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Abstract Locust Bean Gum (LBG, carob bean gum) was investigated as an environmentally friendly, natural, and water-soluble binder for cathode (LFP) and anode (LTO) in lithium-ion batteries (Li-ion). For the first time, we show LBG as an electrode binder and compare to those of the most popular aqueous (CMC) and conventional (PVDF) binders. The electrodes were characterized using TGA/DSC, the galvanostatic charge–discharge cycle test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Thermal decomposition of LBG is seen to begin above 250 °C with a weight loss of about 60 wt% observed at 300 °C, which is sufficient to ensure stable performance of the electrode in a Li-ion battery. For CMC, weight loss at the same temperature is about 45%. Scanning electron microscopy (SEM) shows that the LFP–LBG system has a similar distribution of conductive carbon black particles to PVDF electrodes. The LTO–LBG electrode has a homogeneous dispersion of the electrode elements and maintains the electrical integrity of the network even after cycling, which leads to fast electron migration between LTO and carbon black particles, as well as ion conductivity between LTO active material and electrolyte, better than in systems with CMC and PVDF. The exchange current density, obtained from impedance spectroscopy fell within a broad range between 10−4 and 10−2 mA cm−2 for the LTO|Li and LFP|Li systems, respectively. The results presented in this paper indicate that LBG is a new promising material to serve as a binder. Graphic abstract

We present a promising approach to the electroanalytical detection of a specific nitroaromatic explosive in landfill leachates (LLs) that originated from a municipal solid waste plant. The paper is focused but not limited to the sensing of 4,4’,5,5’-tetranitro-1H,1’H-2,2’-biimidazole (TNBI) using differential pulse voltammetry and cyclic voltammetry. Highly electroactive nanocarbon was applied to determine low concentrations of the analyte in the complex interfering matrix as leachate samples. The mechanism of nitro- group reduction is attributed to the sensing effect, as revealed in the voltammograms of TNBI. The developed sensor model has two linear regions extending from 0.02 ppm to 1.4 ppm and from 2 ppm to 16 ppm resulting from adsorption and diffusion-controlled processes, respectively. The limit of detection was as low as 0.52 ppm ( $1.66\,\,\mu \text{M}\,\,\text{L}^{-1}$ ) thanks to the electrochemical performance of the joint effect of the diamond/graphene composite nanowall surface.

Carbon felts are flexible and scalable, have high specific areas, and are highly conductive materials that fit the requirements for both anodes and cathodes in advanced electrocatalytic processes. Advanced oxidative modification processes (thermal, chemical, and plasma-chemical) were applied to carbon felt anodes to enhance their efficiency towards electro-oxidation. The modification of the porous anodes results in increased kinetics of acetaminophen degradation in aqueous environments. The utilised oxidation techniques deliver single-step, straightforward, eco-friendly, and stable physiochemical reformation of carbon felt surfaces. The modifications caused minor changes in both the specific surface area and total pore volume corresponding with the surface morphology. A pristine carbon felt electrode was capable of decomposing up to 70% of the acetaminophen in a 240 min electrolysis process, while the oxygen-plasma treated electrode achieved a removal yield of 99.9% estimated utilising HPLC-UV-Vis. Here, the electro-induced incineration kinetics of acetaminophen resulted in a rate constant of 1.54 h−1, with the second-best result of 0.59 h−1 after oxidation in 30% H2O2. The kinetics of acetaminophen removal was synergistically studied by spectroscopic and electrochemical techniques, revealing various reaction pathways attributed to the formation of intermediate compounds such as p-aminophenol and others. The enhancement of the electrochemical oxidation rates towards acetaminophen was attributed to the appearance of surface carbonyl species. Our results indicate that the best-performing plasma-chemical treated CFE follows a heterogeneous mechanism with only approx. 40% removal due to direct electro-oxidation. The degradation mechanism of acetaminophen at the treated carbon felt anodes was proposed based on the detected intermediate products. Estimation of the cost-effectiveness of removal processes, in terms of energy consumption, was also elaborated. Although the study was focussed on acetaminophen, the achieved results could be adapted to also process emerging, hazardous pollutant groups such as anti-inflammatory pharmaceuticals. Electrocatalytic performance of oxygen-activated carbon fibre felt anodes mediating degradation mechanism of acetaminophen in aqueous environments

We present an advanced multimodality characterization platform for simultaneous optical and electrochemical measurements of ferrocyanides. Specifically, we combined a fiber-optic Fabry–Perot interferometer with a three-electrode electrochemical setup to demonstrate a proof-of-principle of this hybrid characterization approach, and obtained feasibility data in its monitoring of electrochemical reactions in a boron-doped diamond film deposited on a silica substrate. The film plays the dual role of being the working electrode in the electrochemical reaction, as well as affording the reflectivity to enable the optical interferometry measurements. Optical responses during the redox reactions of the electrochemical process are presented. This work proves that simultaneous opto-electrochemical measurements of liquids are possible.

