Peak potential shift of fast cyclic voltammograms owing to capacitance of redox reactions

AI-Based Discrimination of Faradaic Current against Nonfaradaic Current Inspired by Speech Denoising

Cyclic voltammetry (CV) has been a powerful technique to provide impactful insights for electrochemical systems, including reaction mechanism, kinetics, diffusion coefficients, etc., in various fields of study, notably energy storage and energy conversion. However, the separation between the faradaic current component of CV and the nonfaradaic current contribution to extract useful information remains a major issue for researchers. Herein, we report a deep learning algorithm inspired by speech denoising that utilizes the theoretical faradaic current as a study target and predicts it from the overall current response from cyclic voltammograms. This deep neural network (DNN) is constructed from a series of fully connected layers, which apply a weight matrix to the inputs and transform it using an activation function to obtain the desired regression. Our model performed well with overall mean absolute percentage errors (MAPEs) of 6.36% between theoretical faradaic currents and the predicted responses from the total currents, with a peak position difference of 2.56 mV for anodic peaks and 2.44 mV for cathodic ones. Furthermore, the algorithm is also capable of extracting peak current values from experimental data with 3.37% MAPE and minimal peak position error (less than 0.75 mV). This innovative approach may be used as a tool to assist researchers in studying electrochemical systems using CV.

Decoupling Variable Capacitance and Diffusive Components of Active Solid-Liquid Interfaces with Flex Points

Understanding the current transport characteristics of electrode interfaces is essential for optimizing device performance across a wide range of applications including bio-/chemical sensing and energy storage sectors. Cyclic voltammetry (CV) is a popular method for studying interfacial properties, particularly those involving redox systems. However, it remains challenging to differentiate between electron movements that contribute to capacitive and diffusive behaviors. In this study, we introduce a technique called flex point analysis, which uses a single differentiation step to separate capacitive and diffusive electron movements at the electrode interface during a redox reaction. Our results show that the variable capacitance at the electrode surface exhibited both positive and negative values on the order of 10-6 (micro) Farad. This approach provides a clearer understanding of interfacial electron dynamics, enhancing the interpretation of CV data and potentially improving the design and optimization of related materials and devices.

Optimizing Ni-Cr patterned boron-doped diamond band electrodes: Doping effects on electrochemical efficiency and posaconazole sensing performance

There is growing interest in developing diamond electrodes with defined geometries such as, for example, micrometer-sized electrode arrays to acquire signals for electroanalysis. For electroanalytical sensing applications, it is essential to achieve precise conductive patterns on the insulating surface. This work provides a novel approach to boron-doped diamond patterning using nichrome masking for selective seeding on an oxidized silicon substrate. The optimized process involves nichrome deposition, sonication, chemical etching, seeding, and tailored chemical vapor deposition of boron-doped diamond with an intrinsic layer to suppress boron diffusion. Through a systematic investigation, it was determined that isolated boron-doped diamond band electrodes can be efficiently produced on non-conductive silica. Additionally, the influence of boron doping on electrochemical performance was studied, with higher doping enhancing the electrochemical response of band electrodes. To demonstrate sensing capabilities, boron-doped diamond bands were used to detect posaconazole, an antifungal drug, exploiting its electroactive behaviour. A linear correlation between posaconazole concentration and oxidation peak current was observed over 1.43 × 10-8 - 5.71 × 10-6 M with a 1.4 × 10-8 M detection limit. The developed boron-doped diamond microbands could significantly impact the field of electroanalysis, facilitating detection of diverse biologically relevant molecules. Overall, this diamond patterning approach overcomes major challenges towards all-diamond electrochemical sensor chips.

A simulation-based analysis of optical read-out for electrochemical reactions using composite vortex beams

We propose an optical read-out method for extracting faradaic current in electrochemical (EC) reactions and analyze its performance using opto-EC simulations. Our approach utilizes structured electrodes to generate composite optical vortex (COV) beams upon optical illumination. Through opto-EC simulations, we demonstrate that the EC reaction of 10 mM potassium ferricyanide induces a refractive index (RI) change, Δ RI, of approximately 10 - 4 RI units, leading to the rotation of the COV beam's intensity profile with a peak rotation of 40 ∘ . This rotation's magnitude is proportional to Δ RI, while the rate correlates with the faradaic current ( I f ) density responsible for Δ RI. As the opto-EC information is from bulk Δ RI, it remains unaffected by interfering non-faradaic components at the interface and is advantageous for studying intermediate species and bulk homogeneous reactions. Furthermore, as rotation depends on I f density rather than I f itself, this method proves beneficial in low I f scenarios, such as when employing micro-electrodes to decrease solution resistance or obtain localized EC data. Even in low I f density scenarios, like monitoring slow EC reactions, our method enables signal amplification by accumulating rotation over time. This interdisciplinary approach holds promise for advancing EC research and addressing critical challenges across various fields, including energy storage, corrosion protection, environmental remediation, and biomedical sciences.

