Category Archives: ChemElectroChem

Transparent Conductive Encapsulants for Photoelectrochemical Applications

Posted on 3 October 2023 by

Transparent conductive encapsulants (TCEs) are tested to protect semiconductor photoelectrodes for solar fuel generation. TCE electrochemical performance is characterized and TCEs successfully help retain photovoltage of protected photoelectrodes.

Abstract

Utilizing sunlight to directly perform photoelectrochemical reactions is a promising route to renewable, net carbon-neutral fuels. However, a common problem with solar fuel production is semiconductor degradation in aqueous environments. An ideal protection layer should (1) prevent solution from reaching the semiconductor, (2) maintain charge transfer to and from solution, and (3) be transparent to light above the semiconductor band gap. While there have been substantial advances toward layers that meet these requirements, they are not easily adapted to new surfaces or new reactions, which can make protection difficult for newly developed photoabsorbers and (photo)electrochemical reaction pairings. In this work, we demonstrate the use of transparent conductive encapsulants (TCEs) to meet these requirements while also allowing for photoelectrode- and reaction-agnostic adaptability. TCEs are composed of an ethyl-vinyl acetate matrix with embedded conductive metal-coated microspheres that can be laminated to semiconductors. First, the electrochemical behavior of TCE-coated electrodes for the reduction of methyl viologen is characterized, demonstrating through-TCE electrical conduction. Then, photoelectrochemical measurements on TCE-protected semiconductors demonstrate the flexibility of this protection scheme. Finally, long-term photoelectrochemical measurements probe the efficacy of TCEs as protection layers. These findings demonstrate the potential of TCEs as adaptable protection layers in various photoelectrochemical applications.

In‐situ Construction of CNTs Decorated Titanium Carbide on Ti Mesh Towards the Synergetic Improvement of Energy Storage Properties for Aqueous Zinc Ion Capacitors

Posted on 3 October 2023 by nHai Wang, nJinxia Huang, nXiaobo Wang, nZhiguang Guo, nWeimin Liun

Schematic illustration of TiC/CNTs@Ti free-standing cathodes used in zinc ion capacitor with high capacity and long-term stability.

Abstract

The development of aqueous zinc-ion capacitors (ZICs) is an effective approach to improve the safety and environmental friendliness of energy storage devices. In this paper, TiC/CNTs core-shell array structures (TCT) were synthesized on titanium substrate through in-situ simple chemical vapor deposition and carbon reduction and used as self-supporting cathodes for aqueous ZICs. As expected, as-prepared TCT electrode exhibited excellent electrochemical performance in aqueous electrolytes, demonstrating a high specific capacitance of 275.13 F g⁻¹ at a current density of 1.0 A g⁻¹ and maintaining 90.5 % of its initial capacity after 10000 charge-discharge cycles. The assembled Zn//TCT ZIC displays excellent rate capability, delivering an excellent specific capacitance of 298.2 F g⁻¹ at 0.5 A g⁻¹ and 193.5 F g⁻¹ at a high current density of 10 A g⁻¹. Zn//TCT device can provide an ultra-high energy density of 24.8 Wh kg⁻¹ at a power of 6984.1 W kg⁻¹. DFT calculations further demonstrate that a large number of electrons are transferred at the TiC/CNT interface and stable TIC−C bonds can be formed. This work provides a new strategy for rationally designing transition metal carbide electrodes and constructing ZICs with high energy and power densities.

Nanofiller‐Based Novel Hybrid Composite Membranes for High‐Capacity Lithium‐Sulfur Batteries

Posted on 3 October 2023 by nŞeyma Dombaycıoğlu, nHilal Günsel, nAli Osman Aydınn

Al₂O₃ reinforced Nafion/Aquivion hybrid composite membranes were prepared for Li−S battery applications. Forming a hybrid composite membrane with nano-Al₂O₃ increased the electrochemical capacity. 868 mAhg⁻¹ discharge capacity and 63.8 % capacity retention were obtained at the end of 300 cycles. The properties of the Nafion/Aquivion composite membrane have been improved by utilizing nanomaterial reinforcement.

