Electrochemical Behavior of Electrodeposited Nanoporous Pt Catalysts for the Oxygen Reduction Reaction

Abstract

Nanoporous Pt based nanoparticles (NP’s) are promising fuel cell catalysts due to their high surface area and increased electrocatalytic activity toward the ORR. In this work a direct double-pulse electrodeposition procedure at room temperature is applied to obtain dendritic Pt structures (89 nm diameter) with a high level of porosity (ca. 25%) and nanopores of 2 nm protruding until the center of the NP’s. The particle morphology is characterized using aberration-corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and electron tomography (ET) combined with field emission scanning electron microscopy (FESEM) and macroscopic electrochemical measurements to assess their activity and stability toward the ORR. Macroscopic determination of the active surface area through hydrogen UPD measurements in combination with FESEM and ET showed that a considerable amount of the active sites inside the pores of the low overpotential NP’s were accessible to oxygen species. As a result of this accessibility, up to a 9-fold enhancement of the Pt mass corrected ORR activity at 0.85 V vs RHE was observed at the highly porous structures. After successive potential cycling upward to 1.5 V vs RHE in a deaerated HClO4 solution a negative shift of 71 mV in half-wave potential occurred. This decrease in ORR activity could be correlated to the partial collapse of the nanopores, visible in both the EASA values and 3D ET reconstructions.

A Dewetted‐Dealloyed Nanoporous Pt Co‐Catalyst Formed on TiO2 Nanotube Arrays Leads to Strongly Enhanced Photocatalytic H2 Production

“…The dissolution of the less noble component is coupled with diffusion and aggregation of the more noble metal element at the solid/liquid interface: the overall process leaves behind a porous metal structure (a metal “sponge”) that can be enriched or mainly composed of the nobler element . Nanoporous metals prepared via selective dealloying of solid solutions possess a three‐dimensional (3D) structure of randomly interpenetrating ligaments/pores with sizes between a few nm to several tens of μm; these structural features can be precisely tuned by varying the preparation conditions (such as alloy composition, dealloying time, temperature, and electrochemical parameters) or by subsequent a thermal coarsening step …”

“…[24] Nanoporous metals prepared via selective dealloying of solid solutions possess a three-dimensional (3D) structure of randomly interpenetrating ligaments/pores with sizes between a few nm to several tens of mm; these structural features can be precisely tuned by varying the preparation conditions (such as alloy composition, dealloying time, temperature, and electrochemical parameters) or by subsequent a thermal coarsening step. [18,[25][26][27][28][29] In spite of the large application in heterogeneous catalysis, there is however still a comparably low number of studies on nanoporous metal co-catalysts for photocatalytic applications. Nguyen et al have reported on porous Au, [30] AuPt, [31] or PtPd [32] nanoparticles produced on TiO 2 nanotubes (NTs) by chemical dealloying of dewetted-alloyed nanoparticles.…”

Freestanding Catalyst Layers: A Novel Electrode Fabrication Technique for PEM Fuel Cells via Electrospinning

“…The control of the electrode structure is not easy, as the dispersion medium governs the ink's properties like viscosity, dispersion and aggregation size of the catalyst/ionomer particles, rate of solidification and ultimately the physical and mass transport properties of the catalyst layer. Researchers have come up with various new techniques such as plasma sputtering, ion beam bombardment, electrodeposition, electrospray, inkjet printing etc., for increasing the fuel cell performance and durability. Some of the methods, even though effective, are either too expensive to prepare in large scale or physically not possible to scale up.…”

The influence of deposited potential on the ORR activity of Pt catalysts on glassy carbon electrode

“…It was reported 9,10 that the method of preparation, the microstructure, particle size and shape are the main factors inuencing the ORR activity of Pt-based catalysts. One of the most widely used methods is electrodeposition, [11][12][13][14][15][16] particularly potentiostatic deposition, 13,14 which has been found to be an increasingly attractive route for the preparation of nanostructured catalysts because of its ease of operation, exibility and high purity. In addition, the electrodeposition technique can be used to prepare the catalyst layer directly on the substrate in a single step with uniform particle distribution and selected particle sizes.…”