Hip hip hooray, Hubert! February 2022 marked Hubert Girault's 65^th birthday and this is the year in which he will officially retire from the academic field of Physical and Analytical Electrochemistry – although anyone who knows Hubert well will understand that it is difficult to conceive of him simply retiring. Hubert is many things, but one thing he isn't is the “retiring type”. Over his tenure, Hubert has made significant contributions to the discipline of electrochemistry and to science in general, while simultaneously impacting the lives of many young scientists, often jump-starting their careers. This Special Collection is to celebrate the birthday of Hubert Girault along with his many scientific contributions. This Editorial gives a brief biographical overview.

The Front Cover shows the water-free liquid-liquid interface between an ionic liquid and oil, where base metal nanostructures can be formed via the electron transfer reaction between metal ions on the ionic liquid side and reducing agents on the oil side of the interface. More information can be found in the Research Article by N. Nishi et al.

“The oil-water two-phase system has been an attractive reaction platform to prepare metal nanostructures for over a century. However, the metal nanostructures we can make using this method have been limited to those of noble metals, because the presence of water in the liquid-liquid two-phase systems hinders the reductive deposition of less-noble metals. To overcome this challenge, we propose in this study a water-free liquid-liquid two-phase system composed of a hydrophilic ionic liquid and oil and demonstrate that base metal nanostructures can be formed at this water-free liquid/liquid interface…“ Learn more about the story behind the research featured on the front cover in this issue's Cover Profile. Read the corresponding Research Article at 10.1002/celc.202201000.

Reductive Zn nanodeposition: Reductive metal deposition at the interface between two immiscible electrolyte solutions (ITIES) is an attractive methodology to produce metal nanostructures. However, the metals have been limited to noble metals; otherwise, water molecules are reduced. The present study introduced how to overcome this limitation by utilizing a novel water-free ITIES between a hydrophilic ionic liquid and oil, exemplified by the formation of Zn metal nanostructures at the interface.

The Front Cover illustrates a single microscopic drop which is generated and directed to a reactive surface, where the liquid content is detected. More information can be found in the Research Article by S. Rastgar et al.

Drop by drop: Droplets with volumes between fL to μL are generated as liquid reactors in a viscous carrier liquid and guided to the surface of a microelectrode. The analysis of the current transients for a complete electrolysis of the reactor content allowed to reconstruct the mechanisms by which the reactor interacts with the surface.

Flowing freely: A novel microfluidic free-flow paper electrochromatography (μ-FFPE) device is developed which combines microfluidic free-flow electrophoresis (μ-FFE) and filter paper-based chromatography, enabling the continuous two-dimensional separation of complex analytes. The μ-FFPE shows good analytical performance for the fractionation of glycans and can provide a new platform for the separation of various biological molecules.

Interfacial Cocrystallisation: The potential and the current are monitored simulatenously during the cocrystallisation of caffeine and 1H2N at interface between two immiscible electrolyte solutions polarised by a common ion. Electrochemical noise analysis can offer new insights to charge transfer at the ITIES.

The first iron-based dithiolene complex, iron(III) bis-maleonitriledithiolene, is characterised for carbon dioxide reduction activity and stability. Operating with 2,2,2-trifluoroethanol proton source in acetonitrile electrolyte, the homogeneous catalyst gave 38 % CHOOH faradaic efficiency with H₂ and CO minor products. The catalyst performance is presently limited by parasitic side-reactions with the electrolyte and catalyst decomposition.

Hydrolysis of pyrosulfate was studied by electrochemical experiments and quantum mechanical calculations, revealing Gibbs transfer energies of transfer for pyrosulfate, hydrogen sulfate and sulfate anions at the liquid-liquid interface.

The Cover Feature illustrates a voltammetric investigation of an ionizable lomefloxacin (LOM) transfer reaction across a polarized interface between an organic or organic gel phase and an aqueous solution whose pH was systematically varied, providing photodegradation information and applicability to the analysis of commercial LOM-containing eye drop samples. More information can be found in the Research Article by M. Salman et al.

The ionizable lomefloxacin (LOM) transfer process across ITIES was investigated using various voltammetric techniques, providing an ionic partition diagram, thermodynamic, and photodegradation properties alongside an application to diluted commercial eye drops containing LOM.

A novel electrochemical sensor based on core-shell ZIF-8@ZIF-67-derived Co nanoparticles/N-doped carbon nanotube polyhedron composites has been designed for the efficient determination of antibiotic drug chloramphenicol.

