Electrocatalysts composed of metalic nitrides, carbides, and oxides for the oxygen electrode

Author(s)

Aniélli Martini Pasqualeti

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2017-05-26

Examining board members

Fabio Henrique Barros de Lima; Pedro Henrique Cury Camargo; Maria Valnice Boldrin Zanoni

• Advisor: Fabio Henrique Barros de Lima

Abstract

The development of conductive electrocatalysts with high activity for the oxygen reduction and evolution reactions (ORR and OER) is of extremely importance for devices that electroconvert energy, such as fuel cells and electrolizers, which work in alkaline and acid media. A substantial amount of metals can be employed in alkaline electrolytes once the latter do not require the use of noble metals. The acid medium asks for stable materials, since they are exposed to a high oxidative environment and potentials during the start-up/shutdown events of the device. On the base of these facts, this research work has been divided into three parts: Part I - bifunctional electrocatalysts studies for the ORR and OER in alkaline electrolyte, the materials were composed of spinel manganese-cobalt oxide combined with gold nanoparticles (MnCo2O4/Au). Part II - studies of alternative electrocatalysts for the ORR in acid electrolyte, which included molybdenum carbides and nitrides (Mo2C-MoN), and tantalum oxynitrides (Ta-ON). Part III - alternative supports to the carbon for the ORR in acid electrolyte, which included tantalum and titanium carbonitrides (Ta-CN and Ti-CN). The results for MnCo2O4/Au, in Part I, showed that the addition of gold on the surface of the oxide improved the latter activity for both reactions. The combination of conductive nanoparticles (gold) with active, but non-conductive, nanoparticles (MnCo2O4) seems promising for the development of active electrocatalysts for the ORR and OER. In Part II, the materials composed of Mo2C-MoN were synthesized through carbon and nitrogen insertion, in a high temperature heat treatment, in the presence of Vulcan carbon and NH3. Among the gotten materials, the so called MoN + Mo2C (molybdate) showed the better electrocatalytic activity for the ORR, which could be attributed to its smaller crystallite size and the greater amount of its MoN phase, along with the synergistic effect between MoN and Mo2C. In this way, tantalum oxynitrides materials were obtained via a urea synthesis. The catalyst referred to as Ti-Ta-ON showed the better ORR activity among all the others studied oxynitrides materials. In Part III, besides the activity for the ORR of platinum supported on titanium carbonitride (Pt/Ti-CN) was similar to the activity of platinum supported on carbon (Pt/C), Pt/Ti-CN was also more stable than the latter, after the stability tests. (AU)

• FAPESP's process: 13/03408-0 - Bifunctional Electrocatalysts for Reaction Involved in Regenerative Electrochemical Energy Conversion Devices that Operate with H2/O2.
• Grantee: Aniélli Martini Pasqualeti
• Support Opportunities: Scholarships in Brazil - Doctorate