ChemElectroChem最新文献

There has been an increased effort to replace the expensive and rare platinum and platinum group metals to speed up the sluggish oxygen reduction reaction (ORR) kinetics, which limits the efficiency of fuel cells. One class of promising Pt-alternative catalysts for ORR is metal-free halogen-doped carbon materials. Herein, bromine-doped and iodine-doped graphene were synthesized via mechanochemical activation. The synthesized samples exhibited sub-rounded particles. Mechanical activation via ball milling increased the specific surface area of graphene by reducing particle size. Ball milling also enhanced dopant dispersibility and increased surface roughness, though it reduced surface area compared to ball-milled graphene, likely due to the size difference between carbon and halogen atoms. Among the synthesized catalysts, iodine-doped graphene exhibits the highest limiting current density of 1.806 mA cm⁻² with the highest ORR onset potential of 0.74 V vs reversible hydrogen electrode (RHE). The iodine-doped graphene also showed good stability after 1000 cycles of accelerated degradation test. The enhanced ORR performance of iodine-doped graphene was reached using the optimized iodine-to-graphene mass ratio of 4 : 1 after 48 h ball milling time.

This study focuses on enhancing lithium-sulfur (Li−S) battery performance by using nickel(II) oxide (NiO), as polysulfide adsorbent to mitigate the shuttle effect. Polysulfides have been shown to effectively adsorb onto the hydrophilic surfaces of polar metal oxides and thus suppress this effect. In this work, a NiO – reduced Graphene Oxide/Sulfur (NiO-rGO/S) hybrid composite paper was developed for use as a binder-free, flexible cathode. The characterization of the composite films was done through Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetric analysis (TG), field emission gun scanning electron microscopy (FEG-SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD). To test adsorption of polysulfides by NiO, ultraviolet-visible (UV-Vis) spectroscopy was applied. Electrochemical performance tests of CR2032 cells were also conducted by cyclic voltammetry (CV), charge-discharge tests, electrochemical impedance spectroscopy (EIS). The NiO-rGO/S cathode, particularly the one containing 2 % NiO, exhibited remarkable performance. It delivered an initial discharge capacity of 1230 mAh g⁻¹, maintaining 1029 mAh g⁻¹ after 300 cycles, with a high capacity retention of 83.1 %. This suggests that the NiO-rGO/S hybrid composite is a promising candidate for improving the efficiency and lifespan of Li−S batteries.

The front cover shows a karate fighter who is supposed to represent our electrodes system. She kicks into water and splits the water into O₂ and H₂ bubbles. The feet with which she splits the water are “coated” with our catalyst material NiFe LDH. The same schematic of LDH as in the article was used to illustrate the structure giving reference to our article. Her fists glow with electricity. A wind turbine can be seen in the background to emphasize that green electricity is being used. The woman is standing in a mineral cave and a mineral is shown at the bottom left, which is intended to establish a link to borate/borax minerals. More information can be found in the Research Article by Regina Palkovits and co-workers (DOI: 10.1002/celc.202400457).

This paper reports an electrochemical approach that uses lignin as a resource for renewable and sustainable methanol production. The aromatic rings of lignin have methoxy substituents, which can be oxidatively demethylated to methanol by active oxygen produced at the anode. A graphite electrode fabricated in a sponge form provided sufficient reaction space for the lignin feedstock, efficiently generated active oxygen species from water, and considerably suppressed the overoxidation of methanol to carbon dioxide. As a result, the methanol yield reached approximately 70 % at a temperature of 75 °C, atmospheric pressure, and anode potential of +0.57 V. Another advantage of this technique is that hydrogen evolution reaction (HER) occurred at the cathode and the cathode potential was held at approximately −0.5 V during the HER. Therefore, the cell voltage required for lignin electrolysis was 1.1 V or lower, which means that hydrogen as well as methanol was produced under mild conditions.

The synthesis of hydrogen via water electrolysis is an important step towards resolving the energy crisis and impeding global warming, as hydrogen can be used as a green energy carrier. The oxygen evolution as one half-cell reaction (OER) is currently limiting efficient water splitting due to kinetic inhibition as well as a complex mechanism, causing a large overpotential. Nickel-iron layered double hydroxides (LDH) were found to be suitable OER catalysts, as they are cost effective, stable and highly active. This work focuses on the intercalation of different organic and inorganic borates into the LDH interlayers to study their influence on OER. Besides activity and stability measurements, three borate candidates were chosen for a kinetic study, including steady-state Tafel analysis and reaction order plots. It was found that the Bockris pathway with the second step as rate-determining step was predominant for all three catalysts. Of all candidates, the intercalation of borate resulted in the highest performance, which was associated with a high reducibility affecting the active metal sites.

