Electrochem

For the first time, carbon-particle-supported palladium-based cobalt composite electrocatalysts (abbreviated as Pd_xCo_y/CPs) were prepared using a calcination–hydrothermal process–hydrothermal process (denoted as CHH). The catalysts of Pd_xCo_y/CPs prepared using CoC₂O₄·2H₂O, (CH₃COO)₂Co·4H₂O, and metallic cobalt were named catalyst c₁, c₂, and c₃, respectively. For comparison, the catalyst prepared in the absence of a Co source (denoted as Pd/CP) was identified as catalyst c₀. All fabricated catalysts were thoroughly characterized by XRD, EDS, XPS, and FTIR, indicating that PdO, metallic Pd, carbon particles, and a very small amount of cobalt oxide were the main components of all produced catalysts. As demonstrated by the traditional electrochemical techniques of CV and CA, the electrocatalytic performances of Pd_xCo_y/CP towards the ethanol oxidation reaction (EOR) were significantly superior to that of Pd/CP. In particular, c₁ showed an unexpected electrocatalytic activity for EOR; for instance, in the CV test, the peak f current density of EOR on catalyst c₁ was 129.3 mA cm⁻², being about 10.7 times larger than that measured on Pd/CP, and in the CA test, the polarized current density of EOR recorded for c₁ after 7200 s was still about 2.1 mA cm⁻², which was larger than that recorded for Pd/CP (0.6 mA cm⁻²). In the catalyst preparation process, except for the elements of C, O, Co, and Pd, no other elements were involved, which was thought to be the main contribution of this preliminary work, being very meaningful to the further exploration of Pd-based composite EOR catalysts. Full article

For the first time, nitrogen- and carbon-present tin dioxide-supported palladium composite catalysts (denoted as Pd/N-C-SnO₂) were prepared via an HCH method (HCH is the abbreviation for the hydrothermal process–calcination–hydrothermal process preparation process). In this work, firstly, three catalyst carriers (denoted as cc) were prepared using a hydrothermal-process-aided calcination method, and catalyst carriers prepared using ammonia monohydrate (NH₃∙H₂O), N,N-dimethylformamide (C₃H₇NO) and triethanolamine (C₆H₁₅NO₃) as the nitrogen sources were nominated as cc₁, cc₂ and cc₃, respectively. Secondly, these catalyst carriers were reacted with palladium oxide monohydrate (PdO·H₂O) hydrothermally to generate catalysts c₁, c₂ and c₃. As testified by XRD and XPS, besides carbon materials and the N-containing substances, the main substances of all prepared catalysts were SnO₂ and metallic palladium (Pd). Above all things, all resultant catalysts, especially c₂, showed a prominent electrocatalytic activity towards the ethanol oxidation reaction (EOR). As indicated by the CV (cyclic voltammetry) results, all fabricated catalysts presented a clear electrocatalytic activity towards the EOR. In the CA (chronoamperometry) measurement, the faradaic current density of EOR measured on c₂ at −0.27 V vs. an SCE (saturated calomel electrode) after 7200 s was still maintained at about 5.6 mA cm⁻². Preparing a novel catalyst carrier, N-C-SnO₂, and preparing a new EOR catalyst, Pd/N-C-SnO₂, were the principal dedications of this preliminary work, which was very beneficial to the development of Pd-based EOR catalysts. Full article

In this study, vanadium (3.5⁺) electrolyte was prepared for vanadium redox flow batteries (VRFBs) through a reduction reaction using a batch-type hydrothermal reactor, differing from conventional production methods that utilize VOSO₄ and V₂O_5. The starting material, V₂O₅, was mixed with various concentrations (0.8 M, 1.2 M, 1.6 M, 2.0 M) of citric acid (CA) as the reducing agent and stirred for 60 min at 90 °C using a hot plate to ensure complete dispersion in the solution. The resulting solution was subsequently subjected to a hydrothermal reduction reaction (HRR) furnace at 150 °C for 24 h to generate vanadium (3.5⁺). The mixed states of the produced vanadium (3⁺) and vanadium (4⁺) were confirmed using UV-vis spectroscopy. The electrochemical properties of the electrolyte were investigated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), revealing that the optimal concentration of the CA was 1.6 M. The current efficiency, energy efficiency, and voltage efficiency of the electrolyte produced via the HRR process was compared with that prepared using VOSO₄ in charge and discharge experiments. The results demonstrate that the HRR process yields an enhanced electrolyte across all efficiency metrics produced through the given improved performance in all efficiencies. These findings indicate that the HRR process using citric acid can facilitate the straightforward preparation of vanadium (3.5⁺) electrolyte, making it suitable for large-scale production. Full article

