Water-Based Synthesis of Defect-Rich 20 nm Pd@Pt Core−Shell Nanobranches with Tunable d-Band Centers for Superior Electrocatalytic Performance

Abstract

Integrating strain and ligand effects with surface defects can precisely modulate the d-band center of Pt-based core−shell catalysts for boosting their performance in fuel cell applications. However, it remains a challenge to synthesize defect-rich Pt-based core−shell nanocrystals in a water-based protocol and to establish a clear structure−property relationship. Herein, we present a controllable synthesis of defect-rich 20 nm Pd@Pt core−shell nanobranches (NBs) via a stepwise reduction route that simultaneously exploits surface crystal defects, strain, and ligand effects to enhance both activity and stability toward electrocatalytic methanol oxidation. Multitwinned Pd NBs were first prepared through oriented attachment of primary nanocrystals in a one-pot aqueous wet-chemical method. Defect-rich Pd@Pt core−shell NBs were then obtained by introducing Pt precursors into the same protocol. By carefully tuning the precursor concentrations, we achieved precise control over shell thickness and composition, thereby strategically tuning the d-band center of the Pd@Pt NBs. Electrocatalytic evaluation revealed a distinct volcano-type relationship between the d-band center position and activity for the Pd@Pt NBs. Notably, defect-rich Pd5@Pt1 NBs achieved mass activities of 0.7 mA mECSA−2 and 1.47 A mgPGM−1, representing 11.67-fold and 4.45-fold enhancement compared to commercial Pt/C, respectively.