022). Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion (Small 29/2022 Inside back cover feature). 18(29), p. 2270156–2270156. Full text in Research Archive
• Kang, Xiaolan; Chaperman, Larissa; Galeckas, Augustinas; Ammar-Merah, Souad; Mammeri, Fayna & Norby, Truls [Show all 7 contributors for this article] (2022). Water Vapor Photoelectrolysis in an All Solid-State Photoelectrochemical Cell. Full text in Research Archive
• Chatzitakis, Athanasios; Zhu, Junjie; Gudmundsdottir, Jonina Björg; Strandbakke, Ragnar; Both, Kevin Gregor & Aarholt, Thomas [Show all 12 contributors for this article] (2022). A monolithic and noble metal-free photoelectrochemical device of minimal engineering for efficient, unassisted water splitting. Full text in Research Archive
• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Show all 9 contributors for this article] (2022). Exsolved nanoparticles, galvanically restructured for tunable photo-electrocatalytic energy conversion. Full text in Research Archive
• Both, Kevin Gregor; Reinertsen, Vilde Mari; Kang, Xiaolan; Aarholt, Thomas; Neagu, Dragos & Prytz, Øystein [Show all 8 contributors for this article] (2022). Improved Photoelectrochemical Performance of SrTiO3 by Plasmonically Active Au Nanoparticles. Full text in Research Archive
• Both, Kevin Gregor; Reinertsen, Vilde Mari; Kang, Xiaolan; Neagu, Dragos; Prytz, Øystein & Norby, Truls [Show all 7 contributors for this article] (2022). Thin Film Exsolution of Metal Nanoparticles and Their Galvanic Restructuring for Plasmonically Enhanced Photocatalytic Activity. Full text in Research Archive
• Chatzitakis, Athanasios (2021). Solar Hydrogen Production. Full text in Research Archive
• Chaperman, Larissa; Mammeri, Fayna; Chatzitakis, Athanasios & Ammar, Souad (2021). Functionally graded, soft chemistry processed titania photoanode for water-splitting in liquid and gas phases. Full text in Research Archive
• Chatzitakis, Athanasios (2021). Her splittes vann til hydrogen og oksygen bare ved hjelp av sollys. Full text in Research Archive
• Touni, Aikaterini; Liu, Xin; Chatzitakis, Athanasios Eleftherios; Kang, Xiaolan; Spyridou, Olga & Sotiropoulos, Sotiris (2021). Platinized Black Titania Nanotube HER Cathodes prepared by the Galvanic Deposition Method at CaH2-reduced Titania Nanotubes. Full text in Research Archive
• Chatzitakis, Athanasios Eleftherios (2019). Artificial Photosynthesis: Mimicking nature for a sustainable energy future. Full text in Research Archive
• Chatzitakis, Athanasios Eleftherios (2019). Can we make fuel in the future from… simply air? Full text in Research Archive
• Chatzitakis, Athanasios (2019). Sol + luftfuktighet = hydrogen = ren energi. Full text in Research Archive
• Chatzitakis, Athanasios Eleftherios (2019). Prospects of photoelectrochemical water electrolysis and the production of solar fuels. Full text in Research Archive

View all works in NVA