| 1. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
-
Bifunctional solar electrocatalytic water splitting using CIGS solar modules and WO3-based electrolyzers
- 2019
-
Ingår i: EMRS Spring Meeting 2019.
-
Konferensbidrag (refereegranskat)abstract
- Using energy from the sun to produce a fuel and finally obtaining only water as an exhaust is a promising future technology for renewable energy and environmental sustainability. Solar driven water splitting is a method to produce hydrogen from solar energy. Coupling a solar cell with an electrolyzer is the approach with highest technological readiness. CuInxGa1-xSe2 (CIGS) is here a promising solar cell material for water splitting because it is possible to tune the band gap between 1.0 and 1.7 eV by changing the ratio between Ga and In, thus enabling maximum power point matching with an electrolyzer. Tungsten oxide is known as a photocatalytic material and mainly used for the oxygen evolution reaction in a water splitting process. However, WO3 films also show electrochromic activity together with hydrogen evolution. This result is interesting because it shows that WO3 films can be used as bifunctional materials for both hydrogen and oxygen evolution in water splitting, and provide additional functionalities to the system. In this study, WO3 films coated at different sputtering conditions on Ni foam and indium tin oxide substrates were investigated in the potential range of the hydrogen evolution reaction. The best overpotential of 164 mV vs. RHE at 10 mA/cm2 was obtained for WO3 films on Ni foam in 0.5 M H2SO4. The lowest potential needed for 10 mA/cm2 was measured 1.768 V for the electrolyzers consisting WO3 films on Ni foam as the cathode and non-coated Ni foam as the anode. Optimum solar-to-hydrogen (STH) efficiency of the CIGS solar cell modules and the electrolyzers was examined for different band gaps of the CIGS modules and sputtering conditions of WO3 films. Operation points of the combined system were calculated from the intersection of the voltage-current density curves for the CIGS modules and the electrolyzers. The results showed that the detailed sputtering conditions were not very critical to obtain high STH efficiency, indicating that the system could be robust and easily manufactured. The best-matched band gap of the CIGS was 1.19 eV and the highest STH efficiency of the CIGS driven WO3-based electrolyzers was 12.98 %.
|
|
| 2. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
-
Electrochromic solar water splitting using a cathodic WO3 electrocatalyst
- 2021
-
Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 81
-
Tidskriftsartikel (refereegranskat)abstract
- Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.
|
|
| 3. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
-
NiMoV and NiO-based catalysts for efficient solar-driven water splitting using thermally integrated photovoltaics in a scalable approach
- 2021
-
Ingår i: iScience. - : Cell Press. - 2589-0042. ; 24:1
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, a trimetallic NiMoV catalyst is developed for the hydrogen evolution reaction and characterized with respect to structure, valence, and elemental distribution. The overpotential to drive a 10 mA cm−2 current density is lowered from 94 to 78 mV versus reversible hydrogen electrode by introducing V into NiMo. A scalable stand-alone system for solar-driven water splitting was examined for a laboratory-scale device with 1.6 cm2 photovoltaic (PV) module area to an up-scaled device with 100 cm2 area. The NiMoV cathodic catalyst is combined with a NiO anode in alkaline electrolyzer unit thermally connected to synthesized (Ag,Cu) (In,Ga)Se2 ((A)CIGS) PV modules. Performance of 3- and 4-cell interconnected PV modules, electrolyzer, and hydrogen production of the PV electrolyzer are examined between 25°C and 50°C. The PV-electrolysis device having a 4-cell (A)CIGS under 100 mW cm−2 illumination and NiMoV-NiO electrolyzer shows 9.1% maximum and 8.5% averaged efficiency for 100 h operation.
