Electrochemical Signature Research Articles

CuO@3D graphene modified glassy carbon electrode towards the detection of Orange II and Rhodamine B

Synthetic dyes are illegally used in foodstuffs and cause serious health issues in humans due to their carcinogenic nature. To avoid serious health issues, it is compulsory to detect and remove even the minute quantities of these harmful dyes in foodstuffs. Electrochemical sensors are accredited as an efficient and promising platform for the robust and sensitive determination of food toxins in various foodstuffs. Therefore, an efficient, facile, and competent sensor is devised for the simultaneous detection of Orange II (OR II) and Rhodamine B (RhB) supported by rGO and CuO nanoparticles. The synergism between rGO’s immense surface area and the adsorption properties of CuO enhances selectivity and response time for the detection of OR II and RhB. This work elaborated the synthesis, characterization, and electrochemical behavior of CuO@3DGr electrode towards simultaneous sensing of OR II and RhB. Physicochemical techniques were utilized to validate the fabrication of targeted material. On the other hand, the electrochemical features of the developed sensor were characterized by cyclic voltammetry (CV) and electron impedance spectroscopy (EIS). Differential pulse voltammetry technique was employed to detect simultaneously Orange II and Rhodamine B on the surface of bare (GCE), GO/GCE, CuO/GCE, and CuO@3DGr/GCE. Multi-analyte detection is possible with DPV, a sensitive electrochemical method. Based on each toxin’s specific electrochemical signature, the sensor may generate separate peaks by delivering a sequence of potential pulses and detecting the ensuing current. The parameters which influence the performance of the modified sensor were carefully evaluated. Under ambient conditions, the developed sensor exhibited excellent electrocatalytic activity in oxidation at 0.67 V of OR II and 0.96 V RhB with a low limit of detection 08 nM for OR II and 4.5 nM for RhB in Britton- Robinson buffer (BRB pH:7). The described methodology allowed a robust and fast analysis of food toxins in different foodstuff establishing this sensor as a novel tool for detecting food toxins. Tap water was used to analyze the practical applicability of developed electrode material and suitable results were achieved. These results showed that the as-synthesized novel electrochemical sensor has the potential for ultrasensitive determination and detection of toxins in different foodstuffs.

Electrochemical Signatures as a Diagnostic Tool for SARS-CoV-2 and Its Variant Detection in Real-Time Wastewater Samples

Electrochemical Signatures as a Diagnostic Tool for SARS-CoV-2 and Its Variant Detection in Real-Time Wastewater Samples

Electrochemical Quantification of Enkephalin Peptides Using Fast-Scan Cyclic Voltammetry.

Endogenous opioid neuropeptides serve as important chemical signaling molecules in both the central and peripheral nervous systems, but there are few analytical tools for directly monitoring these molecules in situ. The opioid peptides share the amino acid motif, Tyr-Gly-Gly-Phe-, at the N-terminus. Met-enkephalin is a small opioid peptide comprised of only five amino acids with methionine (Met) incorporated at the C-terminus. Tyrosine (Tyr) and Met are electroactive, and their distinct electrochemical signatures can be utilized for quantitative molecular monitoring. This work encompasses a thorough voltammetric characterization of Tyr and Met redox chemistry as individual amino acids and when incorporated into small peptide fragments containing the shared Tyr-Gly-Gly-Phe- motif. NMR spectroscopy was used to determine the structure and conformation at near-physiological conditions. Voltammetric data demonstrate how the peak oxidation potential and the rate of electron transfer are dependent on the local chemical environment. Both the proximity of the electroactive residue to the C- or N-terminus and the hydrophobicity of the additional nonelectroactive amino acids profoundly affect sensitivity. Finally, the work uses the electrochemical signal for individual amino acids in a "training set", with a combination of principal component analysis and least-squares regression to accurately predict the voltammetric signal for short peptides comprising different combinations of those amino acids. Overall, this study demonstrates how fast-scan cyclic voltammetry can be utilized to discriminate between peptides with small differences in the chemical structure, thus establishing a framework for reliable quantification of small peptides in a complex signal, broadly speaking.