This study investigates the underlying mechanisms of hydrogen peroxide (H₂O₂) sensing using a composite material of bismuth oxide and bismuth oxyselenide (Bi₂O_xSe_y). The antagonistic effect of tungsten (W)-doping on the electrochemical behavior was also examined. Undoped, 2 mol%, 4 mol%, and 6 mol% W-doped Bi₂O_xSe_y nanostructures were synthesized using a one-pot solution phase method involving selenium powder and hydrazine hydrate. W-doping induced a morphological transformation from nanosheets to spherical nanoparticles and amorphization of the bismuth oxyselenide phase. Electrochemical sensing measurements were conducted using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). H₂O₂ detection was achieved over a wide concentration range of 0.02 to 410 µM. In-depth CV analysis revealed the complex interplay of oxidation-reduction processes within the bismuth oxide and Bi₂O₂Se components of the composite material. W-doping exhibited an antagonistic effect, significantly reducing sensitivity. Among the studied samples, undoped Bi₂O_xSe_γ demonstrated a high sensitivity of 83 μA μM⁻¹ cm⁻² for the CV oxidation peak at 0 V, while 6 mol% W-Bi₂O_xSe_y became completely insensitive to H₂O₂. Interestingly, DPV analysis showed a reversal of sensitivity trends with 2 and 4 mol% W-doping. The applicability of these samples for real-world analysis, including rainwater and urine, was also demonstrated. Full article

Manganese- and iron-rich P2-type ${\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{M}\mathrm{n}}_{0.5}{\mathrm{O}}_2 \left(\mathrm{N}\mathrm{F}\mathrm{M}\right)$ has garnered significant interest as a promising cathode candidate due to the natural abundance of Fe and Mn along with a high redox couple of Fe³⁺/Fe⁴⁺ and Mn³⁺/Mn⁴⁺. Despite all these merits, NFM suffers from structural instability during cycling, arising from the destructive Jahn-Teller (JT) distortion effect of Mn³⁺/Mn⁴⁺ during charging and Fe⁴⁺/Fe³⁺ during discharging. In this research, a novel P2-type transition metal-oxide cathode Na_0.67Fe_0.5−2xMn_0.5Ti_xV_xO₂ was synthesized by doping a tiny fraction of two electrochemically inactive elements, Titanium (Ti) and Vanadium (V), into Mn-rich Na_0.67Fe_0.5Mn_0.5O₂ (NFM) that mitigated the JT effect substantially and ameliorated the stability of the SIB during cycling. These exhaustive structural and morphological comparisons provided insights into the effects of V and Ti doping on stabilizing surface structures, reducing Jahn Teller distortion, enhancing stability and capacity retention, and promoting the Na⁺ carrier transport mechanism. Moreover, the electrochemical analysis, such as the galvanostatic charge/discharge profile, validates the capacity improvement via Ti and V co-doping into NFM cathode. The initial discharge capacity of the 2% Ti/V-doped ${\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{F}\mathrm{e}}_{0.48}{\mathrm{M}\mathrm{n}}_{0.5}{{\mathrm{T}\mathrm{i}}_{0.01}{\mathrm{V}}_{0.01}\mathrm{O}}_2 \left(2\mathrm{N}\mathrm{F}\mathrm{M}\mathrm{T}\mathrm{V}\right)$ was found to be 187.12 mAh g⁻¹ at a rate of 0.1 C, which was greater than the discharge capacity of 175.15 mAh g⁻¹ observed for pure NFM ${(\mathrm{N}\mathrm{a}}_{0.67}{\mathrm{M}\mathrm{n}}_{0.5}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{O}}_2).$ In contrast, 2NFMTV exhibited a noteworthy capacity retention of 46.1% when evaluated for its original capacity after undergoing 150 cycles at a rate of 0.1 C. This research also established a structural doping approach as a feasible technique for advancing the progress of next-generation Sodium-ion Batteries. Full article

