Laser Irradiation Induced Electronic Structure Modulation of the Palladium-Based Nanosheets for Efficient Electrocatalysts.

Palladium nanosheets (Pd NSs) are widely used as electrocatalysts due to their high atomic utilization efficiency, and long-term stability. Here, the electronic structure modulation of the Pd NSs is realized by a femtosecond laser irradiation strategy. Experimental results indicate that laser irradiation induces the variation in the atomic structures and the macrostrain effects in the Pd NSs. The electronic structure of Pd NSs is modulated by laser irradiation through the balancing between Au-Pd charge transfer and the macros-strain effects. Finite element analysis (FEA) indicates that the lattice of the nanostructures undergoes fast heating and cooling during laser irradiation. The structural evolution mechanism is disclosed by a combined FEA and molecule dynamics (MD) simulation. These results coincide well with the experimental results. The L-AuPd NSs exhibit excellent mass activity and specific activity of 7.44 A mg-1 Pd and 18.70 mA cm-2 toward ethanol oxidation reaction (EOR), 4.3 and 4.4 times higher than the commercial Pd/C. The 2500-cycle accelerated durability (ADT) test confirms the outstanding catalytic stability of the L-AuPd NSs. Density functional theory (DFT) calculations reveal the catalytic mechanism. This unique strategy provides a new pathway to design the ultrathin nanosheet-based materials with excellent performance.

Laser Irradiation Synthesis of AuPd Alloy with Decreased Alloying Degree for Efficient Ethanol Oxidation Reaction.

The preparation of electrocatalysts with high performance for the ethanol oxidation reaction is vital for the large-scale commercialization of direct ethanol fuel cells. Here, we successfully synthesized a high-performance electrocatalyst of a AuPd alloy with a decreased alloying degree via pulsed laser irradiation in liquids. As indicated by the experimental results, the photochemical effect-induced surficial deposition of Pd atoms, combined with the photothermal effect-induced interdiffusion of Au and Pd atoms, resulted in the formation of AuPd alloys with a decreased alloying degree. Structural characterization reveals that L-AuPd exhibits a lower degree of alloying compared to C-AuPd prepared via the conventional co-reduction method. This distinct structure endows L-AuPd with outstanding catalytic activity and stability in EOR, achieving mass and specific activities as high as 16.01 A mgPd-1 and 20.69 mA cm-2, 9.1 and 5.2 times than that of the commercial Pd/C respectively. Furthermore, L-AuPd retains 90.1% of its initial mass activity after 300 cycles. This work offers guidance for laser-assisted fabrication of efficient Pd-based catalysts in EOR.

Aqueous-phase formation of N-containing secondary organic compounds affected by the ionic strength.

The reaction of carbonyl-to-imine/hemiaminal conversion in the atmospheric aqueous phase is a critical pathway to produce the light-absorbing N-containing secondary organic compounds (SOC). The formation mechanism of these compounds has been wildly investigated in bulk solutions with a low ionic strength. However, the ionic strength in the aqueous phase of the polluted atmosphere may be higher. It is still unclear whether and to what extent the inorganic ions can affect the SOC formation. Here we prepared the bulk solution with certain ionic strength, in which glyoxal and ammonium were mixed to mimic the aqueous-phase reaction. Molecular characterization by High-resolution Mass Spectrometry was performed to identify the N-containing products, and the light absorption of the mixtures was measured by ultraviolet-visible spectroscopy. Thirty-nine N-containing compounds were identified and divided into four categories (N-heterocyclic chromophores, high-molecular-weight compounds with N-heterocycle, aliphatic imines/hemiaminals, and the unclassified). It was observed that the longer reaction time and higher ionic strength led to the formation of more N-heterocyclic chromophores and the increasing of the light-absorbance of the mixture. The added inorganic ions were proposed to make the aqueous phase somewhat viscous so that the molecules were prone to undergo consecutive and intramolecular reactions to form the heterocycles. In general, this study revealed that the enhanced ionic strength and prolonged reaction time had the promotion effect on the light-absorbing SOC formation. It implies that the aldehyde-derived aqueous-phase SOC would contribute more light-absorbing particulate matter in the industrial or populated area where inorganic ions are abundant.