Multimetallic alloys (MMAs) with various compositions enrich the materials library with increasing diversity and have received much attention in catalysis applications. However, precisely shaping MMAs in mesoporous nanostructures and mapping the distributions of multiple elements remain big challenge due to the different reduction kinetics of various metal precursors and the complexity of crystal growth. Here we design a one-pot wet-chemical reduction approach to synthesize core–shell motif PtPdRhRuCu mesoporous nanospheres (PtPdRhRuCu MMNs) using a diblock copolymer as the soft template. The PtPdRhRuCu MMNs feature adjustable compositions and exposed porous structures rich in highly entropic alloy sites. The formation processes of the mesoporous structures and the reduction and growth kinetics of different metal precursors of PtPdRhRuCu MMNs are revealed. The PtPdRhRuCu MMNs exhibit robust electrocatalytic hydrogen evolution reaction (HER) activities and low overpotentials of 10, 13, and 28 mV at a current density of 10 mA cm−2 in alkaline (1.0 M KOH), acidic (0.5 M H2SO4), and neutral (1.0 M phosphate buffer solution (PBS)) electrolytes, respectively. The accelerated kinetics of the HER in PtPdRhRuCu MMNs are derived from multiple compositions with synergistic interactions among various metal sites and mesoporous structures with excellent mass/electron transportation characteristics.
X-ray absorption near-edge structure (XANES) spectroscopy is one of the most effective techniques for determining the valence states of cations. Since K-and L-edge transition processes are different, the validity of X-ray irradiation to evaluate these excitation processes must be determined. In this study, we focus on the valence states of silver cations in aluminophosphate glasses, whose compositions have been used as radiophotoluminescence (RPL) glass detectors for personal monitoring. Slight difference was observed between the Ag K-edge XANES spectra of reference materials and those of experimental samples. It is also challenging to detect spectral changes due to the coloration of Ag-doped glass. However, absorption edge shifts depending on the valence state were observed in Ag L 3 -edge XANES spectra. We found that additional absorption bands, whose peak intensities increase with increasing irradiation doses, were generated at lower absorption energies during the measurement. The degrees of change in absorption intensities depend on the chemical composition of the sample. Considering the nature of the RPL glass detector, we assumed that the species generated are related to the Ag 2+ species, which is an activator after irradiation.
Positron annihilation spectroscopy (PAS) is used for the quantification of cavities in a matrix. Although PAS is sometimes considered a nondestructive measurement method, it is worth investigating the interaction of positrons with the matrix during PAS. Here, we have demonstrated that defects are generated in silver-doped phosphate glasses during positron annihilation measurement and that radiophotoluminescence (RPL) is observed after irradiation. There is a linear correlation between the irradiation duration and the observed RPL intensity of the glasses. We observed RPL after a high irradiation dose even after conventional thermal annealing at 360 °C for 1 h. The formation of Ag 2+ species detectable by electron spin resonance (ESR) was confirmed. From the concentration of ESR-active Ag 2+ and Ag 2 + species, it is expected that approximately 0.1% of Ag + cations were changed after 5 days of positron irradiation.
Ag-doped phosphate glasses have widely been used as radiophotoluminescence (RPL) dosimeters. However, the RPL center formation process is not fully understood. In this study, we investigated the RPL center formation process in Ag-doped Na-Al phosphate glasses. We observed that two RPL centers (Ag 0 and Ag 2+ ) were formed at temperatures higher than 100 and 250 K, respectively. In addition, activation energies of their formation were estimated to be 20 and 267 meV, respectively. These results suggest that the electron transfer process is not a simple thermally activated process.
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