ChemElectroChem最新文献

Iron(II) complexes with 1,10-phenanthroline (phen) and 2,2′;6′,2“-terpyridine (terpy) ligands bearing different functional groups (methyl, 4-pyridyl, chloro, carboxylic acid) were evaluated for aqueous flow battery applications, detecting oxidation processes followed by coupled chemical reactions. Redox potentials of these compounds were sufficiently high for suitable positive electrolytes (0.88–1.29 V vs. SHE). Randles-Ševčík equation and finite element modelling with COMSOL Multiphysics were utilized in evaluating the diffusion coefficient and the apparent rates of the electron transfer and coupled chemical reactions for the compounds studied by cyclic voltammetry. The systems experience weak adsorption of reactants at glassy carbon, leading to difficulties in determining the latter kinetic parameters. Flow battery tests indicate sufficient flow battery performance with dimethyl functionalized phenanthroline complex [Fe(II)(DMe-phen)₃]²⁺ with 0.06 % per cycle (2.78 % per day) capacity decay. However, [Fe(II)(DMe-phen)₃]²⁺, as well as [Fe(II)(phen)₃]²⁺, experience the discharge at two different thermodynamic conditions, suggesting dimer discharge as the source of the lower voltage plateau. The energy efficiency of [Fe(II)(DMe-phen)₃]²⁺ battery was improved by cycling at higher cut-off voltage for 10 cycles, after which the lost capacity was recovered with lower cut-off voltage in one cycle. [Fe(II)(terpy)₂]²⁺ had too many side reactions at lower potentials to be suitable for flow battery applications.

Mathematical models of voltammetric experiments commonly contain a singular point value for the reversible potential, whereas experimental data for surface-confined redox-active species is often interpreted to contain thermodynamic dispersion, meaning the population of molecules on the electrode possess a distribution of reversible potential values. Large amplitude ramped Fourier Transformed Alternating Current Voltammetry (FTacV), a technique in which a sinusoidal potential-time oscillation is overlaid onto a linear potential-time ramp, is known to provide access to higher order harmonic components that are largely devoid of non-Faradaic current. Initially, a theoretical study reveals that the use of very large amplitude sinusoidal oscillations reduces the apparent effects of thermodynamic dispersion; conversely, frequency can be varied to change the sensitivity of the measurement to kinetic dispersion. Subsequently, FTacV measurements are used to probe a highly thermodynamically dispersed surface-confined ferrocene derivative attached to a glassy carbon electrode, with amplitudes ranging from 25 to 300 mV and low frequency, which minimises the impact of kinetic dispersion. The results from the experimental study validate the theoretical predictions, demonstrating that we can vary the amplitude in FTacV experiments to tune in and out of thermodynamic dispersion.

To address the increasing demand for efficient, safe, and sustainable energy storage solutions in the transition towards renewable energy and electrified society, this study explores hybrid polymer-liquid electrolytes (HEs) as a novel solution to overcome challenges of traditional liquid electrolytes used in lithium-ion batteries (LIBs). Particularly, the research is focused on polymerization-induced phase separation (PIPS) synthesized HEs with distinct phase-separated systems, where an ion-conducting liquid phase percolates the macropores and mesopores within the formed thermoset solid phase. This study investigates the feasibility of using HEs with commercial cathodes and highlights their respective merits and challenges. The feasibility of infusing and forming HEs in commercial cathodes via PIPS within both micron-sized and nano-sized confined spaces is proved. By incorporating these HE-infused electrodes into half-cell configurations, the study proves that the HEs are compatible with common cathodes, and they exhibit energy density comparable with traditional systems with liquid electrolyte.

The cycling performance of lithium-sulfur (Li−S) batteries is hampered by polysulfide dissolution which impacts the overall performance of Li−S batteries. Here we report the synthesis and characterization of polysulfide trapping cathode material for Li−S batteries based on Co₃O₄ nanocubes supported within a nitrogen-doped entangled graphene (Co₃O₄/NEGF). The highly porous conductive graphene network is shown to facilitate fast electron transport and ion diffusion while the nitrogen dopants and polar Co₃O₄ offer both abundant active sites for polysulfide conversion while promoting intermediate polysulfide binding. The porous structure allows for high sulfur loading of 76.4 wt % (S@Co₃O₄/NEGF), while efficiently accommodating volumetric expansion during charge-discharge. The Co₃O₄/NEGF cathode composite exhibited a high specific capacity of 1143 mAh g⁻¹ at a current density of C/20 and maintained a 79 % reversible capacity after 200 cycles at C/5.

Sodium metal is often considered as an anode material to improve the energy-density of sodium metal batteries (SMB) respectively sodium ion-based batteries (SIB). However, the active Na metal anode is a particular challenge. To formulate a suitable electrolyte has therefore been a key issue to stabilize sodium metal anodes. Here we report additive strategies by using the additives sodium difluoro(oxalato) borate (NaDFOB) or/and fluoroethylene carbonate (FEC) in the baseline electrolyte solution of 1 M NaPF₆ in ethylene carbonate/propylene carbonate to overcome these issues. For the SMB with sodium anode and carbon-coated Na₃V₂(PO₄)₃ (NVP) cathode, a stable cell cycling up to 600 cycles (capacity retention about 96±3 %) was reached by using only 1–2 wt. % NaDFOB, compared to only less than 75 cycles of the baseline electrolyte. Sodium plating/stripping tests, voltammetry measurements, impedance analysis as well as cell tests were performed in order to reveal the electrochemical characteristics of the electrolytes including additive effects. The optimal SIB cell performance in cells containing hard carbon and NVP was achieved by using 2 wt.-% NaDFOB. NaDFOB electrolyte can be considered as a beneficial additive for Na metal cell and its application could be also extended for full SIBs.

