ChemElectroChem最新文献

Enzymatic fuel cells (EFCs) offer renewable energy conversion via highly selective electrode reactions using enzymes as natural catalysts even under mild conditions. Electrochemical impedance spectroscopy (EIS) is a valuable tool for evaluating EFC performance, providing insights into substrate mass transport, enzyme kinetics, and electrode stability. Despite its acknowledged importance, the use of EIS coupled with distribution of relaxation times (DRT) analysis in EFCs research is limited. Our study addresses this gap by employing EIS and DRT analysis to investigate enzyme-based anodic processes, focusing on the bioelectrocatalytic oxidation of glucose catalyzed by glucose oxidase (GOx). Through careful variation of multiple parameters, it was possible to identify three distinct regions in the DRT plot. Each region has been subsequently associated with a key anodic process. The first region (R₁) is associated with high-frequency phenomena occurring at the electrodes, primarily due to ionic conduction in the electrolyte. Intermediate-frequency processes are associated to charge transfer kinetics in region 2 (R₂). Region 3 (R₃) is linked to diffusion processes occurring at low frequencies. This thorough examination offers an insight into the functioning of enzymatic bioelectrodes, which in turn drives improvements in the design and components of biofuel cells to increase their power output.

Enhancing the supercapacitors’ performance relies on the increased capacitance and voltage window, which are the current key challenges for developing new materials. In this study, the mononuclear Ni^II-bis(oxamato) complex ([ⁿBu₄N]₂[Ni(opba)], 1) has been synthesized and used as a template in polypyrrole (PPy) based conductive polymer as a novel electrode material for supercapacitor applications. The surface and structural properties of PPy and PPy/1 electrodes were studied using SEM and TEM to elucidate their interactions. The results of characterization techniques revealed that complex 1 altered the morphology, creating a prominent three-dimensional globular structure in the PPy/1 hybrid material without significant chemical modification. The electrochemical properties of PPy and PPy/1 were investigated by CV, EIS, and GCD analyses. The PPy/1 electrode demonstrated intense pseudocapacitive behavior, showing a significantly widened potential window and increased current compared to the PPy electrode, resulting in enhanced energy storage capacity within the material. This improvement was evaluated by testing a symmetric supercapacitor in a coin cell architecture with an alginate-based gel acting as both electrolyte and separator. The maximum specific cell capacitance reached 41.6 F g⁻¹ at a current density of 0.2 A g⁻¹, with a remarkable capacity retention of 97 % after 1000 galvanostatic charge/discharge cycles.

The low capacity of activated carbon (AC) electrodes remains as one of the major limiting factors for the development of high energy density lithium-ion capacitors (LICs). Hybridization of capacitive AC electrodes by incorporating faradaic materials into the electrode formulation could be performed to enhance the capacity of the overall device. However, this strategy requires an accurate electrode design to maximize the performance. In this work, Li₃V_1.95Ni_0.05(PO₄)₃ (LVNP) was selected as faradaic material due to its compatibility with AC, showing high capacity, fast ionic diffusion, and relatively high conductivity. Various formulations and mass loadings have been studied to analyze the impact of incorporating LVNP into the positive electrode on the performance of the hybrid electrode. Moreover, for practical LIC applications, a sacrificial salt -dilithium squarate, Li₂C₄O₄- was included in the hybrid electrode as a pre-lithiation additive, developing a ternary electrode. The sacrificial salt oxidized releasing lithium ions, while the electrochemical performance of the hybrid positive electrode remained almost unaltered. Finally, a cycle life test combined with a post-mortem analysis allows understanding the failure mechanisms of the electrode, suggesting the need of further improvements of the electrolyte and electrode-electrolyte interface to develop long lifetime hybrid faradaic-capacitive electrodes based on LVNP-AC active materials.

