Intercalation of O2, H2, and CO beneath epitaxial graphene on Ir(111): A review of atomic-scale decoupling mechanisms and pathways to catalysis, sensing, and energy applications

Intercalation of gases and metal species beneath graphene supported on transition-metal substrates has emerged as a powerful strategy for tuning graphene–substrate interactions and tailoring its electronic, chemical, and mechanical properties. Numerous studies have investigated these phenomena using surface-sensitive techniques, including X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED). This review examines the intercalation of oxygen, carbon monoxide, and hydrogen, with particular emphasis on graphene grown on Ir(111). Oxygen intercalation proceeds under ultrahigh-vacuum conditions through atomic oxygen formation on bare Ir terraces and requires elevated temperatures (~355 K), whereas hydrogen intercalation occurs at much lower temperatures (~140 K). CO intercalation takes place near room temperature but requires millibar-range pressures. In all cases, substrate step edges and graphene flake boundaries serve as critical pathways for intercalant penetration. These structural features have been consistently identified as key entry points for intercalant diffusion. Intercalation provides an additional degree of freedom for controlling the properties of 2D materials, enabling modulation of electrical conductivity, thermoelectric response, and catalytic activity. The process significantly modifies the electronic, chemical, and mechanical characteristics of the graphene layer, while also partially decoupling it from the underlying substrate. Given these effects, gas intercalation beneath graphene represents a promising strategy for applications in catalysis, sensing, and energy storage. Intercalation can also be used to partially separate the graphene overlayer from the underlying metal, leading to considerable enhancement of electronic, chemical and mechanical properties. This review highlights the fundamental mechanisms and technological potential of gas (O 2 , H 2 , and CO) intercalation beneath graphene for applications in catalysis, sensing, energy storage, and next-generation graphene-based devices.