The potential of the indigo chromophore as a long-time stable, redox-active unit in an organic redox flow battery (ORFB) has rarely been considered so far. The present work demonstrates a first synthetic access to thioindigosulfonic acids by sulfonation of the parent dye. To evaluate the electrolytic properties of the thioindigosulfonic acids, the solubility in sulfuric acid, the Nernst potentials, the diffusion coefficients, the charge transfer coefficients, the exchange current densities and the rate constants of the electron exchange reaction have been determined. Furthermore, thioindigo-based electrolytes could be operated successfully over a period of 200 charge/discharge cycles in a flow cell. The electrochemical stability of the electrolytes as well as the absence of crossover phenomena was proven by comparison of their ¹H NMR spectra before and after the charge/discharge study. Therefore, thioindigosulfonic acids could offer an opportunity to develop a stable organic electrolyte for the application in an aqueous ORFB.

Electrocatalysis is essential for facilitating reactions that convert electrical energy into chemical energy or vice versa. This is particularly relevant in the context of renewable energy sources, where efficient hydrogen production through water splitting is critical for energy storage and utilization. This review examines the replacement of platinum group metal (PGM) electrocatalysts with transition metal (TM) thin films synthesized via chemical vapor deposition (CVD) and atomic layer deposition (ALD). TM like nickel, cobalt, and iron have emerged as promising candidates due to their abundance, lower cost, and tunable electronic properties. These materials can achieve comparable or superior performance to PGMs for specific reactions, such as the Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER). CVD and ALD offer precise control over film thickness, composition, and uniformity, critical factors influencing the electrocatalytic performance. The ability to dope or alloy transition metal thin films further optimizes their catalytic properties for specific applications. This review covers key concepts related to hydrogen technology, electrocatalytic performance, and deposition processes. It identifies trends in TM electrocatalyst development, proposes future strategies for enhancing performance, and draws conclusions on the potential of these materials to revolutionize electrocatalysis for renewable energy applications.

Electrocarboxylation, the electrochemical addition of CO₂ to organic substrates using renewable energy, offers a promising approach for carbon capture and utilization. However, commercial viability remains limited due to poor product selectivity and yields. In this work, we investigate how the electrolysis mode – chronoamperometry (CA) versus chronopotentiometry (CP) – influences the electrocarboxylation mechanisms of phenyl-activated substrates, Benzaldehyde, Styrene, and Benzylbromide, on Lead electrodes. By employing cyclic voltammetry (CV), in situ FTIR, and bulk electrolysis, we explore how these modes affect product selectivity and reaction efficiency. Our results show that substrate-activated mechanisms, such as those observed for Benzaldehyde and Benzylbromide, achieve higher selectivity and reduced side-product formation under CA conditions, while CP leads to increased side reactions. In contrast, Styrene exhibits more complex behavior, with CP favoring di-carboxylation, while CA enhances mono-carboxylation. These findings highlight the significant impact of electrolysis mode on controlling electrocarboxylation pathways, providing valuable insights for optimizing selective and efficient synthesis processes.

The electrochemical reduction of carbon dioxide (ERCO₂) to chemical feedstock and fuels is a promising strategy for reducing excessive carbon dioxide emissions. There are various benefits of converting CO₂ to a single product and Pb is one of the active and efficienct catalyst for reducing CO₂ to HCOOH. The current work used the electro-deposition method to produce manganese oxide (Mn₃O₄) (nano particle flakes) and highly active, low-cost lead (Pb) catalysts with a variety of morphologies (Nano crystal Flakes, Nano wires, and Nano crystal sheets). For the first time, the Mn₃O₄ catalyst was employed as the anode in the water oxidation process to produce protons, and the electrocatalytic effects of Mn₃O₄ and Pb on the ERCO₂ reaction were investigated. The influence of CO₂ reduction on catalyst loading is investigated and the lone product HCOOH is detected on the produced Pb catalysts. Using a systematic electrochemical study, the final product of the ERCO₂ reaction is identified and measured. The maximum Faradaic efficiency was measured on Pb (nano crystal flakes) at −1.003 V, yielding efficiency of 77.32 % (10 min) in 1 mg/cm² catalyst loading and 78.4 % on nano wires (10 min) at −1.003 V in 2 mg/cm² catalyst loading, respectively. More specifically, it is discovered that the reaction selectivity and efficiency of CO₂ electroreduction to HCOOH are highly influenced by the morphology and loading of the catalyst. These results provide an intimate understanding of water oxidation on Mn₃O₄ and CO₂ electroreduction on Pb catalyst.

Sodium-ion batteries (NIBs) have gained significant attention in recent years due to the global abundance and cost-effectiveness of sodium, making them a promising alternative to lithium-based batteries. In this study, nitrogen-doped graphene oxide powders (NGO) have been prepared in one step by using chronoamperometric method and then have been used as anode materials for NIBs. The NGO powder surface is covalently doped by C−N formation. The synthesized powder had few layers (~3 layers) with nanocrystalline domain size (Lα) ~46 nm, and the number of sp² carbon rings was calculated to be ~18. The initial discharge capacity recorded 199.8 mAh g⁻¹ at 0.1 C rate. Besides, the capacity retention for long-term cycling of 100 cycles at 2 C rate was 91.78 %. The deduced diffusion coefficient from galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) measurements for NGO as anode in NIBs is in the range of 10⁻¹¹–10⁻¹² cm² s⁻¹. The electrochemical performance was attributed to the enhanced d-spacing of NGO up to 6.8 °A and formation large number of defects.