Abstract

Herein, Al₂O₃ nanofiller-reinforced lithiated Nafion:Aquivion hybrid composite ion-exchange membranes have been produced by mixing lithiated Nafion and Aquivion ionomers. After the electrochemical tests, the Li-Naf : Li-Aqu/1 : 2 compound, which offers the best electrochemical performance, was selected. Lithiated hybrid composite membranes were obtained by reinforcing Al₂O₃ nanofillers at different rates to this composition. The ion exchange capacity, polysulfide transition and solvent uptake of the obtained membranes were investigated and the structural characterizations were applied by tensile test, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and membrane morphology was examined with Field Emission Scanning Electron Microscopy (FESEM). For performing the electrochemical tests, CR2032 half cells were designed. Electrochemical characterizations of the produced membranes were carried out by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and galvanostatic charge-discharge tests. The best electrochemical performance was achieved with 868 mAhg⁻¹ discharge capacity and 63.8 % capacity retention when Li-Naf : Li-Aqu/1 : 2 composition was reinforced with 1 % Al₂O₃ nanofiller. As a result, lithiated hybrid composite ion exchange membranes could prevent the shuttle effect of polysulfides while enabling the passing of Li ions for high-performance Li−S batteries.

Lattice Tuning of Copper Single‐Crystal Surface for Electrochemical Carbon Monoxide Coupling Reaction: A Density Functional Theory Simulation

Posted on 3 October 2023 by

The relationship between strain and reaction selectivity of CO reduction reaction on the deformation of Cu(111) and Cu(100) electrode surface have been studied by using the density functional theory calculation, *CHO and CO coupling is the favorable pathway on expanded Cu(111) surface, two *CO coupling is the favorable pathway on contracted copper surface.

Abstract

CO is a key intermediate of electrocatalytic CO₂ reduction reaction, which determines the product species. Understanding the effect of metal electrode structure on the adsorption ability and reaction activity of CO is helpful for the design of high selective catalysts. Herein, the DFT calculations are used to investigate the relationship between lattice structure and reaction mechanism of CO, with copper electrode of various lattice constants used as catalysts. By analyzing the adsorption and reaction energies of CO at different lattice constants of Cu(111) and Cu(100) surfaces, we found that the CO adsorption ability is proportional to the increase in lattice, and *CO dimerization to *COCO is the main reaction pathway on Cu(100) surface. Furthermore, the forecasted possible reaction mechanism and products suggest that the coupling of *CO and *CHO to *COCHO and then to C₂ products is the preferred pathway on Cu(111) surface for the lattice contraction. Alternatively, reduction of *CO to C₁ products through *CHO intermediate is more beneficial for the normal and expanded lattice of Cu(111). This work offers an example of the geometrical influence factor on the CO adsorption ability and reaction activity, and helps to understanding the fundamental role of lattice expansion and contraction in catalysis.

Alkylamine‐Functionalized Carbon Supports to Enhance the Silver Nanoparticles Electrocatalytic Reduction of CO2 to CO

Posted on 3 October 2023 by

Hydrophobicity and selectivity: The contact angle images (left) show the possibility to tune the hydrophobicity of carbon by changing the chain length of alkylamine functional groups. The CO₂RR selectivity (right), produced by Ag nanoparticles (background) on carbon materials, was influenced by the functionalization: not only H₂ formation was suppressed, but also CO production was enhanced, with an optimum around 6 carbon atoms.

Abstract

Silver electrocatalysts enable the conversion of CO₂ to CO, thereby facilitating the transition to a carbon neutral society. To lower the cost of the expensive metal, silver nanostructures are often supported on carbon. This substrate offers great electrical conductivity, but it enhances the selectivity towards the competing hydrogen evolution reaction. In this work, carbon supports were functionalized with linear alkylamines of different chain lengths, to understand its effect on electrochemical performance. Alkylamines interact with the carbon surface and confer hydrophobic properties to the carbon support as well as making the local environment less acidic. These properties led not only to a suppression of the hydrogen evolution, but also to a remarkable enhancement in CO production. Despite the low silver weight loading (0.0016 mg_Ag cm⁻²), hexylamine-functionalized carbon-based catalysts achieved a CO to H₂ ratio of 2.0, while the same material without the alkylamine functionalization only reached a ratio of 0.3, at −1.3 V vs RHE. This demonstrates the potential of hydrophobic functionalization for enhancing the CO selectivity of carbon-supported catalysts.

