Observation of Structure Evolution and Reaction Intermediates at the Gate-tunable Suspended Graphene/Electrolyte Interface

TL;DR

This study uses sum-frequency spectroscopy to observe how the microscopic structure of a suspended graphene/electrolyte interface evolves with gate voltage, revealing changes during electrochemical reactions and hydrogen adsorption.

Contribution

It provides the first direct spectroscopic observation of structure evolution at a substrate-free graphene/electrolyte interface with gate tunability.

Findings

Stern layer structure remains stable within the electrolysis window

Structural changes occur during electrochemical reactions

Graphene surface becomes hydrophilic near hydrogen evolution onset

Abstract

Graphene serves as an ideal platform to investigate the microscopic structure and reaction kinetics at the graphitic electrode interfaces. However, graphene is susceptible to various extrinsic factors, e.g. substrate, causing much confusion and controversy. Hereby we have obtained cm-sized substrate-free monolayer graphene suspended on electrolyte surface with gate tunability. Using sum-frequency spectroscopy, we have observed the structural evolution versus the gate voltage at the graphene/water interface. The Stern layer structure is invariant within the water electrolysis window, but undergoes drastic change when switching on the electrochemical reactions. The electrode is turned from hydrophobic to hydrophilic near the onset of hydrogen evolution reaction due to hydrogen adsorption. The large-size suspended pristine graphene offers a new platform to unravel the microscopic processes at the graphitic electrode interfaces.