Due to the global problem with plastic contaminating the environment, with bisphenol A (BPA) being one of the highest demand, effective monitoring and purification of the pollutants are required. The electrochemical methods constitute a good solution but, due to polymerization of electrochemical oxidation bisphenol A products and their adsorption to the surfaces, measurement head elements are clogged by the formed film. In this research, we propose a nanocrystalline diamond sheet protection for securing elements in direct contact with bisphenol A during electrochemical processes. The solution was presented on the example of a zinc oxide (ZnO) coating deposited on a fiber-optic end-face by Atomic Layer Deposition. Series of optical and electrochemical measurements were performed in a dedicated hybrid setup. The results show that ZnO can be modified during the electrochemistry leading to the drastic change of its properties. Such degradation did not show in case of nanocrystalline diamond sheet-protected sample proving the solution’s effectiveness, giving a possibility of re-using the measurement element and prolonging its lifespan.

The enormous self-assembly potential that graphene and its derived layered materials offer for responding to the contemporary environmental challenges has made it one of the most investigated materials. Hence, tuning its extraordinary properties and understanding the effect at all scales is crucial to tailoring highly customised electrodes. Vertically orientated graphene nanostructures, also known as carbon nanowalls (CNWs), due to the large surface area and unique maze-like morphology, have attracted attention as a platform for advanced sensing applications. In this work, a holistic investigation approach has been developed to disrupt the synthesis-composition-structure-property paradigm and to dig out the hidden materials relationships. To achieve that, autonomous advanced image-analysis methods (Minkowski Functionals, Fractal Analysis) have been applied to SEM micrographs and successfully classified them. Morphological, electrical, and electrochemical characterisation has been performed for all of the samples. Multivariate data analysis has been employed to mine the relationships between the material features, specifically as it relates to the understanding of the intrinsic properties. As a result, this study is intended to both shed light on CNWs as a promising transparent hybrid electrochemical substrate for perfectly assembled electrochemical devices and to provide a new flexible method for nanomaterial design, characterisation and exploitation.

Quaternary polymer electrolyte (PE) based on poly(acrylonitrile) (PAN), 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (EMImBF4), sulfolane (TMS) and lithium hexafluorophosphate salt (LiPF6) (PAN-EMImBF4-sulfolane-LIPF6) was prepared by the casting technique. Obtained PE films of ca. 0.2–0.3 mm in thickness showed good mechanical properties. They were examined using scanning electron microscopy (SEM), thermogravimetry (TGA, DSC), the flammability test, electrochemical impedance spectroscopy (EIS) and galvanostatic charging/discharging. SEM images revealed a structure consisting of a polymer network (PAN) and space probably occupied by the liquid phase (LiPF6 + EMImBF4 + sulfolane). The polymer electrolyte in contact with an outer flame source did not ignite; it rather underwent decomposition without the formation of flammable products. Room temperature specific conductivity was ca. 2.5 mS cm−1. The activation energy of the conding process was ca. 9.0 kJ mol−1. Compatibility of the polymer electrolyte with metallic lithium and graphite anodes was tested applying the galvanostatic method. Charge transfer resistance for the C6Li → Li+ + e− anode processes, estimated from EIS curve, was ca. 48 Ω. The graphite anode capacity stabilizes at ca. 350 mAh g−1 after the 30th cycle (20 mA g−1).

The interest of 2D materials is constantly increasing because of their very attractive mechanical, electrical and optical parameters. They have been used in many applications, e.g. photodetectors, sensors, modulators, insulators. One of the recently discovered 2D materials is phosphorene. In contrast to graphene, phosphorene has a direct bandgap tuned by numbers of layers in the 2D structure. The phosphorene flakes are strongly anisotropic. This study presents the detailed optical properties of electrochemically obtained phosphorene flakes versus centrifugation speed. A layer of phosphorene on a silicon wafer changes with increased centrifuge speed. A relationship that combines the size of the phosphorene flakes and ellipsometric angles, as well as the transmittance data obtained on a spectrophotometer was received. Hence, such an approach could allow for non-contact comparing the size of phosphorene flakes.

