Efficient Oxygen Reduction Fuel Cell Electrocatalysis on Voltammetrically Dealloyed Pt–Cu–Co Nanoparticles

Abstract

The electrocatalytic oxygen reduction reaction (ORR) on noble metal surfaces [Eq. (1), RHE = reversible hydrogen electrode] is one of the most widely studied reactions in electrochemistry. Its fundamental scientific and technological importance is based on the fact that the oxygen/water half-cell reaction is a strongly oxidizing and ubiquitous redox couple. Combined with an electron-supplying redox process, such as shown in Equation (2), a direct electrochemical conversion ofthe overall Gibbs energy of reaction into electrical potentials is achieved. This conversion is the scientific basis for electrochemical conversion in fuel cells [1] or metal-air batteries. [2,3] The ORR is also used in oxygen depolarization cathodes (ODC) in modern chlorine technologies, [4,5] in which it replaces the hydrogen evolution process to improve electrical efficiencies. The reverse ORR process, that is, the evolution of oxygen from water, is crucial for efficient water (photo)-electrolysis [6,7] into hydrogen or in metal electrodeposition processes in the semiconductor industry. [2] In polymer electrolyte membrane fuel cells (PEMFCs), the ORR electrode catalyst material of choice has been platinum for decades. The ORR on Pt, however, is irreversible, thus causing overpotentials and losses in fuel-cell efficiency. Much research has been dedicated to the identification of more efficient catalysts, that is, materials with reduced precious-metal content and improved ORR activity.[8] Pt-rich alloys, most prominently Pt-Co formulations, have shown promise, with state-of-art activity improvements of two to three times over pure Pt. [9,10] However, a material with an at least fourfold activity improvement, deemed crucial for automotive applications, has remained elusive to date.[11]Herein, we report on carbon-supported Pt-Cu-Co ternary alloy nanoparticle electrocatalysts with previously unachieved four-to fivefold ORR activity improvements. We demonstrate the catalytic activities on rotating disk electrodes (RDEs) as well as in real H 2 /O 2 fuel-cell devices. enriched core-shell particle structures. Since metal dissolution into the membrane electrolyte has very detrimental effects in fuel cells, we also developed a new procedure to form the active catalyst phase in situ inside a fuel-cell electrode layer without compromising the membrane conductance. Figure 1 schematically illustrates our novel three-step procedure for preparation of the active catalyst phase. In step 1, the alloy precursor is applied in the cathode of a fuelcell membrane-electrode assembly (MEA). During step 2, a cyclic voltammetric treatment selectively dissolves the lessnoble metal atoms (mostly Cu) from the alloy particle surface. The Cu atoms migrate into the nafion polyelectrolyte and get trapped at negatively charged sulfonic acid groups. In step 3, the MEA is chemically treated with an inorganic acid, which results in complete exchange of Cu ions inside the polyelectrolyte with protons. After step 3, the catalyst has been converted into its active phase and is re...

Combining theory and experiment in electrocatalysis: Insights into materials design

“…2). Currently, carbon black is the most common support for Pt-based catalysts (82)(83)(84)(85)(86)(87)(88)(89)(90)(91)(92). However, the instability of carbon black under high potentials related to weak Pt-C interactions has prompted the search for more stable supports that can anchor Pt catalysts firmly, including Ti 0.7 Mo 0.3 O 2 (93) and tindoped indium oxide (94), which have been shown to enhance catalytic activities as well.…”

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

“…6 In order to address these requirements, several approaches have been developed, including (i) making nanostructures to increase the surface-to-volume ratio; 7 (ii) using an alloying technique to incorporate non-precious metals into the nanostructures; and (iii) texturing nanostructures, for example, replacing the core atoms in Pt nanoparticles with a non-precious metal, resulting in a Pt-skin 8,9 or Pt monolayer on top of catalysts. [10][11][12] In each such approach, the effects of shape (zero-, one-, two-or three-dimensional nanostructures), morphology (exposed facets), and catalyst composition on electrocatalytic activity and stability should be considered. [13][14][15][16] In synthesis processes, optimizing catalyst shape, morphology and composition with respect to catalytic activity and stability is critical to achieve successful electrocatalysts.…”

Molecular dynamics simulations of ternary PtxPdyAuz fuel cell nanocatalyst growth

“…A possible way consists in combining noble metals (Pt, Pd, Au ...) [5][6][7][8][9][10][11] and non-noble metals for preparing binary and ternary nanocatalysts. While non-noble metals are interesting from a cost reduction point of view, they may lead to reduced stability compared to pure platinum due to their dissolution capability [12][13][14][15][16][17]. Pt x Pd 1-x .…”