During the 1st year of the project, work on the different components of the CONFETI’s prototype for fertilizer production has been conducted in parallel:
(1) We have developed several key components of the electrolyser for urea production from CO2 and N-compounds. Three families of green solvents combining good CO2 sorption properties with high ionic conductivities based on Ionic Liquids (ILs) were examined for this purpose: 7 commercially available ILs, 1 bio-based IL, and 15 synthesised ILs based on aprotic heterocyclic anions (AHA ILs), which were then immobilised into solid (bio)polymer membranes. After implementing different methodologies for determining the CO2 capture efficiency and speciation of these materials, we obtained very positive results for AHA IL-based membranes (capture up to 4.0 mg CO2/g membrane directly from air in about 5 min and long-term stability). Second, different classes of liquid and solid electrolytes have been explored for electrolyser operation. Liquid aqueous electrolytes have been optimised to favour urea production (1.34 µmol/cm²·h at Eapp = -1.5 V vs Ag/AgCl). Interestingly, for NO₃⁻-containing ILs and membranes, urea production could be observed at relatively low voltages (-1.77 V vs Ag/AgCl) and with significant current densities (up to 85 mA/cm²). Third, a range of electrocatalysts have been prepared, including metal-containing N-doped carbon materials (Ni, Ag, Cu and In), VO-InOOH, quaternary chalcohalide semiconductors, and ternary II-III2-VI4 colloidal nanocrystals. Combined experimental and computational efforts are under way to design and produce better electrocatalysts.
(2) For powering the electrolyser, work has been carried out to optimise the performance of soil microbial fuel cells (SMFCs) in terms of soil type, bioanode preparation (co-immobilisation of bacteria and redox mediators in silk) and cell configuration (parallel stacks). Moreover, printed circuit boards have been successfully developed and tested for both storing the energy provided by SMFCs and, if necessary, solar panels as well as powering and controlling the electrolyser at low voltage ranges.
(3) For valorising the residual nitrates generated upon soil fertilisation, a library of photocatalysts were synthesised at a large scale (> 5 g). The photocatalytic activity for nitrate reduction of most of these materials has been tested at the lab and pilot reactor scales, obtaining very successful results for the TiO2-CuO system: total NO₃⁻ conversion with 78.7% selectivity for NH₄⁺ formation after 4 hours of irradiation (50 kJ/L).
In parallel to these scientific-technological activities, a life cycle assessment of the materials and technologies developed is under progress to allow identification and minimisation of their environmental impact, which so far has focused on the CO2 sorbents prepared.