Black phosphorus is a 2D material, which properties are still being discovered. In this paper, the sensitivity to the temperature of a few-layer black phosphorus coating deposited, on the surface of a microsphere-based fiber-optic sensor, by a dip-coating method is presented. The coating was investigated after 2, 3, and 5 deposition cycles and during temperature growth from 50 °C to 300 °C in an interferometric setup. The intensity of the reflected signal increases with each applied layer. During the investigation of the thermal properties, in the range of 50 °C–200 °C, the polynomial growth rate of the reflected signal can be observed, whereas, for the temperatures over 200 °C, the measured peak intensity of the reflected signal stabilizes at a nearly constant level.

Few and monolayer black phosphorus is currently intensively resaearch due to its excellent mechanical, electrical and optical properties [1]. Its application in the area of biosensors is a result of low cytotoxic cell-viability effects and excellent cytocompatibility [2]. Phosphorene has much higher surface to volume ratio compared to graphene and transition metal dichalcogenides. “Puckered” lattice structure and direct and tunable band gap of phosphorene distinguish it from other 2 D materials. These properties are advantages in sensing applications [3]. The major hurdle for phosphorene in processing and application is its fast oxidation and degradation in ambient conditions. Simultaneous disposition of light, oxygen and water causes the aging process [4,5]. The covalent and noncovalent functionalization of 2D black phosphorus with organic molecular materials is a very common approach that is used to protect its surface from air degradation and also to tailor its electrical properties [3]. Anthraquinone derivatives such as 1,4-diamino-9,10-anthraquinone (1,4DA-9,10-AQ) have an extended π-electron system that can increase the strength of noncovalent attractions. Anthraquinone (AQ) is a redox active small organic molecule frequently utilized for electrochemical labeling of biomolecules or providence of additional charge storage capacity [6]. In this study, we present an electrochemical performance of covalently and noncovalently functionalized few-layer black phophorus by 4-azidobenzoic acid [7] and anthraquinone derivatives, respectively. The few-layer back phosphorus were obtained by liquid phase exfoliation in the anhydrous N.N-dimethylformamide. Next, the resultant suspension was centrifuged to remove the residual un-exfoliated particles, yielding supernatant. We functionalized few-layer black phosphorus (FLBP) by direct bonding of the phosphorus atom bearing lone electron pair with nitrogen during reaction with 4-azidobenzoic acid, leading to the formation of P=N double bonds, which passivate the reactive FLBP effectively. A covalent combining few-layered black phosphorus (FLBP) with 4-azidobenzoic acid can function as a bridge between FLBP and biomolecules. The functionalized phosphorene (f-FLBP) results in the possibility of using it as a biosensor platform for the detection of Heamophillus Influenza - one of the most common bacteria that cause infections in humans [8]. The detection of Haemophilus Influenzae was carried out by the electrochemical impedance spectroscopy (EIS) method. The changes of the charge transfer resistance were associated with the variation in bacteria protein concentration. The biosensor of bacteria has been prepared in several steps: phosphorene preparation, functionalization with 4-azidobenzoic acid, followed by coating with an antibody layer. The limit of detection achieved was 5.82 µg mL-1, while the Haemophilus Influenzae bacterial protein determination sensitivity was equal to 1.2763%µg-1 mL. The developed electrochemical biosensor displayed a wide linear range from 3.37∙10−6 to 3.37 µg mL−1 for the determination of Haemophilus Influenzae bacterial protein. Noncovalent functionalization of FLBP was performed by drop casting method on glassy carbon (GC) electrode. The GC electrode with FLBP on the surface was immersed in a methanol solution of 1,4DA-9,10-AQ for two hours. Next, the noncovalently functionalized FLBP with 1,4DA-9,10-AQ (f-FLBP) was washed distilled water and dried under vacuum. The electrochemical properties of f-FLBP electrode such as stability, potential window, dependence of electrochemical properties on pH, electron transfer were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Additionally the electrodes were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). The obtained non-covalently functionalized FLBP was used for electrochemical detection of ascorbic acid by differential pulse voltammetry. ACKNOWLEDGEMENTS This work was supported by the Polish National Science Centre [2016/22/E/ST7/00102]; and the National Centre for Science and Development [347324/12/NCBR/2017]. The DS funds of the Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged. References [1] Y. Yi, X. Yu, W. Zhou, J. Wang, P. K. Chu, Materials Science and Engineering: R: Reports, 120, 1–33 (2017) [2] H. Fu, Z. Li, H. Xie, Z. Sun, B. Wang, H. Huang, G. Han, H. Wang, P. K. Chu, X-F. Yu, RSC Adv., 7, 14618-14624 (2017) [3] A. Yang, D. Wang, X. Wang, D. Zhang, N. Koratkar, M. Rong, Nano Today, 20, 58-73 (2018) [4] J. Plutnar, Z. Sofer, M. Pumera, ACS Nano. 12, 8390–8396 (2018) [5] Q. Zhou, Q. Chen, Y. Tong, J. Wang, Angew. Chemie - Int. Ed. 55, 11437–11441 (2016) [6] R. Gusmão, Z. Sofer, M. Pumera, ACS Nano, 12, 5666-5673 (2018) [7] P. Jakóbczyk, M. Kowalski, M. Brodowski, A. Dettlaff, B. Dec, D. Nidzworski, J. Ryl, T. Ossowski, R. Bogdanowicz, Appl. Surf. Sci. 539, 148286 (2021) [8] C. Joseph, Y. Togawa, N. Shindo, Influenza and other Respiratory Viruses, 7, 105–113 (2013)