Scalable solid-state synthesis of 2D transition metal oxide/graphene hybrid materials and their utilization for microsupercapacitors

Two-dimensional metal oxide (MO) nanostructures have unique properties compared with their bulk or 0D and 1D (nanoparticle and nanowire) counterparts. Their abundant surface area and atomically thin 2D structure are advantageous for their applications in catalysis and energy, as well as integration with 2D layered materials such as graphene and reduced graphene oxide (rGO). However, fast and scalable synthesis of 2D MOs and their nanocomposites remains challenging. Here, we developed a microwave-assisted solid-state synthesis method for the scalable generation of 2D MOs and 2D MO/rGO nanocomposites with tunable structure and composition. The structures and properties of 2D Fe2O3 and 2D ZnO as well as their nanocomposites with rGO were systematically investigated. The excellent electrochemical properties of such 2D MO/rGO nanocomposites also enable us to use them as electrode materials to fabricate microsupercapacitors. This work provides new insights into the scalable and solid-state synthesis of 2D nanocomposites and their potential applications in catalysis, energy conversion and storage.

Enhanced electrochemical performance of li-ion battery via ultrasonic-assisted inorganic-rich and thin SEI layer

Lithium-ion batteries (LIBs) stand as a compelling solution to energy source transition in various applications such as the vehicle industry due to their energy and power density. However, the impact of mechanical factors on them remains understudied. Of particular interest is the effect of vibration, an inherent characteristic of vehicles, on battery performance. Ultrasound has been reported to improve mass transfer and surface cleaning, yet its effects on LIBs are still not thoroughly investigated. This study investigates the influence of ultrasound on the solid electrolyte interphase (SEI) layer, resulting in a thin, inorganic-rich layer. The induced SEI layer alteration improves charge transfer, showing enhanced kinetics. We also reveal that ultrasound application enhances cycling stability, maintains discharge capacity at high charging rates, and facilitates inorganic-rich SEI layer creation. This novel combination of ultrasound and LIBs presents a promising pathway for achieving high-performance batteries.

Preparation and Characterization of Functionalized Surgical Meshes for Early Detection of Bacterial Infections

Isotactic polypropylene (i-PP) nonabsorbable surgical meshes are modified by incorporating a conducting polymer (CP) layer to detect the adhesion and growth of bacteria by sensing the oxidation of nicotinamide adenine dinucleotide (NADH), a metabolite produced by the respiration reactions of such microorganisms, to NAD+. A three-step process is used for such incorporation: (1) treat pristine meshes with low-pressure O2 plasma; (2) functionalize the surface with CP nanoparticles; and (3) coat with a homogeneous layer of electropolymerized CP using the nanoparticles introduced in (2) as polymerization nuclei. The modified meshes are stable and easy to handle and also show good electrochemical response. The detection by cyclic voltammetry of NADH within the interval of concentrations reported for bacterial cultures is demonstrated for the two modified meshes. Furthermore, Staphylococcus aureus and both biofilm-positive (B+) and biofilm-negative (B-) Escherichia coli cultures are used to prove real-time monitoring of NADH coming from aerobic respiration reactions. The proposed strategy, which offers a simple and innovative process for incorporating a sensor for the electrochemical detection of bacteria metabolism to currently existing surgical meshes, holds considerable promise for the future development of a new generation of smart biomedical devices to fight against post-operative bacterial infections.

A wearable, minimally-invasive, fully electrochemically-controlled feedback minisystem for diabetes management

Diabetes is a chronic disease affecting 10% of the population globally, and can lead to serious damage in the heart, kidneys, eyes, blood vessels or nerves. Commercial artificial closed-loop feedback systems can significantly improve diabetes management and save lives. However, they are large and expensive for users. Here, we demonstrate for the first time a wearable, minimally-invasive, fully electrochemically-controlled feedback minisystem for diabetes management. Both the working principles of the sensor and pump in the feedback system are based on electrochemical reactions. The smart minisystem was constructed based on integrating the thermoplastic polyurethane hollow microneedles with an electrochemical biosensing device on its outer layer and an electrochemical micropump facing the inner layer of the microneedles. The sensing device was constructed based on sputtering thin metal films through a shadow mask and electroplating Prussian blue on the surface of the microneedles, followed by the immobilization of glucose oxidase on the working electrode. The electrochemical micropump was constructed by sputtering the interdigital electrodes, followed by sealing with a thin elastic film, which was further integrated with the inner channels of the microneedles. Both the sensor and the pump were electrically powered. Via being controlled by a printed circuit board, the biosensing device monitored the levels of interstitial glucose continuously to drive the electrochemical pump to deliver insulin intelligently, in order to control blood glucose within the normal range. The closed-loop feedback system was studied for its capability in maintaining the blood glucose levels of diabetic rats under various physiological conditions. The utility of the intelligent feedback system was successfully demonstrated on diabetic rats for controlling the blood glucose levels within the normal range. The minisystem is wearable, small, cost-effective, precise, stable and painless. It is anticipated that this approach opens a new paradigm for the development of closed-loop diabetes minisystems and may lead to a compelling future for diabetes management.

