Category Archives: ChemElectroChem

New Insights into the Behaviour of Commercial Silicon Electrode Materials via Empirical Fitting of Galvanostatic Charge‐Discharge Curves

Posted on 12 October 2023 by nFrederik T. Huld, nObinna E. Eleri, nFengliu Lou, nZhixin Yun

The fast fading of silicon electrodes is a known issue preventing commercialization. Using empirical equations and electrochemical impedance spectroscopy, we isolate the lithiation phases of silicon and show that the capacity fade of commercial silicon electrodes is reversible and related to the iR drop of the cell.

Abstract

Silicon (Si) materials for use in Lithium ion batteries (LIBs) are of continued interest to battery manufacturers. With an increasing number of commercially available Si materials, evaluating their performance becomes a challenge. Here, we use an empirical fitting function presented earlier to aid in the analysis of galvanostatic charge-discharge data of commercial Si half-cells with relatively high loading. We find that the fitting procedure is capable of detecting dynamic changes in the cell, such as reversible capacity fade of the Si electrode. This fading is found to be due to the highly lithiated Li₂Si Li_3.5Si phase and that the behaviour is strongly dependent on the potential of this phase. EIS reveals that the Si electrode is responsible for the reversible behaviour due to progressive loss of Li⁺ leading to increasing resistance. SEM/EDX and XPS characterization are also employed to determine the origin of the irreversible resistance growth on the Si electrodes.

Metal Carbide Additives in Graphite‐Silicon Composites for Lithium‐Ion Batteries

Posted on 12 October 2023 by

Graphite-silicon composites for batteries: Molybdenum and Chromium Carbides are used as additives to stabilize graphite/silicon composites. Spark plasma sintering technology is used to sinter the electrode powders. The presence of molybdenum or chromium carbides promotes the performance of C/Si electrodes in lithium cells, improving the cycling stability compared to pristine graphite/silicon compounds.

Abstract

The pathway for improving lithium-ion batteries′ energy density strongly depends on finding materials with enhanced performance. Although great efforts have been done, on the anode-side, graphite is still the best choice. In the last decade, silicon elements are attracting growing attention as anode since their use can theoretically increase specific capacity of the negative electrode side. However, as the electrochemical mechanism involves the alligation of a large amount of Li, the silicon electrode experiences huge volume changes (more than 300 % of its initial volume), leading to fractures and pulverizations of the electrode. Herein, we propose for the first time using Molybdenum and Chromium Carbides as additive to stabilize graphite/silicon composites. Spark plasma sintering technology is used to sinter the electrode powders. We demonstrated that the presence of molybdenum or chromium carbides promotes the performance of C/Si electrodes, improving the cycling stability compared to pristine graphite/silicon electrodes.

Double S‐Scheme Polydopamine/TiO2/Chlorophyll as Stable and Efficient Green Photoelectrocatalyst

Posted on 11 October 2023 by

Anodization of titanium plated in ethylene glycol forms high surface area TiO₂ nanotubes with a hierarchical structure. Combining the properties of TiO₂ nanotubes obtained by anodization, Chlorophyll-a extracted from spirulina, and Polydopamine derived from mussels, a new photocatalyst is developed. This new photocatalyst has remarkable properties in photocatalysis applications.

Abstract

Inspired by natural photosynthesis, a new green catalyst with better photocatalytic properties was obtained. Nanostructured TiO₂, a cheap cost natural Chlorophyll-a as an electron promotor and a mussel-inspired polydopamine (PD) bio adhesive were synergistically combined in the double S-scheme hybrid photocatalysts The role of PD as a bridging molecule between the pigments of Chl and TiO₂ was clearly demonstrated by improved charge transfer and recombination rate. Methylorange as a probe molecule was used to test the stability and efficiency of the new photocatalyst. This challenging approach on obtaining new green bioinspired catalysts avoiding critical raw materials is in line with the new vision on catalysts. The results of this study show the effectiveness and stability of the new photocatalyst. Based on the combined effect of PD functionalization and Chl sensitization, the NT/PD-Chl heterostructure photocatalyst had the best photo(electro)catalytic performance for MO degradation which was shown to be 97.74 % after 180 min.