Addressing Mass Conservation in Two-Dimensional Modeling of Lithium Metal Batteries with Electrochemically Plated/Stripped Interfaces

Several previous studies have aimed to develop mathematical models based on the moving boundary approach for predicting changes in lithium morphology during the cycling of lithium metal batteries under different operating conditions. These modeling frameworks play a crucial role in enhancing our fundamental understanding of the transport and reaction mechanisms and guide experimentalists in developing safer and more efficient lithium metal anodes. In this work, using a simple two-dimensional model for the lithium metal battery, we aim to bring attention to the bulk convection in the liquid electrolytes induced by the movement of the lithium metal surface modeled as a moving boundary. The back-and-forth motion of the lithium metal surface during the plating and stripping of lithium introduces a weak fluid motion in the liquid electrolyte that should be incorporated in the model equations and corresponding boundary conditions (Figure 1). The results for the electrochemical signatures and morphology evolution thus obtained by solving a coupled fluid model are compared with the case where the velocity distribution in the liquid electrolyte is ignored. This work extends our previously reported perspective on the convective flux correction to rectify the mass conservation failures at moving boundaries in one-dimensional models to two dimensions. This careful implementation of the correct boundary conditions ensures the mass conservation of lithium in two-dimensional simulations for predicting the morphological evolution of lithium metal electrodes over cycles. These revised battery models with accurate mass and charge conservation are crucial for predicting the performance of the battery over cycles. Additionally, these relative fluxes at the moving and fixed boundaries are sometimes ignored by assuming a bulk concentration condition at the far end, especially at the cathode/separator interface. While it may not affect overpotential signatures at the anode, it leads to mass conservation issues with implications for the accuracy of cycling simulations. Thus, with the help of a two-dimensional electro-convection model, this study addresses the role of bulk convection in liquid electrolytes and the importance of ensuring mass conservation in lithium metal battery models.

Novel Electrochemical Methodology for the Removal of HF from Carbonate-Based LiPF6-Containing Li-Ion Battery Electrolytes

Baseline Li-ion battery (LIB) electrolytes typically consist of LiPF6 salt dissolved in carbonate solvents. Due to trace amounts of water and the hydrolysis of PF6 - in carbonate solvents, these electrolytes always contain trace amounts of HF. [1] On the cathode, HF has negative effects, including transition metal dissolution and capacity fading. [2] On the anode, HF is involved in the formation and evolution of the solid electrolyte interphase (SEI). [3] The SEI originates in the thermodynamic instability of electrolyte moieties (salt, solvent, impurities) on the anode surface. As a result, electrolyte moieties are reduced and may then react with Li+ ions to form solid, insoluble products on the anode surface. This limits electron and solvent transport while permitting Li+ transport, kinetically stabilizing the interface. [4] The mechanism of nucleation and growth remains poorly understood despite their significance. The formation of LiF is one example. Although it is believed that direct PF6 - anion reduction is important, it is difficult to observe this reaction unambiguously because it frequently coexists with electrochemical signatures of electrocatalytic HF reduction or even acts in concert with one another. [5]The objective of this work is to remove ppm-levels of HF from carbonate-based LiPF6-containing electrolytes to enable foundational studies of SEI nucleation (e.g., direct PF6 - anionic direction) without interfering HF effects. We propose an electrochemical purification approach, which is complementary to conventional approaches using scavenging molecules. [6] Utilizing the knowledge that all other electrolyte moieties in baseline carbonate LiPF6-containing LIB electrolyte remain intact at relatively high potentials (significantly > 1.5 V vs. Li/Li+), we postulate to solely and selectively electrocatalytically reduce HF on metal electrodes. Therefore, our basic hypothesis is that all the HF in the electrolyte will be electrocatalytically reduced when an appropriate potential is applied to a high-surface area catalytically active electrode, while all other moieties essentially stay unchanged. To achieve this, we employed a porous Cu-foam working electrode that is integrated into a Teflon cone-type cell that has a second Pt working electrode. This allows us to use cyclic voltammetry (CV) to electrochemically test the HF concentration in the electrolyte. We report on the successful removal of HF to levels below a few ppm. Additionally, we observe CV features which we tentatively assign to direct anion reduction. Investigations are underway to gain deeper insight into the specifics of this reaction. We anticipate that the developed electrochemical method could lead to new opportunities for HF removal and basic research on the SEI reaction in electrolytes containing LiPF6.Literatur:[1] S.F. Lux, J. Chevalier, I.T. Lucas, R. Kostecki, HF Formation in LiPF6-Based Organic Carbonate Electrolytes, ECS Electrochemistry Letters, 2 (2013) A121.[2] C. Ye, W. Tu, L. Yin, Q. Zheng, C. Wang, Y. Zhong, Y. Zhang, Q. Huang, K. Xu, W. Li, Converting detrimental HF in electrolytes into a highly fluorinated interphase on cathodes, Journal of Materials Chemistry A, 6 (2018) 17642-17652.[3] D. Strmcnik, I.E. Castelli, J.G. Connell, D. Haering, M. Zorko, P. Martins, P.P. Lopes, B. Genorio, T. Østergaard, H.A. Gasteiger, F. Maglia, B.K. Antonopoulos, V.R. Stamenkovic, J. Rossmeisl, N.M. Markovic, Electrocatalytic transformation of HF impurity to H2 and LiF in lithium-ion batteries, Nature Catalysis, 1 (2018) 255-262.[4] A. Wang, S. Kadam, H. Li, S. Shi, Y. Qi, Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries, npj Computational Materials, 4 (2018) 15.[5] C. Cao, T.P. Pollard, O. Borodin, J.E. Mars, Y. Tsao, M.R. Lukatskaya, R.M. Kasse, M.A. Schroeder, K. Xu, M.F. Toney, H.-G. Steinrück, Toward Unraveling the Origin of Lithium Fluoride in the Solid Electrolyte Interphase, Chemistry of Materials, 33 (2021) 7315-7336.[6] J.-G. Han, M.-Y. Jeong, K. Kim, C. Park, C.H. Sung, D.W. Bak, K.H. Kim, K.-M. Jeong, N.-S. Choi, An electrolyte additive capable of scavenging HF and PF5 enables fast charging of lithium-ion batteries in LiPF6-based electrolytes, Journal of Power Sources, 446 (2020) 227366.

