Replication Data for: ATR THz Spectroelectrochemistry - Development and Investigation of Hydrophobic Electrolyte Films at a Gold Electrode

The datasets used to test the measurement routine and the two initial studies are presented. In this study, tetrabutylammonium (TBA) Cl and TBA Br are investigated over a wide potential window, demonstrating a significant influence on the electric double layer at the aqueous metal interface. Based on the observations, a mechanism by which it enhances hydrogen evolution reaction (HER) activity is suggested.

It opens new possibilities for targeted engineering of the aqueous electric double layer (EDL). Dataset Description: Information for file Format: Spectral data: - Opus files (.0 and .0000-.0500): can be read with OPUS (Bruker) or with non-commercial Python add-ons, etc. - .txt files: tab-separated file with columns Wavenumber and Intensity - see header for details in all other files Description of files in Datasets copied from Nicolai S. Wichmann.

ATR THz Spectroelectrochemistry - Development and Investigation of Hydrophobic Electrolyte Films at a Gold Electrode, PhD Thesis, Ruhr-Universität Bochum, 2026, unpublished • Attachment – Contains THz spectra of water and H2SO4 measurements with and without a gold grid as raw-data (Opus Bruker file, Attachement/Raw-Data) and .txt format (Attachement/TXT). Using Script_Attachement-1.py the absorption (𝛼) plot can be calculated (Attachement/Calculated/Attachement.txt). – used in: Fig. 2.7 • CVs – Contains Cyclic voltammetry (CV) not directly collected with THz spectroelectrochemistry – 0.1 M TBA Cl at 50 mV/s (CVs/TBACl50mVs_All-CV.txt) and 0.1 M K3[Fe(CN)6] 50 mV/s (CVs/K3FeCN6_All_CVs.txt) – used in: Fig. 2.5, Fig. 2.9 • KCLPoison – Contains THz spectra of THz spectroelectrochemistry measurements of 0.1 M TBA Cl mixed with a 0.1 M KCl solution.

The data is split into the two measured percentages and contains raw-data (Opus Bruker file, KCLPoison/X_percent_KCl/Raw-Data) and .txt format (KCLPoison/X_percent_KCl/TXT), and the current response of the potential jump (KCLPoison/X_percent_KCl/ElChem). Using Script_KCl_Poisom-1.py the difference absorption (Δ𝛼) plot can be calculated (KCLPoison/Calculated/KClPoison.txt). – used in: Fig. 2.8 • Scripts – Contains all mentioned scripts to calculate results shown in calculated-folder • TBABr-Anodic – Contains THz spectra of THz spectroelectrochemistry measurements of 0.1 M TBA Br with a potential window isolating the first anodic peak.

The data contains raw-data (Opus Bruker file, TBABr-Anodic/Raw-Data) and .txt format (TBABr-Anodic/TXT), and the current response of the CV (TBABr-Anodic/ElChem). Using Skript_TBABr_Anodic-1.py the difference absorption (Δ𝛼) plot can be calculated (TBABr-Anodic/Calculated) with spectrum of minimum current response as reference (TBABr-Anodic/Calculated/DifToMinI.txt) and an estimate for the potential (TBABr-Anodic/Calculated/Potential.txt) to correlate it to the CV. – used in: Fig. 5.1, Fig. 8.1 • TBABr-Cathodic – Contains THz spectra of THz spectroelectrochemistry measurements of 0.1 M TBA Br with a LSV going until the HER disrupt the spectral and electrochemical response.

The data is split into two measurement series and contains raw-data (Opus Bruker file, TBABr-Cathodic/MeasurementX/Raw-Data) and .txt format (TBABr-Cathodic/MeasurementX/TXT), and the current response of the LSV (TBABr-Cathodic/ElChem). Using Skript_TBABr_Cathodic-1.py the difference absorption (Δ𝛼) plot can be calculated (TBABr-Cathodic/Calculated) with first spectrum (TBABr-Cathodic/Calculated/MXDifToStart.txt) or spectrum of hydrogen evolution reaction (HER) onset (TBABr-Cathodic/Calculated/MXDifToOnsetHER.txt) as reference.