In this paper, various passivation schemes were applied at few-layer black phosphorus (FLBP) to achieve covalent functionalisation with 4-azidobenzoic acid, improving its electrochemical response intended for analytical and biosensing applications. The thermal and microwave assisted modification procedures in toluene and dimethylformamide resulted in high reversibility of reactions on functionalised FLBP using a ferricyanide/ferrocyanide redox probe. The lowest peak-to-peak separation of 91 mV, and high kinetics were obtained by thermal synthesis in dimethylformamide. Attachment of a = N-phenylene-COOH moiety to the FLBP limits its degradation under ambient conditions delivering a linker for a peptide bond with proteins in the NH2 groups. The functionalised FLBP was applied for impedimetric detection of the Haemophilus Influenzae (HI) bacterial protein with a low limit of detection (LOD) of 5.82 µg mL−1 along with high sensitivity equal to 1.267% µg−1 mL. The proposed strategy delivers a novel phosphorene-based electrode for sensitive detection of various bacterial pathogens.

Nanomaterials and assemblies of the aforementioned into complex architectures constitute an opportunity to design efficient and selective solutions to widespread and emerging environmental issues. The limited disposal of organic matter in modern landfills generates extremely concentrated leachates characterised by high concentrations of refractory compounds. Conventional biochemical treatment methods are unsuitable, while advanced treatment, such coagulation, reverse osmosis and ultrafiltration can be very costly and generate additional waste. Electrochemical oxidation is an established technique to efficiently mineralise a plethora of recalcitrant pollutants, however the selectivity and efficiency of the process are strongly related to the anode material. For this reason, a nanoarchitectured carbon material has been designed and synthesised to improve the capability of the anode towards the adsorption and decomposition of pollutants. Instead of simple nanostructures, intelligently engineered nanomaterials can come in handy for more efficient advanced treatment techniques. In this study, a carbon nanoarchitecture comprising boron-doped vertically aligned graphene walls (BCNWs) were grown on a boron-doped diamond (BDD) interfacial layer. The results show how the peculiar maze-like morphology and the concurrence of different carbon hybridisations resulted in a higher current exchange density. The BDD performed better for the removal of NH4+ while the BCNW-only sample exhibited a faster deactivation. The BDD/BCNW nanoarchitecture resulted in an enhanced COD removal and a NH4+ removal similar to that of BDD, without the intermediate production of NO2− and NO3−.

In the present study, a type of polymer electrolyte (PE) based on a polyacrylonitrile (PAN) polymer network, sulfolane, composite TiO2-SiO2 and vinylene carbonate (VC) as the solid-electrolyte interface (SEI) forming additive were prepared by the casting technique. Liquid electrolyte (LE) was the 1 M LiPF6 in sulfolane (TMS). The produced PE and LE working together with the LiFePO4 (LFP) and Li4Ti5O12 (LTO) was characterized by thermal gravimmetry (TG), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charging/discharging. PE had a high ionic conductivity of 9.8×10−4 S cm−1 at 25 °C (containing sub-microsize TiO2-SiO2 with vinyl groups of the surface—10% by weight). Charging/discharging capacity of the LFP │LE│LTO system was ca. 150 mAh g−1 (VC content 5 wt.%) (C/10 rate). This is much higher in comparison to that characteristic of LFP│PE│LTO cell—charging and discharging capacity stabilizes at a value of ca. 120 mAh g−1.