Synthetic Biology Toolbox, Including a Single-Plasmid CRISPR-Cas9 System to Biologically Engineer the Electrogenic, Metal-Resistant Bacterium Cupriavidus metallidurans CH34

Cupriavidus metallidurans CH34 exhibits extraordinary metabolic versatility, including chemolithoautotrophic growth; degradation of BTEX (benzene, toluene, ethylbenzene, xylene); high resistance to numerous metals; biomineralization of gold, platinum, silver, and uranium; and accumulation of polyhydroxybutyrate (PHB). These qualities make it a valuable host for biotechnological applications such as bioremediation, bioprocessing, and the generation of bioelectricity in microbial fuel cells (MFCs). However, the lack of genetic tools for strain development and studying its fundamental physiology represents a bottleneck to boosting its commercial applications. In this study, inducible and constitutive promoter libraries were built and characterized, providing the first comprehensive list of biological parts that can be used to regulate protein expression and optimize the CRISPR-Cas9 genome editing tools for this host. A single-plasmid CRISPR-Cas9 system that can be delivered by both conjugation and electroporation was developed, and its efficiency was demonstrated by successfully targeting the pyrE locus. The CRISPR-Cas9 system was next used to target candidate genes encoding type IV pili, hypothesized by us to be involved in extracellular electron transfer (EET) in this organism. Single and double deletion strains (ΔpilA, ΔpilE, and ΔpilAE) were successfully generated. Additionally, the CRISPR-Cas9 tool was validated for constructing genomic insertions (ΔpilAE::gfp and ΔpilAE::λ_Prgfp). Finally, as type IV pili are believed to play an important role in extracellular electron transfer to solid surfaces, C. metallidurans CH34 ΔpilAE was further studied by means of cyclic voltammetry using disposable screen-printed carbon electrodes. Under these conditions, we demonstrated that C. metallidurans CH34 could generate extracellular currents; however, no difference in the intensity of the current peaks was found in the ΔpilAE double deletion strain when compared to the wild type. This finding suggests that the deleted type IV pili candidate genes are not involved in extracellular electron transfer under these conditions. Nevertheless, these experiments revealed the presence of different redox centers likely to be involved in both mediated electron transfer (MET) and direct electron transfer (DET), the first interpretation of extracellular electron transfer mechanisms in C. metallidurans CH34.

Enhancement of the Negative Capacitance Associated with the Dissolution of Silver by Salt Concentrations by Means of Anodic Stripping Voltammetry

The amount of anodically dissolved charge of silver by linear sweep stripping voltammetry has been observed to be smaller than that of the potentiostatically deposited charge. The imbalance in the charge is opposite to the participation in the double-layer capacitance. This can be explained in terms of the negative capacitive current, which is caused by dipoles of generated redox charge (Ag+) with counterions (NO3−). Lower concentrations of counterions may suppress the capacitance to retain the equality of the charge. This prediction is examined in this work by the oxidation of silver film at various concentrations of NO3− by anodic stripping voltammetry. The capacitance decreased with a decrease in the salt concentrations less than 0.05 mol dm−3. Low concentrations of salts prevent loss of the anodic charge in electroanalysis. This dependence was related with the lifespan of generated silver nitrate dipoles and is described theoretically.

Participation in Negative Capacitance of Diffusion-Controlled Voltammograms of Hemin

Hemin in dimethyl sulfoxide solution has exhibited voltammograms controlled by diffusion at glassy carbon electrodes for slow scan rates, although it is adsorbed slightly. In contrast, voltammograms for high scan rates, v > 1 V s^-1, were governed by some kinds of kinetics judging from the scan rate dependence of peaks. The kinetics is close to that of a ferrocenyl derivative, in which the currents include the capacitive component with negative values. The capacitive one can be identified with the proportionality to the scan rates. The variation of the peak currents with v yielded -200 μF cm^-2. This negative value, being associated with the charge transfer reaction, makes cyclic voltammograms deviated downward from the diffusion-controlled behavior, resembling an irreversible reaction of the Butler-Volmer kinetics. Double layer capacitances are generally formed so that the applied electric field may be relaxed. The reduction of hemin forms a dipole coupled with a cation of the salt. The dipole orients from the electrode to the bulk, whereas the solvent dipoles orients in the opposite direction. Therefore, the capacitance is observed negatively. The capacitance determined by ac impedance took also negative values when the applied dc potential was only in the potential domain for the charge transfer. These complications can be avoided in electrocatalysis by use of such slow voltammetry as scan rates of 0.1 V s^-1 and ac frequency of 0.2 Hz.