(Ni,Mo)-TiO2 electrodes for electrochemical applications

• Autor(a) principal: Santos, Rodrigo Miguel Franco dos
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/28071
• topic: Electrochemical properties; Ceramic materials; Magnéli phases; Ni-Mo alloy; SOFC; Electrolysis

One of the major issues of the renewable energies is their dependence of the weather conditions. If those are favourable, the energy will be produced in excess and wasted, due to limited capacity of the existing storage technologies. On the contrary, if the weather conditions are unfavourable, the energy produced will be insufficient, thus requiring the consumption of fossils fuels to assure a constant electrical output. The reversible solid oxide fuel cells (RSOFC) can contribute to the solution of this problem, provided by capability to operate in two different modes, with the hydrogen or carbon as the energy carrier. In one mode, the electricity is produced by the transformation of hydrogen into water, this is to be used when the weather conditions are unfavourable. In reverse operation mode, hydrogen is produced from the water using the excess of electricity produced by renewable energies, when the conditions are favourable. Although being fairly efficient and highly promising, this technology is still not widely available due to high electrode degradation, expensive catalytic materials, low resistance to carbon deposition and difficulties of the hydrogen storage, among others. This work was initially focusing on development of a composite material for fuel electrodes of Reversible Solid Oxide Fuel Cells (RSOFC). Base on the literature review, the nominal NiTiO3 (reference), NiTiO3 (90% mol.)- MoO3 (10% mol.) and NiTiO3 (80% mol.)- MoO3 (20% mol.) compositions were selected, prepared and characterized in the conditions, relevant for RSOFC operation. The electrical measurements combined with structural studies revealed fast degradation due to oxidation even at low temperatures, rendering their application problematic for RSOFC technology. Additional assessment of the prepared materials as electrocatalysts for alkaline water electrolysis was performed and demonstrated their potential applicability for boosting hydrogen evolution process if the applied cathodic polarization is sufficient to prevent oxidation of the Magnéli phases and decomposition of metallic phases, or redox cycling can be applied to recover the electrode surface. The obtained experimental results were correlated with thermodynamic predictions made by calculation of Ellingham and Pourbaix diagrams.