Modulating Catalytic Activity and Durability of PtFe Alloy Catalysts for Oxygen Reduction Reaction Through Controlled Carbon Shell Formation

Abstract

Demand on synthetic approaches to high performance electrocatalyst with enhanced durability is increasing for fuel cell applications. In this work, we present a facile synthesis of carbon shell-coated PtFe nanoparticles by using acetylacetonates in metal precursors as carbon sources without an additional polymer coating process for the carbon shell formation. The carbon shell structure is systematically controlled by changing the annealing conditions such as the temperature and gas atmosphere. PtFe catalysts annealed at 700 °C under H2-mixed N2 gas show much higher oxygen reduction reaction (ORR) activity and superior durability compared to a Pt catalyst due to the ultrathin and porous carbon shells. In addition, when increasing the annealing temperature, the carbon shells encapsulating the PtFe nanoparticles improves the durability of the catalysts due to the enhanced crystallinity of the carbon shells. Therefore, it is demonstrated that the developed hybrid catalyst structure with the carbon shells not only allows the access of reactant molecules to the active sites for oxygen reduction reaction but also prevents the agglomeration of metal nanoparticles on carbon supports, even under harsh operating conditions. The proposed synthetic approach and catalyst structure are expected to provide more insights into the development of highly active and durable catalysts for practical fuel cell applications.

Graphene Blocks Oxidative Segregation of Iron Dissolved in Platinum: A Model Study

“…In this respect, carbon-based graphitic or graphene-like coatings were found to be more promising, as they do not only inhibit oxidation, but also suppress the aggregation of nanoparticles [7,14] while preserving (or even increasing) the catalytic activity of the Fe-Pt systems. [8][9][10][11] Model studies carried out under idealized ultrahigh vacuum (UHV) conditions revealed that epitaxial graphene (Gr) may act as a protective layer against oxidation of metal single-crystal surfaces, including those of catalytically-active [111]-oriented platinum (Pt(111)) [15][16][17] and ferromagnetic nickel (Ni(111)). [18] Even though the Gr layer covers the surface of the metal, it still allows the diffusion of oxygen atoms chemisorbed on the metal substrate to the confined space between the carbon sheet and the metal support [19][20][21] and further reaction of gaseous species (e.g., carbon monoxide (CO)) with the oxygen atoms residing underneath graphene (which is referred to as catalytic reactions "under cover" [22] ).…”

“…In this respect, carbon‐based graphitic or graphene‐like coatings were found to be more promising, as they do not only inhibit oxidation, but also suppress the aggregation of nanoparticles [ 7,14 ] while preserving (or even increasing) the catalytic activity of the Fe–Pt systems. [ 8–11 ]…”

“…[1] Those composed of iron and platinum (Fe-Pt), typically in the form of nanoparticles, are the well-known hard ferromagnets [2][3][4][5][6][7] and electrocatalysts. [8][9][10][11] The main technological problems related to the industrial application of Fe-Pt compounds include the segregation of iron and iron oxides formation under oxidative conditions (such as exposure to air [12] ), as well as aggregation of nanoparticles, [13] all of which alter the properties of Fe-Pt systems. Several approaches were used to protect the Fe-Pt compounds from oxidation: Han et al have shown that reveal a blocking effect of Gr on the iron oxide formation, even though oxygen can still diffuse underneath the carbon layer.…”

Metal Organic Framework Derived MnO2-Carbon Nanotubes for Efficient Oxygen Reduction Reaction and Arsenic Removal from Contaminated Water

“…These efforts resulted in promising ORR catalysts which can be broadly classified into three categories: non-PGM metal catalysts [2], metal-free catalysts especially hetero-atom doped carbons [3] and hybrids of non-PGM catalysts with carbon nano-structures [4]. Amongst these three, the third type of carbon-metal hybrids which consists of nano sized non-PGM metal compounds of iron [5], cobalt [6], manganese [7] etc. embedded/dispersed/anchored on nano scaled carbons such as graphene [8], carbon nanotubes [9] and carbon nanofibers [10] have rapidly evolved as attractive alternatives to PGM based ORR electro-catalysts.…”

N8− Polynitrogen Stabilized on Nitrogen-Doped Carbon Nanotubes as an Efficient Electrocatalyst for Oxygen Reduction Reaction

“…However, among the factors hampering the widespread application of PEMFCs, are the high-cost and low-performance electrocatalysts, which are responsible for accelerating the sluggish oxygen reduction reaction (ORR) at the cathode, and still need to be improved [10,11]. Pt/C, the current state-of-the-art ORR catalyst, suffers from inherent scarcity, insufficient stability, and high cost [12,13]. Although nonprecious metal catalysts, such as Fe-, Co-, Cu-, and Ni-based materials, can lower the cost, activity and metal leaching are the two major issues to be solved [14][15][16].…”