Presentation Date: Feb 14, 2026
AGSA Abstract
The structure and composition of solid–liquid interfaces govern key processes in electrochemical energy storage, electrocatalysis, and corrosion, yet are challenging to probe with molecular and nanoscale resolution. Conventional ATR-FTIR spectroscopy accesses micrometer-scale depths and is dominated by bulk liquid response, limiting sensitivity to the electric double layer (EDL). In this experiment we develop a graphene-based liquid cell for Fourier transform infrared nanospectroscopy (nano-FTIR) that enables in situ, nanoscale-resolved vibrational characterization of graphene–electrolyte interfaces under applied potential. A perforated Si₃N₄ membrane coated with Au is capped by monolayer graphene, which simultaneously seals microliter electrolyte reservoirs and serves as a conductive working electrode. Broadband synchrotron IR illumination of a metallized AFM tip generates a strongly confined near field, yielding ~20 nm spatial resolution and depth sensitivity concentrated within the EDL and diffuse layer. We first benchmark the approach on graphene–water, showing that nano-FTIR spectra closely track ATR-FTIR results while exhibiting slight blue shifts and enhanced interfacial contributions. We then interrogate a 0.1 M (NH₄)₂SO₄ aqueous electrolyte, where nano-FTIR reveals pronounced enhancement of sulfate and ammonium vibrational modes relative to the water bending band and detects additional interfacial features near 1200–1300 cm⁻¹ that are absent in bulk-sensitive ATR-FTIR. Applying a +0.5 V bias to graphene relative to a Pt counter electrode further amplifies sulfate and interfacial species signals, consistent with electrostatically driven anion enrichment within the EDL. These results establish graphene-capped nano-FTIR as a versatile, minimally invasive platform for operando spectroscopy of electrochemical interfaces and provide a foundation for future combined experimental–theoretical studies of EDL structure at technologically relevant solid–liquid interfaces.
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