Crystal Phase-Tailored Metal Heterojunction for Dual-Site Acceleration of Alkaline Hydrogen Evolution

Abstract

Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is hindered by sluggish water dissociation kinetics and suboptimal hydrogen adsorption/desorption. Here, we present a crystal phase-tailored metal heterojunction, composed of close-packed hexagonal (hcp) Ni and face-centered cubic (fcc) Rh (hcp Ni/fcc Rh), synthesized through a galvanic replacement strategy. Impressively, hcp Ni/fcc Rh exhibits exceptional HER performance, achieving an ultralow overpotential of 20 mV at 10 mA cm-2, which is 2.25 times lower than that of fcc Ni/fcc Rh. Additionally, this catalyst demonstrates long-term stability with a current density of 500 mA cm-2 at 1.73 V for over 150 h in an anion exchange membrane water electrolyzer. Mechanistic investigations reveal that the hcp Ni scaffold plays a critical role in enhancing water dissociation by promoting efficient hydrogen generation and facilitating the desorption of *OH to regenerate the Ni sites. Simultaneously, the fcc Rh sites effectively optimize hydrogen adsorption due to the directional interfacial electron transfer from hcp Ni to fcc Rh. This work highlights the potential of crystal phase engineering in advancing heterostructure electrocatalysts for efficient HER.