Examination of the Brønsted−Evans−Polanyi Relationship for the Hydrogen Evolution Reaction on Transition Metals Based on Constant Electrode Potential Density Functional Theory

In the search for efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER), the hydrogen binding energy (ΔG*H) is often used as a descriptor to represent the catalytic activity....

Review—Reference Electrodes in Li-Ion and Next Generation Batteries: Correct Potential Assessment, Applications and Practices

This review provides an accessible analysis of the processes on reference electrodes and their applications in Li-ion and next generation batteries research. It covers fundamentals and definitions as well as specific practical applications and is intended to be comprehensible for researchers in the battery field with diverse backgrounds. It covers fundamental concepts, such as two- and three-electrodes configurations, as well as more complex quasi- or pseudo- reference electrodes. The electrode potential and its dependance on the concentration of species and nature of solvents are explained in detail and supported by relevant examples. The solvent, in particular the cation solvation energy, contribution to the electrode potential is important and a largely unknown issue in most the battery research. This effect can be as high as half a volt for the Li/Li+ couple and we provide concrete examples of the battery systems where this effect must be taken into account. With this review, we aim to provide guidelines for the use and assessment of reference electrodes in the Li-ion and next generation batteries research that are comprehensive and accessible to an audience with a diverse scientific background.

Comparative study on high-voltage nanosecond pulses and dielectric barrier discharge effects on surface morphology and physico-chemical properties of natural pyrrhotite

In this paper we used analytical electron microscopy, potentiometric titration (electrode potential), sorption and flotation measurements and other methods to study changes in the surface morphology, electrochemical, and physicochemical properties of the natural pyrrhotite exposed to nonthermal action of the repetitive nanosecond high-power electromagnetic pulses and low-temperature plasma of dielectric barrier discharge in air at atmospheric pressure. As a result of exposure to high-voltage nanosecond pulses, a sharp shift in the electrode potential of pyrrhotite to the region of negative values caused a decrease in the sorption of the anionic collector on the mineral, a decrease in the hydrophobicity of the surface and flotation of the mineral was due to an increase in the content of oxidized ferric iron on the mineral surface. Dielectric barrier discharge treatment caused the shift of the electrode potential to the region of negative values (–60 mV) in the range of pH 9.7-12, which causes the effect of a decrease in the sorption and flotation activity of pyrrhotite. The advantages of using the short-term (10-30 seconds) energy impacts for structural and chemical modification of the surface and physicochemical properties of sulfide minerals of iron are shown.

Fundamentals of Electrochemistry

Fundamentals of Electrochemistry build on basic oxidation-reduction reactions and present an overview of their use in electrochemical cells. The construction and operation of a galvanic cell is described with cell diagrams including the function of the electrodes (cathode and anode). Also covered are the standard electrode potential and its applications, including calculations involving the standard electrode potential, the Gibbs free energy and the equilibrium constant, determination of the spontaneity in redox reactions and the dependence of cell potential on concentration (the Nernst equation). Finally a qualitative and quantitative overview of electrolysis is presented with a focus on predicting the products of electrolysis and the stoichiometry of electrolysis, which relates the charge flowing through an electrolytic cell to the amount of products formed at the electrodes.

Metagenomic and metatranscriptomic characterization of a microbial community that catalyzes both energy-generating and energy-storing electrode reactions

Electroactive bacteria are living catalysts, mediating energy-generating reactions at anodes or energy storage reactions at cathodes via extracellular electron transfer (EET). The Cathode-ANode (CANode) biofilm community was recently shown to facilitate both reactions, however, the identity of the primary constituents and underlying molecular mechanisms remain unknown. Here, we used metagenomics and metatranscriptomics to characterize the CANode biofilm. We show that a previously uncharacterized member of the family Desulfobulbaceae, Desulfobulbaceae -2, which had <1% relative abundance, had the highest relative gene expression and accounted for over 60% of all differentially expressed genes. At the anode potential, differential expression of genes for a conserved flavin oxidoreductase (Flx) and heterodisulfide reductase (Hdr) known to be involved in ethanol oxidation suggests a source of electrons for the energy-generating reaction. Genes for sulfate and carbon dioxide reduction pathways were expressed by Desulfobulbaceae -2 at both potentials and are the proposed energy storage reactions. Reduction reactions may be mediated by direct electron uptake from the electrode, or from hydrogen generated at the cathode potential. The Desulfobulbaceae -2 genome is predicted to encode at least 85 multi-heme (≥3 hemes) c -type cytochromes, some with as many as 26 heme-binding domains, that could facilitate reversible electron transfer with the electrode. Gene expression in other CANode biofilm species was also affected by the electrode potential, although to a lesser extent, and we cannot rule out their contribution to observed current. Results provide evidence of gene expression linked to energy storage and energy-generating reactions and will enable development of the CANode biofilm as a microbially-driven rechargeable battery. IMPORTANCE Microbial electrochemical technologies (METs) rely on electroactive bacteria to catalyze energy-generating and energy storage reactions at electrodes. Known electroactive bacteria are not equally capable of both reactions and METs are typically configured to be unidirectional. Here we report on genomic and transcriptomic characterization of a recently described microbial electrode community called the Cathode-ANode (CANode). The CANode community is able to generate or store electrical current based on the electrode potential. During periods where energy is not needed, electrons generated from a renewable source, such as solar power, could be converted into energy storage compounds to later be reversibly oxidized by the same microbial catalyst. Thus, the CANode system can be thought of as a living “rechargeable battery”. Results show that a single organism may be responsible for both reactions demonstrating a new paradigm for electroactive bacteria.

Constant inner potential DFT for modelling electrochemical systems under constant potential and bias

Electrochemical interfaces and reactions play a decisive role in e.g. clean energy conversion but understanding their complex chemistry remains an outstanding challenge. Constant potential or grand canonical ensemble (GCE) simulations are indispensable for unraveling the properties of electrochemical processes as a function of the electrode potential. Currently, constant electrode potential calculations at the density functional theory (DFT) level are carried out by fixing the Fermi level of the simulation cell. However, the Fermi level from DFT calculations does does not always reflect the experimentally controlled electrode potential or describe the thermodynamic independent variable in GCE-DFT i.e the electrochemical potential of an electron reservoir. Here we develop and implement the constant inner potential (CIP) method as a more robust and general approach to GCE-DFT simulations of electrochemical systems under constant potential or bias conditions. The CIP is shown to directly control the reservoir electron electrochemical potential making the method widely applicable in simulating electrochemical interfaces. We demonstrate that the CIP and Fermi level GCE-DFT approaches are equivalent for metallic electrodes and inner sphere reactions. The CIP method is shown to be applicable in simulating also semiconductor electrodes, outer sphere reactions, and a biased two-electrode cell for which the Fermi level approach does not reflect the experimental electrode potential. Unlike the Fermi level method, CIP does not require any electronic structure information as only the inner potential is needed, which makes the approach more compatible with classical force field or machine learning potentials. The CIP approach emerges as a general GCE DFT method to simulate (photo)electrochemical interfaces from first principles.