Studies of oxygen reduction activity and stability of carbon-supported PdNi and PdCu nanoparticles of different compositions

• Autor(a) principal: Khan, Muhammad Sufaid
• Data de Publicação: 2018
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/152940
• topic: Oxygen reduction reaction; Pd-based catalysts; PdM nanoparticles; Electrocatalysis; Fuel cell cathode; Redução de oxigênio; Catalisadores baseados em Pd; Nanopartículas PdM; Eletrocatálise; Cátodo

The slow kinetics of the oxygen reduction reaction is the main cause of the severe performance losses of fuel cell cathode. Pt is the most active pure metal to catalyze this reaction. However, because of their limited availability and high price, the use of cheaper metals to act as catalysts in fuel cell electrodes is highly desirable. In this context, Pd-based catalysts are getting increasing attention. Thus, the main objective of this work was to study the oxygen reduction reaction on carbon-supported PdM (M = Ni, Cu) catalysts with different atomic ratios (Ni and Cu 10-50% in atoms), in acidic and alkaline solutions. The modified polyol method was used for the preparation of PdM nanoparticles that were then supported on carbon powder. The catalysts were characterized by X-ray diffraction (XRD) to investigate the crystalline structure and by X-ray absorption spectroscopy (XAS) to examine the electronic properties. The electrochemical behavior was studied by cyclic voltammetry. The PdNi/C and PdCu/C catalyst and a Pd/C reference sample were evaluated as electrocatalysts for the oxygen reduction reaction in acidic and alkaline solutions using the rotating ring disk electrode technique. Results showed formation of PdM alloys and an increase in the electronic occupation of the Pd 4d band. In both media, all PdM/C samples were more active for oxygen reduction than Pd/C, with activity increasing as the percentage of Ni or Cu increased. The production of hydrogen peroxide was small indicating that the reduction of oxygen proceeds mainly via the four-electron path. PdCu/C catalysts were more active than PdNi/C materials in acidic medium, but PdNi/C samples had better performance in alkaline solution. In addition, stability tests revealed that the presence of Ni and Cu considerably decreases the dissolution of Pd in acidic medium, although the stability of the materials was lower in alkaline than in acidic medium.