Ca2V2O7 as an Anode‐Active Material for Lithium‐Ion Batteries: Effect of Conductive Additive and Mass Loading on Electrochemical Performance

Posted on 3 October 2023 by

Ca₂V₂O₇ (CVO) used as an anode material in lithium-ion batteries develops cracks during cycling. These cracks improve contact with the electrolyte, promoting new electrochemical reactions, not only increasing the capacity over cycling but also leads to undesired side reactions. Unfortunately, these negative effects eventually overshadow the benefits, resulting in capacity decline and performance deterioration after max. capacity at 123 cycles.

Abstract

Lithium-ion batteries (LIBs) play a crucial role in using renewable sources. Vanadates have been applied as anode material due to the combined diffusion mechanisms and higher and stable capacities. Despite the interest in vanadates as anode materials, only a few studies have considered Ca₂V₂O₇ (CVO) as an active material for LIBs. This work focuses on the use of CVO as a potential alternative anode-active material for LIBs. Additionally, we investigate the effect of the conductive additive (C65) on the electrochemical properties of the electrodes, utilizing densified electrodes with a porosity of about 40 %. In doing so, this study provides important insights into new materials for LIBs, where the electrodes were manufactured using the commercial slurry methodology, replacing graphite by CVO – which was synthesized via the Pechini route (D50: 8 μm after milling). In summary, the results reveal that the amount of C65 positively affects the electrode‘s capacity. An increase in specific capacity was observed by up to 30 % using 10 wt.% C65. Such electrodes showed 235 mAh/g_AM at C/10 and, when cycled at 1 C, completed 300 cycles with a retained capacity of 39 %. The results demonstrate that CVO might be a promising anode material for LIB energy storage systems.

Preparation of Nitrogen‐Doped Graphene with Hollow Nano‐Hemispheres from FexOy@Fe‐N‐GN: Towards High Capacity and Durable Anode for Li‐Ion Batteries by Chemical Modifications

Posted on 3 October 2023 by nEdip Bayram, nBerkay Sungurn

Carbon-based anode: Nitrogen-doped graphene (N-GN), nitrogen-doped graphene-coated Fe _x O _y (Fe _x O _y @Fe-N-GN), and nitrogen-doped graphene with hollow nano-hemispheres (Fe-N-GN) were produced as anode materials for lithium ion batteries. The Fe-N-GN obtained from acid leaching of Fe _x O _y @Fe-N-GN outperformed other samples showing the significance of simple chemical post-processes to enhance the performance of carbon-based materials.

Abstract

The development of high-performance Li-ion battery anodes is closely dependent on understanding the effect of chemical and physical properties of active materials played in the storage mechanism. In this study, mesoporous high surface area nitrogen-doped graphene (N-GN) and nitrogen-doped graphene-coated nano-spherical Fe _x O _y containing composite (Fe _x O _y @Fe-N-GN) were synthesized by a bottom-up solvothermal process using required starting materials. Acid leaching of Fe _x O _y @Fe-N-GN resulted in a highly microporous structure consisting of a hollow graphene nano-hemisphere and a large basal plane monoblock structure with 63 % N-doped graphene and 37 % graphitic N-doped graphene (Fe-N-GN). While N-GN and Fe _x O _y @Fe-N-GN exhibited 310 and 571 mAh g⁻¹ reversible capacity, respectively, after 100 cycles, Fe-N-GN showed 940 mAh g⁻¹ reversible capacity through >70 % diffusion-controlled process with beneficially lower intercalation potential below ~0.25 V and 87 % capacity retention demonstrating the impact of the chemical composition and structural properties on the capacity of carbon-based anodes.

Modification of Conductive Carbon with N‐Coordinated Fe−Co Dual‐Metal Sites for Oxygen Reduction Reaction

Posted on 3 October 2023 by

Dual sites: Carbon black-supported, N-coordinated Fe−Co dual sites for the oxygen reduction reaction (ORR) were prepared from metal-coordinated polyurea aerogels. FeCoNC/BP outperformed commercial Pt/C in alkaline medium and had moderate ORR activity and durability in acidic medium. The macro-/mesoporous graphitic N-doped carbon enhanced mass transport properties.

