Pt Single Atoms Supported on Defect Ceria as an Active and Stable Dual-Site Catalyst for Alkaline Hydrogen Evolution.

This work evaluates the feasibility of alkaline hydrogen evolution reaction (HER) using Pt single-atoms (1.0 wt %) on defect-rich ceria (Pt1/CeOx) as an active and stable dual-site catalyst. The catalyst displayed a low overpotential and a small Tafel slope in an alkaline medium. Moreover, Pt1/CeOx presented a high mass activity and excellent durability, competing with those of the commercial Pt/C (20 wt %). In this picture, the defective CeOx is active for water adsorption and dissociation to create H* intermediates, providing the first site where the reaction occurs. The H* intermediate species then migrate to adsorb and react on the Pt2+ isolated atoms, the site where H2 is formed and released. DFT calculations were also performed to obtain mechanistic insight on the Pt1/CeOx catalyst for the HER. The results indicate a new possibility to improve the state-of-the-art alkaline HER catalysts via a combined effect of the O vacancies on the ceria support and Pt2+ single atoms.

Synergistic effect of Pt-Ni dual single-atoms and alloy nanoparticles as a high-efficiency electrocatalyst to minimize Pt utilization at cathode in polymer electrolyte membrane fuel cells.

Pt-Ni (111) alloy nanoparticles (NPs) and atomically dispersed Pt have been shown to be the most effective catalysts for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs) as well as less expensive compared to pure Pt NPs. To meet reaction kinetic demands and minimize the Pt utilization at cathode in PEMFCs, we propose a novel electrocatalyst composed of dual single-atoms (Pt, Ni) and Pt-Ni alloy NPs dispersed on the surface of N-doped carbon (NDC); collectively, PtNiSA-NPS-NDC. The optimized PtNiSA-NPS-NDC catalyst displays excellent mass activity and durability compared to commercial Pt/C. Electrocatalytic measurements show that the PtNiSA-NPS-NDC catalyst, with a metal loading of 4.5 wt%, exhibited distinguished ORR performance (E1/2 = 0.912 V) through a 4-electron (4e-) pathway, which is higher than that of commercial 20 wt% Pt/C (E1/2 = 0.857 V). The DFT simulations indicate Pt-Ni alloy NPs and PtNiN2C4 atomic structure are the mobile active sites for ORR catalytic activity in PtNiSA-NPS-NDC. As a cathode catalyst in PEMFC, the Pt utilization efficiency in the PtNiSA-NPS-NDC catalyst is 0.033 gPt kW-1, which is 5.6 times higher than that of commercial Pt/C (0.185gPt kW-1). Therefore, the consumption of precious metals is effectively minimized.