Operando-XRD of Electrochemical Reactors for Selective Li+ Extraction from Brines and Seawater

In times of rising demand of Li for use in Li-ion batteries (LIBs), and ensuring its supply for aluminum electrolysis, ultralight alloys, optics, synthesis, nuclear research, and pharmaceuticals, it is essential to simplify the processing of Li sources in a sustainable manner. Current extraction from ores is complex and requires large energy input while generating high amounts of waste. This causes the danger of making Li a limited resource and even more expensive.[1] A new promising way is the electrochemical extraction of Li by desalination batteries (DBs) from brines or seawater[2]. Thereby, selective extraction of ions can be promoted by the chemistry of the electrode material, e.g., by using FePO4. To further enhance the selectivity, potentiostatic application proved to be useful[3]. DBs are superior to other extraction methods in terms of energy efficiency, and waste generation. Still, varying Li+ concentrations in brines[1b], competitive intercalation of other cations with similar size - especially Na+ [2] -, and degradative effects of anions[4], H2O, and O2 [5] are major challenges to overcome for DBs with FePO4.In this contribution, we focus on the selective extraction of Li+ using FePO4 electrodes by specifically-designed multi-step potentiostatic application. Results are shown for salt solutions containing a mixture of Na+/Li+, and artificial seawater. It is vital to understand the atomic-scale processes so that the electrodes, and electrochemical parameters can be optimized. Therefore, we used operando high-energy X-ray diffraction (HEXRD) microscopy to investigate the crystal structure of FePO4 during the electrochemical process. The experiments showed that the energy barrier for Na+ (de)intercalation was higher than that of Li+ during galvanostatic cycling, i.e., FePO4 is selective for Li+. Using a multi-step potentiostatic procedure, the (de)intercalation process could be enhanced, as evident from our HEXRD results and simultaneous conductivity measurements. Our tentative interpretation is that Li+ is highly selectively (de)intercalated, although electrochemical signatures hinted on a two-step process during deintercalation, which may indicate the intercalation of Na+. To selectively deintercalate the remaining Na+ over Li+, we further optimized the applied potentials. During galvanostatic cycling in artificial seawater, the (de)intercalation potentials were at more positive and more negative potentials, respectively, likely caused by the variety of cations. We expect that our results contribute to the design of high-performance DBs and inspire the exploration of further systems based on our proposed multi-step process.

