Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ARCADIA (Advanced devices for the Reduction of CArbon DIoxide and Artificial photosynthesis)

Teaser

Natural photosynthesis is the process through which green plants, algae and cyanobacteria produce their energetic reservoirs by storing solar energy. The ARCADIA project focuses on mimicking this process by developing new photochemical cells able to exploit renewable resources...

Summary

Natural photosynthesis is the process through which green plants, algae and cyanobacteria produce their energetic reservoirs by storing solar energy. The ARCADIA project focuses on mimicking this process by developing new photochemical cells able to exploit renewable resources and feedstock (namely sunlight, water and the greenhouse gas CO2), while producing value-added products and clean fuels, alternative to fossil fuels. Thus, the ARCADIA project addresses two of the major environmental/energy issues of our society, i.e. (i) the increased worldwide competition for the depleting fossil fuel reserves; and (ii) the ever-increasing atmospheric levels of carbon dioxide, predicted to cause uncontrollable impact on the world climate.
The overall objectives of the ARCADIA project are: (i) the preparation of new devices via the independent development of photoelectrodes, able to efficiently absorb solar energy and convert it in charge separated states, ultimately driving the semireactions of water oxidation (anodic side) and CO2 reduction (cathodic side); (ii) the full characterization of these electrodes with advanced electrochemical and spectroscopic techniques, achieving mechanistic insights pivotal for the identification of the involved kinetic processes and, thus, for the further optimization of the electrodic interfaces.

Work performed

The first Work Package (WP1) regarded the development of (photo)cathodes, i.e. the optimization of the reduction site of the final (photo)electrochemical cell. The corresponding scientific objective (SO-1) was pursued in close conjunction to SO-3, since the preparation of the (photo)cathodes encompasses the in-depth analysis of their performances, employing the advanced photo- and electrochemical techniques described in Work Package 3 (WP3).
In particular, we identified the deposition of an ultrathin layer of titanium as an optimal protection strategy for p-type silicon electrodes, intended to be used as photocathodic platforms for the reduction of carbon dioxide. A scouting functionalization with platinum nanoparticles gave interesting results for the proton reduction to yield hydrogen, another clean alternative to fossil fuels, giving only water as the combustion product. These results were published on “Electrochimica Acta” (2018, 271, 472) and presented as an oral communication at the Spring Meeting of the European Materials Research Society (Strasbourg, 2017). Current efforts are directed towards the functionalization of the same interfaces with copper nanostructures, the selected catalytic domains for CO2 reduction. At the same time, we investigated alternative strategies using novel Au-nanoarchitectures, which turned out to be excellent cathodes, producing CO and H2, the major components of synthesis gas.
The second Work Package (WP2) regarded the development of photoanodes able to perform water oxidation at the anodic compartment of the final (photo)electrochemical cell. Also in this case, the corresponding scientific objective (SO-2) was pursued in close conjunction to SO-3. The main achievements were: (i) the preparation of optimized WO3 photoanodes displaying a BiVO4 overlayer to enhance visible light absorption. The further functionalization with a molecular ruthenium water oxidation catalyst led to an enhancement of the evolved oxygen. These results have been recently published on “Sustainable Energy & Fuels”; (ii) the preparation of different anodic interfaces exploiting the stacking of perylenic aggregates on wide band-gap oxides. Their characterization with advanced techniques was published on the “Journal of Physical Chemistry C” (2017, 121, 17737), as well as presented as a poster at the “2nd International Solar Fuels Conference” (San Diego, 2017) and as an oral communication at the “Italian Photochemistry Meeting” (Perugia, 2017); (iii) the optimization of hematite photoanodes via their functionalization with earth-abundant catalysts, able to boost water oxidation. We could evidence that the catalysts’ morphology is pivotal to yield enhanced performances. The results were published on “ACS Applied Materials and Interfaces” (2016, 8, 20003), as well as presented as a poster at the “NanoGe September Meeting on Solar Fuels” (Berlin, 2016) and at the “Joint Congress of the French and Italian Photochemists and Photobiologists” (Bari, 2016). In the latter case, I was awarded the poster prize and I gave a flash oral presentation. We further extended this study to different hematite/catalyst interfaces, and the corresponding manuscript is currently under preparation. Meanwhile the results were presented as a poster at the “NanoGe September Meeting on Solar Fuels” (Barcelona, 2017).
Furthermore, during the MSCA fellowship, I promoted the ARCADIA project participating to different outreach activities for students and the general public by means of presentations and experiments related to my activity.

Final results

The outcomes of ARCADIA contributed to broaden the knowledge of the scientific community in the field of solar fuels generation by developing new systems able to convert renewable sources and feedstocks into value-added products, with special attention to maximize the use of earth abundant and low toxicity materials, in view of possible industrial implementation. Thus, the ARCADIA project also contributed to provide new solutions for two of the major issues of modern society, i.e. the depletion of fossil fuels and the increase of the atmospheric levels of the greenhouse gas CO2.
Indeed, the novel (photo)electrodic materials and interfaces developed during the ARCADIA project resulted able to perform demanding oxidation and reduction reactions in optimized (photo)electrochemical set-ups. In particular, protected p-silicon electrodes used in combination with platinum nanoparticles or copper nanofoams were respectively employed as efficient photocathodes for the reduction of protons and carbon dioxide, while novel gold nanoarchitectures were shown to be effective for the electrochemical production of syn-gas from CO2 and water.
As regards the oxidation side, the exploitation of different functionalization strategies of bare semiconductor materials (such as hematite, WO3, SnO2 and Sb-doped SnO2) led to the development of photoanodes with enhanced oxygen evolution. In particular, the absorption properties were improved by the introduction of layers with extended spectral response (namely BiVO4 on the top of WO3, and perylenic aggregates on Sb-doped SnO2, WO3 and SnO2), while the interface kinetics were boosted by the functionalization with catalysts (namely Fe and Ni-based metal oxides for hematite and a molecular ruthenium complex for WO3-BiVO4).
Furthermore, all the electrodic interfaces were characterized by means of electrochemical impedance and ultrafast spectroscopies, which are not routinely implemented in this kind of studies yet, allowing for a more innovative contribution of the ARCADIA outcomes to the research field of solar fuels. In particular, the use of these techniques in all the investigated set-ups had contributed to shed light on the mechanistic pathways involved in the oxidation/reduction reactions, allowing for the identification of bottlenecks and paving the way for the further design of materials with enhanced performances.

Website & more info

More info: http://www.unife.it/ricerca/finanziamenti-gestione/ricerca-internazionale/progetti/arcadia.