Electrochemical science advances最新文献

Gustav Theodor Fechner (Figure 1) was a German physicist, psychologist, and philosopher. His scientific contributions were mostly in the area of experimental psychology. He was a founder of psychophysics and he is particularly credited for discovering the non-linear relationship between psychological sensation and the physical intensity of a stimulus. However, for the purpose of this historical note, his contribution to electrochemistry must be emphasized.

Fechner extensively performed electrochemical experiments, particularly testing Ohm's law for electrolyte solutions in galvanic cells. He was the first to introduce into electrochemical science the parameter of the charge transfer resistance at an electrode/electrolyte interface. This factor is highly important for electrochemical kinetics in modern electrochemistry. Fechner was the first who reported in 1828 the observation of electrochemical oscillations during the anodic dissolution of nickel in nitric acid (Figure 2A). From that time, numerous systems with non-stationary oscillating behavior have been discovered.

Fechner designed an electroscope (electrometer) with improved sensitivity. This instrument consisted of 800 to 1000 pairs of metal foils charging two metal condenser plates. A thin strip of gold foil was hung between these plates (Figure 2B). A deviation of the gold foil from its vertical position was used for sensing an electric charge on it with very high sensitivity.

Fechner was very influential by translating and completely rewriting volume 3 (Lehrbuch des Galvanismus und der Elektrochemie) of Jean Baptiste Biot's textbook on experimental physics in which he gives a full account of the state of knowledge in electrochemistry of his time, including his findings.

This article is part of a series featuring historic contributions in and around electrochemistry. At least one such article appears in every issue of Electrochemical Science Advances.

The author declares no conflict of interest.

Gas diffusion electrode (GDE) setups have been recently introduced as a new experimental approach to test the performance of fuel cell catalysts under high mass transport conditions, while maintaining the simplicity of rotating disk electrode (RDE) setups. In contrast to experimental RDE protocols, for investigations using GDE setups only few systematic studies have been performed. In literature, different GDE arrangements were demonstrated, for example, with and without an incorporated proton exchange membrane. Herein, we chose a membrane-GDE approach for a comparative RDE–GDE study, where we investigate several commercial standard Pt/C fuel cell catalysts with respect to the oxygen reduction reaction (ORR). Our results demonstrate both the challenges and the strengths of the new fuel cell catalyst testing platform. We highlight the analysis and the optimization of catalyst film parameters. That is, instead of focusing on the intrinsic catalyst ORR activities that are typically derived in RDE investigations, we focus on parameters, such as the catalyst ink recipe, which can be optimized for an individual catalyst in a much simpler manner as compared to the elaborative membrane electrode assembly (MEA) testing. In particular, it is demonstrated that ∼50% improvement in ORR performance can be reached for a particular Pt/C catalyst by changing the Nafion content in the catalyst layer. The study therefore stresses the feasibility of the GDE approach used as an intermediate “testing step” between RDE and MEA tests when developing new fuel cell catalysts.

The present article is fully confined to cyclic voltammetric measurements of a series of bridged and non-bridged annulenediones (quinones of large conjugated rings of aromatic character). The evaluation of their electrochemical redox properties shed light on remarkable and interesting conclusions such as aromaticity, electrostatic repulsion, disproportionation constants, and stability of their reduced charged intermediates. The results reveal that in the case of the non-bridged quinones 1–4, as the number of fused rings increases the reduction becomes gradually more difficult because the aromatic stabilization of the ‘quinone’ on conversion to aromatic ‘hydroquinone’ system decreases. However, since all studied annulenediones 5–11 possess a ‘C₂’ bridge that keeps the macrocycles flat, causing better aromaticity, they are relatively easily reduced at both E₁ and E₂ potentials and therefore, they could be considered as quinones of aromatic systems. On the other hand, when the bridge is longer (as in 12 and 13) the macrocycles tend to bend, causing a decrease in the degree of aromaticity and as a consequence, their reduction becomes more difficult.

