We have investigated platinum catalysts containing iron as a modifier to obtain catalysts with superior electrocatalytic activity toward glycerol electro-oxidation in an alkaline medium. The electrocatalysts, supported on carbon Vulcan, were synthesized by the polyol method. The physicochemical characterization data showed that the metals were well distributed on the carbon support and had small particle size (2 nm). The Pt:Fe metal ratio differed from the nominal composition, indicating that reducing iron with platinum was difficult, even though some parameters of the synthesis process were changed. Electrochemical analyses revealed that PtFe/C was more active and stable than commercial Pt/C was, and analysis of the electrolysis by-products showed that iron addition to Pt/C boosted the glycerol conversion and selectivity for glyceric acid formation.

Complex oxides have emerged as potential next-generation components for photoelectrodes in reactors for solar energy conversion, due to their improved sunlight harvesting and enhanced stability in comparison to well-known semiconductors based on binary oxides. However, the experimental performances achieved with these emergent materials are still far from the theoretical values. The properties of these complex oxides largely depend on structure, particle-size, morphology and other tuneable characteristics that can be controlled by the synthesis methodology. The aim of this review is to discuss recent progress in synthesizing multinary complex oxides, presenting some common and also less conventional synthesis approaches, which are organized here into “dry” or “wet” methods. Then, we hope to contribute to the development of n and p-type semiconductors for photoelectrochemical generation of fuels like H₂ from water splitting and C-based products from CO₂ reduction or biomass valorisation, as well as, other reactions in the field of sustainable energy.

Complex oxides can present interesting semiconductor properties since the simultaneous presence of different metallic cations can modulate the conduction and valence band edges, affecting the bandgap energy, the onset potential for reactions and also the photocatalyst long-term stability. Here, we demonstrated that the synthesis of multinary oxides, very challenging using “traditional” methodologies, can be fast achieved by melting the precursor binary oxides in an arc furnace. As a proof of concept, arc-melting a mixture of Bi2O3 and V2O5 (Bi:V molar ratio of 1:1.05) resulted in almost pristine BiVO4 (97.3% from Rietveld refinement of X-ray diffraction (XRD) data); photoelectrochemical (PEC) measurements indicated a promising application as a photoanode for O2 evolution reaction. Conversely, the arc-melting of Bi2O3 and WO3 mixture (Bi:W molar ratio of 2:1.15) resulted in the biphasic Bi2WO6/Bi2W2O9; preliminary PEC analysis revealed characteristics of n-type semiconductor electrode with photoactivity under UV irradiation. Finally, the hierarchical Ag@α-AgVO3/Fe2O3 consisted of micrometric Fe2O3 particles decorated by AgVO3 nanoribbons and Ag nanoparticles, was obtained from melting Ag2O, Fe2O3 and V2O5 as precursors (Ag:Fe:V molar ratio of 3:1:2); PEC measurements also revealed possible application as a photoanode. The results for these three materials demonstrated the arc-synthesis as a fast, effective and scalable methodology for synthesizing complex oxides.

Photoelectrodes based on earth‐abundant elements, FTO|BiVO ₄ and Ni _foam |Cu ₂ O/CuO/TiO ₂ , were assembled in a parallel‐configured flow photoelectrochemical (PEC) electrolyser and provided unassisted conversion of glycerol and CO ₂ into value‐added chemicals under solar‐simulated irradiation. The photoelectrodes PEC properties were firstly evaluated in aqueous NaHCO ₃ electrolyte, using platinum as auxiliary electrode, for determination of wavelength‐resolved light harvesting, flat band potential, conduction and valence band edges, charge‐separation and injection efficiencies. Comparison of Ni _foam |Cu ₂ O, Ni _foam |Cu ₂ O/CuO and Ni _foam |Cu ₂ O/CuO/TiO ₂ for PEC CO ₂ reduction revealed that Cu ₂ O/CuO improved light harvesting and selectivity for ethanol production, while TiO ₂ protected the photocathode against photodegradation. Under illumination, the PEC flow electrolyser assembled with FTO|BiVO ₄ and Ni _foam |Cu ₂ O/CuO/TiO ₂ exhibited + 0.56 V of open‐circuit photovoltage and a spontaneous short‐circuit photocurrent (1.7 to 1 mA in 2 h), attributed to the suitable alignment of the band edges of these photoelectrodes. After 2 h PEC electrolysis, formate (229 µg cm ⁻² h ⁻¹ ) and glycolate (58.5 µg cm ⁻² h ⁻¹ ) were produced in the anodic compartment with faradaic efficiencies of 69% and 13%, respectively. The cathodic compartment generated 26 µg cm ⁻² h ⁻¹ of ethanol (FE = 32%). This flow PEC electrolyser demonstrates a proof‐of‐concept for a practical solar‐to‐chemicals production using industrial by‐products as feedstocks.