A Study on the Synthesis of Multiphase PdxSey with Organometallic Precursors and Investigation of Phase Dependent Electrocatalytic Properties

Abstract

Platinum has excellent performance in fuel cells and has established itself as a representative catalyst for electrochemical reactions, but its use is still limited due to its high price and scarcity. Palladium-based catalysts, which have an electronic structure similar to the platinum, are expected to have analogous electrical activity, and they have emerged as a substitute for platinum, especially in the oxygen reduction reaction (ORR) field. However, their strong bonding with oxygen resulted in a decrease in electrochemical catalyst performance, and studies were conducted to control the intrinsic electronic structure of the catalyst surface through metal alloying, strain control, defect design, and facet adjustment. Among them, it has been reported that palladium-nonmetal catalysts can increase the active sites of the catalyst, including many surface dangling bonds and defects for amorphous phases, or make changes in the electronic structure due to strain made by being physically included in the crystal structure, thereby increasing electrocatalytic performance. Additionally, when an oxygen group nonmetallic element such as Se and Te are included, it is many multiple phases are present (Pd17Se15, Pd7Se4, etc..), that is, the catalyst properties can be arbitrarily adjusted according to changes in the distribution of the multiple phases. Based on these advantages, we synthesize multiphase palladium selenides (PdxSey) containing selenium in palladium. More efficient Pd-Se bond formation was induced through a single organometallic precursor introduced in the synthesis process, and a uniform film was formed by a synthesis method that proceeded through the solvent process. The phase composition of multiphase PdxSey was confirmed by Rietveld refinement based on the X-ray diffraction (XRD) result, and it was revealed that the ORR performance of the catalyst was superior to commercial Pd/C and Pt/C with a half-wave potential of 0.931V. In particular, the sample synthesized under a specific temperature condition of 1000 ℃ showed the smallest half-wave potential change of about 0.007V after 20K cycles in the accelerated durability test, proving that multiphase PdxSey can be used as an efficient ORR catalyst. Based on these results, the effect of a specific palladium selenides phase on the overall ORR catalyst characteristics was analyzed.