Work packages
In this WP the objective is to develop titanium oxide- and copper chalcogenide-based catalyst materials, since these materials are the most promising for the conversion of CO2 into methanol. Different synthesis approaches for different catalysts are followed, based on the experience and expertise of the consortium:
The process starts with the deposition of a metal layer on a substrate, followed by the introduction of the chalcogenide atom in the structure, through thermal annealing in presence of H2S, H2Se or elemental Se. The target materials will be Cu2-xS, Cu2-xSe, and CuInS2.
Plasma enhanced Atomic Layer Deposition (PE-ALD) is the technique explored for the synthesis of copper, indium and gallium sulfides and selenides. The method consists of the reaction of a metal precursor, e.g. Cu(dmap)2, and H2S or H2Se in a plasma phase. In this way, a catalyst film with a subnanometer level of control can be achieved, resulting in a layer in the range of 0.1 to 100 nm. Moreover, PE-ALD can be used to modify other materials' surfaces as well.
Delafossites offer the advantage to enhance the photostability of copper-based photoelectrocatalysts. The selection of the metal cation, optimization of the solvothermal synthesis protocol and catalyst composition is crucial to obtaining a stable catalyst and will be studied.
Titanium dioxide is one of the most studied materials in the field of photo(electro)catalysis due to its stability and abundance. The strategy in this project is to synthesize titania with precise structures, such as nanotubes, and modify them to enhance its light-harvesting capability. Modification techniques include the reduction to black/blue titania and the coupling with Cu- and Ni-based spinels, to obtain a Z-scheme photoelectrocatalyst for the conversion of CO2 to methanol.
In this WP the objective is to develop titanium oxide- and copper chalcogenide-based catalyst materials, since these materials are the most promising for the conversion of CO2 into methanol. Different synthesis approaches for different catalysts are followed, based on the experience and expertise of the consortium:
The process starts with the deposition of a metal layer on a substrate, followed by the introduction of the chalcogenide atom in the structure, through thermal annealing in presence of H2S, H2Se or elemental Se. The target materials will be Cu2-xS, Cu2-xSe, and CuInS2.
Plasma enhanced Atomic Layer Deposition (PE-ALD) is the technique explored for the synthesis of copper, indium and gallium sulfides and selenides. The method consists of the reaction of a metal precursor, e.g. Cu(dmap)2, and H2S or H2Se in a plasma phase. In this way, a catalyst film with a subnanometer level of control can be achieved, resulting in a layer in the range of 0.1 to 100 nm. Moreover, PE-ALD can be used to modify other materials' surfaces as well.
Delafossites offer the advantage to enhance the photostability of copper-based photoelectrocatalysts. The selection of the metal cation, optimization of the solvothermal synthesis protocol and catalyst composition is crucial to obtaining a stable catalyst and will be studied.
Titanium dioxide is one of the most studied materials in the field of photo(electro)catalysis due to its stability and abundance. The strategy in this project is to synthesize titania with precise structures, such as nanotubes, and modify them to enhance its light-harvesting capability. Modification techniques include the reduction to black/blue titania and the coupling with Cu- and Ni-based spinels, to obtain a Z-scheme photoelectrocatalyst for the conversion of CO2 to methanol.
Material and surface analysis and characterization are crucial to assess the reproducibility of the synthesis method, and chemical and morphological properties, to confirm mechanistic simulation and validate the simulation method. Therefore, materials obtained in WP1 will be analyzed at a chemical, structural and functional level, using XRD, FT-IR, UV-vis DR, TGA-DSC-MS, Raman, sorption trials, TPR and TPO. Furthermore, XPS and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) coupled with Atomic Force Microscopy (AFM) will be employed to study the surface of the electrodes and correlate topography and chemistry. Structural information will be gathered through SEM, XRD and AFM.
To obtain a deeper understanding of the material property-activity relationship, the catalysts that show promising results in WP3 (15 % better performance in selectivity or activity), are altered in a controlled way and characterized. Here the aim is to obtain insight into the mechanistic feature of the catalyst via In-situ IT, to study the interaction with single molecules (CO2, H2,...), and In-situ Raman.
It is important to know how the applied potential is distributed over the current collector, semiconductor and electrolyte interface to lower the ohmic resistances in the reactor. To this end, TiO2 deposited films are used to model the effect of the film thickness on the electrochemical behavior of the catalyst. From this, the catalysts synthesized in WP1 can be investigated. Through Mott-Schottky analysis, the flat-band potential is determined and with the use of well-known redox couples, the relative band edge positions are acquired. Eventually, the markers will be used in presence of CO2, to assess the band edge position for the CO2 redox potentials, and determine which one results in which specific product.
Based on the results of the material characterization, the properties of the catalysts can be exploited in a SCAPS-1D model. Being a solar cell simulator, the software can be adjusted to model the optical and electrical properties of the electrode. With this SCAPS model, Z-scheme materials can be simulated and electrode parameters such as recombination rate and total conversion efficiencies derived.
Material and surface analysis and characterization are crucial to assess the reproducibility of the synthesis method, and chemical and morphological properties, to confirm mechanistic simulation and validate the simulation method. Therefore, materials obtained in WP1 will be analyzed at a chemical, structural and functional level, using XRD, FT-IR, UV-vis DR, TGA-DSC-MS, Raman, sorption trials, TPR and TPO. Furthermore, XPS and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) coupled with Atomic Force Microscopy (AFM) will be employed to study the surface of the electrodes and correlate topography and chemistry. Structural information will be gathered through SEM, XRD and AFM.