The Cover Feature illustrates that saturation of the organic electrolyte anion (orange balls) in the electric double layer on the organic side of a positively polarized liquid|liquid interface is compensated by an accumulation of protons (blue balls) on the aqueous side. The latter enhances the kinetics of interfacial electron transfer between protons and organic soluble decamethylferrocene in the presence of O₂, yielding H₂O₂ (image design by Dr Shayon Bhattacharya, University of Limerick). More information can be found in the Research Article by A. Gamero-Quijano, M. D. Scanlon and co-workers.

Biphasic interfacial electron transfer: Using the biphasic 2-electron O₂ reduction reaction at a polarised liquid|liquid interface, the applied interfacial Galvani potential difference is shown to provide no direct driving force to realise a thermodynamically uphill interfacial electron transfer (IET) reaction. Thermodynamically spontaneous IET is kinetically inhibited until is tuned to modulate the ion distributions such that all species involved in the biphasic reaction are present at the interface in significant concentrations simultaneously.

Makes sense: Copper metal organic framework (MOF) nanoelectrodes are prepared by depositing copper benzene tricarboxylate MOF (HKUST-1) into open carbon nanopipettes and used for sensing hydrogen peroxide.

The Cover Feature illustrates a computational prediction of the adsorption equilibrium for ionic surfactants at the electrified oil/water interface. It is shown that a cationic surfactant, hexadecyltrimethylammonium ion, adsorbs at the nitrobenzene/water interface depending on the interfacial potential difference. More information can be found in the Research Article by A. Yamauchi et al.

Potential dependent adsorption: A new calculation method based on a non-Bornian solvation model was proposed for predicting the adsorption equilibrium for ionic surfactants at the polarized oil (O)/water (W) interface. The electrostatic potential of an ionic surfactant in the electric double layer of the O/W interface was successfully considered together with the chemical potential.

Ion transfer at the interfaces: Thermodynamic and kinetic behaviors of simple ion transfers at the water/trifluorotoluene (W/TFT) interface are investigated in this work. Two novel types of liquid/liquid (L/L) interfaces, W/o- and p-methylbenzotrifluoride (W/o- and p-MBTF) interfaces, have also been established and their application in electrochemistry at L/L interfaces are discussed.

Crossing that bridge: Ionic diffusion coefficients are determined in highly charged ion-exchange membranes. In particular, the transport of weak electrolytes with dissociation equilibria are emphasized. Calculations are corroborated with COMSOL simulations, which is a facile way to tackle hard transport problems.

The Cover Feature shows the interfacial cation exchange reaction facilitated by the presence of a neutral ligand in the non-aqueous phase. In addition, the proton transfer facilitated by the interfacially formed complex is included. Special emphasis is placed on the environment of the processes responsible for electrochemical signals. More information can be found in the Research Article by T. A. Hernández et al.

A model for facilitated ion transfer reactions across liquid|liquid interfaces based on a neutral weak acid and its conjugate base was developed and takes into account acid–base, complex formation and partition equilibria. In certain experimental conditions with two different cations present, the facilitated ion transfer reactions involve an interfacial cation exchange reaction. The effect of the hydrophobicity of the ligand that assists the cation exchange is interpreted using pH-potential diagrams.

Electroluminescence: To investigate the structure correlations to electroluminescence (ECL) performance, the relative ECL efficiencies of eight silole compounds have been determined in coreactant processes with benzoyl peroxide (BPO). The results reveal that the extended π-conjugated systems and donor groups of the silole emitters affect both the radical stability and emission efficiencies. Spooling ECL spectroscopy provides more insights into the mechanisms of silole/BPO coreactant systems.

Electrochemiluminescence quantum efficiency (ECL-QE): ECL-QE of Ru(bpy)₃²⁺/TPrA system was calculated in terms of a kinetic reaction model, which could reveal the root cause of ECL-QE change and could potentially be used as a criterion of selecting efficient luminophores and analytical conditions.

The Cover Feature illustrates the effect of adding water as a component of a DES (ethaline). Diffusion and viscosity increase as the charge transfer rate constant does not change. More information can be found in the Research Article by F. Zhen and P. Hapiot.

Challenging the theory: The effects of water on the charge-transfer kinetics in deep eutectics solvents (DESs) are investigated in ethaline, which is taken as a prototypical example of a hydrophilic DES. As the viscosity or the diffusion coefficients show the expected variations when adding water, kinetic rate constants show very little variations, in an apparent contradiction with the Marcus theory model.

