IrO2 as a promising support to boost oxygen reduction reaction on Pt in acid under high temperature conditions.

Metal oxide nanoparticle (NP) supports of both good conductivity and stability have the potential to enhance both the reaction activity and stability of the loaded electrocatalysts. In this paper, a facile two-step approach to disperse Pt nanoparticles on the surface of an IrO2 NP support (Pt/IrO2) was developed. Physical characterization by x-ray diffraction spectroscopy and transmission/scanning electron microscopy suggests a good dispersion of the Pt NPs. The temperature effect (from 293 to 353 K) of oxygen reduction reaction on Pt/IrO2 was studied by using a rotating ring disk electrode The results show that although the kinetic current density on Pt/IrO2 is close to that on commercial Pt/C at room temperature, the apparent activation energy (Ea,app) in the former case is much lower, suggesting a much higher activity at elevated temperatures. The superiority in Ea,app is attributed to the electron interaction between Pt and the IrO2 support, as supported by the change of surface chemical state given by x-ray photo-electron spectroscopy.

Ordered Intermetallic PtCu Catalysts Made from Pt@Cu Core/Shell Structures for Oxygen Reduction Reaction.

Platinum-based ordered intermetallic compounds are promising low-Pt catalysts toward the oxygen reduction reaction (ORR) for high-performance fuel cells. However, the synthesis of ordered intermetallic catalysts usually requires high-temperature annealing to overcome the energy barrier for atom diffusion, which leads to inevitable sintering of catalysts and greatly reduced mass-specific activity. Herein, we developed a new strategy to synthesize PtCu-ordered intermetallic catalysts by the generation of the Pt@Cu core/shell nanoparticles (Pt@Cu NPs) by Pt-assisted H2 reduction of Cu2+ with subsequent annealing at 500-1000 °C. Compared to the commonly used wet-impregnation method, the core/shell structure starts to form ordered PtCu alloys at a lower annealing temperature (500 °C). The Pt@Cu core/shell structure avoids the necessary process of Cu atoms diffusing to Pt NPs across the carbon supports occurred during high-temperature annealing in the wet-impregnation method, which ensures the formation of PtCu NPs with higher ordering degree while annealing at the same temperature. The highly ordered small-sized PtCu catalysts prepared by the core/shell strategy exhibit higher mass activity and specific activity compared to those prepared by the wet-impregnation method. Moreover, a positive correlation between the ORR activity and the ordering degree of the intermetallic PtCu NPs is identified, which could be associated with the increase of compressive strain with the ordering degree.

Highly Active and Stable Metal Single-Atom Catalysts Achieved by Strong Electronic Metal-Support Interactions.

Developing an active and stable metal single-atom catalyst (SAC) is challenging due to the high surface free energy of metal atoms. In this work, we report that tailoring of the 5d state of Pt1 single atoms on Co3O4 through strong electronic metal-support interactions (EMSIs) boosts the activity up to 68-fold higher than those on other supports in dehydrogenation of ammonia borane for room-temperature hydrogen generation. More importantly, this catalyst also exhibits excellent stability against sintering and leaching, in sharp contrast to the rapid deactivation observed on other Pt single-atom and nanoparticle catalysts. Detailed spectroscopic characterization and theoretical calculations revealed that the EMSI tailors the unoccupied 5d state of Pt1 single atoms, which modulates the adsorption of ammonia borane and facilities hydrogen desorption, thus leading to the high activity. Such extraordinary electronic promotion was further demonstrated on Pd1/Co3O4 and in hydrogenation reactions, providing a new promising way to design advanced SACs with high activity and stability.