Enhanced electrochemical oxidation and machine learning-assisted sensing of tetrabromobisphenol A using activated carbon facilitated CoWO4 heterostructures

The escalating levels of environmental pollution, particularly from commercially used products, highlight the imperative of efficient sensor technologies to facilitate timely and effective remediation strategies. Herein, a simple method is proposed to enhance the electrochemical performance of CoWO4 structures by coupling them with activated carbon (AC) for direct tetrabromobisphenol A (TBPA) oxidation. The systematic comparison shows that incorporation of AC with CoWO4 not only improves the overall effective surface area (ESA) of the catalyst by 1.8-fold but also improves the cyclic voltammetry (CV) based irreversible oxidation current by 2.0-fold owing to improved conductivity and surface characteristics. Differential pulse voltammetry (DPV) based optimization of the sensory characteristics confirmed robust electrocatalytic TBPA oxidation within a 0.1 to 1.0 µM concentration range, achieving a 0.024 µM detection limit within PBS (0.1 M) (pH 5.0). Moreover, density functional theory (DFT) analysis confirms the non-covalent interaction favorability between TBPA and CoWO4 surface, validating TBPA’s easy adsorption onto the catalytic surface and, thus, facilitated electron mobility between the molecule and the catalyst during the surface oxidation process. The DPV sensing interpreted using machine learning (ML) algorithms confirmed the detection accuracy of the developed sensor. Among the adopted models, artificial neural networks (ANN) achieved the highest R2 score (0.9659) and the lowest values across Mean Squared Error (MSE), Mean Absolute Error (MAE), and Root Mean Squared Error (RMSE) error matrices confirming its suitability in deciphering DPV correlations.Integrating ANN with DPV based electrocatalytic oxidation sensing underscores machine learning’s potential in analyzing complex electrochemical signatures, thus advancing intelligent sensing for precise environmental monitoring.

Lithium Plating Characteristics in High Areal Capacity Li-Ion Battery Electrodes.

Li-ion battery degradation and safety events are often attributed to undesirable metallic lithium plating. Since their release, Li-ion battery electrodes have been made progressively thicker to provide a higher energy density. However, the propensity for plating in these thicker pairings is not well understood. Herein, we combine an experimental plating-prone condition with robust mesoscale modeling to examine electrode pairings with capacities ranging from 2.5 to 6 mAh/cm2 and negative to positive (N/P) electrode areal capacity ratio from 0.9 to 1.8 without the need for extensive aging tests. Using both experimentation and a mesoscale model, we identify a shift from conventional high state-of-charge (SOC) type plating to high overpotential (OP) type plating as electrode thickness increases. These two plating modes have distinct morphologies, identified by optical microscopy and electrochemical signatures. We demonstrate that under operating conditions where these plating modes converge, a high propensity of plating exists, revealing the importance of predicting and avoiding this overlap for a given electrode pairing. Further, we identify that thicker electrodes, beyond a capacity of 3 mAh/cm2 or thickness >75 μm, are prone to high OP, limiting negative electrode (NE) utilization and preventing cross-sectional oversizing the NE from mitigating plating. Here, it simply contributes to added mass and volume. The experimental thermal gradient and mesoscale model either combined or independently provide techniques capable of probing performance and safety implications of mild changes to electrode design features.

Crystallographic and electrochemical corrosion resistance analyses of cataphoretically co-deposited spinel Co>0.5Mn0.1-0.3O0.1-0.4@rGO composites over α-Fe(110) as current collector for supercapatteries

Binder free spinel Co>0.5Mn0.1-0.3O0.1-0.4@rGO composite electrode films were fabricated via galvanostatic electrochemical deposition technique over α-Fe(110) as current collector for hybrid supercapattery. Self-designed, n-MOSFET embedded ATMega328P microcontroller assisted modules were deployed to record the chronopotentiometric as well as galvanostatic charging-discharging analysis for specific capacitance (Cs) measurements. Partial, exchange as well as limiting current densities(iL) and cathodic current efficiency were estimated. Electrochemical signature was analyzed from cyclic voltammetry data. Morphology and chemical nature of the composites were scrutinized with scanning electron microscopy, X-ray photoelectron, FT-IR and Raman spectra. Indigenously designed computer simulation programs coded in Python were used to optimize the deposition parameters and to analyze the crystalline structure from XRD data. The unit cell length for the FCC crystal with an octahedral geometry was ∼ 4.28 Å. An in-depth analysis of potentiodynamic polarization as well as electrochemical impedance spectral data were carried out to scrutinize the corrosion resistance and capacitance characteristics of the composites in KOH. From the Tafel constants, Ecorr, Icorr, Ru, RCT and ZW data, it was accentuated that rGO incorporated composite films offer enhanced corrosion protection for Fe(110) substrates than their individual counterparts along with augmented specific capacitance. Estimated Cs was about 1166 F.g−1 at a scan-rate of 10 mV.s−1. Impact of time-constant (τ) and current density over Cs was analyzed via GCD technique and was about 1458.73 F.g−1 at 2 τ and at 0.5 A.g−1. And the corresponding specific energy and power density were about 183.23 W.h.kg−1 and 237.75 W.kg−1 respectively. These composite electrode films impregnated with rGO not only improved the specific capacitance but also imparts the sacrificial corrosion resistance over the α-Fe(110) as current collector in presence of OH−as electrolyte and can serve as a sustainable electrode material for supercapatteries.