The lithium-ion battery (LIB) is the key energy storage device for electric transportation. The thick electrode (single-sided areal capacity >4.0 mAh/cm²) design is a straightforward and effective strategy for improving cell energy density by improving the mass proportion of electroactive materials in whole cell components and for reducing cost of the battery cell without involving new chemistries of uncertainties. Thus, selecting a low-cost and environmentally friendly fabrication process to achieve a thick cathode electrode with good electrochemical performance is of strong interest. This study investigated the impact of fabrication processes on the performance of thick LiNi_0.75Mn_0.25O₂ (NM75) cathode electrodes in pouch cells. Two fabrication methods were compared: the conventional polyvinylidene fluoride (PVDF)-based slurry casting method (C-NM75) and the polytetrafluoroethylene (PTFE)-based powder fibrillating process (F-NM75). The pouch cells with F-NM75 electrodes exhibited significantly improved discharge and charge rate capabilities, with a discharge capacity ratio (3 C vs. C/3) > 62% and a charge capacity ratio (2 C vs. C/3) > 81%. Furthermore, F-NM75 cells demonstrated outstanding C/3 cycling performance, retaining 86% of discharge capacity after 2200 cycles. These results strongly indicated that the PTFE-based powder fibrillating process is a promising solution to construct high-performance thick cathode electrodes for electric vehicles (EVs) applications. Full article

The extensive use of the alkaloid quinine (QN) in the cosmetic and food industries has induced major concerns relating to its impact on human health, considering its potential toxicity. Therefore, developing sensitive and selective electrochemical sensors is crucial for monitoring QN in environmental, food, and pharmaceutical samples. To respond to this need, a surfactant-supported green synthesis approach, based on a straightforward, organic solvent-free hydrothermal method was employed to synthesize highly crystalline pseudospherical bismuth oxychloride (BiOCl) nanoparticles. This material was used for the enrichment of carbon paste electrodes and its further utilization for the detection and quantification of quinine. They have superior electrocatalytic performance, due to their size and morphology, and facilitate the interactions of the target with the electrode surface. Under optimal operating conditions, differential pulse voltammetry demonstrated a remarkable feature: a broad linear working range of 10 to 140 μM, a detection limit of 0.14 μM, and a high sensitivity of 1.995 μA μM⁻¹ cm⁻². The suggested method’s satisfactory sensitivity, along with its good stability, repeatability, and reproducibility, strongly point to a possible use for identifying quinine in real samples. Full article

New homogeneous bilayer membranes with a thin anion-exchange layer have been developed based on the copolymer of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and ethyl methacrylate (EMA) on the surface of a membrane substrate made from polyfluorosulfonic acid (PFSA). The overall and partial current–voltage characteristics, as well as external and internal diffusion-limiting currents, were theoretically and experimentally investigated. Parameters such as specific conductivity, sorption, and diffusion permeability of individual membrane layers were determined, along with effective transport numbers and specific permselectivity of the bilayer homogeneous membranes in mixed solutions of calcium chloride and sodium chloride. It was found that applying a thin anion-exchange layer of DADMAC and EMA to the homogeneous membrane allows for the creation of a charge-selective bilayer membrane with enhanced selectivity toward monovalent metal cations. The specific selectivity of the bilayer membrane for sodium cations increases more than 6-fold (from 0.8 to 4.8). Verification of the obtained experimental data was performed within a four-layer mathematical model with quasi-equilibrium boundary conditions for the diffusion layer (I)/modifying layer (II)/membrane substrate (III)/diffusion layer (IV) in ternary NaCl+CaCl₂ solutions. Full article

