Graphite Plate Electrodes Research Articles

Novel strategy for cathode in iron-lead single-flow battery: Electrochemically modified porous graphite plate electrode

Porous electrodes play a pivotal role in shaping the electrochemical performance, cost, and the assembly complexity of redox flow batteries. In this paper, the effects of porous structure on the electrochemical performance of graphite electrodes are first studied. Subsequently, a low-cost, high-performance graphite plate cathode is developed for redox flow battery using controlled electrochemical corrosion as a facile and effective electrode modification method. As a result, the electrochemical performance of the porous graphite electrode is significantly enhanced, and a revolutionary design of the iron‑lead single-flow battery is implemented by substituting graphite felt cathode with the modified porous graphite plate electrode. The iron‑lead battery with modified flat graphite plate cathode demonstrates high energy efficiencies, ranging from 90.91 % to 77.13 % between 10 and 40 mA/cm2, comparable to those obtained with graphite felt cathode. By combining the anode, bipolar plate, and cathode into one piece of graphite plate, a novel stack design is achieved with significant thickness reduction of the unit cell from 9 mm to 3 mm, resulting in notably increased energy and power density, improved assembly efficiency and reduced components cost of stacks.

Investigation of microbial fuel cell performance based on the nickel thin film modified electrodes

Microbial fuel cells (MFCs) are a self-sustaining and environmentally friendly system for the simultaneous was tewater treatment and bioelectricity generation. The type and material of the electrode are critical factors that can influence the efficiency of this treatment process. In this study, graphite plates and carbon felt were modified through the electrodeposition of nickel followed by the formation of a biofilm, resulting in conductive bio-anode thin film electrodes with enhanced power generation capacity. The structural and morphological properties of the electrode surfaces were characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, elemental mapping, and field-emission scanning electron microscopy techniques. Maximum voltage, current density, and power generation were investigated using a dual-chamber MFC equipped with a Nafion 117 membrane and bio-nickel-doped carbon felt (bio-Ni@CF) and bio-nickel-doped graphite plate (bio-Ni@GP) electrodes under constant temperature conditions. The polarization and power curves obtained using different anode electrodes revealed that the maximum voltage, power and current density achieved with the bio-Ni@CF electrode were 468.0 mV, 130.72 mW/m2 and 760.0 mA/m2 respectively. Moreover, the modified electrodes demonstrated appropriate stability and resistance during successful runs. These results suggest that nickel-doped carbon-based electrodes can serve as suitable and stable supported catalysts and conductors for improving efficiency and increasing power generation in MFCs.

Fabrication of MnO<sub>2</sub> - based electrochemical electrodes for the determination of copper (II) ion in water

Porous MnO2 with a hexagonal crystalline structure was facilely prepared at a low hydrothermal temperature of 90°C, without using any template or capping agent. The as-prepared MnO2 only presented an exceptional electrocatalytic ability by the typical amperometric detection of copper (II) in the presence of super P carbon black as conducting agent, and Nafion as binder. In the present work, to evaluate the detection ability of copper (II) of the MnO2, the graphite plate electrodes (GPE) were modified with MnO2 microflowers and super P carbon and used as electrochemical electrodes for the determanation of copper (II) present in water sources. From the measured results, the fabricated electrodes with excellent copper detection and rapid response demonstrated has high application potential for electrochemical sensors in detection of copper in water resources.

A one-pot electrochemical synthesis of 2-aminothiazoles from active methylene ketones and thioureas mediated by NH4I.

The electrochemical preparation of 2-aminothiazoles has been achieved by the reaction of active methylene ketones with thioureas assisted by ᴅʟ-alanine using NH4I as a redox mediator. The electrochemical protocol proceeds in an undivided cell equipped with graphite plate electrodes under constant current conditions. Various active methylene ketones, including β-keto ester, β-keto amide, β-keto nitrile, β-keto sulfone and 1,3-diketones, can be converted to the corresponding 2-aminothiazoles. Mechanistically, the in situ generated α-iodoketone was proposed to be the key active species.