Mix and match: An aerosol-based synthesis technique was developed as a simple method for the production of multi-metallic catalyst particles. 22 different quinary catalyst compositions were synthesized and investigated for the oxygen evolution reaction (OER) as it is the limiting step during water electrolysis and hydrogen production. As an alternative to OER, all catalysts were further investigated for the glycerol oxidation reaction (GOR).

H₂, O₂, and H₂O₂ generation at liquid|liquid interface: The efficiency of these reactions can be increased by appropriate polarization of the interface, selection of electron donor, light, assembly of catalyst or photosensitizer at interface, addition of molecular catalyst to organic phase, electrochemical or photochemical recycling of electron donor in organic phase and others. The organic phases include hydrophobic molecular solvents and hydrophobic ionic liquids.

Biphasic in situ electrodeposition: A nanocomposite catalyst with Cu nanoparticles electrodeposited on reduced graphene oxide was prepared using GO and CuCl₂ precursors in the aqueous phase and decamethylferrocene in the organic phase. The heterojunction formed between reduced graphene oxide and Cu nanoparticles lead to increased catalyst active sites because it displayed more homogenous particle distribution and less agglomeration.

The Cover Feature illustrates ion transfer and adsorption processes of anthracycline antibiotics affected by the dendritic polymer at liquid|liquid interfaces. More information can be found in the Research Article by T. Takami et al.

Specific interfacial behavior: Anthracycline antibiotics, daunorubicin (DNR) and doxorubicin (DOX), exhibit specific interactions with amphoteric phospholipid layers and carboxylate-terminated PAMAM dendrimers at liquid|liquid interfaces. Spectroelectrochemical analysis demonstrates that the phospholipid layer at the interface induces the facilitated ion transfer of anthracycline cations, HDNR⁺ and HDOX⁺, and the negatively charged PAMAM dendrimer modifies their interfacial behavior through the pH-responsive association.

Electrifying: The electrified liquid-liquid interface was simultaneously modified with polyamide (Nylon-6,6) and silver based particles under electrochemical control. Silver was dissolved in the aqueous phase together with 1,6-diaminohexane (soluble complex is formed), whereas the organic phase was the solution of adipoyl chloride and ferrocene.

Adsorption of bovine serum albumin (BSA) at a polarized water/1,2-dichloroethane interface is investigated by measuring the dynamic interfacial tension. Analysis of the effect of BSA concentration enables to establish the adsorption isotherm, and to evaluate the surface excess concentration and the adsorption Gibbs energy. Adsorbed BSA have a negligible effect on the rate constant of the interfacial transfer of the tetraethylammonium or Cs⁺ ion.

Electrode matters: The electrode material used for nanoimpact electrochemistry is crucial for visualizing simultaneously the reduction of AgBr nanoparticles (NPs) and the electrocatalytic activity of the resulting Ag NPs for oxygen reduction reaction. While with gold only the reduction is analyzed, with carbon both descriptors are quantified for the very same NPs, paving the way for establishing NPs size-activity relationships.

The Cover Feature illustrates the mass change of a Pt thin film measured during oxygen adsorption/desorption and Pt dissolution during electrochemical cycling in alkaline conditions. More information can be found in the Research Article by L. Strandberg, B. Wickman and co-workers.

A hydrophobic ionic liquid, TDDA⁺TB⁻, highly soluble in toluene, enables a polarizable interface with an aqueous solution with Li⁺Cl⁻ dissolved. The water/toluene micro-interface is polarized at potentials more positive than the onset potential for Li⁺ transfer to drag hydrated Li⁺ into toluene, waiting for Li⁺–ionosomes assembly. Reversing the electric field unveils a train of quantized ionic current spikes that are relevant to the single fusion events of Li⁺–ionosomes with the interface.

SECM for bacterial biofilms studies: This review article introduces state-of-the-art applications of scanning electrochemical microscopy (SECM) in bacterial biofilm studies, by summarizing the relevant biochemical cues that can be detected using SECM and highlighting the specific bacterial species as well as their corresponding applications.

When the crime happened: Scanning electrochemical microscopy in the surface interrogation mode has been first introduced to determine the time since deposition (TSD) of bloodstains, which is based on the changes of the tip current over bloodstains with different TSDs. Furthermore, this strategy is expanded to differentiate blood fingermarks between 3.5+1.5 h and 75.5+1.5 h and exhibits great promise for practical application.

Better understanding of pathogenesis of Alzheimer: Truncated β-amyloids with a paraglutamate at the N-terminus are common in senile plaques. Here, we have studied the redox activity of pAβ(3-16)−Cu(II) complexes for the first time. This is important for better understanding of the oxidation and reduction processes that occur in the brains of people affected by Alzheimer's Disease.