We use an array of laboratory techniques in order to characterise the new materials synthesised and their chemical (ICP-OES, EA, NMR, FTIR, Raman, MS), structural (XRD, TEM) and morphological (SEM, nitrogen adsorption-desorption isotherms) composition and electronic properties (UV-Vis spectroscopy, EIS, photovoltages, UPS).
We use a range of laboratory and synchrotron in-situ and operando techniques such as FTIR, Raman, XRD, XPS and XAS to probe the electronic state of the main actors involved in the photocatalytic process at operando conditions. These experiments allow us to monitor the oxidation state of the catalyst and to identify reaction intermediates and products at its surface under UV-irradiation and CO2/H2O atmosphere.
Solar Fuels Generation by Photoelectrochemical Cells
Solar energy can be transformed into chemical energy by means of photocatalytic reactions and photoelectrochemical cells (PEC), which can be call artificial photosynthesis. In this way, semiconductor materials have demonstrated their ability as photocatalyst to split water into O2 and H2 and to reduce CO2. In this lab, we design and prepare different semiconductors with specific optical and electronic properties and use them to build hybrid and smart materials. For that, we carry out inorganic (metal oxides) and organic (conjugated organic polymers with high-conductivity) synthesis.
To test these materials, we use two different set-ups: a conventional and a tandem PEC cell. A conventional PEC consists of two main parts: efficient light collectors as working electrodes (anode, figure a, or cathode, figure b) and a metal as a counter electrode. A promising approach is the combination of stable and efficient materials in a tandem photoelectrochemical device (figure c). Our photoelectrochemistry line research is focused on the design and use of these smart and hybrid materials to be used as photoelectrodes (photoanodes and photocathodes) in water splitting and CO2 reduction reactions using a LOT-QuantumDesign solar simulator as an energy source.
Laser Flash Photolysis
The laser flash photolysis equipment is based on a pump-probe setup purchased from Edinburgh Co (LP980-K). The pump source is an optical parametric oscillator (OPO) pumped by the third harmonic of a Nd:YAG laser (EKSPLA). The wavelength can be set from 210 nm to about 2600 nm, with a pulse width of about 5 nm using an OPO mod. NT342A-10 with an UV extension NT242 with typical pulse duration of 5 ns. A pulsed xenon flash lamp (150 W) is employed as detecting light source. A monochormator (TMS302-A, grating 150 lines/mm) disperses the probe light after it has passed the sample. The probe light is then passed on to a PMT detector (Hamamatsu Photonics) to obtain the temporal resolved picture. The time resolution in each window is about 10 % of the temporal window width. All components are controlled by the software L900 provided by Edinburgh.
This solar reactor has been specifically designed for gas-phase photocatalytic and photoelectrochemical reactions (water splitting, photoreforming, CO2 reduction) and for the specific location of the IMDEA Energy Institute. The solar photoreactor prototype has been designed by the HYMAP team and built according to this design. The equipment consists of six parallel annular tubular borosilicate glass reactors than can be connected in series or used independently depending on the scale of the experiment to be carried out. The tubes are externally fed by gases and closed with gastight Teflon clamps specifically designed for this application, which can be used both for photochemical and photoelectrochemical experiments. The solar collection is provided by a compound parabolic collector (CPC) with concentration factor 1 for each tube, made of high-reflectance anodized aluminium. The system includes micro gas chromatograph for the analysis and quantification of the outlet gas and a radiometer to measure the incident solar irradiance.