The α-hemolysin nanopore has attracted much attention as a tool for the single-molecule analysis of DNA due to its potential as an ultra-sensitive, specific, and label-free sensing technique. The vast majority of DNA sensing research with the α-hemolysin nanopore has focused on interrogating single-stranded DNA. Nevertheless, the structure of the α-hemolysin pore, specifically the circa 32.6 cubic nanometer vestibule, is of sufficient size for a short section of double-stranded DNA (dsDNA) to reside before unzipping into its single-stranded constituents. In this review, we describe past and current literature relating to the rich information that can be obtained from the interrogation of dsDNA while residing within the α-hemolysin nanopore vestibule, and the subsequent voltage-driven unzipping of the residing DNA into its single-stranded constituents. Applications for dsDNA interrogation and unzipping that have been implemented include DNA sequencing, disease diagnosis, and the identification of epigenetic modifications.

Insertion-type layered Na₂Ti₃O₇ has attracted the attention of the researchers and is considered to be one of the promising low-voltage anode materiasl for sodium-ion batteries. In spite of its fascinating electrochemical properties, the low electronic conductivity and structural instability of Na₂Ti₃O₇ are major drawbacks that restrict its practical application. Surface modification with pyrolytic carbon is one of the effective ways to reduce irreversible capacity loss caused by electrolytic degradation. In this work, attempts have been made to investigate the effects of different carbon coating approaches on the electrochemical properties of sol-gel-synthesized Na₂Ti₃O₇ microrods. The as-synthesized Na₂Ti₃O₇ rods are coated with a uniform carbon layer both by in-situ and ex-situ methods using citric acid and polyvinyl alcohol as carbon source, respectively. Ex-situ carbon-coated Na₂Ti₃O₇ (Na₂Ti₃O₇@C), due to better coating uniformity and higher graphitized carbon percentage, shows enhanced cyclability and rate performance compared to bare material and in-situ carbon composite (Na₂Ti₃O₇/C). Following the ex-situ carbonization method using PVA as carbon source, it is found that increase of carbon content from 5wt% to 10wt% significantly improves its electrochemical properties. However, further increase in PVA amount has adverse effect on the cycling as well as rate performance of Na₂Ti₃O7@C. Surface modified Na₂Ti₃O₇@C with optimum carbon content (10wt% C) shows improved cycling capacity (capacity retention ∼74.75% after100 cycle) and rate performance (∼67 mAhg-1 at 1.5 Ag-1). Both excess and inadequate carbon content have detrimental effect on the electrochemical properties of Na2Ti3O7 anode.

Machine learning algorithms trained on data gathered from stochastically generated gas diffusion layers (GDLs) were used to predict key transport properties that govern effective mass transport behaviour in polymer electrolyte membrane fuel cells. Specifically, we present the largest database in the present literature of stochastically generated fibrous GDL substrates (containing over 2000 unique materials) and the associated structural and transport properties determined via pore network modelling. Seven established machine learning algorithms were trained to predict the effective single-phase permeability (k_sp) and diffusivity (D_sp), and the relative permeability (k_r) and diffusivity (D_r) of the generated materials using well-defined material properties as input features. Gradient boosting regression (GBR), artificial neural network, and support vector regression were the best performing predictors of the single-phase properties, all of which exhibited statistically insignificant differences in error. GBR provided the best prediction accuracy of relative transport properties.

Electrochemical conversion of CO₂ (CO₂RR) has received significant attention since it could provide pathways for renewable energy storage to energy-dense chemicals and synthetic fuels. We developed a novel CuO_x/Cu/C type electrocatalyst via pyrolysis, which we used to convert CO₂ at industrially relevantly current densities using gas diffusion electrodes. The influence of the pyrolysis conditions on the electrocatalytic CO₂RR activity and selectivity was evaluated. Optimization of the electrode structure to mitigate electrowetting was done by mixing the catalyst with polytetrafluoroethylene (PTFE). We found that mixing the most active catalyst with PTFE in a mass ratio of 1 to 0.25 substantially increased the formation of C₂H₄ displaying 41% Faradaic efficiency (FE) at –240 mA cm^–2. Prolonged CO₂RR at different current densities shows that the electrode containing 25 wt.% PTFE in the catalyst layer display FE_C2H4 > 40% at –280 mA cm^–2 for 2 h.