Properties of CF x /Li and CF x /Na cells were examined while using galvanostatic charging/discharging, electrochemical impedance spectroscopy and scanning electron microscopy (SEM). The capacity during the first cycle was as high as ca. 1000 mAh g−1. Such an electrode is suitable for primary CF x /Li and CF x /Na batteries. SEM images of CF x cathode showed that during discharging it was transformed into amorphous carbon and LiF or NaF crystals (of diameter of ca. 5–20 μm). These systems (C + LiF or C + NaF) cannot be reversibly converted back into CF x /Li or CF x /Na, respectively. Exchange current densities are between 10−7 Acm−2 and 10−9 Acm−2 when working with LiPF6 and NaPF6 electrolytes (1.12 × 10−7 Acm−2 and 6.82 × 10−9 Acm−2, respectively). Those values are low and indicate that the charge transfer process may be the rate-determining step. Activation energies for the charge transfer process were 57 and 72 kJ mol−1 for CF x /LiPF6 and CF x /NaPF6 systems, respectively. Higher activation energy barrier for the CF/Na+ + e− → C + NaF reaction results in lower observed exchange current density in comparison to the system with lithium ions.

A composite of aminosilane-grafted TiO2 (TA) and graphene oxide (GO) was prepared via a hydrothermal process. The TiO2/graphene oxide-based (TA/GO) anode was investigated in an ionic liquid electrolyte (0.7 M lithium bis(trifluoromethanesulfonyl)imide (LiNTf2)) in ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (MPPyrNTf2)) at room temperature and in sulfolane (1 M lithium hexafluorophosphate (LiPF6) in tetramethylene sulfolane (TMS)). Scanning and transmission electron microscopy (SEM and TEM) observations of the anode materials suggested that the electrochemical intercalation/deintercalation process in the ionic liquid electrolyte with vinylene carbonate (VC) leads to small changes on the surface of TA/GO particles. The addition of VC to the electrolyte (0.7 M LiNTf2 in MPPyrNTf2 + 10 wt.% VC) considerably increases the anode capacity. Electrodes were tested at different current regimes in the range 5–50 mA g−1. The capacity of the anode, working at a low current regime of 5 mA g−1, was ca. 245 mA g−1, while a current of 50 mA g−1 resulted in a capacity of 170 mA g−1. The decrease in anode capacity with increasing current rate was interpreted as the result of kinetic limits of electrode operation. A much lower capacity was observed for the system TA/GO│1 M LiPF6 in TMS + 10 wt.% VC│Li.

Analysis of literature values of electrolyte flammability parameters does not show any correlation. This can be interpreted as a result of electrolyte flame risk being characterized by different research teams applying incomparable experimental methods. Therefore, in order to obtain a consistent set of data five different safety (flammability) parameters, i.e. flash point Fp (the open cup method), self-extinguishing time SET, flame propagation time FPT, flame propagation velocity FPV and differential scanning calorimetry (DSC) peak temperature, were measured in the same way for 33 electrolytes or solvents applied in lithium-ion batteries. No correlation was found between SET and FPV, SET and FPT, SET and Fp as well as DSC data with all the other parameters. However, on the FPT vs Fp and FPV vs Fp plots two electrolyte groups were seen. The first group consists of liquids based on dimethyl carbonate and diethyl carbonate, characterized by the lowest Fp values (Fp ≤ 29 °C). The other systems belong to the second group of liquid systems (58 °C ≤ Fp ≤ 91 °C). A general conclusion is that determination of flammability parameters in a standardized way can lead to a correlation between at least three of them: flash point, flame propagation velocity and flash propagation time.