The potential for each spectrum can be calculated by the LSV scan rate of 60 mV/min and the spectrum collection over 1 min (60 mV/spectrum) with an offset of +0.1 V for V vs. PZC. – used in: Fig. 5.1, Fig. 8.1 • TBACl-Drift – Contains THz spectra of THz spectroelectrochemistrymeasurements of 0.1 M TBA Cl with a CV isolating the first anodic peak. The data contains raw-data (Opus Bruker file, TBACl-Drift/Raw-Data) and .txt format (TBACl-Drift/MeasurementX/TXT), and the current response of the LSV (TBACl-Drift/ElChem).

Using Skript_TBACl_Drift-1.py the difference absorption (Δ𝛼) plot can be calculated (TBACl-Drift/Calculated) with first spectrum (TBACl-Drift/Calculated/DifToStartAfterRev.txt) or spectrum of minimum current response (TBACl-Drift/Calculated/DifToMinIAfterRev.txt) as reference. Additional the amplitude of a Gaussian (TBACl-Drift/Calculated/Amp170AfterRev.txt) and the slope of a linear fit (TBACl-Drift/Calculated/AllSlopeAfterRev.txt) are calculated.

The potential for each spectrum can be calculated by the CVs scan rate and the spectrum collection over 1 min (see equation in script). – used in: Fig. 2.13 • TBACl-Spec – Contains THz spectra of THz spectroelectrochemistrymeasurements of 0.1 M TBA Cl with a CV isolating the first anodic peak. The data contains raw-data (Opus Bruker file, TBACl-Spec/Raw-Data) and .txt format (TBACl-Spec/MeasurementX/TXT), and the current response of the LSV (TBACl-Spec/ElChem).

Using Skript_TBACl_Spec-1.py the difference absorption (Δ𝛼) plot can be calculated (TBACl-Spec/Calculated) with first spectrum (TBACl-Spec/Calculated/DifToStartAfterRev.txt) or spectrum of minimum current response (TBACl-Spec/Calculated/DifToMinIAfterRev.txt) as reference. The amplitude of a Gaussian (TBACl-Spec/Calculated/Amp170AfterRev.txt) and the slope of a linear fit (TBACl-Spec/Calculated/AllSlopeAfterRev.txt) are calculated.

The parameters for a singel sigmoidal fit for slope and gaussian (TBACl-Spec/Calculated/SigmoidalA1S1.txt) and for a double sigmoidal fit for slope and gaussian (TBACl-Spec/Calculated/SigmoidalA2A2S2S2.txt) was calculated. An SVD was carried out with S (TBACl-Spec/Calculated/STBAClSAfterRev.txt), U (TBACl-Spec/Calculated/UTBAClSAfterRev.txt), and Vh (TBACl-Spec/Calculated/VhTBAClSAfterRev.txt) for the different matrices.

The potential for each spectrum can be calculated by the CVs scan rate and the spectrum collection over 1 min (TBACl-Spec/Calculated/Potential.txt). – used in: Fig. 2.10, Fig. 2.11, Fig. 2.12, Fig. 2.13, Fig. 4.1, Fig. 4.2 METHODOLOGICAL INFORMATION: used instruments: - Bruker Vertex v80 (Bruker, Billerica, MA) - Bolometer (Infrared Laboratories, Tucson, AZ) - MVP-Pro (Harrick Scientific, Pleasantville, NY) with 2x3 mm^2 diamond prism - In-house THz spectroelectrochemical cell (see details in thesis text or doi.org/10.1021/jacs.5c11586) -> Prior to experiments, the cell was pretreated with 0.5 M H2SO4 via cycling CVs until stable conditions. - PalmSens4 (PalmSense, Houten, The Netherlands) Samples: - Milli-Q water - TBA Cl (≥97% NT, Sigma-Aldrich, Darmstadt, Germany) - TBA Br (≥99.0%, Sigma Aldrich) - KCl (≥99.0%, Sigma Aldrich) - K3[Fe(CN)6] (99%, Grüssing, Filsum, Germany) - H2SO4 (≥95%, Fisher Chemical, Schwerte, Germany) -> all samples were degassed with N2 prior to the experiment Settings: - Spectral settings: 30-680cm^-1 window, 2cm^-1 resolution (except for folder KClPoison with 1cm^-1), evacuated interferometer, vented sample chamber, MIR globar radiation source, Mylar Multilayer beam splitter, one spectrum is averaged over 1 min (ca. 37 scans) - The electrochemical settings can be read out of the datasets