Oxygen reduction and evolution in alkaline media on Pd nanoparticles supported on Ti-based materials

Electrocatalysts for the oxygen reduction and/or the oxygen evolution reactions play a key role determining the performance of energy conversion/storage devices, such as fuel cells, electrolysers, regenerative fuel cells or, recently, metal-air batteries [1, 2]. In particular, the life and cost of these devices are directly related to the durability of the catalysts [3, 4]. The high potentials reached, particularly during the oxygen evolution, limit the use of carbonaceous materials as catalysts' supports [2]. The corrosion of the carbon support is one of the main issues affecting the catalyst durability, given that carbon is unstable under such conditions [5]. Thus, highly stable catalysts are required. Titanium suboxides are recognized for their high stability under harsh electrochemical conditions [6, 7]. They were successfully used as a support for iridium oxide in PEM-electrolysers [8]. In the present work, titanium oxides have been studied as Pd-catalysts' supports for their use towards the oxygen reduction and the oxygen evolution reactions (ORR/OER) in alkaline media. In previous works, Pd/C catalysts have been proved to be efficient bifunctional materials for ORR/OER [9,10]. Nevertheless the stability of these materials was not optimal. For this reason, titanium based materials were selected as support with the aim of improving the durability of catalysts towards these reactions (ORR and OER). Pd nanoparticles were supported on titanium-based materials by a sulphite complex route. Catalysts were characterized by means of X-ray diffraction, transmission electron microscopy and N 2 adsorption. Polarization curves were performed in a half-cell system in alkaline solution (KOH) studying the behavior of catalysts for both reactions: the oxygen reduction reaction and the oxygen evolution reaction. All catalysts were compared to a Pd/C catalyst made in-house by using Vulcan as support. Pd on Vulcan proved to be more performing than Pd supported on the titanium-based materials for both reactions. This was ascribed to the better metallic dispersion of Pd particles on the carbon support, favouring a higher surface area and, thus, a higher activity. Catalysts were submitted to several stress tests (ST) in order to analyze the stability of the catalysts, evaluating the activity before and after the ST. Pd supported on the titanium-based materials presented a higher activity after ST than Pd/C.