This review provides a comprehensive overview on the development of highly active and durable platinum catalysts with ultra-low Pt loadings for polymer electrolyte membrane fuel cells (PEMFCs) through a combined mathematical modeling and experimental work. First, simulation techniques were applied to evaluate the validity of the Tafel approximation for the calculation of the mass activity (MA) and specific activity (SA). A one-dimensional agglomeration model was developed and solved to understand the effects of exchange current density, porosity, agglomerate size, Nafion®film thickness, and Pt loading on the MA and SA. High porosity (> 60%) and agglomerations at high Pt loadings cause the loss of the Tafel approximation and consequently the decrease in MA and SA. A new structure parameter was introduced to estimate the real porous structure using the fractal theory. The volumetric catalyst density was corrected by the fractal dimension (measured by Hg porosimetry), which gave a good agreement with the experimental values. The loading-dependent Tafel equation was then derived, which contains both the utilization and the non-linear scaling factor. Second, activated carbon composite support (ACCS) with optimized surface area, porosity, pore size, and pore size distribution was developed. The hydrophilic/hydrophobic ratio, structural properties (amorphous/crystalline ratio), and the number of active sites were optimized through metal-catalyzed pyrolysis. Stability of ACCS and Pt/ACCS were evaluated using an accelerated stress test (AST). The results indicated that Pt/ACCS showed no significant loss of MA and power density after 5,000 cycles at 1.0–1.5 V, while the commercial Pt/C catalysts showed drastic losses of MA and power density. Finally, monolayers of compressed Pt (core–shell-type Pt3Co1) catalysts were structured by diffusing Co atoms (previously embedded in ACCS) into Pt. Compressive Pt lattice (Pt*) catalysts were synthesized through an annealing procedure developed at the University of South Carolina (USC). The Pt*/ACCS catalyst showed high initial power density (rated) of 0.174 gPtkW−1and high stability (24 mV loss) at 0.8 A cm−2after 30,000 cycles (0.6–1.0 V). The outstanding performance of Pt*/ACCS is due to the synergistic effect of ACCS and compressive Pt*lattice.
Oxygen evolution reaction (OER) is of great significance for hydrogen production via water electrolysis, which, however, demands development of highly active, durable, and cost‐effective electrocatalysts in order to stride into a renewable energy era. Herein, highly efficient and long‐term durable OER by coupling B and P into an amorphous porous NiFe‐based electrocatalyst is reported, which possesses an amorphous porous metallic bulk structure and high corrosion resistance, and overcomes the issues associated with currently used catalyst nanomaterials. The PB codoping in the activated NiFePB (a‐NiFePB) delocalizes both Fe and Ni at Fermi energy level and enhances p–d hybridization as simulated by density functional theory calculations. The harmonized electronic structure and unique porous framework of the a‐NiFePB consequently improve the OER activity. The activated NiFePB thus exhibits an extraordinarily low overpotential of 197 mV for harvesting 10 mA cm−2OER current density and 233 mV for reaching 100 mA cm−2under chronopotentiometry condition, with the Tafel slope harmoniously conforming to 34 mV dec−1. Impressive long‐term stability of this new catalyst is evidenced by only limited activity decay after 1400 h operation at 100 mA cm−2. This work strategically directs a way for heading up a promising energy conversion alternative.
more » « less- Award ID(s):
- 1665265
- NSF-PAR ID:
- 10372145
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 15
- Issue:
- 28
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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