The development of conductive coatings has significant implications for microelectronics and electrochemistry. However, conductive coatings may exhibit different electrochemical properties when prepared on different substrate materials. This research explores the comparative performance of graphene, graphene oxide (GO), and silver nanoparticle (Ag NP) composites as conductive coatings on diverse substrate materials, including polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), and glass. The study employed various preparation methods, such as mixing conductive materials with substrate materials and preparing copolymer composite materials. The conductive coating approach was found to be the most straightforward and convenient, with broader development prospects and fewer restrictive conditions. The results indicate that the distinct surface characteristics of the substrate materials influence the conductive properties of coating materials. Consequently, results show that graphene exhibits the highest conductivity on all three substrates, while GO is more conductive than Ag NPs on PMMA and PDMS but less conductive than Ag NPs on glass. That offers valuable insights into the selection of substrate materials and coating materials for the preparation of conductive materials. Full article

An electrochemical bioassay based on rotating droplet electrochemistry by using an electron-transfer mediator was developed for the evaluation of a wide variety of pollutants such as antibiotics, heavy metals, and pesticides in the water environment. Ferricyanide was used as an electron-transfer mediator for obtaining the catalytic response of Escherichia coli. The electrochemical response of E. coli was measured via hydrodynamic chronoamperometry in a microdroplet on a screen-printed carbon electrode (SPCE). The constructed electrode system successfully evaluates the catalytic response of E. coli solution in the presence of ferricyanide. An assay for antibiotic toxicity on E. coli was carried out. The EC₅₀ for ampicillin, sulfamonomethoxine, chlorotetracycline, tetracycline, and oxytetracycline evaluated by the pre-incubation method were 0.26, 0.77, 5.25, 18.5, and 19.0 µM, respectively. The toxicity order was ampicillin > sulfamonomethoxine > chlorotetracycline > tetracycline > oxytetracycline. The proposed method can be used to evaluate the antibiotic toxicities in different real samples, such as pond water, powder, and raw milk. Recoveries were found in the range of 90 and 99%. The developed methods do not require additional incubation time to evaluate toxicity. Full article

Cu₂(ZnSn)(S)₄ (copper, zinc, tin, and sulfide (CZTS)) provides possible advantages over CuInGaSe2 for thin-film photovoltaic devices because it has a higher band gap. Preparing CZTS by electrodeposition because of its high productivity and lower processing costs, electroplating is appealing. Recently published studies reported that the electrodeposition process of CZTS still faces significant obstacles, such as the sulfur atomic ratio (about half of the whole alloy), deposits’ adhesion, film quality, and optical properties. This work introduces an improved bath that facilitates the direct electroplating of CZTS from one processing step. The precursors used were significantly more diluted than the typical baths mentioned in the last few years. An extensive analysis of the electrochemical behavior at various rotation speeds is presented at room temperature (~22 °C). The deposited alloy’s composition and adherence to the molybdenum back contact are examined with agitation. The annealing process was carried out in an environment containing sulfur, and the metal was not added at this stage. The ultimate sulfur composition was adjusted to 50.2%, about the desired atomic ratio. The compound’s final composition was investigated using the Energy-Dispersive X-ray Spectroscopy technique. Finally, X-ray diffraction analysis was applied to analyze CZTS crystallography and to measure thickness. Full article

Direct testing of pesticide contaminants in drinking water is a challenge. Portable and sensitive sensor platforms are desirable to test water contaminants directly at farm and consumer levels. In this study, we have demonstrated the feasibility of an electrochemical sensor for the direct detection of paraquat (PQ) in drinking water samples. An immunoassay-based sensing platform was fabricated using PQ-specific antibody immobilized on the surface of the electrochemically reduced graphene oxide (rGO) modified screen-printed carbon electrode (rGO-SPCE). Using non-faradaic electrochemical impedance spectroscopy (EIS) as a detection tool, the sensor platform demonstrated a dynamic response for PQ concentration in drinking water ranging from 0.05 ng/mL to 72.9 ng/mL (0.19 to 243.8 nM), with a coefficient of determination (r²) of 0.997 and a limit of detection of 0.05 ng/mL (0.19 nM). Percentage recovery within ±20% error was obtained, and the sensor cross-reactivity test showed a selective response against glyphosate antigen. With the flexibility to use single-frequency EIS and low sample volume, the developed sensor demonstrated testing in water samples directly without any sample pre-processing. This low-volume electroanalytical sensor platforms can be translated into portable testing tools for the detection of various water contaminants. Full article

