Electrochemical activity of PtM (M=Co, Cu, Ni) catalysts supported on carbon vulcan for oxygen reduction reaction (ORR) in fuel cells

In this work, nanoscale bimetallic PtNi, PtCo, PtCu catalysts on carbon Vulcan XC72R as supports were synthesized by reduction method under ultrasonic irradiation. The morphology, structure and specific area of synthesized materials were characterized by X-Ray diffraction (XRD), transmission electron microscopy (TEM). The catalytic activity for oxygen reduction reaction (ORR) of PtM/C was investigated by CV and linear sweep voltammetry (LSV) under simulated fuel cell working conditions.
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Electrochemical activity of PtM (M=Co, Cu, Ni) catalysts supported on carbon vulcan for oxygen reduction reaction (ORR) in fuel cellsVietnam Journal of Science and Technology 56 (2A) (2018) 81-88 ELECTROCHEMICAL ACTIVITY OF PtM (M=Co, Cu, Ni)CATALYSTS SUPPORTED ON CARBON VULCAN FOR OXYGEN REDUCTION REACTION (ORR) IN FUEL CELLS Vu Thi Hong Phuong1,*, Tran Van Man2, Le My Loan Phung2 1 Faculty of Chemical Engineering, University of Ba Ria-Vung Tau, 80 Truong Cong Dinh St., Ward 3, Vung Tau City, Viet Nam 2 Applied Physical Chemistry Laboratory, Faculty of Chemistry VNUHCM - University of Science, 227 Nguyen Van Cu St., Ward 4, District 5, Ho Chi Minh City, Viet Nam * Email: fashionhandp@gmail.com Received: 10 March 2018; accepted for publication: 14 May 2018 ABSTRACT PEMFC - proton exchange membrane fuel cell is electrochemical devices producingelectricity and heat from reaction between a fuel (often hydrogen) and oxygen. Therefore,energy production is generally clean and effective without burning the fuel like the tradition wayin combustion engines. The obstacles encountered fuel cell commercialization are mainly due toexpensive catalyst materials (Platinum) and long-term instability performance. For this reason,numerous investigations have been undertaken with the goal of developing low-cost, efficientelectrocatalysts that can be used as alternatives to Pt. In this paper, a two-step procedure at roomtemperature was applied to prepare a bimetallic Pt-M(M = metal) supported carbon Vulcan.First, the chemical reduction of M metal ions by sodium borohydride in the presence of carbonpowder is performed. Second, the partial galvanic replacement of M particle layers by Pt isachieved upon immersion in a chloroplatinate solution. The major size of synthesized metallicparticles was around 2-3 nm. From the slope of Koutecky-Levich plot for ORR using PtM/Cmaterials as catalysts it was found that the overall electron transfer number ranged from 3 to 4,leading to the suggestion of H2O2 formation as an intermediate of the ORR.Keywords: catalyst, electrochemical, oxygen reduction reaction, fuel cell. 1. INTRODUCTION Fuel cells are attractive power sources for both stationary and electric vehicle applicationsdue to their high conversion efficiencies and low pollution [1]. The commonest electrocatalystfor fuel cells is Pt, which is highly effective for accelerating the slow kinetics of oxygenreduction reaction (ORR) where io is 2.8×10 7 mA/cm2 at 30 °C. However, challenges for thiscatalyst are its scarcity and high cost, as well as the poisoning by the intermediates of the fueloxidation, such as carbon monoxide (CO). For this reason, numerous investigations have beenundertaken with the goal of developing low-cost, efficient electrocatalysts that can be used as Le Minh Ha, Ngo Thi Phuong, Le Ngoc Hung, Vu Thi Hai Ha, Bùi Kim Anh, Pham Quoc Longalternatives to Pt. In recent years, bimetallic PtM materials have attracted much attentionbecause of their active and stable electrocatalytic performance for alcohol oxidation and oxygenreduction reaction at low temperatures in proton exchange membrane fuel cells (PEMFCs). Avariety of techniques have been applied to synthesize electrocatalysts for fuel cell, one of theseis chemical reduction method [2]. The advantage of this method is generating nano alloyparticles with comparatively unique size in short time. These extreme conditions allowhomogenization of the alloy phases and lead to the formation of uniformly distributed and nanosized bimetallic materials [3]. In this work, nanoscale bimetallic PtNi, PtCo, PtCu catalysts oncarbon Vulcan XC72R as supports were synthesized by reduction method under ultrasonicirradiation. The morphology, structure and specific area of synthesized materials werecharacterized by X-Ray diffraction (XRD), transmission electron microscopy (TEM). Thecatalytic activity for oxygen reduction reaction (ORR) of PtM/C was investigated by CV andlinear sweep voltammetry (LSV) under simulated fuel cell working conditions. 2. EXPERIMENTALS2.1. Synthesis of nano PtM/C catalysts Briefly, Ni(NO3)2(or Co(NO3)2.6H2O; CuSO4 -SigmaeAldrich) was dissolved in ultrapurewater. After 15 min of constant stirring carbon Vulcan and citric acid (CA) was added to thesolution. M material nanoparticles supported on carbon were formed by reduction of the metalprecursor with NaBH4 which was added as a solid to the mixture in a weight ratio of 3:1 tometal. The resulting mixture was then left under constant stirring over night and the formedsupported catalyst was collected via suction filtration, washed thoroughly with ultrapure water,ethanol, and acetone and finally dried over night at 80 oC. Afterwards, the synthesized M/C, CAand H2PtCl6 0.05 M (Aldrich) were dissolved in ultrapure water. After 1 hour of constantstirring, the mixture was treated with NaBH4 0.15 M which was added and left under stirringover night and the formed Pt(M) supported on carbon was collected via suction filtration,washed thoroughly with ultrapure water, ethanol, and acetone and finally dried over night at80 0C. The ratio of total metal loading to carbon support was 20 wt%.2.2. Electrode preparation 2.50 mg of PtM/C (M = Co, Cu, Ni) (carbon Vulcan - supported) catalysts and 10 µl of 5wt% Nafion (Sigma Aldrich, 65 %) were added to 1.0 mL of ethanol solution. The formed inkwas irradiated ultrasonically in 1 hour. A volume of 75 µl of the ink was dropped on a glassycarbon support (12.56 mm2), and the prepared working electrode was dried at room temperaturein 1 hour.2.3. Physical – chemical and electroch ...