|
|
| 4. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
-
Optimum Band Gap Energy of ((Ag),Cu)(InGa)Se2 Materials for Combination with NiMo–NiO Catalysts for Thermally Integrated Solar-Driven Water Splitting Applications
- 2019
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Solar-driven water splitting is considered one of the promising future routes to generate fuel in a sustainable way. A carbon-free solar fuel, molecular hydrogen, can here be produced along two different but intimately related routes, photoelectrochemical (PEC) water splitting or photovoltaic electrolysis (PV-electrolysis), where the latter builds on well-established solar cell and electrolysis materials with high efficiency. The PV-electrolysis approach is also possible to construct from an integrated PEC/PV-system avoiding dc-dc converters and enabling heat exchange between the PV and electrolyzer part, to a conventionally wired PV-electrolysis system. In either case, the operating voltage at a certain current needs to be matched with the catalyst system in the electrolysis part. Here, we investigate ((Ag),Cu)(In,Ga)Se-2 ((A)CIGS)-materials with varying Ga-content modules for combination with NiMo-NiO catalysts in alkaline water splitting. The use of (A)CIGS is attractive because of the low cost-to-performance ratio and the possibility to optimize the performance of the system by tuning the band gap of (A)CIGS in contrast to Si technology. The band gap tuning is possible by changing the Ga/(Ga + In) ratio. Optoelectronic properties of the (A)CIGS materials with Ga/(Ga + In) ratios between 0.23 and 0.47 and the voltage and power output from the resulting water splitting modules are reported. Electrolysis is quantified at temperatures between 25 and 60 degrees C, an interval obtainable by varying the thermal heat exchange form a 1-sun illuminated PV module and an electrolyte system. The band gaps of the (A)CIGS thin films were between 1.08 to 1.25 eV and the three-cell module power conversion efficiencies (PCE) ranged from 16.44% with 1.08 eV band gap and 19.04% with 1.17 eV band gap. The highest solar-to-hydrogen (STH) efficiency was 13.33% for the (A)CIGS-NiMo-NiO system with 17.97% module efficiency and electrolysis at 60 degrees C compared to a STH efficiency of 12.98% at 25 degrees C. The increase in STH efficiency with increasing temperature was more notable for lower band gaps as these are closer to the overpotential threshold for performing efficient solar-driven catalysis, while only a modest improvement can be obtained by utilizing thermal exchange for a band gap matched PV-catalysts system. The results show that usage of cost-effective and stable thin film PV materials and earth abundant catalysts can provide STH efficiencies beyond 13% even with PV modules with modest efficiency.
|
|
| 5. |
- Calnan, Sonya, et al.
(författare)
-
Development of Various Photovoltaic‐Driven Water Electrolysis Technologies for Green Solar Hydrogen Generation
- 2021
-
Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 6:5
-
Tidskriftsartikel (refereegranskat)abstract
- Direct solar hydrogen generation via a combination of photovoltaics (PV) and water electrolysis can potentially ensure a sustainable energy supply while minimizing greenhouse emissions. The PECSYS project aims at demonstrating asolar-driven electrochemical hydrogen generation system with an area >10 m2 with high efficiency and at reasonable cost. Thermally integrated PV electrolyzers(ECs) using thin-film silicon, undoped, and silver-doped Cu(In,Ga)Se2 and silicon heterojunction PV combined with alkaline electrolysis to form one unit are developed on a prototype level with solar collection areas in the range from 64 to2600 cm2 with the solar-to-hydrogen (StH) efficiency ranging from 4 to 13%. Electrical direct coupling of PV modules to a proton exchange membrane EC test the effects of bifacially (730 cm2 solar collection area) and to study the long-term operation under outdoor conditions (10 m2 collection area) is also investigated. In both cases, StH efficiencies exceeding 10% can be maintained over the test periods used. All the StH efficiencies reported are based on measured gas outflow using mass flow meters.
|
|
| 6. |
- Langhammer, David, 1991-, et al.
(författare)
-
Bonding of CO2 to TiO2 : Chemical Activation During Artificial Photosynthesis
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- There is a growing interest to develop materials for artificial photosynthesis of fuels by CO2 reduction. Titanium dioxide (TiO2) is frequently used as a model system to study photosynthetic heterogenous catalytic reactions due to its well-characterized properties and wide-spread use within the field of photocatalysis. It is ideal for use in industrial applications due to its large abundance and low cost, although the wide band gap of this material has limited its use in solar-driven technologies. Apart from being used as a pigment in white paint, it is primarily used in industry as a photocatalyst for the degradation of surface contaminants and air pollutants, both of which appear in low concentrations. Despite this, there is great hope that the properties of TiO2 will be developed to enable large scale deployment in technological applications. Artificial photosynthesis is considered by many to be an attractive application of large-scale photochemistry, and TiO2 has been studied extensively for this purpose. The most crucial step in the process of reducing CO2 is the activation of the stable CO2 molecule through chemical bonding. In this article, the interaction between CO2 and various surfaces of TiO2 is investigated to evaluate its catalytic properties. The usefulness of TiO2 for CO2 reduction is critically discussed based on its photocatalytic ability and on previously reported efficiencies during different types of photochemical reactions.
|
|
| 7. |
- Langhammer, David Michael, 1991-
(författare)
-
Capturing Air Pollutants : Photochemical Adsorption and Degradation of SO2, NO2 and CO2 on Titanium Dioxide
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Titanium dioxide (TiO2) is a material with many useful properties. It is used most widely as a pigment in white paint, although in technological research it is better known for its ability to catalyze chemical reactions during light absorption. This process is referred to as photocatalysis, where the energy of the light is used to power the chemical reactions. This has enabled several interesting applications of TiO2, where it can for instance be applied to windows or façade walls to make their surfaces self-cleaning. Another implementation that has received much attention lately is artificial photosynthesis, where the light energy is used to transform CO2 and H2O into synthetic fuels. This thesis work contributes to the development of both these applications, although the main ambition is to show how three of the most common ambient air pollutant molecules, SO2, NO2 and CO2, can be captured at the surface of TiO2 by means of photocatalysis. Specifically, infrared (IR) spectroscopy and density functional theory (DFT) has been used as complementary tools of analysis to study the photocatalytic reactions that enable transformation of SO2, NO2 and CO2 into strongly bound sulfates, nitrates and carbonates, respectively. This combined experimental and theoretical approach has enabled a detailed description of how these reactions proceed and has further shown how the fundamental reactivity of the TiO2 surface changes upon light absorption.The work presented herein contributes to an increased understanding of photocatalysis and shows, quite generally, how molecules can be effectively captured at the surface of metal oxides by forming surface-integrated ionic adsorbates.
|
|
| 8. |
- Montero Amenedo, José, 1983-, et al.