The interest of phosphorene as 2D material is high due to its excellent mechanical, electrical and optical properties [1]. However, the possibility of its application in the area of biosensors is a result of low cytotoxic cell-viability effects and excellent cytocompatibility [2]. Phosphorene has much higher surface to volume ratio compared to graphene and transition metal dichalcogenides. This due to its “puckered” lattice structure. These properties are advantages in sensing applications [3]. But puckered layer is quite reactive to oxygen and water adsorbed on the surface of phosphorene [4]. One way to change it and improve the ambient stability of layered black phosphorus is to modify the surface so that covalently or non-covalently attached chemical compounds passivate the surface to prevent damage [4, 5]. The biosensing device consists of chemical part and biological unit with unique specifities towards corresponding analytes for example proteins. In this work the biosensor of bacteria has been prepared in several steps: phosphorene preparation, functionalization with 4-azidobenzoic acid, followed by coating with an antibody layer. Phosphorene (few layered black phosphorus, FLBP) was prepared from pre-crushed black phosphorus (BP) dispersed in anhydrous dimethylformamide or toluene under an argon atmosphere by the liquid exfoliation. Afterwards, the resultant suspension was centrifuged to remove the residual un-exfoliated particles, yielding supernatant. We functionalized few layered black phosphorus (FLBP) by direct bonding of the phosphorus atom bearing lone electron pair with nitrogen during reaction with 4-azidobenzoic acid, leading to the formation of P=N double bonds, which passivate the reactive FLBP effectively. A covalent combining few-layered black phosphorus (FLBP) with 4-azidobenzoic acid can function as a bridge between FLBP and biomolecules. The functionalized phosphorene (f-FLBP) results in the possibility of using it as a biosensor platform for the detection of Heamophillus Influenza - one of the most common bacteria that cause infections in humans [6, 7]. It is very important to determine the presence of a given bacterial strain, because nowadays strains resistant to numerous antibiotics are more and more often observed. In the US alone, antibiotic-resistant bacteria cause at least 2 million infections and 23,000 deaths per year, which cause losses of 55-70 billion dollars a year [8]. The efficient functionalization of BP flakes was revealed by infrared spectroscopy. The cyclic voltammetry and electrochemical impedance spectroscopy measurements were carried out in Na2SO4 solution containing reference redox systems: [Fe(CN)6]3−/4−. Heamophillus Influenza bacteria were detected by the impedimetric method. The changes of the charge transfer resistance (Rct) can be attributed to the selective protein binding on the surface of the electrode. This was preceded by the attachment of antibodies to f-FLBP and obtaining a stable sensory surface. The procedure is shown in Figure 1. Consequently: - the benzoic groups enhance electric conductivity delivering fast direct electron transfer. - antibody-coated functionalized phosphorene were used to detect a bacteria (Haemophilus influenzae). - modified FLBP can work as surface for determination of organic molecules, e.g., nucleic acid bases or peptides and proteins, while it offers the promising possibility for biosensing. ACKNOWLEDGEMENTS This work was supported by the Polish National Science Centre [2016/22/E/ST7/00102]; and the National Centre for Science and Development [347324/12/NCBR/2017]. The DS funds of the Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged. References [1] Y. Yi, X. Yu, W. Zhou, J. Wang, P. K. Chu, Two-dimensional black phosphorus: Synthesis , modification, properties, and applications, Materials Science and Engineering: R: Reports, 120, 1–33 (2017); doi: 10.1016/j.mser.2017.08.001 [2] H. Fu, Z. Li, H. Xie, Z. Sun, B. Wang, H. Huang, G. Han, H. Wang, P. K. Chu, X-F. Yu, Different-sized black phosphorus nanosheets with good cytocompatibility and high photothermal performance, RSC Adv., 7, 14618-14624 (2017); doi: 10.1039/C7RA00160F [3] A. Yang, D. Wang, X. Wang, D. Zhang, N. Koratkar, M. Rong, Recent advances in phosphorene as a sensing material, Nano Today, 20, 58-73 (2018); doi: 10.1016/j.nantod.2018.04.001 [4] R. Gusmão, Z. Sofer, M. Pumera, Functional Protection of Exfoliated Black Phosphorus by Noncovalent Modification with Anthraquinone, ACS Nano, 12, 5666-5673 (2018), doi: 10.1021/acsnano.8b01474 [5] C. Joseph, Y. Togawa, N. Shindo, Bacterial and viral infections associated with influenza, Influenza and other Respiratory Viruses, 7, 105–113 (2013); doi: 10.1111/irv.12089 [6] S. K. Morris, W. J. Moss, N. Halsey, Haemophilus influenzae type b conjugate vaccine use and effectiveness, The Lancet Infectious Diseases, 8, 435-443 (2008); doi: 10.1016/S1473-3099(08)70152-X [8] B. Li, T. J. Webster, Bacteria Antibiotic Resistance: New Challenges and Opportunities for Implant-Associated Orthopaedic Infections, J Orthop. Res., 36, 22-32 (2017); doi: 10.1002/jor.2365 Figure 1

