Graphene‐Supported Substoichiometric Sodium Tantalate as a Methanol‐Tolerant, Non‐Noble‐Metal Catalyst for the Electroreduction of Oxygen

Abstract

For the oxygen reduction reaction (ORR) in acidic medium, a good combination of an active and stable catalyst highly dispersed on a conductive and durable support is required. Moreover, for direct methanol fuel-cell applications, a suitable tolerance to methanol poisoning is also necessary. In this communication, we report on a new graphene-supported sodium tantalate (Na 2 Ta 8 O 21Àx ) electrocatalyst obtained at high temperature and characterized by significant substoichiometry. The synthesis includes the precipitation of tantalum oxide on a high surface area graphene and subsequent thermal treatment at 900 8C. A novel sodium tantalate phase with oxygen vacancies is thereafter obtained. This catalyst formulation shows promising activity towards the ORR especially in the presence of a high methanol concentration, as evidenced by a high tolerance to methanol poisoning. Accelerated stress tests and chemical leaching experiments also show the remarkable stability of the catalyst. This material presents good perspectives for application in cost-effective fuel cells.A highly active, durable, and cost-effective catalyst for the oxygen reduction reaction (ORR) is essential for the large-scale application of low-temperature fuel cells. State-of-the-art catalysts for fuel cells are based on precious metals, essentially platinum (Pt). The prohibitive cost of Pt, its scarce resources, and its insufficient durability hinder the commercialization of this fuel-cell technology. [1,2] Direct alcohol fuel cells (DAFCs) will presumably reach wide-scale commercialization earlier than hydrogen-fuelled cells owing to the easy handling and high energy density of organic fuels, especially covering portable power application (laptops, mobile phones, etc.) and auxiliary power units (APUs). Application of DAFCs in portable and APU devices can accelerate the fuel-cell technology diffusion. [2,3] In the case of a DAFC, the poisoning effect of the alcohol that permeates through the membrane is an additional concern to the sluggishness of the electrochemical reactions at both the anode and the cathode. [3,4] Now, only a few types of electrocatalysts based on nonprecious metal formulations have been found to be active towards the ORR in acid media. These include carbon-supported transition-metal/nitrogen compounds (Fe/N/C, Co/N/C), [5][6][7][8][9][10][11] metal-free nitrogen-doped carbon materials, [12,13] and transition-metal chalcogenides. [14,15] Although Fe-and Co-based catalysts have been studied for the ORR for over 50 years, a suitable enhancement in the catalytic activity has been achieved only very recently. [5,8,16] These catalysts are potential competitors to Pt in terms of activity, [5,8] whereas significant efforts are still required to further enhance their stability. [6,7] Piela et al. have also reported promising tolerance to methanol poisoning for a Co-based catalyst. [17] Graphene, a free-standing atomic thin layer of sp 2 carbon atoms, has emerged as the most interesting carbon material in the last decade because of its unp...

Transition Metal–Nitrogen–Carbon (M–N–C) Catalysts for Oxygen Reduction Reaction. Insights on Synthesis and Performance in Polymer Electrolyte Fuel Cells

“…To be effective as support, the C-based material must have a sufficiently high surface area (to ensure high active sites density) and a good electrical conductivity. Several types of carbon-based materials have been used, such as different types of carbon black (e.g., Ketjen Black, Vulcan XC72, Black Pearls, acetylene black) [46,[52][53][54][55][56][57], carbon nanotubes [58][59][60][61], carbon nano-networks [62], reduced graphene oxide [47,[63][64][65][66], and ordered mesoporous carbons [50,67,68]. Some studies have put in evidence the great importance of the carbon support to provide a good ORR activity to the catalyst.…”

Enhancing Oxygen Reduction Reaction Catalytic Activity Using a Sub‐Stoichiometric CaTiO3−δ Additive

“…Nevertheless, non‐stoichiometric transition metal oxides are more active towards the ORR thanks to the introduction of oxygen vacancies at their surface. These can modify the oxidation state of metal species, forming active catalytic sites able to adsorb O 2 , and introduce new electronic levels in the energy gap …”

Application of a non-noble Fe-N-C catalyst for oxygen reduction reaction in an alkaline direct ethanol fuel cell

“…One of the main problems of PEMFC is the slow kinetics of the oxygen reduction reaction (ORR), which requires the use of noble metals (mainly Pt) as catalysts, with a consequent rise of the fabrication costs [10]. For DAFC, the electro-oxidation of the organic molecules occurring at the anode is a kinetically slow process as well, requiring the use of noble-metal based catalysts also at the anode [11].…”