Simultaneous Improvements in Performance and Durability of an Octahedral PtNi_x/C Electrocatalyst for Next-Generation Fuel Cells by Continuous, Compressive, and Concave Pt Skin Layers

Abstract

Simultaneous improvements in oxygen reduction reaction (ORR) activity and long-term durability of Ptbased cathode catalysts are indispensable for the development of next-generation polymer electrolyte fuel cells but are still a major dilemma. We present a robust octahedral core−shell PtNi x /C electrocatalyst with high ORR performance (mass activity and surface specific activity 6.8−16.9 and 20.3−24.0 times larger than those of Pt/C, respectively) and durability (negligible loss after 10000 accelerated durability test (ADT) cycles). The key factors of the robust octahedral nanostructure (core−shell Pt 73 Ni 27 /C) responsible for the remarkable activity and durability were found to be three continuous Pt skin layers with 2.0−3.6% compressive strain, concave facet arrangements (concave defects and high coordination), a symmetric Pt/Ni distribution, and a Pt 67 Ni 33 intermetallic core, as found by STEM-EDS, in situ XAFS, XPS, etc. The robust core−shell Pt 73 Ni 27 /C was produced by the partial release of the stress, Pt/Ni rearrangement, and dimension reduction of an as-synthesized octahedral Pt 50 Ni 50 /C with 3.6−6.7% compressive Pt skin layers by Ni leaching during the activation process. The present results on the tailored synthesis of the PtNi x structure and composition and the better control of the robust catalytic architecture renew the current knowledge and viewpoint for instability of octahedral PtNi x /C samples to provide a new insight into the development of next-generation PEFC cathode catalysts. KEYWORDS: robust octahedral core−shell PtNi x /C electrocatalyst, polymer electrolyte fuel cell, high performance and durability, continuous, compressive and concave Pt skin layers, structural and electronic property, in situ XAFS/STEM-EDS/XPS/ICP-AES

TePtFe Nanotubes as High‐Performing Bifunctional Electrocatalysts for the Oxygen Reduction Reaction and Hydrogen Evolution Reaction

“…[37] As shown in Figure S1 bi nt he Supporting Information, U-Te PtNTs/C shows ad iffractionp eak at 30.28,w hich can be assignedt oT e; this indicates that, without KOH treatment of NTs, excessu nreactedT em ay appear on the outer wall of NTs. [7,39,40] The Fe 2p 3/2 signal also appearsi n Te PtFe NTs ( Figure 2c). The chemical states of Pt in Te PtFe NTs/C, TePt NTs/C, and Pt/C are shown in Figure2ba nd Figure S2 in the Supporting Information.…”

Key Factors for Simultaneous Improvements of Performance and Durability of Core‐Shell Pt3Ni/Carbon Electrocatalysts Toward Superior Polymer Electrolyte Fuel Cell

“…Particularly, the degradation of cathode electrocatalysts during startup/shutdown cycles due to carbon corrosion, Pt detachment and dissolution, etc. should be significantly suppressed . A low mass transportation resistance is also necessary for achieving a high‐power output .…”

“…However, it is not an easy task for electrocatalysts to meet all these properties simultaneously because the activity, durability and mass transportation often cause interplay and dilemma in the design of optimal catalyst structures. Numerous monometallic Pt and bimetallic Pt−M electrocatalysts with different shapes, exposed planes, sizes, compositions, stresses, d‐band centers, Pt−O strength, etc., which have been demonstrated as key performance issues, have been synthesized ––. Nevertheless, it remains a big challenge for such Pt and Pt−M alloys to sustain their activities in the harsh cathode environment over a long period of time.…”

“…Recently, several bimetallic Pt−M cathode catalysts with remarkable performances have been reported . Unfortunately, most of them show insufficient durability except for specific samples, such as nanoframe Pt 3 Ni/C, Mo−Pt 3 Ni/C, jagged nanowire Pt/C (fabricated from Pt@NiO with H 2 ), and thin‐nanoplate Pt@PtPb/C at rotating disk electrodes (RDE) as listed in Table .…”

“…More recently, we reported a robust octahedral core‐shell Pt 73 Ni 27 /C(Vulcan XC‐72) electrocatalyst with high ORR performance (mass activity (MA) and surface specific activity (SA): 6.8–16.9 and 20.3–24.0 times larger than Pt/C, respectively) and durability (negligible loss after 10,000 accelerated durability test (ADT) (rectangular‐wave 0.6–1.0 V RHE ) cycles) . The key issues of the robust octahedral Pt 73 Ni 27 /C (denoted as Oh Pt 3 Ni/C hereinafter) responsible for the remarkable activity and durability were addressed to be continuous three Pt skin layers with about 2.0–2.3 % compressive strain, concave facet arrangements, a symmetric Pt/Ni distribution and a Pt 2 Ni intermetallic core by STEM‐EDS, in situ XAFS, XPS, etc .…”