Electrochemical sensors have attracted increasing interest due to their low cost, high sensitivity of detected analytes, and the possibility of sensor miniaturization, which allows for portable and field applications. These devices provide information about the system composition in real-time by combining a chemically selective layer with an electrochemical transducer. Thereby, the chemical energy of the specific interaction between the chemical substances and the sensor is converted into an analytically useful signal. Herein we demonstrate the electrochemical sensor based on boron-doped diamond/graphene nanowall electrodes (B:DGNW). A B:DGNW electrode is a hybrid electrode, which combines the extraordinary features of boron-doped diamond and a graphene nanowall on the same surface. B:DGNW is a sp2 -rich phase material with multilayered graphene walls oriented vertically to the substrate. Moreover, the presence of the boron-doped diamond phase enhances the electrochemical performance and kinetics of the electrode surface when compared with typical carbon nanowalls. The electrodes were fabricated in a one-step growth process using chemical vapor deposition without any additional modifications (thin films were grown on (100)-oriented silicon substrates). Two different sensing platforms will be presented: i) impedimetric biosensor for detection of pathogenic bacteria (e.g., Haemophilus influenzae), and ii) voltammetric sensor for determination of important nitroaromatic explosive compounds (2,4,6-trinitrotoluene (TNT), 2,4,6-trinitroanisole (TNA), 4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole (TNBI)). The proposed B:DGNW electrodes were revealed to have a high electroactive area towards the voltammetric detection of various nitroaromatic compounds. The biosensor platform was obtained by B:DGNW surface functionalization firstly by electrografting of diazonium salt and secondly by the attachment of antibodies. The electrochemical biosensor shows high sensitivity and selectivity towards Haemophilus influenzae. The measurements were conducted in the presence of three non-target pathogens S. pyogenes, S. pneumoniae, and B. parapertussis. The proposed B:DGNW nonmodified carbon electrodes were revealed to have a high electroactive area towards the voltammetric determination of various nitroaromatic compounds, thus appearing to be an attractive nanocarbon surface for further applications. The B:DGNW electrode exhibits high sensing performance for TNT detection with linearity between 0.05 to 2 ppm and 4 to 15 ppm, and a limit of detection (LOD) of 73 ppb. The LOD for 2,4,6-trinitroanisole, in turn, is equal to 0.27 ppm, whereas the limit of detection of TNBI is equal to 0.52 ppm. To the authors' knowledge, this is the first time B:DGNW has been used to detect the nitroaromatic compounds electrochemically [1]. Acknowledgment This work was supported by the Science for Peace Programme of NATO [Grant no. G5147], Polish National Science Centre [2016/22/E/ST7/00102], and the National Centre for Science and Development [347324/12/NCBR/2017]. The DS funds of the Faculty of Electronics, Telecommunications, and Informatics of the Gdansk University of Technology are also acknowledged. Reference: [1] A. Dettlaff et al., J. Hazard. Mater [In press]. Doi: 10.1016/j.jhazmat.2019.121672.

The study is devoted to the electrochemical detection of trace explosives on boron-doped diamond/graphene nanowall electrodes (B:DGNW). The electrodes were fabricated in a one-step growth process using chemical vapour deposition without any additional modifications. The electrochemical investigations were focused on the determination of the important nitroaromatic explosive compounds, 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitroanisole (TNA). The distinct reduction peaks of both studied compounds were observed regardless of the pH value of the solution. The reduction peak currents were linearly related to the concentration of TNT and TNA in the range from 0.05–15 ppm. Nevertheless, two various linear trends were observed, attributed respectively to the adsorption processes at low concentrations up to the diffusional character of detection for larger contamination levels. The limit of detection of TNT and TNA is equal to 73 ppb and 270 ppb, respectively. Moreover, the proposed detection strategy has been applied under real conditions with a significant concentration of interfering compounds – in landfill leachates. The proposed bare B:DGNW electrodes were revealed to have a high electroactive area towards the voltammetric determination of various nitroaromatic compounds with a high rate of repeatability, thus appearing to be an attractive nanocarbon surface for further applications.

The general aim of the present paper was to compare and correlate factors describing operation rate limits of electrochemical double layer capacitors (EDLCs), under both ac and dc conditions. Six laboratory-made and six commercial EDLCs were investigated with the use of electrochemical impedance spectroscopy (EIS) and galvanostatic charging/discharging. A typical EIS spectrum, taken under ac conditions, consisted of two straight lines. The intersection of both straight lines indicates the frequency (transition frequency ftr) at which the device loses its capacitive properties. Similarly, during dc charging/discharging the I(dU/dt)−1 value (often called EDLCs capacitance), expressed as a function of the current I, also shows two straight lines. The intersection of the lines indicates a transition current Itr and the corresponding (dU/dt)tr voltage changes rate. A linear correlation was found between transition parameters determined under ac and dc conditions ((Redrftr)−1 and Itr(dU/dt)tr−1), with a high correlation parameter r2 = 0.99. The correlation enables estimation of the limiting operation rate of EDLCs under dc conditions based on the analysis of ac impedance spectroscopy curves.

