Homogeneous Metastable Hexagonal Phase Iridium Enhances Hydrogen Evolution Catalysis

Abstract

Catalytic reactions are surface-sensitive processes. Fabrication of homogeneous metastable metals can be used to promote phase-dependent catalytic performance; however, this has been a challenging task. Herein, homogeneous metastable hexagonal close-packed (hcp) Ir is epitaxially grown onto metastable phase hcp Ni, as demonstrated using spherical aberration electron microscopy. The as-fabricated metastable hcp Ir exhibits high intrinsic activity for the alkaline hydrogen evolution reaction (HER). In particular, metastable hcp Ir delivers a low overpotential of 17 mV at 10 mA cm −2 and presents a high specific activity of 8.55 mA cm −2 and a high turnover frequency of 38.26 s −1 at −0.07 V versus the reversible hydrogen electrode. Owing to its epitaxially grown structure, metastable hcp Ir is highly stable. Theoretical calculations reveal that metastable hcp Ir promotes H 2 O adsorption and fast H 2 O dissociation, which contributes to its remarkable HER activity. Findings can elucidate the crystal phase-controlled synthesis of advanced noble metal nanomaterials for the fundamental catalytic applications.

N-doped branched metal–organic framework derivatives to boost multiband microwave absorption with ultrathin thickness

“…04-0850). 38 Furthermore, the two distinct diffraction peaks observed at 44.4°, 51.6°,and 76.2° in the spectra of CoNi@PC/CNTs and CoNi@NPC/NCNTs located in-between those of Co and Ni confirm the successful synthesis of the single-phase CoNi alloys. 24,36…”

Unconventional Bilateral Compressive Strained Ni–Ir Interface Synergistically Accelerates Alkaline Hydrogen Oxidation

“…The Ir L 3 -edge XANES spectra (Figure c) of both Ni–Ir­( BCS )/G and Ir/C (Figure S31) are very close to the Ir foil, indicating the dominant metallic state of Ir species in those samples. The very slight shift of absorption edge (Figure c inset) and slightly higher white line intensity for Ni–Ir­( BCS )/G and Ir/C compared to the Ir foil should be ascribed to tiny oxidation of the surface. − This could be caused by the air exposure and XAS measurements given the tiny size. The XPS spectra obtained in vacuum conditions corroborate the metallic state of Ir in those samples.…”

Emerging two dimensional metastable‐phase oxides: insights and prospects in synthesis and catalysis

“…The Gibbs free energy of the metastable-phase is higher than that of the stable phase; thus, 2D metastable-phase oxide materials may have higher catalytic activity. [28]…”

“…The energy barrier ensures metastability and prevents the transformation of metastable‐phase materials to stable states. The Gibbs free energy of the metastable‐phase is higher than that of the stable phase; thus, 2D metastable‐phase oxide materials may have higher catalytic activity [28] …”