Go Alloy Technology Preparation Of Oxygen-reduction Catalyst

Oxygen reduction reaction (ORR) plays an important role in fuel cells, such as polymer electrolyte fuel cells and proton exchange membrane fuel cells. Electrocatalysts including nanoparticles (NPs), macrocycles and pyrolysis products, carbons, chalcogenides, enzymes, and coordination complexes have been reported for ORR use and reviewed recently. Comparatively, among the reported electrocatalysts, NPs of platinum and platinum based alloy are the most widely used and studied catalysts. However, because of the high cost and low abundance of Pt, practical use and introduction of fuel cells into markets are limited. So the most critical challenges for the study and application of fuel cells have been to develop alternative electrocatalysts that will retain the high activity of Pt while lowering the cost.The main works are as follows:1. Generation of OH Radicals in Oxygen Reduction Reaction at Pt-Co Nanoparticles Supported on Graphene in Alkanline SolutionsPt-Co alloy nanoparticles supported graphene were studied for electrocatalytic oxygen reduction. The alloy catalysts showed higher ORR activity than pure Pt catalysts. The compositon of the alloy affected had effects on ORR activities and rate constants, proportion of hydroperoxide, number of electron transfer. In the region of 1:0.25 to 1:1 of the Pt:Co atomic ratio, ORR activities and rate constants, proportion of hydroperoxide increased with increasing Co content, but number of electron transfer decreased. When Co content was higher than 50 at.%, ORR activities and rate constants, proportion of hydroperoxide decreased. Thus, obtaining a volcano dependence of ORR activity upon alloy composition. OH radicals was found during ORR at alloy catalyst in alkaline solutions and the generation also had a volcano dependence of ORR activity upon alloy composition with Pt1Co1 alloy giving highest quantity of OH radicals. This study may be helpful to designing ORR alloy catalysts with higher activity but low yield of OH radicals, because OH radicals are detrimental to the membrane electrode assembly of fuel cells.2. Effects of Acid Treatment of Pt-Ni Alloy Nanoparticles@Graphene on the Kinetics of the Oxygen Reduction Reaction in Acidic and Alkaline SolutionsAcidic dissolution of transition metals from Pt based alloy catalysts for oxygen reduction reaction (ORR) is an unavoidable process during fuel cell operation. In this work we studied effect of acid treatment of graphene-supported Pt₁Ni_x (x=0, 0.25, 0.5, 1 and 2) alloys on the kinetics of the ORR in both alkaline and acidic solutions together with the generation of OH radicals in alkaline solutions. The alloy nanoparticles were synthesized through co-impregnation and chemical reduction. The electronic and structural features of the alloy were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. The ORR performances were studied using cyclic voltammetry and rotating ring disk electrode techniques in 0.05 M H₂SO₄ and 0.1 M NaOH, respectively. The alloy catalysts were more active than pure Pt toward ORR, and after acid treatment the ORR activity of Pt-Ni alloy was enhanced in both acidic and alkaline media. The maximum activity of the Pt-based catalysts was found with ca. 50 at.% Ni content in the alloys (Pt₁Ni₁@graphene). OH radicals were generated through dissociation of hydroperoxide at the catalysts'surface and detected by fluorescence technique using terephthalic acid as capture reagent, which readily reacts with OH radical to produce highly fluorescent product, 2-hydroxyterephthalic acid. More OH radicals were found to be generated at Pt1Ni1@graphene catalyst. This work may be valuable to design ORR electrocatalysts with higher ORR activity but lower efficiency of OH radical generation.