Extracellular electron transfer (EET) by sulfate-reducing bacteria (SRB), such as Desulfovibrio ferrophilus IS5, enables bacterial interactions with minerals, which are vital for biogeochemical cycling and environmental chemistry. Here, we explore the direct EET mechanisms through outer-membrane cytochromes (OMCs) using IS5 as a model SRB. We employed nanostructured electrodes arrayed with 0, 50, 200, and 500 nm long nanowires (NWs) coated with indium–tin–doped oxide to examine the impact of electrode morphology on the direct EET efficacy. Compared to flat electrodes, NW electrodes significantly enhanced current production in IS5 with OMCs. However, this enhancement was diminished when OMC expression was reduced. Differential pulse voltammetry revealed that NW electrodes specifically augmented redox peaks associated with OMCs without affecting those related to redox mediators, suggesting that NWs foster direct EET through OMCs. Scanning electron microscopy observations following electrochemical analyses revealed a novel vertical cell attachment and aggregation on NW electrodes, contrasting with the horizontal monolayer cell attachment on flat electrodes. This study presents the first evidence of the critical role of electrode nanoscale topography in modulating SRB cell orientation and aggregation behavior. The findings underscore the significant influence of electrode morphology on the direct EET kinetics, highlighting the potential impact of mineral morphology on mineral reduction and biogeochemical processes. Full article

The escalating concern over environmental pollutants, particularly brominated flame retardants (BFRs), demands sophisticated detection methodologies for compounds like Tetrabromobisphenol A (TBBPA) and Hexabromocyclododecane (HBCD). Amidst these challenges, advancements in electrochemical detection have notably focused on the integration of inorganic modifiers within carbon electrodes. Inorganic nanoparticles, known for their catalytic and surface-enhancing properties, play a pivotal role in augmenting the sensitivity and selectivity of electrode-based detection systems. These modifiers, encompassing materials such as graphene, CeO₂ nanocubes, and metal-organic frameworks, among others, have revolutionized the capabilities of carbon-based electrodes in accurately identifying specific BFRs. Full article

Battery-type hybrid supercapacitors (HSCs) (otherwise known as supercapatteries) are novel electrochemical energy storage devices bridge the gap between rechargeable batteries and traditional SCs. Herein, we report the synthesis of layered two-dimensional (2D) nickel disulfide (NiS₂) nanosheets (NSNs) modified with poly(3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) and their successful implementation in battery-type SCs. Initially, a layered 2D NSN is synthesized via a microwave-assisted hydrothermal method and further used as a template to coat PEDOT:PSS in order to prepare NiS₂@PEDOT:PSS nanocomposite electrodes by a facile drop-casting method. This is the first-time report on the synthesis of a hierarchical NiS₂@PEDOT:PSS nanocomposite electrode for battery-type HSC applications. An asymmetric battery-type HSC fabricated with NSN@PEDOT:PSS nanocomposite as positrode and activated carbon as negatrode delivers a maximum energy density of 52.1 Wh/kg at a current density of 1.6 A/g with a corresponding power density of 2500 W/kg. Full article

Ni–W alloys have received considerable interest as a promising structural material for microelectromechanical systems (MEMS) due to their exceptional properties, including hardness, ductility, corrosion resistance, and thermal stability. However, the electrodeposition of Ni–W alloys in the MEMS fabrication process to achieve intact structures with a thickness of several tens of micrometers is challenging due to the occurrence of cracking caused by side reactions and internal stresses during the electrodeposition process. To address this issue, our focus was on pulsed reverse electrodeposition (PRE) as a potential solution. The utilization of the PRE technique allows for a high concentration of reactive species on the electrode surface, thereby mitigating side reactions such as hydrogen generation. In this study, we examined the effects of the PRE method on the morphological characteristics, average crystal grain size, Vickers hardness, and micro-mechanical properties of Ni–W alloys. Full article

