Tuning the Performance and the Stability of Porous Hollow PtNi/C Nanostructures for the Oxygen Reduction Reaction

Abstract

Due to their increased surface area to volume ratio and molecular accessibility, microporous and mesoporous materials are a promising strategy to electrocatalyze the cathodic oxygen reduction reaction (ORR), the key reaction in proton-exchange membrane fuel cells (PEMFC). Here, we synthesized and provided atomically resolved pictures of porous hollow PtNi/C nanocatalysts, investigated the elemental distribution of Ni and Pt atoms, measured the Pt lattice contraction, and correlated these observations to their ORR activity. The best porous hollow PtNi/C nanocatalyst achieved 6 and 9-fold enhancement in mass and specific activity for the ORR, respectively over standard solid Pt/C nanocrystallites of the same size. The catalytic enhancement was 4 and 3-fold in mass and specific activity, respectively, over solid PtNi/C nanocrystallites with similar chemical composition, Pt lattice contraction, and crystallite size. Furthermore, 100% of the initial mass activity at E = 0.90 V vs RHE (0.56 A mg −1 Pt) of the best electrocatalyst was retained after an accelerated stress test composed of 30 000 potential cycles between 0.60 and 1.00 V vs RHE (0.1 M HClO 4 T = 298 K), therefore meeting the American Department of Energy targets for 2017−2020 both in terms of mass activity and durability (0.44 A mg −1 Pt, mass activity losses < 40%). The better catalytic activity for the ORR of hollow PtNi/C nanocatalysts is ascribed to (i) their opened porosity, (ii) their preferential crystallographic orientation ("ensemble effect"), and (iii) the weakened oxygen binding energy induced by the contracted Pt lattice parameter ("strain effect").

The oxygen reduction on Pt-Ni and Pt-Ni-M catalysts for low-temperature acidic fuel cells: A review

“…The SA Pt‐Ni /SA Pt vs Ni content data are rather scattered, but they are roughly represented by a curve presenting a maximum for a nickel content of 48 at%. The dependence of PtNi fcc lattice parameters from different datasets on nickel content in the catalysts can be seen in Figure B: almost all data are above the dashed line representing the relationship between the fcc lattice parameter and the Pt 1‐ x Ni x alloy composition, which follows Vegard law for x ranging from 0 to 0.5 . The positive deviation from Vegard law is likely because of an alloying degree <1, that is, only a fraction of the total nickel atoms in the catalyst forms a Pt‐Ni alloy.…”

“…Many papers have been addressed to the oxygen reduction on both supported and unsupported disordered solid cubo‐octahedral fcc Pt 1‐ x Ni x nanoparticles and disordered fcc Pt 1‐ x Ni x thin films . The Pt‐Ni to Pt ORR specific activity ( SA Pt‐Ni /SA Pt ) in acid media of carbon‐supported cubo‐octahedral disordered solid fcc Pt 1‐ x Ni x nanoparticles and electrodeposited Pt 1‐ x Ni x thin films by different datasets vs Ni content in the catalyst plot is shown in Figure A. The SA Pt‐Ni /SA Pt vs Ni content data are rather scattered, but they are roughly represented by a curve presenting a maximum for a nickel content of 48 at%.…”

Atomic-scale restructuring of hollow PtNi/C electrocatalysts during accelerated stress tests

“…In the "hard templating" method, an inorganic or organic sacrificial template is first produced, coated with the metal of interest, and then selectively removed to obtain a hollow nanostructure [1][2][3][4][5][6][7][8][9][10]. In the "soft templating" method, cooperative interactions between inorganic or organic species such as micelles, reverse micelles, and microemulsions are used to design the porous materials [5].…”

“…In the "soft templating" method, cooperative interactions between inorganic or organic species such as micelles, reverse micelles, and microemulsions are used to design the porous materials [5]. Recently, using a "hard templating" method based on galvanic replacement and the nanoscale Kirkendall effect, we and other groups synthesized hollow PtCo/C or PtNi/C nanoparticles to electrocatalyze the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs) [3,4,[7][8][9]11]. Alloying Pt with a 3d transition metal such as Co, [12][13][14][15][16][17][18] Ni, [14,15,[19][20][21] Y, [22,23] Sc, [24] or Gd, [25] is a common way to tailor the chemisorption energies of oxygen-containing ORR intermediates via strain [26][27][28][29][30] and ligand [31][32][33] effects.…”

Nonsiliceous Mesoporous Materials: Design and Applications in Energy Conversion and Storage

“…Mesoporous nano/micro noble metal particles and their applications in catalysts have been reviewed . Metal‐based catalysts with mesoporous structures have an open porosity, a preferential crystallographic orientation, and a modified surface and therefore achieve better activity than other catalysts …”