Micheal Diarmaid Scanlon

Extended Gouy–Chapman–Stern modelling reveals charge density dependent Helmholtz capacitance at polarisable liquid|liquid interfaces, governed by ion penetration into the mixed layer, electrolyte composition, and Galvani potential difference.

Polyoxometalates (POMs) are versatile molecular redox systems, yet their electrochemical behavior at polarizable liquid|liquid interfaces remains unexplored. Here, we investigate Keggin-type phosphomolybdic acid (PMA) and phosphotungstic acid (PTA) at a polarizable aqueous|α,α,α-trifluorotoluene interface and demonstrate their use as molecular oxidants and dopants for the interfacial electrosynthesis of free-standing POM-poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid thin films. Voltammetry and in situ spectroscopy reveal potential-dependent adsorption and accumulation of POM anions at the interface. Under controlled interfacial polarization, accumulated POMs generate a highly acidic nanoscale reaction environment and catalyze the initial C−C coupling steps of EDOT oligomerization, enabling POM-PEDOT film formation despite thermodynamically unfavorable direct electron transfer between EDOT and the POMs. The resulting PEDOT nuclei evolve into conductive films that sustain growth through a redox cycle in which the POMs act as terminal oxidants and dopant anions. Mixing PMA and PTA markedly enhances growth kinetics, yielding robust, transferable hybrid films with hierarchical three-dimensional morphologies, high POM loadings, and preserved Keggin structures. Ex situ electrochemical characterization reveals the coexistence of PEDOT charging and highly reversible POM-centered redox processes, producing capacitances of up to 48 F g ^–1 in organic electrolyte and >90% capacitance retention at scan rates up to 1 V s ^–1 . These findings establish polarizable liquid|liquid interfaces as a powerful platform for synthesizing free-standing electroactive hybrid materials.

Electrosynthesis traditionally requires solid electrodes and a power source, yet a soft interface itself can encode the required driving force. Here, Electrodeless Interfacial Electrosynthesis (ELIE) exploits the intrinsic polarization of immiscible liquid|liquid interfaces to drive oxidative polymerization of conducting polymer thin films without applied power. ELIE reframes electrosynthesis as a chemically polarized interfacial process, producing high‑quality free-standing films using only simple glassware and solution preparation. Salts dissolved in the organic phase comprising hydrophilic cations and hydrophobic anions function as chemical polarizers, generating a tuneable interfacial Galvani potential that mediates electron transfer between aqueous Ce ⁴⁺ and organic monomers, producing conducting films of PEDOT, PProDOT, and PProDOT‑Et ₂ . Polarizer identity programs the interfacial potential, directing oligomer growth and nanoscale film morphology. ELIE‑grown films exhibit reversible p‑doping, conductivities up to ~20 S cm ^–1 , and low hysteresis, without post‑treatments. As an initial regenerative‑medicine demonstration, the films exhibit high retinal cell viability, surpassing that of PEDOT:PSS.

Measuring interfacial phenomena on the microscopic level is a current frontier topic across science, technology, and engineering. The potential/point of zero charge (pzc) is a fundamental parameter used to describe the electrostatics of a polarizable electrochemical interface. The pzc is a reference quantity at which no excess net charge is present at either side of the electrical double layer (EDL) of an electrochemical interface. A polarizable molecular interface, known as the interface between two immiscible electrolyte solutions (ITIES), may be formed between two ionic conducting electrolytes. Electrochemistry at a microscopic ITIES is an emerging field with broad applications in chemical/biosensing, scanning electrochemical microscopy imaging, mechanistic studies, and single-entity electrochemistry (SEE). Herein, we demonstrate the direct measurement of the pzc and EDL structure at ITIES composed of molecular interfaces formed either between water and α,α,α-trifluorotoluene or between water and α,α,α-trifluorotoluene methylated derivatives by utilizing SEE in conjunction with the charged characteristics of ionosomes and a double potential step chronoamperometry technique. The harmony of qualitative and quantitative analyses proves the reliability of this method. For comparison, the pzc of each complementary macro-ITIES is also measured with the differential capacitance method in a four-electrode configuration. The pzc values obtained by both methods are basically consistent. The collisional ionosome method overcomes the difficulty in measuring the pzc at the ITIES at the microscopic scale. Besides, our work supports the validity of the discrete Helmholtz model for describing the EDL at a polarizable ITIES at least at micro- and/or nano-ITIES. Furthermore, this work provides new mechanistic insights into the universal emulsification route via ionosomes.

