# Confined Reactivity in the van der Waals Gap beneath Graphene: Supply-Limited Kinetics and Emergent Reaction Pathways

## TL;DR

This study explores how molecules react within a confined space between graphene and a metal surface, revealing new reaction pathways and how confinement affects reaction rates.

## Contribution

The paper introduces a new understanding of confined reactivity in the van der Waals gap, showing how it enables unique reaction pathways not observed on open surfaces.

## Key findings

- Etching reactions in the van der Waals gap are supply limited for O2 and H2 under the tested conditions.
- CO exhibits enhanced transport due to the lifting of the van der Waals gap, but the reaction-limited regime is not observed.
- Confinement enables new CO-mediated etching pathways not present on open platinum surfaces.

## Abstract

The confinement of molecules within the van der Waals
(vdW) gap
between a two-dimensional (2D) material and a catalytic substrate
offers a promising route toward the development of molecule-selective
catalysts with increased reaction rates and access to chemically distinct
reaction environments. However, identifying the kinetic limitations
and mechanistic consequences of such confined reactions remains challenging.
Here, we employ an inverted wedding cake configuration of multilayer
graphene on platinum to study the dynamics of graphene etching within
the vdW gap by O2, H2, and CO using in situ
scanning electron microscopy. Under the experimental conditions explored
(up to p = 1.4 × 10–2 Pa and T = 1000 °C), the etching reactions are supply limited
for O2 and H2. The reaction-limited regime is
not observed even for CO, despite its anomalously enhanced transport
resulting from a pronounced lifting of the vdW gap. Reactive molecular
dynamics simulations reveal that confinement within the vdW gap enables
additional CO-mediated etching pathways that are absent on open Pt
surfaces. Our results demonstrate that intercalation does not primarily
reduce reaction barriers but instead creates a confined, high-chemical-potential
nanoreactor in which new reaction pathways can be accessed at comparatively
low external pressures.