Electrochemical Behavior of Pyridinium and N-Methyl Pyridinium Cations in Aqueous Electrolytes for CO2 Reduction

Robust battery interphases from dilute fluorinated cations

Controlling solid electrolyte interphase (SEI) in batteries is crucial for their efficient cycling. Herein, we demonstrate an approach to enable robust battery performance that does not rely on high fractions of fluorinated species in electrolytes, thus substantially decreasing the environmental footprint and cost of high-energy batteries. In this approach, we use very low fractions of readily reducible fluorinated cations in electrolyte (∼0.1 wt%) and employ electrostatic attraction to generate a substantial population of these cations at the anode surface. As a result, we can form a robust fluorine-rich SEI that allows for dendrite-free deposition of dense Li and stable cycling of Li-metal full cells with high-voltage cathodes. Our approach represents a general strategy for delivering desired chemical species to battery anodes through electrostatic attraction while using minute amounts of additive.

CO2 Electrolysis via Surface-Engineering Electrografted Pyridines on Silver Catalysts

The electrochemical reduction of carbon dioxide (CO₂) to value-added materials has received considerable attention. Both bulk transition-metal catalysts and molecular catalysts affixed to conductive noncatalytic solid supports represent a promising approach toward the electroreduction of CO₂. Here, we report a combined silver (Ag) and pyridine catalyst through a one-pot and irreversible electrografting process, which demonstrates the enhanced CO₂ conversion versus individual counterparts. We find that by tailoring the pyridine carbon chain length, a 200 mV shift in the onset potential is obtainable compared to the bare silver electrode. A 10-fold activity enhancement at −0.7 V vs reversible hydrogen electrode (RHE) is then observed with demonstratable higher partial current densities for CO, indicating that a cocatalytic effect is attainable through the integration of the two different catalytic structures. We extended the performance to a flow cell operating at 150 mA/cm², demonstrating the approach’s potential for substantial adaptation with various transition metals as supports and electrografted molecular cocatalysts.

Efficient Intermolecular Charge Transport in π-Stacked Pyridinium Dimers Using Cucurbit[8]uril Supramolecular Complexes

Intermolecular charge transport through π-conjugated molecules plays an essential role in biochemical redox processes and energy storage applications. In this work, we observe highly efficient intermolecular charge transport upon dimerization of pyridinium molecules in the cavity of a synthetic host (cucurbit[8]uril, CB[8]). Stable, homoternary complexes are formed between pyridinium molecules and CB[8] with high binding affinity, resulting in an offset stacked geometry of two pyridiniums inside the host cavity. The charge transport properties of free and dimerized pyridiniums are characterized using a scanning tunneling microscope-break junction (STM-BJ) technique. Our results show that π-stacked pyridinium dimers exhibit comparable molecular conductance to isolated, single pyridinium molecules, despite a longer transport pathway and a switch from intra- to intermolecular charge transport. Control experiments using a CB[8] homologue (cucurbit[7]uril, CB[7]) show that the synthetic host primarily serves to facilitate dimer formation and plays a minimal role on molecular conductance. Molecular modeling using density functional theory (DFT) reveals that pyridinium molecules are planarized upon dimerization inside the host cavity, which facilitates charge transport. In addition, the π-stacked pyridinium dimers possess large intermolecular LUMO-LUMO couplings, leading to enhanced intermolecular charge transport. Overall, this work demonstrates that supramolecular assembly can be used to control intermolecular charge transport in π-stacked molecules.

Synthesis, structural analysis, electrochemical and magnetic properties of tetrachloroferrate ionic liquids

Eight ionic liquids have been synthesized with the tetrachloroferrate anion and varying cations, with the general formula of [RA]⁺[FeCl₄]⁻ (R = –CH₃, –CH₂C₆H₅; A = pyridine, benzimidazole, trimethylamine, triphenylphosphine).

TEMPO-Me: An Electrochemically Activated Methylating Agent

Bench- and air-stable 1-methoxy-2,2,6,6-tetramethylpiperidine (TEMPO-Me) is relatively unreactive at ambient temperature in the absence of an electrochemical stimulus. In this report, we demonstrate that the one-electron electrochemical oxidation of TEMPO-Me produces a powerful electrophilic methylating agent in situ. Our computational and experimental studies are consistent with methylation proceeding via a S_N2 mechanism, with a strength comparable to the trimethyloxonium cation. A protocol is developed for the electrochemical methylation of aromatic acids using TEMPO-Me.

The True Fate of Pyridinium in the Reportedly Pyridinium-Catalyzed Carbon Dioxide Electroreduction on Platinum

Protonated pyridine (PyH⁺ ) has been reported to act as a peculiar and promising catalyst for the direct electroreduction of CO₂ to methanol and/or formate. Because of recent strong incentives to turn CO₂ into valuable products, this claim triggered great interest, prompting many experiments and DFT simulations. However, when performing the electrolysis in near-neutral pH electrolyte, the local pH around the platinum electrode can easily increase, leading to Py and HCO₃ ^- being the predominant species next to the Pt electrode instead of PyH⁺ and CO₂ . Using a carefully designed electrolysis setup which overcomes the local pH shift issue, we demonstrate that protonated pyridine undergoes a complete hydrogenation into piperidine upon mild reductive conditions (near 0 V vs. RHE). The reduction of the PyH⁺ ring occurs with and without the presence of CO₂ in the electrolyte, and no sign of CO₂ electroreduction products was observed, strongly questioning that PyH⁺ acts as a catalyst for CO₂ electroreduction.