Unlocking the electrochemical signature of Naringenin: Implications for screening in pharmaceutical formulations

Naringenin (NAR) is a versatile herbal flavonoid known for its broad pharmacological benefits, including antioxidant, anti-inflammatory, and anticancer properties. These properties underscore its potential and necessity for industrial applications within the pharmaceutical sector, making its detection and quantification crucial for ensuring the quality and efficacy of pharmaceutical products. Addressing the imperative for a sensitive and sustainable screening approach, this research leverages electrochemical analysis techniques including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). Complementary to experimental investigations, the electronic structure of NAR was probed using B3LYP/Def2-TZVPPD calculations alongside Fukui and dual descriptor analyses. Our findings delineate the dissociation kinetics of the hydroxyl groups within NAR, with particular emphasis on the phenolic group’s proton as the primary dissociation site, elucidating pivotal insights into the oxidation mechanism of NAR. Noteworthy is the irreversibility of the electrochemical oxidation process observed on both non-modified glassy carbon electrode (GCE) and gold electrode (GE), indicating a one-electron-one-proton mechanism. Utilizing the external calibration method and GCE, a linear range from 1.36 to 19.1 mg L-1 in Britton-Robinson (BR) supporting electrolyte was established, exhibiting a limit of detection (LOD) of 0.11 mg L-1 (R2 = 0.9945). For GE, the standard addition calibration approach revealed one linear range, from 0.27 to 0.48 mg L-1 (LOD of 0.04 mg L-1, R2 = 0.9960). Importantly, the proposed methodologies demonstrate satisfactory selectivity against potential interferences, with intra- and inter-day precision exhibiting low relative standard deviation (RSD) values. This study introduces a simple, sensitive, stable, selective, and sustainable electroanalytical method for the detection of NAR in pharmaceutical formulations, harnessing the advantages of unmodified electrodes and rigorous experimental validation.

Reducing Voltage Hysteresis in Li-Rich Sulfide Cathodes by Incorporation of Mn.

Conventional intercalation-based cathode materials in Li-ion batteries are based on charge compensation of the redox-active cation and can only intercalate one mole of electron per formula unit. Anion redox, which employs the anion sublattice to compensate charge, is a promising way to achieve multielectron cathode materials. Most anion redox materials still face the problems of slow kinetics and large voltage hysteresis. One potential solution to reduce voltage hysteresis is to increase the covalency of the metal-ligand bonds. By substituting Mn into the electrochemically inert Li1.33Ti0.67S2 (Li2TiS3), anion redox can be activated in the Li1.33-2y/3Ti0.67-y/3Mn y S2 (y = 0-0.5) series. Not only do we observe substantial anion redox, but the voltage hysteresis is significantly reduced, and the rate capability is dramatically enhanced. The y = 0.3 phase exhibits excellent rate and cycling performance, maintaining 90% of the C/10 capacity at 1C, which indicates fast kinetics for anion redox. X-ray absorption spectroscopy (XAS) shows that both the cation and anion redox processes contribute to the charge compensation. We attribute the drop in hysteresis and increase in rate performance to the increased covalency between the metal and the anion. Electrochemical signatures suggest the anion redox mechanism resembles holes on the anion, but the S K-edge XAS data confirm persulfide formation. The mechanism of anion redox shows that forming persulfides can be a low hysteresis, high rate capability mechanism enabled by the appropriate metal-ligand covalency. This work provides insights into how to design cathode materials with anion redox to achieve fast kinetics and low voltage hysteresis.

