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D1.4 Scale up process for PEcats synthesis - Executive Summary

The aim of deliverable 1.4 is to collect all the work carried out in task 1.3 to validate at pilot scale the synthesis protocols of BiVO4 and Cu2O/SnO2 photoelectrocatalysts, previously defined at lab–scale in task 1.2. Main criteria for processes optimization were defined in tasks 1.1 and 1.2 and correspond with appropriate crystal phase, nanoparticle size and morphology, and chemical composition.

Scanning electron microscopy demonstrated that sort of spherical BiVO4 clusters were obtained, with sizes mainly ranging from 2 μm to 3 μm regardless the addition flow employed for the NaOH precursor. The spherical BiVO4 clusters are constituted by smaller BiVO4 building blocks with various sizes and morphologies, depending on the addition flow employed for the NaOH precursor. The lower was the addition flow the smaller were the BiVO4 building blocks.

X–ray powder diffraction was employed to determine the BiVO4 crystalline phase. The samples always exhibited monoclinic crystalline phase, regardless the addition flow employed for the NaOH precursor. However, presence of bismuth oxides and vanadium oxides mixtures were found when addition flows of 63.0 mL·min–1 were employed.

Considering scanning electron microscopy as well as X–ray powder diffraction experiments, BiVO4–II and BiVO4–III samples seem to be the most promising samples, while we consider BiVO4–I sample must be discarded due to the presence of impurities.

Scanning electron microscopy demonstrated that Cu2O nanoparticles always exhibited cubic morphologies regardless the addition flows employed for both the NaOH and the L–ascorbic acid precursors. Cu2O nanoparticle size depends on the addition flow employed for both the NaOH and the L–ascorbic acid precursor. The higher was the addition flow the smaller was the nanoparticle size. No changes in both morphology and size were observed by scanning electron microscopy when the Cu2O nanoparticles were covered by the SnO2 shell during the coordination etching process. Mapping experiments revealed good composition homogeneity in all the evaluated Cu2O/SnO2 nanoparticles, demonstrating that the SnO2 shell is properly covering the Cu2O nanoparticle. Microanalysis experiments were reproducible and revealed slightly higher although acceptable measured Cu:Sn molar ratios than the expected 40:1 Cu:Sn molar ratios.

Considering scanning electron microscopy, mapping, and microanalysis experiments, we considered the 40–Cu2O–IV/SnO2 sample as the most promising sample as exhibited the less nanoparticle size, and as far as we know the less nanoparticle size the higher SBET surface, which is a key characteristic for the Cu2O/SnO2 electrochemical activity.