The general aim of the present study was to conduct phenomenological investigation of EDLCs capacitance ‘stability’ under direct current conditions. Commercial EDLCs and laboratory test-devices were tested from the point of view of their ‘capacitance’ stability. Changes of potential with time during EDLCs galvanostatic charging/discharging (constant current I ) had linear character, typical of capacitors. Values of I (Δ U /Δ t ) −1 should be the same at each time, indicating the device capacitance C . However, analysis of galvanostatic charging/discharging data showed that I (Δ U /Δ t ) −1 values were not constant during the process. Current flowing through the circuit during EDLC cyclic voltammetry experiments, may be almost constant, but I (Δ U /Δ t ) −1 (pointing to the capacitance value) changed significantly. When a capacitor was discharged through a resistor, the following function of time t , resistance R and potential U should be constant: t / R ln( U 0 / U ) and equal device capacitance C . However, t / R ln( U 0 / U ) values calculated from discharge curves were not constant. Changes were considerably high at the beginning of the discharge. The substantial instability of ‘capacitance’ value during the operation of EDLCs suggests that it can hardly be used as the proportionality constant between energy accumulated by an EDLC and the voltage in the second power.

Spontaneous voltage drop between EDLC electrodes, when it is kept under the open-circuit condition, is commonly called 'self-discharge' and is interpreted as a result of energy loss by the device. Three mechanisms of self-discharge were proposed: due to a leakage-current, faradaic reactions and charge redistribution. According to the law of energy preservation, if the voltage drop is associated with the energy loss, the energy would more likely be exchanged with the environment. While heat generation was measured during EDLC charging and discharging, the corresponding effect during storage under open-circuit conditions has not been reported. This may support the conclusion that voltage changes during 'self-discharge' are not related to a considerable energy loss. Moreover, it has been shown that a two-stage charging process, i.e. first galvanostatic charging followed by a potentiostatic charge redistribution, resulted in considerably slower potential changes when the device was switched to the open circuit. All discussed models were based on the assumption that the energy accumulated by EDLCs is proportional to the voltage in the second power, with capacitance (C/2) as the proportionality constant. However, it has been shown that during EDLC charging or discharging through a resistance R, equations valid for 'dielectric' and electrolytic capacitors, do not hold in the case of EDLCs. Consequently, the assumption that the energetic state of the EDLC is proportional at any time to the voltage in the second power may not be valid due to considerable variability of the 'constant' C. Therefore, voltage changes may not reflect the energetic state of the device.

Eight commercial 10F electrochemical double-layer capacitors (EDLCs) were connected together and placed in a container filled with mineral oil. The whole system was placed into a Dewar container. Temperature variation and heat exchanged between the test EDLC and the environment during its charging, discharging, and “self-discharge” were measured, together with voltage U changes. Charge separation during charging was equivalent to a transition into a more ordered system, which results in entropy decrease, while discharging caused entropy increase (the Peltier–Seebeck effect). Consequently, a number of charging/discharging cycles led to a corresponding series of entropy and temperature changes. The final shape of temperature versus time curve during charging/discharging cycles was due to overlapping of irreversible Joule–Lenz and reversible Peltier heats. When charged EDLC was kept under the open-circuit condition, measured heat flow was negligible in comparison to energy loss calculated from potential drop, assuming that energy E accumulated is proportional at any time to voltage to the second power (i.e., E ~ U2). The result was interpreted assuming that the EDLC “self-discharge” phenomenon is not associated with energy loss by the device, but rather with charge redistribution between EDLC particles characterized by different time constants.

The graphene anode was investigated in an ionic liquid electrolyte (0.7 M lithium bis(trifluoromethanesulfonyl)imide (LiNTf2)) in room temperature ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (MPPyrNTf2)). SEM and TEM images suggested that the electrochemical intercalation/deintercalation process in the ionic liquid electrolyte without vinylene carbonate (VC) leads to small changes on the surface of graphene particles. However, a similar process in the presence of VC results in the formation of a coating (SEI—solid electrolyte interface) on the graphene surface. During charging/discharging tests, the graphene electrode working together with the 0.7 M LiNTf2 in MPPyrNTf2 electrolyte lost its capacity, during cycling and stabilizes at ca. 200 mAh g−1 after 20 cycles. The addition of VC to the electrolyte (0.7 M LiNTf2 in MPPyrNTf2 + 10 wt.% VC) considerably increases the anode capacity. Electrodes were tested at different current regimes: ranging between 50 and 1,000 mA g−1. The capacity of the anode, working at a low current regime of 50 mA g−1, was ca. 1,250 mAh g−1, while the current of 500 mA g−1 resulted in capacity of 350 mAh g−1. Coulombic efficiency was stable and close to 95 % during ca. 250 cycles. The exchange current density, obtained from impedance spectroscopy, was 1.3 × 10−7 A cm−2 (at 298 K). The effect of the anode capacity decrease with increasing current rate was interpreted as the result of kinetic limits of the electrode operation.