The development of electrochemical approaches to the valorization of abundant natural products into high value medications and metabolites is of pharmaceutical interest. In this study, we explored the electrosynthetic behavior of the abundant legal psychoactive, caffeine, a representative member of the purine alkaloid class. Initial screening of the cyclic voltammetric behavior of eleven exemplar purine alkaloids revealed a structure electroactivity relationship (SeAR) for determining the initial oxidation site of caffeine. Optimization of the current controlled electrochemical (CCE) reaction enabled the dialing-in/out of differential oxidative metabolic products using both undivided and divided cells. Sequential desmethylation around the purine ring was observed both by isolation and comparison to authentic metabolite reference standards via HPLC measurements. Amide, imide, and a novel N-methyl heteroaryl oxidation mechanism were observed. Tractable quantities of the high-value medication, theophylline, and the dietary supplement, paraxanthine, were isolated in 17 % and 8 % b.r.s.m. This approach offers a marked improvement compared to the best-in-class techniques (chemical 0.8 % and enzymatic 0.97 % yields) and may have potential in other natural product and drug discovery settings to prepare valuable metabolites.

The seemingly advantageous features of carbon-based materials, such as large pore volume and lightweight structure, could actually lead to low tap density for the sulfur cathode and excessive electrolyte consumption, potentially significantly decreasing the energy density of lithium–sulfur battery. Recently, non-carbon-based materials composed of inorganic matter have emerged as promising candidates for creating dense sulfur cathodes and reducing electrolyte intake. Additionally, inorganic matter exhibits strong interactions with lithium polysulfides, which can address the intrinsic problems of the severe shuttling effect and poor reaction kinetics. In this review, we first discuss the relationship between the tap density of the sulfur cathode and the energy density of lithium–sulfur battery. Subsequently, we systematically summarize recent advances in non-carbon-based materials as sulfur hosts. Finally, we propose future research directions and perspectives for sulfur host materials to inspire the realization of practical lithium–sulfur battery with high energy density.

Zn-ion capacitors (ZICs) are emerging as promising energy storage devices due to their low cost. Currently, aqueous-based electrolytes are primarily used in ZIC which have shown issues related to low Zn deposition/stripping efficiencies, and Zn dendrites formation, resulting in device failure. To overcome these issues and to develop environmentally benign energy storage devices, here we have studied bio-ionic liquid electrolytes (bio-ILs) in both symmetric and asymmetric capacitors. Choline acetate (ChOAc) and betaine acetate (BetOAc) in water were investigated as electrolytes for capacitors in the presence and absence of Zn salts. Spectroscopic analysis showed that Zn solvation in the electrolytes changes significantly with the change in cation which affects the electrochemical reactions and capacitor performance. Raman analysis showed the Zn complex formed in the case of ChOAc is [Zn(OAc)₄]²⁻ whereas for BetOAc is [Zn(OAc)₅]³⁻ thereby the Zn deposition/stripping in ChOAc-based electrolyte is quite stable whereas in case of BetOAc, Zn deposition/stripping is unstable. In the ChOAc electrolyte, the Zn/activated carbon asymmetric cell showed a capacity of >90 F g⁻¹ at 0.1 A g⁻¹ and a capacitance close to 40 F g⁻¹ at 0.5 A g⁻¹ with ∼82 % capacity retention after 3000 cycles, whereas BetOAc could only be used in symmetric cell capacitor. This study shows that bio-ILs can be used as sustainable electrolytes in energy storage devices wherein the cation plays a significant role in the capacitor performance.

In this study, bilayer MoS₂ was synthesized on graphene film using chemical vapor deposition (CVD) to get a hetero-film photo-catalyst for the photo-assisted charging of Li-oxygen battery. The synthesized hetero-film exhibited an optical band gap of 1.8 eV and a valence band edge potential of −1.23 V_Ag/AgCl (2.04 V_Li+/Li). Fast-responding photocurrents in the microampere range were achieved through on-off cycles under visible-light irradiation. The anodic nature of the photocurrents indicated that the synthesized semiconductor film was n-type. Photo-assisted testing demonstrated that the MoS₂/graphene hetero-film photo-catalyst significantly reduced the charging potential and increased the discharging potential at a current density of 0.1 mA cm⁻², thereby greatly enhancing the cyclic performance of the Li-oxygen battery.

Redox flow batteries (RFBs) play a crucial role in large-scale energy storage, with electrode design being essential to their performance. Porous electrodes enhance macroscopic/mesoscopic flow, microscopic ion diffusion, and interfacial electrochemical reactions, leading to improved power density and energy efficiency. This review focuses on the design and strategies of RFB optimized electrodes, promoting the achievement of carbon neutrality. More information can be found in the Review Article by Xinzhuang Fan, Wenjia Li, Lei Wei, and co-workers (10.1002/celc.202400460).