DNA Mismatch Repair Assessment in Gastric and Colon Cancers Using Stochastic Microdisks

Posted on 11 October 2023 by

Assessing of DNA mismatch repair in gastric and colon cancers was done by molecular recognition and quantification of MLH1, MSH2, MSH6, PMS2, and KRAS in whole blood, urine, saliva, and tumor tissues, using two stochastic microdisks. The design of the stochastic microdisks was based on a graphene layer adorned with nitrogen, boron, and sulfur, modified with solutions of inutec (SP) and frutafit (FT).

Abstract

Two stochastic microdisks were designed and validated for the DNA mismatch repair assessment in gastric and colon cancers, through determining simultaneously the concentrations of MLH1, MSH2, MSH6, PMS2, and of KRAS in whole blood, urine, saliva, and tumoral tissues. The active surface of the stochastic microdisks was composed of a thin layer of graphene paste decorated with nitrogen, boron, and sulfur and modified with inutec (SP) and with frutafit (FT), respectively. High sensitivities were recorded when the SP was used as modifier. All limits of determination were of fg mL⁻¹ magnitude order. The paired student-t-test done at 99.00 % confidence level revealed that there are no significative differences between the results obtained using the two stochastic microdisks. Validation of the screening tests of whole blood, urine, saliva, and tumoral tissues was also done using the recovery tests when % recovery was higher than 87.00 %, with %RSD values lower than 1.00 %.

Geopolymer Based Electrodes as New Class of Material for Electrochemical CO2 Reduction

Posted on 5 October 2023 by

“Geoploymers offer great potential for reducing CO₂ emissions in the construction sector by replacing ordinary cement. Here, we successfully functionalized a geopolymer with tin and applied the hybrid material as an electrode for CO₂ electrolysis. Our results show current efficiencies of up to 14 % for formate production….“ 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.202300122.

Abstract

Invited for this issue's Front Cover are the groups of Eddie Koenders and Markus Stöckl. The cover feature illustrates a chimney made of Sn-modified geopolymer-bricks. Functionalized geopolymers can be applied as hybrid material for construction and as an electrode for CO₂ electrolysis to formate. The cover was designed by one of the authors Jürgen Schuster and the designer Verena Stöckl. Read the full text of the Research Article at 10.1002/celc.202300122.

Adsorption of Glucose Molecules on Stainless Steel Enables Ni‐Rich Passivation Film

Posted on 5 October 2023 by

For diverse applications of stainless steel, precise control of the surface layer's composition and morphology is essential. In this work, we study the formation of a nickel-rich passive film via electrochemical potential sweep in an alkaline solution containing glucose. In addition, the nickel- or iron-rich passive surface layer is capable of reversible interchange by adding or removing glucose.

Abstract

Stainless steel (SS) is well known for its remarkable versatility. Besides the importance of passivation film for durability and stability of SS, the composition and morphology of passive surface layer have to be precisely modified to create an alloy that is optimal for specific purposes. Herein, we report on the electrochemical preparation of nickel-enriched passive film which is accomplished by the preferential adsorption of glucose on nickel species among constituents of SS. The presence of nickel-rich surface and the exposure of nickel on the outmost surface layer participating in surface reactions are verified by monitoring redox couple of Ni²⁺/Ni³⁺ as well as elemental analyses (TEM-Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy). Reversible interchange of nickel-rich into iron-rich surface and vice versa is possible by adding or removing glucose. We find that molecules having more than tri-dentate of hydroxy groups (e. g. glycerol) is required for the formation of Ni-rich surface (chelate effect).

Graphene Doped Carbon‐Gels and MnO2 for Next Generation of Solid‐State Asymmetric Supercapacitors

Posted on 5 October 2023 by

Solid-state asymmetric supercapacitors: The supercapacitor with asymmetric configuration with the graphene-doped carbon xerogel in the negative electrode and the manganese oxide in the positive electrode, along with the use of Na⁺-form Aquivion electrolyte membrane as solid electrolyte, presents great stability in a wide operational voltage window and a very low self-discharge rate.

Abstract

Supercapacitors are playing a very relevant role in many applications due to their capability to supply high power density and long durability. However, there is a growing demand to increase their energy density, in gravimetric and volumetric basis. There are different strategies to increase supercapacitor performance by improving the active materials used in the electrodes, the type of electrolyte used or even the configuration employed in the cell. In this work, a combination of these strategies is presented with the use of different active materials, electrolytes, and symmetric vs. asymmetric configuration. The supercapacitor with asymmetric configuration using the graphene-doped carbon xerogel in the negative electrode and the manganese oxide in the positive electrode, along with the use of Na⁺-form Aquivion electrolyte membrane as solid electrolyte, seems to be a promising combination to obtain a substantial enhancement of both gravimetric and volumetric capacitance. Furthermore, the device presents great stability in a wide operational voltage window from 0 to 1.8 V and with a neutral pH polymer electrolyte which contributes to improve the performance, safety, and long cycle life of the device.

