Sensing it: A simple and easy-to-use electrochemical sensor connected to a smartphone was designed for rapid and sensitive detection of bisphenol A (BPA) in water samples. By combining a nanocomposite of Mg_0.5Co_2.5(PO₄)₂ and carbon black on screen printed electrode surface, the sensor displayed high electrocatalytic activity towards BPA with a wide range of linearity and low detection limit.

Abstract

Bisphenol A (BPA) widely recognized as an endocrine disruptor can induce serious threats to human health such as sexual anomalies and cancer. Unfortunately, BPA has been increasingly used since 1950s; specifically during the manufacturing of polycarbonates and plastics such as food containers and water bottles. Thus, there is an urgent need to develop low-cost, simple, portable and sensitive sensors for in-situ detection of this contaminant in food and water. The combination of nanostructured carbon materials and metal/metal oxide nanoparticles can result in materials with unique physicochemical properties as well as excellent catalytic behaviors. Herein, we propose a smartphone-assisted electrochemical sensor based on the combination of Mg_0.5Co_2.5(PO₄)₂ and carbon black (CB) modified screen-printed electrode (SPE) for a rapid and sensitive determination of BPA. Structural characterization confirmed the formation of Mg_0.5Co_2.5(PO₄)₂/CB nanocomposite on SPE surface. Very low oxidation potential of BPA was observed during the differential pulse voltammetry (DPV) experiments at 0.16 V vs. Ag/AgCl. The sensor revealed two-step linear response from 0.5–6.5 μm and from 16.5–100 μm with a lower limit of detection (LOD) of 0.15 μm. A good reproducibility, excellent stability, and high interference-free ability were obtained. Furthermore, the developed sensor showed satisfactory recoveries for BPA detection in real water samples.

The changes in net charge during the redox reaction indicated that the transition metal serves as the redox center in olivine materials and aqua-complexes, whereas the O atom serves as the redox center in oxide-based layered and spinel materials. A correlation exists between the redox center and electrode potential of these materials.

Abstract

Li-insertion materials employed as electrode materials in Li-ion batteries undergo solid-state redox reactions wherein ions within a solid matrix are oxidized and reduced, in contrast to the conventional redox reactions of ions in solution. However, owing to the lack of a comprehensive theory for solid-state redox reactions, the electrode potential of Li-insertion materials remains unexplained from a theoretical standpoint. This limitation impedes the rational design of positive and negative electrodes with higher and lower potentials, respectively. This study employs the DV-Xα method to calculate the electronic structures of various Li-insertion materials and transition-metal aqua-complexes associated with the redox reaction to shed light on the corresponding solid-state redox potentials. Notably, the transition-metal ion is identified as the redox center in olivine materials and aqua-complexes, which exhibit similar electrode potentials, whereas the oxide ion is identified as the redox center in layered and spinel oxide materials, which show significant differences in electrode potential compared with olivine materials. These findings imply a correlation between the electrode potential and redox center in Li-insertion materials. The results of this study reveal that the electrode potential of Li-insertion materials is determined by their redox center rather than their constituent elements.

The Front Cover illustrates a TCE sheet, where the rainbow is the light reaching the photoelectrode, the spheres are the conductive pathway through the polymer matrix to the electrochemical interface, and the methyl viologen redox couple is reduced in the solution. Cover design by Talysa Klein (www.tk2.design). More information can be found in the Research Article by G. A. Rome et al.

Kerf-loss powder from wafering of solar cells are characterized thoroughly and shown to consist of nanoscale crystallites in an amorphous matrix. The powders are analyzed for chemical composition, morphology, crystallinity, and finally the amorphous influence on the first electrochemical cycle.

Abstract

Silicon powder kerf loss from diamond wire sawing in the photovoltaic wafering industry is a highly appealing source material for use in lithium-ion battery negative electrodes. Here, it is demonstrated for the first time that the kerf particles from three independent sources contain ~50 % amorphous silicon. The crystalline phase is in the shape of nano-scale crystalline inclusions in an amorphous matrix. From literature on wafering technology looking at wafer quality, the origin and mechanisms responsible for the amorphous content in the kerf loss powder are explained. In order to better understand for which applications the material could be a valuable raw material, the amorphicity and other relevant features are thoroughly investigated by a large amount of experimental methods. Furthermore, the kerf powder was crystallized and compared to the partly amorphous sample by operando X-ray powder diffraction experiments during battery cycling, demonstrating that the powders are relevant for further investigation and development for battery applications.

Electrochemical ethanol oxidation reaction: The reaction pathway significantly influences the overall performance of the electrochemical ethanol oxidation reaction (EOR), which can be effectively characterized through in situ Raman spectroscopy. In this concept, we concentrate on the fundamentals of the EOR pathway and the notable advancements made in EOR mechanism studies utilizing in situ Raman spectroscopy.

Abstract

The Electrochemical Ethanol Oxidation Reaction (EOR) plays a pivotal role in next-generation energy conversion devices. A clear understanding of the EOR reaction mechanism is critical for rational catalyst design, a task complicated by the numerous reaction intermediates and pathways involved. To this end, in situ Raman spectroscopy has proven invaluable in identifying many such intermediates at the electrode/electrolyte interface under varying applied potentials. Therefore, this technique allows for inference of the reaction mechanism based on the detected Raman signals of intermediates and observed structural changes, positioning in situ Raman spectroscopy as one of the most suitable methods for studying the EOR reaction mechanism. In this short review, with an eye towards future applications, we concentrate on the essential fundamentals of EOR and highlight recent advancements in understanding the EOR mechanism by in situ Raman spectroscopy.

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.

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.

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.

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.

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.