We examine the electrochemical behavior of pyridine (py) and pyridinium ion (pyrH + ) on gold electrodes in inert nitrogen (N 2 ) and carbon dioxide (CO 2 ) environments to evaluate potential catalytic roles of nitrogen heterocycles in electrochemical CO 2 reduction. Analysis of the pyridine and pyridinium systems shows that gold electrodes exhibit unique pyrH + and CO 2 electrochemistry compared with previous work on platinum electrodes or photoelectrode systems. Specifically, analysis of the data shows specific adsorption of pyridine/pyridinium, an irreversible reduction wave at −1.0 V vs Ag/AgCl associated with the one-electron reduction of pyridinium, and an enhanced reductive current when CO 2 and pyrH + are included together in the aqueous solution. Our results show no evidence to support formation of carbon-containing reduction products and implicate CO 2 as a possible weak acid catalyst for production of dihydrogen.

In this paper, the capacitive electrochemical behavior of the 1-butyl-3methylimidazolium tetrafluoroborate (Bmim BF 4 )−polycrystalline gold electrode interface is reported over the potential range from −0.37 to 0.53 V vs Fc/Fc + (Fc = ferrocene). Experimental results are generated by analysis of data (RC model) obtained from largeamplitude Fourier-transformed alternating current voltammetry (FT-ACV) over the frequency range of 10 Hz to 1 kHz. Results suggest a parabolic, U-shaped capacitance versus potential relationship, in stark contrast to present ionic liquid (IL) electrochemical double-layer (EDL) theory. The potential range analyzed was carefully selected to be free of Faradaic current and displays minimal hysteresis with respect to the potential scan direction. Over the selected potential window spanning 0.9 V, the capacitance versus potential curve at 9 Hz exhibits a Ushape, with a capacitance minimum of 19.9 ± 1.3 μF cm −2 at 0.13 ± 0.04 V, flanked by maximum values of 21.2 ± 1.3 and 20.8 ± 1.4 μF cm −2 at −0.37 and 0.53 V vs Fc/Fc + , respectively. This capacitance versus potential profile is consistent with traditional Gouy−Chapman−Stern theory for dilute aqueous electrolyte solutions and high-temperature molten salts but distinctly misaligned with bell-or camel-shaped relationships that have recently been proposed in IL model systems. The minimum capacitance exhibits a small level of frequency dispersion, which increases linearly versus the logarithm of the applied frequency. The potential at which the minimum capacitance is located is also slightly dependent on frequency. This work demonstrates that large-amplitude FT-ACV provides a sensitive probe of the EDL from a single experiment and advances the convergence between theoretical predictions and experimental observations of IL−electrode EDL systems.

Capacitance vs. potential relationships help electrochemists better understand electrode-liquid interfacial behaviors. However, the current ionic liquid literature does not have a unified experimental approach, and hysteresis effects are of significant concern. Known experimental variables that can influence capacitance-potential data include electrode material and morphology, potential scan direction, equivalent circuit model applied during analysis, and, to some extent, the electrochemical technique employed. To our knowledge, the present work is the first systematic study of four major variables that are relevant to IL-based capacitance measurements, and of their effects on resulting capacitance curvature. We examine: (1) the potential range explored, (2) the potential scan direction applied, (3) the data acquisition protocol used to collect data, and (4) the electrochemical technique used to generate capacitance data. Specifically, we find that all four of these (some more than others) 'user-defined' experimental variables influence the resulting capacitance-potential curvature for a typical ionic liquid electrochemical system. In an effort to minimize bias and to permit better comparisons of data collected from different laboratories we provide guidelines to help critically assess IL capacitance-potential data.