Pekka Peljo

Towards a thermally regenerative all-copper redox flow battery

An all-copper redox flow battery based on strong complexation of Cu(+) with acetonitrile is demonstrated, exhibiting reasonable battery performance. More interestingly, the battery can be charged by heat sources of 100 °C, by distilling off the acetonitrile. This destabilizes the Cu(+) complex, leading to recovery of the starting materials.

Surprising acidity of hydrated lithium cations in organic solvents

Lithium cations are shown to have a significant role in catalyzing oxygen and proton reduction along with S(N)1 reactions in biphasic systems. We propose that this catalytic effect is due to the surprising acidity of the hydrated cations; interactions between the cation and its surrounding solvation shell will make the constituent water molecules more acidic.

All-vanadium dual circuit redox flow battery for renewable hydrogen generation and desulfurisation

An all-vanadium dual circuit redox flow battery is an electrochemical energy storage system able to function as a conventional battery, but also to produce hydrogen and perform desulfurization when a surplus of electricity is available by chemical discharge of the battery electrolytes. The hydrogen reactor chemically discharging the negative electrolyte has been designed and scaled up to kW scale, while different options to discharge the positive electrolyte have been evaluated, including oxidation of hydrazine, SO2 and H2S. The system is well suited to convert sulfur dioxide and hydrogen sulfide to harmless compounds while producing hydrogen, with overall system efficiencies from 50 to 70% for hydrogen production.

Gold Nanofilms at Liquid–Liquid Interfaces: An Emerging Platform for Redox Electrocatalysis, Nanoplasmonic Sensors, and Electrovariable Optics

The functionality of liquid-liquid interfaces formed between two immiscible electrolyte solutions (ITIES) can be markedly enhanced by modification with supramolecular assemblies or solid nanomaterials. The focus of this Review is recent progress involving ITIES modified with floating assemblies of gold nanoparticles or nanofilms. Experimental methods to controllably modify liquid-liquid interfaces with gold nanofilms are detailed. Also, we outline an array of techniques to characterize these gold nanofilms in terms of their physiochemical properties (such as reflectivity, conductivity, catalytic activity, or plasmonic properties) and physical interfacial properties (for example, interparticle spacing and immersion depth at the interface). The ability of floating gold nanofilms to impact a diverse range of fields is demonstrated: in particular, redox electrocatalysis, surface-enhanced Raman spectroscopy (SERS) or surface plasmon resonance (SPR) based sensors, and electrovariable optical devices. Finally, perspectives on applications beyond the state-of-the-art are provided.

Electrochemical Dynamics of a Single Platinum Nanoparticle Collision Event for the Hydrogen Evolution Reaction

Chronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0u2005mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen-containing atmospheres. The particle size distribution estimated from the diffusion-controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry.

High energy density MnO4-/MnO42- redox couple for alkaline redox flow batteries

The MnO4-/MnO42- redox couple has a positive redox potential, high electrochemical reversibility and high solubility, up to 3.62 M at room temperature. Careful optimization of the electrolyte composition and the potential limits eliminates the side reactions, making this redox couple an attractive option for alkaline redox flow batteries.

Photoproduction of Hydrogen by Decamethylruthenocene Combined with Electrochemical Recycling

The photoinduced hydrogen evolution reaction (HER) by decamethylruthenocene, Cp2 *RuII (Cp*=C5 Me5 ), is reported. The use of a metallocene to photoproduce hydrogen is presented as an alternative strategy to reduce protons without involving an additional photosensitizer. The mechanism was investigated by (spectro)electrochemical and spectroscopic (UV/Vis and 1 Hu2005NMR) measurements. The photoactivated hydride involved was characterized spectroscopically and the resulting [Cp2 *RuIII ]+ species was electrochemically regenerated inu2005situ on a fluorinated tin oxide electrode surface. A promising internal quantum yield of 25u2009% was obtained. Optimal experimental conditions- especially the use of weakly coordinating solvent and counterions-are discussed.

Gold Raspberry-Like Colloidosomes Prepared at the Water–Nitromethane Interface

In this study, we propose a simple shake-flask method to produce micron-size colloidosomes from a liquid-liquid interface functionalized with a gold nanoparticle (AuNP) film. A step-by-step extraction process of an organic phase partially miscible with water led to the formation of raspberry-like structures covered and protected by a gold nanofilm. The distinctive feature of the prepared colloidosomes is a very thin shell consisting of small AuNPs of 12 or 38 nm in diameter instead of several hundred nanometers reported previously. The interesting and remarkable property of the proposed approach is their reversibility: the colloidosomes may be easily transformed back to a nanofilm state simply by adding pure organic solvent. The obtained colloidosomes have a broadband absorbance spectrum, which makes them of great interest in applications such as photothermal therapy, surface-enhanced Raman spectroscopy studies, and microreactor vesicles for interfacial electrocatalysis.

Electrochemical potential window of battery electrolytes: the HOMO–LUMO misconception

A widespread misconception in the lithium ion battery literature is the equality of the energy difference of HOMO and LUMO of the solvent with the electrochemical stability window. HOMO and LUMO are concepts derived from approximated electronic structure theory while investigating electronic properties of isolated molecules, and their energy levels do not indicate species participating in redox reactions. On the other hand, redox potentials are directly related to the Gibbs free energy difference of the reactants and products. While redox potentials in some cases show strong correlation with HOMO energies, the offset can be of several eVs. Presence of electrolytes and other molecules can also significantly affect the redox potentials of the solvent leading to offset as high as 4 eV from the HOMO energies. In this opinion we provide a correct thermodynamic representation for the electrochemical stability of the electrolyte, based on redox potentials and Fermi level of the electron in solution, and demonstrate that the use of terms HOMO and LUMO should be avoided when talking about the electrochemical stability of electrolytes. Instead, it is more correct to speak of potential of electrolyte reduction at negative potentials, and of potential of solvent oxidation at positive potentials.