In the present work, novel composite material comprising of corn husk derived activated carbon and siloxene nanosheets have been explored as new class of multicomponent electrode material for fabricating high energy density supercapacitors with wide temperature tolerance. The activated carbon obtained from corn husk (ACH–900) with high surface area and pore volume acts as an ideal framework for hosting siloxene nanosheets (S) that allows the overall siloxene–corn husk derived activated carbon (ACH–900/S) composite to deliver excellent electrochemical performance. The as-prepared ACH–900/S composite electrode exhibited a high specific capacitance of 415 F g⁻¹ at 0.25 A g⁻¹ and retained 73.4 % of its initial capacitance even at a high current density of 30 A g⁻¹ in 1 M Na₂SO₄ electrolyte. In addition, the symmetric supercapacitor assembled with “acetonitrile/water-in-salt (AWIS)” electrolyte exhibited an energy density of 57.2 W h kg⁻¹ at 338 W kg⁻¹ with a cyclic stability of 92.8 % after 10000 cycles at 5 A g⁻¹ current density. Besides, the fabricated ACH–900/S supercapacitor can operate over wide temperature range from 0 to 100 °C. This work opens up new frontiers to develop low-cost safe supercapacitors with wide temperature tolerance and excellent electrochemical performance.

We present a unique, one-step, hydrothermal process to prepare nickel sulfide (Ni₃S₂) foam by a simple and direct conversion from nickel foam, which contributes both as a scaffold for the reaction and as reactant. The Ni₃S₂ foam exhibits remarkable mechanical stability, retaining the structural integrity of the foam and excellent crystallinity even after ultrasonication at 200 W for 30 mins. We document the transformation of the nickel foam template into a Ni₃S₂ foam, highlighting the role of synthesis duration on the phase evolution and unique morphology of Ni₃S₂. PXRD and SEM analyses reveal a complete transformation after 24 hours from the nickel foam to a pure Ni₃S₂ foam, which has a highly porous and interconnected ultra-thin nanosheet architecture. This significantly enhances the surface area and provides many electrochemical reaction sites. In a three-electrode cell, the capacity of the Ni₃S₂ foam electrode is 3.9 C cm⁻² at 8 mA cm⁻², which is higher than previous reports for Ni₃S₂. In a hybrid supercapacitor device, the Ni₃S₂ foam demonstrates significant increase in capacitance through 500 cycles and the capacitance plateaus after 2000 cycles. Even after 8500 continued charge-discharge cycles, the device exhibits excellent cycle stability indicating improvement with age.

High-nickel cathode materials are widely used in lithium-ion batteries because of their advantages of high energy density and high safety. High-nickel cathode materials need to further improve cycling stability because they are prone to structural changes and capacity degradation. This paper proposes a method to improve high-nickel cathode materials by Mg doping. XRD proves that Mg-doped high-nickel materials still have R-3 m spatial structural characteristics; Rietveld refinement confirms that the c-axis gradually increases with the increase of Mg content. Combined with DFT calculations, the presence of Mg can inhibit structural collapse during charge and discharge, reduce Li/Ni antisite defects, improve the electronic conductivity of the material, and improve the cyclic stability of the material. The 0.6 mol % Mg-doped sample has an initial discharge capacity of 233 mAh g⁻¹ at 0.1 C in the range of 2.7–4.3 V, a capacity retention rate of 91.0 % after 50 cycles at 1 C, still retains 79.9 % after 100 cycles. The dQ/dV curves further indicate that the presence of Mg improves the structural stability of the material.

The development of highly conjugated metalloporphyrin assemblies is a crucial step to improve their catalytic activity for optimal energy conversion processes. Herein, di-thienyl substituted nickel(II) porphyrin is used to form a highly conjugated porphyrin structure. The resulting porphyrin-based conjugated polymer catalyst exhibited exceptional oxygen evolution reaction “OER” performances, featuring a low onset overpotential of 266 mV and high reaction kinetics (Tafel slope of 69.9 mV/dec) under alkaline pH conditions, achieving a current density of 4.5 mA/cm². The remarkable OER catalytic activity of porphyrin-based conjugated polymer catalyst is attributed to the enhancement of the conjugation, which occurs through a unique process involving direct fusion of the porphyrins followed by thienyl bridging of the fused porphyrin tapes, ultimately leading to the establishment of a highly cross-linked porphyrinic network.