Electron paramagnetic resonance as a tool to determine the sodium charge storage mechanism of hard carbon

Hard carbon is a promising negative electrode material for rechargeable sodium-ion batteries due to the ready availability of their precursors and high reversible charge storage. The reaction mechanisms that drive the sodiation properties in hard carbons and subsequent electrochemical performance are strictly linked to the characteristic slope and plateau regions observed in the voltage profile of these materials. This work shows that electron paramagnetic resonance (EPR) spectroscopy is a powerful and fast diagnostic tool to predict the extent of the charge stored in the slope and plateau regions during galvanostatic tests in hard carbon materials. EPR lineshape simulation and temperature-dependent measurements help to separate the nature of the spins in mechanochemically modified hard carbon materials synthesised at different temperatures. This proves relationships between structure modification and electrochemical signatures in the galvanostatic curves to obtain information on their sodium storage mechanism. Furthermore, through ex situ EPR studies we study the evolution of these EPR signals at different states of charge to further elucidate the storage mechanisms in these carbons. Finally, we discuss the interrelationship between EPR spectroscopy data of the hard carbon samples studied and their corresponding charging storage mechanism.

Towards Long-Term Monitoring of Commercial Lithium-Ion Batteries Enabled by Externally Affixed Fiber Sensors and Strain-Based Prognostic Strategies

Real-time monitoring of both continuous and spontaneous degradation in lithium-ion batteries is challenging due to the limited number of quantitative metrics available during cycling. In this regard, improved sensing approaches enabled by sensors of high accuracy, precision, and durability are key to achieving comprehensive state estimation and meeting rigorous safety standards. In this work, external temperature and strain monitoring in commercial Li-ion button cells was carried out using tandem pairs of polymer-based and silica-based optical fiber Bragg grating sensors. The decoupled data revealed that the sensors can reliably track strain and temperature evolution for over 500 cycles, as evidenced by periodic patterns with no sign of sensor degradation or loss of fidelity. Moreover, monitoring the strain signal enabled early detection of an anomalous cell over ∼60 cycles ahead of an electrochemical signature and abrupt drop in capacity, suggesting that mechanical sensing data may offer unique benefits in some cases. Detailed mechanical monitoring via incremental strain analysis suggests a parallel path toward understanding cell degradation mechanisms, regardless of whether they are continuous or discrete in nature. The accuracy and durability of such a package-level optical fiber sensing platform offers a promising pathway for developing robust real-time battery health monitoring techniques and prognostic strategies.

Characterization by NMR Spectroscopy of the SEI Layer Formed on Ti3C2 MXene Materials Prepared with Various Terminations

The nature and content of surface terminations are one of the key factors that define the electrochemical signature of the widely studied MXene materials. In this paper, the surface termination of molten salt synthesized Ti3C2Tx MXene with -O and -Cl terminations (T=Cl,O) are studied for the first time using solid state NMR technique, with respect to conventional HF synthesized Ti3C2Tx (T=F, O, OH). Both materials have been further used as negative electrode of Li-ion battery. The evolution of surface terminations during the Solid Electrolyte Interphase (SEI) layer formation was studied from the SEI components formed in both MXenes. Analysis of the NMR signal provided insights into the porous nature of SEI with LiF as main component in HF terminated MXenes. While a thick uniform formation of the SEI was observed for the molten salt synthesized Ti3C2Tx (T=Cl,O) with Li2CO3 as dominant component.

Single-Response Duplexing of Electrochemical Label-Free Biosensor from the Same Tag.

Multiplexing is a valuable strategy to boost throughput and improve clinical accuracy. Exploiting the vertical, meshed design of reproducible and low-cost ultra-dense electrochemical chips, the unprecedented single-response multiplexing of typical label-free biosensors is reported. Using a cheap, handheld one-channel workstation and a single redox probe, that is, ferro/ferricyanide, the recognition events taking place on two spatially resolved locations of the same working electrode can be tracked along a single voltammetry scan by collecting the electrochemical signatures of the probe in relation to different quasi-reference electrodes, Au (0V) and Ag/AgCl ink (+0.2V). This spatial isolation prevents crosstalk between the redox tags and interferences over functionalization and binding steps, representing an advantage over the existing non-spatially resolved single-response multiplex strategies. As proof of concept, peptide-tethered immunosensors are demonstrated to provide the duplex detection of COVID-19 antibodies, thereby doubling the throughput while achieving 100% accuracy in serum samples. The approach is envisioned to enable broad applications in high-throughput and multi-analyte platforms, as it can be tailored to other biosensing devices and formats.