To obtain a deeper understanding of the material property-activity relationship, the catalysts that show promising results in WP3 (15 % better performance in selectivity or activity), are altered in a controlled way and characterized. Here the aim is to obtain insight into the mechanistic feature of the catalyst via In-situ IT, to study the interaction with single molecules (CO2, H2,...), and In-situ Raman.
It is important to know how the applied potential is distributed over the current collector, semiconductor and electrolyte interface to lower the ohmic resistances in the reactor. To this end, TiO2 deposited films are used to model the effect of the film thickness on the electrochemical behavior of the catalyst. From this, the catalysts synthesized in WP1 can be investigated. Through Mott-Schottky analysis, the flat-band potential is determined and with the use of well-known redox couples, the relative band edge positions are acquired. Eventually, the markers will be used in presence of CO2, to assess the band edge position for the CO2 redox potentials, and determine which one results in which specific product.
Based on the results of the material characterization, the properties of the catalysts can be exploited in a SCAPS-1D model. Being a solar cell simulator, the software can be adjusted to model the optical and electrical properties of the electrode. With this SCAPS model, Z-scheme materials can be simulated and electrode parameters such as recombination rate and total conversion efficiencies derived.
Catalysts synthesized in WP1 are electrochemically characterized, using an in-house designed H-cell setup, allowing to perform electrochemical characterization techniques such as Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV) in combination with a Rotating Disk Electrode (RDE), from which it is possible to study onset potential, reaction kinetics and diffusion aspects. At the same time, a flow electrochemical cell is used that allows chronoamperometric and chronopotentiometric experiments coupled with in-line GC and HPLC analysis of the products, yielding data about the selectivity of the catalysts, expressed in Faradaic Efficiency (FE). Through long-term experiments, information on the lifetime of the catalyst is obtained.
A gas-phase photocatalytic reactor is exploited to evaluate the performance of the WP1 catalysts. The catalysts are deposited on an inert glass support and it is illuminated by a solar simulator. A gas feed with variable CO2 and H2O content is provided to the reactor, which is connected to a micro-GC for fast in-line analysis of the products, able to detect H2, CO, CH4, and CH3OH. In the next step photoelectrochemical characterization of the catalysts is performed. At first, a photoelectrochemical batch cell is used to screen the properties of the materials, e.g. n-type/p-type behavior, on-set potential (Eonset), flat band potential (Efb) and short circuit photocurrent density (jsc), achievable by electrochemical characterization techniques (CV, LSV, OCP measurements) in dark and illumination conditions. Via Mott-Schottky analysis, the flat band potential and energy band alignment can be achieved.
At first, a three-compartment flow photoelectrochemical cell is designed. This configuration allows better potential control of the photoelectrode. The reactor is designed to work with a Gas Diffusion Electrode (GDE), with which the well-known low solubility of CO2 in the aqueous electrolyte can be overcome. Engineering this kind of electrodes to maximize light absorption and CO2 transport is crucial. To maximize the latter, different flow fields will be examined. From this, a selection of the most promising catalysts will be deposited on the GDE to be tested in a photoelectrochemical mode (illumination and electrical bias). Eventually, a zero-gap configuration cell will be designed. The zero-gap reactors have lower ohmic losses and more concentrated product streams than a three-compartment reactor. Next to this also the influence of the operating parameters will be investigated, such as light intensity, pH, temperature, and pressure.
Catalysts synthesized in WP1 are electrochemically characterized, using an in-house designed H-cell setup, allowing to perform electrochemical characterization techniques such as Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV) in combination with a Rotating Disk Electrode (RDE), from which it is possible to study onset potential, reaction kinetics and diffusion aspects. At the same time, a flow electrochemical cell is used that allows chronoamperometric and chronopotentiometric experiments coupled with in-line GC and HPLC analysis of the products, yielding data about the selectivity of the catalysts, expressed in Faradaic Efficiency (FE). Through long-term experiments, information on the lifetime of the catalyst is obtained.
A gas-phase photocatalytic reactor is exploited to evaluate the performance of the WP1 catalysts. The catalysts are deposited on an inert glass support and it is illuminated by a solar simulator. A gas feed with variable CO2 and H2O content is provided to the reactor, which is connected to a micro-GC for fast in-line analysis of the products, able to detect H2, CO, CH4, and CH3OH. In the next step photoelectrochemical characterization of the catalysts is performed. At first, a photoelectrochemical batch cell is used to screen the properties of the materials, e.g. n-type/p-type behavior, on-set potential (Eonset), flat band potential (Efb) and short circuit photocurrent density (jsc), achievable by electrochemical characterization techniques (CV, LSV, OCP measurements) in dark and illumination conditions. Via Mott-Schottky analysis, the flat band potential and energy band alignment can be achieved.
At first, a three-compartment flow photoelectrochemical cell is designed. This configuration allows better potential control of the photoelectrode. The reactor is designed to work with a Gas Diffusion Electrode (GDE), with which the well-known low solubility of CO2 in the aqueous electrolyte can be overcome. Engineering this kind of electrodes to maximize light absorption and CO2 transport is crucial. To maximize the latter, different flow fields will be examined. From this, a selection of the most promising catalysts will be deposited on the GDE to be tested in a photoelectrochemical mode (illumination and electrical bias). Eventually, a zero-gap configuration cell will be designed. The zero-gap reactors have lower ohmic losses and more concentrated product streams than a three-compartment reactor. Next to this also the influence of the operating parameters will be investigated, such as light intensity, pH, temperature, and pressure.