Synthesis of Ag@Pd Nanocubes and Pd-based Nanoframes via One-shot Injection of a Halide-free Precursor for Continuous Production in a Flow Reactor.

Noble-metal open nanostructures have remarkable catalytic capabilities toward a wide range of reactions. In particular, Pd-based open nanostructures have been synthesized and validated for superior catalytic performance toward formic acid oxidation. However, most of the syntheses are based on dropwise addition, making it challenging to increase the production volume. In this work, we present a facile approach to the synthesis of Ag@Pd core-frame nanocubes and then Pd-based nanoframes through one-shot injection. In a typical synthesis, Ag nanocubes are dispersed in an aqueous solution of ascorbic acid and polyvinylpyrrolidone at room temperature, followed by the injection of Pd(NH3)4(NO3)2 precursor in one shot. The Pd(NH3)4(NO3)2 precursor has a much slower reduction kinetics relative to Na2PdCl4, preventing self-nucleation and enabling controlled deposition of Pd atoms on the Ag nanocubes. The lower reduction potential of Pd(NH3)4(NO3)2 also helps minimize the galvanic replacement reaction, facilitating uniform deposition of Pd atoms. After selectively etching away the Ag template, Pd-based nanoframes with a rigid cubic structure are obtained. Finally, the synthesis is successfully adapted to a continuous flow system, generating Ag@Pd nanocubes with comparable quality to those obtained via one-shot synthesis, demonstrating a practical route to large-scale production of Pd-based nanoframes with H2O2 etching.