Electrochemical Signatures of Potassium Plating and Stripping

Alkali metal anodes can enable unmatched energy densities in next generation batteries but suffer from insufficient coulombic efficiencies. To deduce details about processes taking place during galvanostatic cycling, voltage profiles are commonly analyzed, however the interpretation is not straightforward as multiple processes can occur simultaneously. Here we provide a route to disentangle and interpret features of the voltage profile in order to build a mechanistic understanding on alkali metal stripping and deposition, by investigating potassium metal deposition as a model case where processes and reactions are exaggerated due to the high reactivity of potassium. In particular, the importance of separating SEI formation and nucleation to correctly estimate the energy barrier for nucleation is demonstrated. Further, we show how the native layer formed on alkali metal foils gives rise to strong features in the voltage profile and propose forming alkali metal electrode through electrodeposition to mitigate these effects.

Insights into soft short circuit-based degradation of lithium metal batteries.

The demand for electric vehicles with extended ranges has created a renaissance of interest in replacing the common metal-ion with higher energy-density metal-anode batteries. However, the potential battery safety issues associated with lithium metal must be addressed to enable lithium metal battery chemistries. A considerable performance gap between lithium (Li) symmetric cells and practical Li batteries motivated us to explore the correlation between the shape of voltage traces and degradation. We coupled impedance spectroscopy and operando NMR and used the new approach to show that transient (i.e., soft) shorts form in realistic conditions for battery applications; however, they are typically overlooked, as their electrochemical signatures are often not distinct. The typical rectangular-shaped voltage trace, widely considered ideal, was proven, under the conditions studied here, to be a result of soft shorts. Recoverable soft-shorted cells were demonstrated during a symmetric cell polarisation experiment, defining a new type of critical current density: the current density at which the soft shorts are not reversible. Moreover, we demonstrated that soft shorts, detected via electrochemical impedance spectroscopy (EIS) and validated via operando NMR, are predictive towards the formation of hard shorts, showing the potential use of EIS as a relatively low-cost and non-destructive method for early detection of catastrophic shorts and battery failure while demonstrating the strength of operando NMR as a research tool for metal plating in lithium batteries.

In Situ Investigation of Electrochemically Mediated Carbon Capture and Release Via Quinone Chemistry in Aqueous Media

The development of devices capable of capturing and sequestering carbon dioxide emissions directly from air or at point sources is motivated by mitigating climate change. Electrochemically driven carbon capture and release at ambient temperature and pressure through the formation of complexes with organic redox active molecules [1,2] or via pH swing caused by proton-coupled electron transfer during molecular redox events [3,4] has shown promising results for carbon capture and release in terms of energy cost, scalability and safety compared to the state of the art amine scrubbing technologies [5].Quinones are organic molecules containing an unsaturated six-member ring with two carbonyl groups. They exhibit two potential mechanisms of CO2 capture. (a) Upon electrochemical reduction, the carbonyl groups within quinones provide sites for nucleophilic addition of carbon dioxide which results in the formation of a quinone-CO2 adduct (CO2reversibly bound by quinones). (b) Depending on the pKa of the quinone and the local pH, the electrochemical reduction of the compound can be proton-coupled, creating hydroxide, which captures CO2 as carbonate or bicarbonate.In this work, we introduce in situ electrochemical characterization and in situ fluorescence microscopy to separately quantify the two aforementioned contributions toward capture of CO2 at partial pressures ranging from 0.1 bar to 0.4 mbar. The non-invasive in situ analytical methods introduced in this work are used to distinguish, with sub-second time resolution, between the oxidized, reduced and adduct species by their electrochemical and fluorescence signatures. The results of this study permits us to understand the underlying simultaneous contributions of quinone-CO2 adduct path and the pH-swing path toward carbon capture and release and, additionally, introduces powerful non-invasive methods for gathering insights on similar systems. 1X. Li, X. Zhao, Y. Liu, T.A. Hatton, and Y. Liu, "Redox-tunable lewis bases for electrochemical carbon dioxide capture", Nature Energy 7, 1065 (2022). 2Y. Liu, H.Z. Ye, K.M. Diederichsen, T. Van Voorhis, and T.A. Hatton, "Electrochemically mediated carbon dioxide separation with quinone chemistry in salt-concentrated aqueous media", Nat Commun 11, 2278 (2020). 3S. Jin, M. Wu, Y. Jing, R.G. Gordon, and M.J. Aziz, "Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing", Nat Commun 13, 2140 (2022). 4S. Jin, M. Wu, R.G. Gordon, M.J. Aziz, and D.G. Kwabi, "pH swing cycle for CO2 capture electrochemically driven through proton-coupled electron transfer", Energy & Environmental Science 13, 3706 (2020). 5G.T. Rochelle, "Amine scrubbing for CO2 capture", Science 325, 1652.

