Abstract
The durability and long-term applicability of catalysts are critical parameters for the commercialization and adoption of fuel cells. Even though a few studies have been conducted on hollow carbon spheres (HCSs) as supports for Pt in oxygen reduction reactions (ORR) catalysis, in-depth durability studies have not been conducted thus far. In this study, Pt/HCSs and Pt/nitrogen-doped HCSs (Pt/NHCSs) were prepared using a reflux deposition technique. Small Pt particles were formed with deposition on the outside of the shell and inside the pores of the shell. The new catalysts demonstrated high activity (>380 μA cm−2 and 240 mA g−1) surpassing the commercial Pt/C by more than 10%. The catalysts demonstrated excellent durability compared to a commercial Pt/C in load cycling, experiencing less than 50% changes in the mass-specific activity (MA) and surface area-specific activity (SA). In stop-start durability cycling, the new materials demonstrated high stability with more than 50% retention of electrochemical active surface areas (ECSAs). The results can be rationalised by the high BET surface areas coupled with an array of meso and micropores that led to Pt confinement. Further, pair distribution function (PDF) analysis of the catalysts confirmed that the nitrogen and oxygen functional groups, as well as the shell curvature/roughness provided defects and nucleation sites for the deposition of the small Pt nanoparticles. The balance between graphitic and diamond-like carbon was critical for the electronic conductivity and to provide strong Pt-support anchoring.
Highlights
The global dependence on fossil fuels for everyday energy needs is detrimental to the long-term sustainability of the earth
The Raman spectra of the hollow carbon spheres (HCSs) and nitrogen doped HCSs (NHCSs) were recorded to determine the extent of carbon graphitization and the presence of defects in the material
Characterization studies on the HCSs, NHCSs and Pt/HCSs and Pt/NHCSs catalysts revealed that the porosity of the supports and their high surface areas promoted good dispersion of the Pt nanoparticles as revealed by BET analysis
Summary
The global dependence on fossil fuels for everyday energy needs is detrimental to the long-term sustainability of the earth. Carbon supports are favoured due to their different structured forms, their lightweight that is important for mobile applications, thermal stability for high-temperature applications, high surface area for nanoparticle deposition and gas diffusion, as well as their earth abundance In these catalysts, the metal nanoparticles exist in high loadings to mitigate the slow kinetics and high overpotential, especially for ORR at the cathode (Park et al, 2020). Yan and co-workers deposited highly stable small-sized Pt particles on mesoporous hollow carbon spheres for the oxygen reduction reaction They observed that the supports had a high BET surface area (1,163 m2 g−1), large pore volume (2.8 cm g−1) and mesoporous structure and they attributed the distribution and dispersion of small-sized Pt particles to these textual properties. Cycling was carried out for a total of 6,000 cycles with ECSA CVs sampled after 10, 100 and 1,000 cycles until the 6,000th cycle was reached after 27 h of continuous cycling and argon saturation (Ohma et al, 2011)
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