(författare)
-
Photobleaching of dyes by CuOx-based heterojunction bi-catalysts
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present the synthesis and characterization of thin film heterojunction, or bi-catalyst, comprising of photocatalytic coatings based on a combination of two different materials exhibiting p-type and n-type conductivity, respectively. Here we show results for the combination of CuOx together with zinc oxide (ZnO) and tungsten oxide (WO3). The purpose of such compounds is to create an intrinsic electrical field at the np-junction that helps to separate electron-hole pairs formed upon interband photon absorption. At the same time desired photochemical properties implies that the constituent catalysts have appropriate bandgap and band edge position. For this purpose, CuOx/WO3 compound films have been prepared onto glass substrates by co-sputtering of tungsten and copper targets in an argon and oxygen atmosphere. CuOx/ZnO bi-catalyst have also been prepared on glass substrates by a two-step process consisting of deposition of CuOx by reactive magnetron sputtering, followed by the ap plication of ZnO particles by drop coating. The obtained bi-catalyst have been characterized by SEM, XRD, XPS, Raman and spectrophotometry. Finally, the photocatalytic activity of the different compound films is assessed by studying their photobleaching rate of methylene blue and orange II in water solution.
|
|
| 9. |
- Thyr, Jakob, 1979-, et al.
(författare)
-
Energy Alignment of Quantum-Confined ZnO Particles with Copper Oxides for Heterojunctions with Improved Photocatalytic Performance
- 2022
-
Ingår i: ACS Nanoscience Au. - : American Chemical Society (ACS). - 2694-2496. ; 2:2, s. 128-139
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to control electronic states by utilizing quantum confinement of one of the material components in heterojunctions is a promising approach to perform energy-level matching. In this work, we report the possibility to achieve optimum energy alignment in heterojunctions made from size-controlled quantum dots (Q-dots) of ZnO in combination with three copper oxides: Cu2O, Cu4O3, and CuO. Quantum confinement effects on the ZnO nanoparticles in the diameter range 2.6–7.4 nm showed that the direct optical band gap decreased from 3.99 to 3.41 eV, with a dominating shift occurring in the conduction band (CB) edge, and thus the possibility to obtain close to 0.6 eV CB edge shift by controlling the size of ZnO. The effect was utilized to align the electronic bands in the ZnO Q-dot/copper oxide heterojunctions to allow for charge transfer between the materials and to test the ability to improve the photocatalytic performance for the system, evaluated by the transformation of a dye molecule in water. The catalyst materials were investigated by X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis), photoluminescence, and Raman spectroscopy. The most promising material combination was found to be the Cu2O copper oxide in combination with an energy aligned ZnO Q-dot system with approximately 7 nm diameter, showing strong synergy effects in good agreement with the energy-level analysis, outperforming the added effect of its individual components, ZnO-Q-dots and Cu2O, by about 140%. The results show that utilization of a heterojunction with controllable energy alignment can provide a drastically improved photocatalytic performance. Apart from increased photocatalytic activity, specific surface states of ZnO are quenched when the heterojunction is created. It is anticipated that the same approach can be utilized in several material combinations with the added benefit of a system with controllable overpotential and thus added specificity for the targeted reduction reaction.
|
|
| 10. |
- Thyr, Jakob, 1979-, et al.
(författare)
-
Photocatalytic properties and polarized Raman of different ZnO crystal planes
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Zinc oxide (ZnO) is a well-studied wide band gap semiconductor photocatalyst. The activities of ZnO nanomaterials with different ratios of exposed crystal planes are however less understood. In this work, three different ZnO single crystals exposing different crystal planes were studied: (0001), (1-100), and (11-20). The ZnO samples were characterized with polarized Raman spectroscopy and XRD, and their photocatalytic activities were quantified by means of methylene blue degradation using in situ spectrophotometry. The ZnO (1-100) surface showed three times higher photocatalytic activity than the other two surfaces. The results are discussed in terms of crystal facet dependent reactivity due to differences in surface structure and surface potential. Since it is possible to synthesize ZnO particles and structures with different ratios of exposed crystal planes, this finding may be of importance to guide synthesis of more efficient, tailor-made ZnO photocatalysts for water cleaning.
|
|