Abstract

Earth-abundant commercial conductive carbon materials are ideal electrocatalyst supports but cannot be directly utilized for single-atom catalysts owing to the lack of anchoring sites. Therefore, we employed crosslink polymerization to modify the conductive carbon surface with Fe−Co dual-site electrocatalysts for oxygen reduction reaction (ORR). First, metal-coordinated polyurea (PU) aerogels were prepared using via crosslinked polymerization at ambient temperature. Then, carbon-supported, atomically dispersed Fe−Co dual-atom sites (FeCoNC/BP) were formed by high-temperatures pyrolysis with a nitrogen source. FTIR and ¹³C NMR measurements showed PU linkages, while ¹⁵N NMR revealed metal–nitrogen coordination in the PU gels. Asymmetric, N-coordinated, and isolated Fe−Co active structures were found after pyrolysis using XAS and STEM. In alkaline media, FeCoNC/BP exhibited excellent ORR activity, with a E _1/2 of 0.93 V vs. RHE, higher than that of Pt/C (20 %) (0.90 V), FeNC/BP (0.88 V), and CoNC/BP (0.85 V). An accelerated durability test (ADT) on FeCoNC/BP indicated good durability over 35000 cycles. FeCoNC/BP also showed moderate ORR and ADT performance in acidic media. The macro/mesoporous N-doped carbon structures enhanced the mass transport properties of the dual Fe−Co active-sites. Therefore, modifying carbon supports with nonprecious metal catalysts may be a cost-effective-strategy for sustained electrochemical energy conversion.

Laser‐Induced Carbon Nanofiber‐Based Redox Cycling System

Posted on 29 September 2023 by nAntonia Perju, nNongnoot Wongkaewn

Laser-induced carbon nanofibers are used to create porous freestanding electrode systems for redox cycling. Either by closely spacing the interdigitated electrodes carbonized directly onto the nanofibrous network, or by fabricating an additional nanofibers layer onto the electrodes, amplification via redox cycling was achieved in these new approaches, facilitating a flow-through electroanalytical device with favorable sensitivity.

Abstract

Redox cycling is a powerful amplification strategy for reversible redox species within miniaturized electrochemical sensors. Herein, we generate three-dimensional (3D) porous carbon nanofiber electrodes by CO₂ laser-writing on electrospun polyimide (PI) nanofiber mats, referred to as laser-induced carbon nanofibers (LCNFs). The technique allowed the fabrication of interdigitated electrode (IDE) arrays with finger width and gap distance of ~400 μm and ~40 μm, respectively, offering approximately 3.5 times amplification efficiency (AF) and 95 % collection efficiency (CE). Such dimensions could not be achieved with IDEs fabricated on conventional PI film because the devices were short-circuited. Stacked electrodes were also constructed as an alternative to the IDE design. Here, nanofiber mats as thin as ~20 μm were fabricated and used as vertical insulation between two LCNF band electrodes. While redox cycling efficiency was similar, the IDE design is more favorable considering the lower complexity and better signal reproducibility. Our strategy thus paves the way for creating flexible 3D porous electrodes with redox cycling ability that can be integrated into microfluidics and lab-on-a-chip systems. In particular, the devices offer inherent flow-through features in miniaturized analytical devices where separation and sensitive detection could be further realized.

Quantitative and Non‐Quantitative Assessments of Enzymatic Electrosynthesis: A Case Study of Parameter Requirements

Posted on 29 September 2023 by

Compare, contrast, scrutinize and decide: Various process options can be used to bring enzyme processes to industrial application; these include electroenzymatic processes. To evaluate the processes quantitatively, appropriate performance indicators must be determined. In addition, there are non-quantitative variables that need to be considered. This article shows how laboratory processes can be evaluated and how options for action can be identified.

Abstract

The integration of enzymatic and electrochemical reactions offers a unique opportunity to optimize production processes. Recently, an increasing number of laboratory-scale enzymatic electrosyntheses have shown impressive performance indicators, leading to scientific interest in technical implementation. However, important process parameters are missing in most of the relevant literature. On one hand, this is due to the large variety of relevant performance indicators. On the other hand, enzyme technologists and electrochemists use different parameters to describe a process. In this article, we review the most important performance indicators in electroenzymatic processes and suggest that in order to allow quantitative comparison, these indicators should be reported in all respective publications. In addition to quantitative parameters, non-quantitative assessments often need to be included in a final evaluation. Examples of such parameters are sustainability, contribution to the UN Sustainable Development Goals or interactions with the overall process. We demonstrate the evaluation of processes using hydrogen peroxide-dependent peroxygenases. The strength of the proposed evaluation system lies in its ability to identify weaknesses in a process at an early stage of development. Finally, it can be concluded that all evaluated enzymatic electrosynthesis do not yet meet typical industrial requirements for an enzyme-based process.