This work describes the fabrication and characterization of a new high surface area nanocomposite electrode containing reduced graphene oxide (rGO) and titanium nitride (TiN) for electrochemical applications. This approach involves electrochemically depositing rGO on a high surface area TiN nanorod array electrode to form a new nanocomposite electrode. The TiN nanorod array was first formed by the glancing angle deposition technique in a DC (Direct Current) sputtering system. GO flakes of ~1.5 μm in diameter, as confirmed by Dynamic Light Scattering (DLS), were electrodeposited on the nanostructured TiN electrode via the application of a fixed potential for one hour. The surface morphology of the as-prepared rGO/TiN electrode was evaluated by scanning electron microscopy (SEM) and the presence of rGO on TiN was confirmed by Raman Microscopy. The CV shows an increase in the capacitive current at rGO/TiN as compared to TiN. The rGO decorated TiN electrode was then used for analyzing the electrocatalytic oxidation of ascorbic acid and dopamine, and the reduction of nitrate by CV and linear sweep voltammetry (LSV), respectively. CV or LSV show that the electrochemical kinetics of these three analytes are significantly faster on rGO/TiN than TiN itself. Overall, the rGO/TiN electrode showed better electrochemical behavior for biomolecules like ascorbic acid and dopamine as well as another target analyte, nitrate ions, compared to TiN by itself. Full article

The influence of the component composition of coal batches and the final temperature of the coking process on the resistivity of coke was studied. Taking into account that the resistivity and reactivity are influenced by some common factors, such as the temperature level and coke readiness, which indicates the orderliness of its structure, the relationship between these indicators was established. The electrical resistivity can be considered a cumulative characteristic of coke properties, as evidenced by the mathematical dependencies of the change electrical resistance on the ash content, sulfur content, volatile yield, and petrographic composition. Analysis of the dependencies and their statistical evaluation indicate that the studied relationships are characterized by high values of correlation (0.6–0.84). The proposed regression equations can be recommended for optimizing the component composition and quality of production batches, given their significant impact on the resistivity of coke. This is especially relevant when coke is used in electrothermal processes, since the productivity and the electrical and thermal efficiency of the furnace depends on the resistivity of the coke in electrochemical processes in which carbon materials are used as anodes and lining elements and in the production of capacitor technology. As the resistivity test requires much less time to perform than the reactivity test, it can be considered as an alternative approach to the reactivity testing currently performed for quality control purposes. Full article

Electrochemical biosensors are valued for their sensitivity and selectivity in detecting biological molecules. Having the advantage of generating signals that can be directly or indirectly proportional to the concentration of the target analyte, these biosensors can achieve specificity by utilizing a specific biorecognition surface designed to recognize the target molecule. Electrochemical biosensors have garnered substantial attention, as they can be used to fabricate compact, cost-effective devices, making them promising candidates for point-of-care testing (POCT) devices. This study introduces a label-free electrochemical biosensor employing a gold screen-printed electrode (SPE) to detect lysophosphatidic acid (LPA), a potential early ovarian cancer biomarker. We employed the gelsolin–actin system, previously introduced by our group, in combination with fluorescence spectrometry, as a biorecognition element to detect LPA. By immobilizing a gelsolin–actin complex on an SPE, we were able to quantify changes in current intensity using cyclic voltammetry and differential pulse voltammetry, which was directly proportional to the LPA concentration in the solution. Our results demonstrate the high sensitivity of the developed biosensor for detecting LPA in goat serum, with a limit of detection (LOD) and a limit of quantification (LOQ) of 0.9 µM and 2.76 µM, respectively, highlighting its potential as a promising tool for early-stage diagnosis of ovarian cancer. Full article