The present review focuses on the interplay between electrochemistry and life, events on the border of electrochemistry-biology-life science, electrochemistry as the basis, and the information source on oxidative stress (OS) or Red/Ox state of biological systems and food to be investigated. Electroanalytical chemistry provides rapid, relatively simple, and sensitive approaches to assess the redox characteristics and antioxidant activity of biologically active compounds in various samples.

OS is a relatively new physiological response concept, recognized in medicine and biology in the last three decades. This phenomenon is caused by an imbalance between (pro)oxidants and antioxidants in living organisms and it is related to the fundamental redox reactions that underlie health signaling and life processes in general. OS can contribute to many pathological conditions and diseases. In particular, it is recognized that a highly contagious infectious disease, coronavirus disease 2019, is associated with an inflammation process related to OS-induced cellular changes. Recent years have shown a marked increase in electrochemical studies of OS and quantitation of its reductant-oxidant markers (signaling agents), such as reactive oxygen species and antioxidants.

The goal of this overview is to cover the brief scope of modern electrochemical analysis and sensor devices for monitoring biomarkers of OS and antioxidant status of biological systems. By discussing the great potential of potentiometric and voltammetric methods for human health assessment, it is hoped to bridge between recent electrochemical research and medical diagnostic treatment in the 21st century.

A multi-responsive photo and electrochromic salt based on a viologen derivative ([(C₁₀)₂Bpy]²⁺) as organic cation combined with diarylethene anion ([DTE]²⁻) is synthesized and characterized for the first time. The coloration of this functional salt can be modulated by light and electricity according to further applications. Photochemical determination of the quantum yields in solution for the ring-opening and closure of [(C₁₀)₂Bpy][DTE-COO] ionic liquid have been determined. The electrochemical and electrochromism performance have been also studied in order to evaluate the reduction of bipyridinium cation as well as the oxidation of the DTE anion in its open and closed forms. The possibility of individually addressing the redox state of the anion and cation is seen as a very attractive approach to designing photo-electrochromic devices.

Porous gas-diffusion electrodes (GDEs) are widely used in electrochemical applications where a gaseous reactant is converted to a target product. Important applications for silver-based GDEs are the chlor-alkali and the CO₂ electrolysis processes in which silver catalyzes the oxygen- or carbon dioxide reduction reaction. The wetting of the porous GDEs is of utmost importance for the achieved performance of the electrode: a completely dry electrode will result in low current densities due to the reduced active surface area while on the other hand, a completely flooded electrode will deteriorate the access of the gaseous reactant. Therefore, we investigated silver-based GDEs for the oxygen reduction reaction with different amounts of the hydrophobic agent polytetrafluoroethylene (PTFE) and analyzed the potential-induced wetting behavior (electrowetting). The electrolyte breakthrough was recorded by a digital microscope and subsequently evaluated via imaging analysis of the observed breached electrolyte droplets. In order to characterize the wetting state during transition to the steady-state, we applied electrochemical impedance spectroscopy measurements and retrieved the double-layer capacitance. Our results indicate that a higher overvoltage facilitates the breakthrough of electrolytes through the gas-diffusion electrode. Surprisingly, a faster breakthrough of electrolyte was observed for electrodes with higher PTFE content. Porometry measurements revealed that the GDE with low PTFE content has a monomodal pore size distribution, whereas electrodes with higher PTFE amount exhibit a bimodal pore size distribution. In GDEs with monomodal pore size distribution the time in which the double layer capacitance is leveling off correlates with the breakthrough time of the electrolyte. In summary, we emphasize that the wetting of GDEs is a complex interplay of the applied potential, electrode composition, and resulting porous structure which requires further advanced measurements and analysis considering the parameters affecting the wetting behavior as a whole.