The Micron-Droplet-Confined Continuous-Flow Synthesis of Freestanding High-Entropy-Alloy Nanoparticles by Flame Spray Pyrolysis.

Alloying multiple immiscible elements into a nanoparticle with single-phase solid solution structure (high-entropy-alloy nanoparticles, HEA-NPs) merits great potential. To date, various kinds of synthesis techniques of HEA-NPs are developed; however, a continuous-flow synthesis of freestanding HEA-NPs remains a challenge. Here a micron-droplet-confined strategy by flame spray pyrolysis (FSP) to achieve the continuous-flow synthesis of freestanding HEA-NPs, is proposed. The continuous precursor solution undergoes gas shearing and micro-explosion to form nano droplets which act as the micron-droplet-confined reactors. The ultrafast evolution (<5 ms) from droplets to <10 nm nanoparticles of binary to septenary alloys is achieved through thermodynamic and kinetic control (high temperature and ultrafast colling). Among them, the AuPtPdRuIr HEA-NPs exhibit excellent electrocatalytic performance for alkaline hydrogen evolution reaction with 23 mV overpotential to achieve 10 mA cm-2, which is twofold better than that of the commercial Pt/C. It is anticipated that the continuous-flow synthesis by FSP can introduce a new way for the continuous synthesis of freestanding HEA-NP with a high productivity rate.

Ni-CeO2 Heterostructure Promotes Hydrogen Evolution Reaction via Tuning of the O-H Bond Length of Adsorbed Water at the Electrolyte/Electrode Interface.

Understanding the properties and structure of reactant water molecules at the electrolyte solution/electrode interface is relevant to know the mechanisms of hydrogen evolution reaction (HER). However, this approach has rarely been implemented due to the elusive local microenvironment in the vicinity of the catalyst. Taking the Ni-CeO2 heterostructure immobilized onto carbon paper (Ni-CeO2 /CP) as a model, the dynamic behavior of adsorbed intermediates during the reaction was measured by in situ surface-enhanced infrared absorption spectroscopy with attenuated total reflection configuration (ATR-SEIRAS). Theoretical calculations are used in combination to comprehend the potential causes of increased HER activity. The results show that the O-H bond of adsorbed water at the electrolyte solution/electrode interface becomes longer for promoting the dissociation of water and accelerating the kinetically slow Volmer step. In addition, forming the Ni-CeO2 heterostructure interface optimizes the hydrogen adsorption Gibbs free energy, thus increasing HER activity. Therefore, the Ni-CeO2 /CP electrode exhibits remarkably low HER overpotentials of 37 and 119 mV at 10 and 100 mA cm-2 , which are close to commercial Pt/C (16 and 102.6 mV, respectively).