Reversible Electrochemical Conversion Reaction for Selective Ion Removal and Recovery

Posted on 5 October 2023 by nYilong Yang, nJiaming Miao, nKan Zhangn

Getting ions back! Due to the high selectivity and reversibility of the conversion reaction, it is possible to selectively remove and recover ions from the solution. This Concept highlights the great advantages and state-of-the-art efforts of the conversion reaction for selective removal and recovery of ions and puts forward further improvement.

Abstract

Capacitive deionization (CDI) is a green and pollution-free emerging technology that can be used for ions removal and recovery from water. However, the traditional electro-adsorption process to achieve ions removal faces the challenges of non-selectivity, low efficiency and difficult ion recovery. In recent years, the conversion reaction has attracted wide attention due to its high selectivity, reversibility and excellent desalination ability for ions removal and recovery. This concept article will focus on the connotation and representative applications of conversion reactions that can be used for ion-selective removal and recovery and put forward the perspectives and outlooks of conversion reactions.

Investigating the Influence of Amorphous/Crystalline Interfaces on the Stability of IrO2 for the Oxygen Evolution Reaction in Acidic Electrolyte

Posted on 5 October 2023 by nThi Hong Nga Ngo (Sarah Ngo), nJonathan Love, nAnthony P. O'Mullanen

Electrodeposited amorphous thin films of IrO₂ are annealed at different temperatures to produce amorphous/crystalline interfaces. During oxygen evolution reaction at high current density their presence is found to influence both activity and stability/solubility of the electrode. Although increased performance is found, films are still prone to dissolution.

Abstract

A major challenge with water splitting technology is to develop highly active and stable electrocatalysts for the oxygen evolution reaction (OER). IrO₂ – based electrocatalysts are one of the most active electrocatalysts for proton exchange membrane (PEM) electrolysers, due to their excellent activity for the OER in acidic conditions. However, IrO₂ often suffers from dissolution during electrolysis due to phase transitions into more soluble forms. Herein, a range of electrodeposited IrO₂ films annealed to different temperatures of up to 500^°C are prepared to understand the influence that crystalline/amorphous interfaces have on performance during accelerated degradation tests in concentrated acidic solutions. This study showed that an IrO₂ film annealed at 300 °C exhibited the highest catalytic activity with a low overpotential of 150 mV at 10 mA cm⁻², the smallest Tafel slope of 51 mV dec⁻¹, with a less progressive decay in activity over a period of 8 h of accelerated degradation testing. This contrasts with both fully amorphous or more crystalline IrO₂ films that decayed much more rapidly within 1 h of testing indicating the role that amorphous/crystalline regions have on OER performance.

Reaction Engineering and Comparison of Electroenzymatic and Enzymatic ATP Regeneration Systems

Posted on 5 October 2023 by

An electrochemically coupled ATP regeneration by pyruvate oxidase and acetate kinase for the phosphorylation of mevalonate was established and expanded by a polyphosphate kinase. The reaction was characterized and compared with other ATP regenerating systems in terms of the phosphate donor properties and biocatalytic metrics.

Abstract

Adenosine-5’-triphosphate (ATP) plays a crucial role in many biocatalytic reactions and its regeneration can influence the performance of a related enzymatic reaction significantly. Here, we established electrochemically coupled ATP regeneration by pyruvate oxidase and acetate kinase (ACK) for the phosphorylation of mevalonate catalyzed by mevalonate kinase. A yield of 84 % for the product mevalonate phosphate was reached and a total turnover number for ADP of 68. These metrics are promising for the development of an economic feasible bioprocess and surpass many other enzymatic ATP regeneration systems. A comparison was made to polyphosphate kinases (PPKs), ACK, pyruvate kinase, and creatine kinase in terms of the phosphate donor properties and biocatalytic metrics of exemplary reactions. Furthermore, our system was expanded by a PPK that enables the phosphorylation of AMP, which can broaden the spectrum of applications even further.