Conducting polymer (CP) thin films find widespread use, for example in bioelectronic, energy harvesting and storage, and drug delivery technology. Electrosynthesis at a polarizable liquid|liquid interface using an aqueous oxidant and organic soluble monomer provides a route to free-standing and scalable CP thin films, such as poly(3,4-ethylenedioxythiophene) (PEDOT), in a single step at ambient conditions. Here, using the potentiodynamic technique of cyclic voltammetry, interfacial electrosynthesis involving ion exchange, electron transfer, and proton adsorption charge transfer processes is shown to be mechanistically distinct from CP electropolymerization at a solid electrode|electrolyte interface. During interfacial electrosynthesis, the applied interfacial Galvani potential difference controls the interfacial concentration of the oxidant, but not the CP redox state. Nevertheless, typical CP electropolymerization electrochemical behaviors, such as steady charge accumulation with each successive cycle and the appearance of a nucleation loop, were observed. By combining (spectro)electrochemical measurements and theoretical models, this work identifies the underlying mechanistic origin of each feature on the cyclic voltammograms (CVs) due to charge accumulated from Faradaic and capacitive processes as the PEDOT thin film grows. To prevent overoxidation during interfacial electrosynthesis with a powerful cerium aqueous oxidant, scan rates in excess 25 mV·s^-1 were optimal. The experimental methodology and theoretical models outlined in this article provide a broadly generic framework to understand evolving CVs during interfacial electrosynthesis using any suitable oxidant/monomer combination.

Optical second-harmonic generation (SHG) is achieved using adsorbed gold nanoparticles (AuNPs) with an average diameter of 16 nm at the aqueous solution–air interface in reflection. A detailed analysis of the depth profile of the SHG intensity detected shows that two contributions appear in the overall signal, one arising from the aqueous solution–air interface that is sensitive to the AuNP surface excess and one arising from the bulk aqueous phase. The latter is an incoherent signal also known as hyper-Rayleigh scattering (HRS). The results agree with those of an analysis involving Gaussian beam propagation optics and a Langmuir-like isotherm. Discrepancies are revealed for the largest AuNP concentrations used and indicate a new route for the design of soft metasurfaces.

Conducting polymer (CP) thin films find widespread use, for example in bioelectronic, energy harvesting and storage, and drug delivery technology. Electrosynthesis at a polarisable liquid|liquid interface using an aqueous oxidant and organic soluble monomer provides a route to free-standing and scalable CP thin films, such as poly(3,4-ethylenedioxythiophene) (PEDOT), in a single step at ambient conditions. Here, using the potentiodynamic technique of cyclic voltammetry, interfacial electrosynthesis involving ion-exchange, electron transfer, and proton adsorption charge transfer processes is shown to be mechanistically distinct from CP electropolymerisation at a solid electrode|electrolyte interface. The applied interfacial Galvani potential difference controls the interfacial concentration of the oxidant, EDOT monomers and oligomers, but not the CP redox state. Nevertheless, typical CP electropolymerisation electrochemical behaviours, such as steady charge accumulation with each successive cycle and the appearance of a nucleation loop, were observed. By combining (spectro)electrochemical measurements and theoretical models, this work identifies the underlying mechanistic origin of each feature on the cyclic voltammograms (CVs) due to charge accumulated from Faradaic and capacitive processes as the PEDOT thin film grows. The experimental methodology and theoretical models outlined in this article provide a broadly generic framework to understand evolving CVs during interfacial electrosynthesis using any suitable oxidant/monomer combination.

An aqueous colloidal suspension of gold nanoparticles (AuNPs) may be condensed into a thin fractal film at the polarizable liquid-liquid interface formed between two immiscible electrolyte solutions upon injection of millimolar concentrations of sodium chloride to the aqueous phase. By adjusting the interfacial polarization conditions (negative, intermediate, and positive open-circuit potentials), the morphology of the film is modified, resulting in unique surface plasmon properties of the film, which enable in situ surface-enhanced Raman spectroscopy (SERS). Intense SERS signals are observed at the polarizable liquid-liquid interface when micromolar concentrations of tolmetin, a nonsteroidal anti-inflammatory drug, are entrapped in the AuNP fractal film. The change in the signal intensity, averaged over multiple spectra, with respect to the concentration of tolmetin, depends on the polarization conditions and suggests the presence of chemical-induced damping effects on the surface plasmons of the gold film.

An aqueous colloidal suspension of gold nanoparticles (AuNPs) may be condensed into a thin fractal film at the polarisable liquid-liquid interface formed between two immiscible electrolyte solutions (ITIES) upon injection of millimolar concentrations of sodium chloride to the aqueous phase. By adjusting the interfacial polarisation conditions (negative, intermediate, and positive open-circuit potentials), the morphology of the film is modified, resulting in unique surface plasmon properties of the film, which enable in situ surface-enhanced Raman spectroscopy (SERS). Intense SERS signals are observed at the polarisable liquid-liquid interface when micromolar concentrations of tolmetin, a non-steroidal anti-inflammatory drug, are entrapped in the AuNP fractal film. The change in signal intensity, averaged over multiple spectra, with respect to the concentration of tolmetin, depends on the polarisation conditions and suggests the presence of chemical-induced damping effects on the surface plasmons of the gold film.