Mechanistic Underpinnings of Heterogeneities in Solid-State Battery Cathode

Solid-state batteries (SSBs) are regarded as the potential candidate for next-generation energy storage systems due to their enhanced energy density and safety characteristics. However, realizing the true potential of the SSBs is predicated on addressing several interfacial and mechanistic challenges stemming from the mechanically rigid nature of the solid electrolyte (SE). In this regard, the presence of solid-solid point contacts within the solid-state cathode poses a critical bottleneck. Point contacts not only result in transport and kinetic limitations but also lead to stress hotspots within the composite cathode. Moreover, microstructural heterogeneities govern the spatial variability of these point contacts, thereby influencing the coupled electrochemical, thermal, and mechanical signatures. Thus, understanding the critical role of cathode microstructural heterogeneity in dictating the mesoscale interactions and its implications on the SSB performance is necessary. In this work, mechanistic underpinnings of heterogeneities in solid-state cathode will be studied and its implications on the coupled electrochemical-thermal-mechanical response of SSBs will be delineated. Lastly, the effect of cathode architecture will be explored towards achieving high energy density SSBs.

Electrochemical Signatures of Potassium Plating and Stripping

Alkali metals are attractive anodes for high energy density batteries, but practical utilization of these materials in rechargeable cells has so far been hindered by safety concerns, limited Coulombic efficiencies and short cycle lives. These issues are all connected to the uneven electrodeposition and stripping of alkali metals; dendritic metal deposits can short circuit the cell and deposits with large surface areas consume more electrolyte and active material in side reactions.[1] To circumvent these problems, one of the approaches which have been attempted is electrolyte engineering. For instance, electrolytes with higher salt concentration, so called highly concentrated electrolytes, have been shown to suppress both dendrite growth and increase the Coulombic efficiency of metal anodes.[2,3] When different metal anode stabilization strategies are evaluated, it is common to perform galvanostatic cycling experiments in symmetric or asymmetric cells. This allows the cycling stability and Coulombic efficiency of the plating/stripping to be analyzed. Additionally, it is common to use features of the voltage profile as signatures on the mechanisms responsible for changes in electrochemical performance. For instance, a sharp decrease in (over)voltage during plating/stripping is a sign of a short circuit. A gradually increasing overvoltage during cycling on the other hand can be a result of continuous solid electrolyte interphase (SEI) buildup. However, several processes often occur in parallel when symmetric/asymmetric cells are cycled galvanostatically, each giving different contributions to the voltage profile which need to be deconvoluted to make sense of the data. In this contribution, we use three-electrode cells in combination with simple electrochemical experiments like cyclic voltammetry, chronoamperometry and chronopotentiometry to disentangle the contributions to different features in the galvanostatic voltage profiles of alkali metal anodes.In particular, we dissect the voltage profiles of potassium-copper (K-Cu) cells with highly concentrated electrolytes. Due to the higher reactivity of K compared to other alkali metals, certain features in the voltage profiles of these cells become exaggerated compared to lithium or sodium metal cells. We show that during galvanostatic deposition on a fresh Cu substrate, SEI formation and nucleation occur partly in parallel. If an SEI-formation step is performed prior to the galvanostatic deposition, a much sharper ‘nucleation peak’ in the voltage profile can be observed, indicative of the higher rate of nucleation that needs to occur in this case. Further, the potassium metal anode exhibits a steplike voltage profile from the second cycle and onwards. We confirm that this feature arises because bulk K is covered by a resistive native layer, whereas another type of, less resistive, interphase covers the freshly deposited K. This inhomogeneous interphase will inevitably promote preferential and inhomogeneous plating/stripping.