Oxic microbial electrosynthesis (oMES) allows the utilization of renewable electricity and industrial gas streams containing CO₂ and O₂ for biomass production by cultivating aerobic, autotrophic, hydrogen-oxidizing bacteria, commonly known as Knallgas bacteria. oMES is likely not a direct competitor to conventional anoxic microbial electrosynthesis as harnessing aerobic hydrogen-oxidizing bacteria depends on energetically inefficient assimilatory CO₂ reduction pathways. However, it might be a complementary approach to classical biomass production from the perspective of limited land use and the availability of cheap renewable energy. The best characterized Knallgas bacterium is Cupriavidus necator. Extensively studied as lithoautotrophic production host, C. necator already offers a broad arsenal of genetic tools. In contrast, mechanistical knowledge about the recently discovered Kyrpidia spormannii is limited, but this species shows remarkable growth when cultivated as cathodic biofilm in bioelectrochemical systems. In addition, first experiments indicate a low energy demand for biomass production, which is in the order of magnitude of gas fermentation with C. necator or heterotrophic and methanotrophic technologies. Still, many aspects of the electrochemical cultivation of K. spormannii need to be better understood and rigorously improved to be a competitive technology in the making, including electron transfer and microbial kinetics, cultivation conditions, mass and energy balances, and reactor design.

Understanding the internal reactions in Li-ion batteries is crucial to analyze them more accurately and improve their efficiency since they are involved in almost every aspect of everyday life. Electrochemical impedance spectroscopy is a valuable research technique to investigate such batteries, as it reveals sensitive properties and essential information about cell reaction mechanisms and kinetics. Physical understanding of the electrochemical process and system of a battery can be analyzed using equivalent electric circuits (EECs) with rational selection of electric circuit elements and their combination. However, impedance analysis of a battery is often conducted using oversimplified EEC models in practice due to the complexity and difficulty of the physics and mathematics of the modeling. This study proposes and verifies an EEC model that represents a three-stage mechanism for intercalation-type materials. For the systematic model study and verifications, we investigated cathode half cells using four different layered structured cathode materials, namely, LiCoO₂, LiNi_1/3Mn_1/3Co_1/3O₂, LiNi_0.9Mn_0.05Co_0.05O₂, and Ni_0.815Co_0.15Al_0.035O₂. Parametric analysis of the impedance fittings for the four different cathode materials showed similar behavior depending on the states of charge. We also provided the complete set of parameters of the four systems: charge transfer resistance, double-layer capacitance, and solid-electrolyte interphase (SEI) resistance and capacitance. Lastly, we explain how different electrochemical processes, such as intercalation and alloying, can be analyzed and modeled in EEC models.

In this work, iron- and nitrogen-doped carbide-derived carbon and carbon nanotube (CDC/CNT) composites are prepared and used as oxygen reduction reaction (ORR) electrocatalysts in acidic conditions. Three different approaches are taken to mix iron and nitrogen precursors, namely iron(II) acetate and 1,10-phenanthroline, with the nanocarbon materials. The doping is done via high-temperature pyrolysis. The success of doping is proved by several physicochemical methods indicating that iron is atomically dispersed. The Fe−N−C catalyst materials possess similar textural properties with high specific surface area and plenty of pores in different sizes. The evaluation of the ORR activity using the rotating (ring−)disk electrode method shows that the prepared Fe−N−C materials have very similar and good electrocatalytic performance in acidic media and low yield of H₂O₂ formation. This excellent ORR performance of the Fe−N−C catalyst materials is attributed to the presence of Fe−N_x and pyridinic-N moieties, as well as a feasible porous structure.