Surface-Engineered Twinned PdIr Nanorods for the Electrocatalytic Hydrogen Evolution Reaction

Metallic nanocrystals with defined structure and composition serve as ideal model systems for probing their fundamental growth mechanisms and, more importantly, unraveling structure–function correlations in nanocatalysis. In this work, we address the synthetic challenges associated with PdIr nanorods (NRs) featuring 5-fold twinned structures through an underpotential deposition (UPD)-assisted approach. The synergistic influence of brominated surfactants and the UPD of Ir is demonstrated to promote the formation of the NRs with customizable lengths and rough surfaces. As a model catalyst for the hydrogen evolution reaction (HER), these twinned PdIr NRs exhibit excellent electrocatalytic performance in both alkaline media and acid media. The PdIr NRs exhibit reduced overpotentials by 0.217, 0.176, and 0.243 V and decreased Tafel slopes of 0.108, 0.091, and 0.122 V relative to the Pd NRs, PdIr nanocubes (NCs), and Pd NCs under alkaline conditions, respectively. The PdIr NRs also exhibit the lowest overpotential and Tafel slope in all the investigated catalysts in acid media. The maximum HER catalytic activity of the 5-fold twinned PdIr NRs results from the rough surface with Ir 4+ sites and the presence of twinned structural defects. This study elucidates the unique application of UPD for designing twinned metal nanocrystals and offers insights for the structure-dependent performance of PdIr-based electrocatalysts.