Effect of Electrode Type on Bacteria Removal and Chlorine and Radical Production in Electrochemical Water Disinfection

Formation and contamination of malicious microorganisms and viruses remain to be major problem of water resources. This is mostly due to the fact that, groundwater, which constitutes a large share of available fresh water content, is prone to contamination from urban and industrial wastes. In this work, electrochemical treatment is considered as a disinfection mechanism. The literature presents several cases of individual of electrochemical disinfection experiments. In this particular work, we aim to focus on the comparative disinfection efficiency of Boron-doped diamond electrodes, Iridium metal-oxide electrodes and Graphite plate electrodes at various electrochemical settings, whilst monitoring formation of toxic bi-products, such as chlorine and other radicals. Experiments of electrochemical water disinfection were carried out on real groundwater samples deliberately contaminated with E. coli culture. During the reaction, microorganisms die due to both direct physical damage and due to the electrochemically generated radicals. Therefore, there is a gentle balance of bacteria elimination versus avoiding excessive radical production in the treated water. Since the biological behaviour of the microorganisms and the chemical properties of the available groundwater cannot be changed, the research parameters boil down to experimenting through various popular electrode types and electrical current settings. In both continuous-flow and recursive systems, the Boron-doped diamond electrodes are observed to provide desirable level of disinfection (as good as Iridium metal-oxide), while yielding lower radicals (as low as those of Graphite-plate), making an ideal compromise for the process.

Biodiesel production from the Chlorella vulgaris and Spirulina platensis microalgae by electrolysis using CaO/KOH-Fe3O4 and KF/KOH-Fe3O4 as magnetic nanocatalysts

Based on the results from recent studies on biodiesel production, in addition to cost reduction, the electrolysis method has both quantitative and qualitative advantages over the reflux method. Thus, in this study, biodiesel was produced by the electrolysis of the oil of two sea microalgae strains, namely Chlorella vulgaris and Spirulina platensis, using methanol and prepared CaO/KOH-Fe3O4 and KF/KOH-Fe3O4 magnetic nanocatalysts. At the first step, magnetic nanocatalysts were prepared, Scanning electron microscope and X-ray diffraction patterns of the prepared nanocatalysts were studied, and the calculated average crystal size of CaO/KOH-Fe3O4 and KF/KOH-Fe3O4 was 55.91 nm and 42 nm, respectively. Brunauer-Emmett-Teller analysis was performed for the determination of the active surface area. Then, two types of mentioned nonfood microalgae were cultured, and the oil of them was extracted. The most suitable microalgae between these two types with regard to the culture condition was chosen for the last step. Then, electrolysis technique contains two graphite plate electrodes (3 cm × 3 cm) that are separated by a distance of 2 cm and potential difference of 54 V with the electrolysis cell which was filled with 100 mL of reaction mixture containing methanol, the aforementioned microalgae oil, Tetrahydrofuran (THF), water, and nanocatalysts was performed for biodiesel production. The effect of catalyst weight percentage (1, 1.5, 2 wt%), molar ratio of alcohol to oil (5:1, 6:1, 7:1), and the reaction time (30, 60, 120, 180 min) in the efficiency of biodiesel production was investigated, and the physical properties of the prepared biodiesel were quantified. Based on the results, Chlorella vulgaris microalgae because of the more obtainable oil shows the priority of microalgae over Spirulina platensis and KF/KOH-Fe3O4 is an optimal choice catalyst for biodiesel production. The optimal condition was using 1.5 wt% of catalyst, methanol/oil molar ratio of 1:6, temperature of 25 °C, stirring speed of 400 rpm, and the reaction time of 2 h. Furthermore, B20 was prepared using the obtained biodiesel, and the quality was in accordance with the world standard of fuel ASTM D975, with the process yield of 96.8%, and no saponification side reaction, and KF/KOH-Fe3O4 showed the higher mass yield in transesterification reaction.

Gradient-microstructural porous graphene gelatum/flexible graphite plate integrated electrode for vanadium redox flow batteries

A novel 3D electrochemically reduced graphene oxide (ERGO) porous gelatum material was self-assembled on graphite plate (GP) by the simple and controllable electrodeposition method to construct a new-type integrated electrode (ERGO-GP) for all vanadium redox flow batteries (VRFBs). Benefited from the ideal preparation method, a porous and gradient microstructure of ERGO was formed easily and facilitated the electrolyte, ions and electron transport simultaneously. Besides, the direct growth of ERGO on GP could reduce the contact resistance between the reaction layer and the conduction layer effectively. As a result, the electrochemistry and battery performance for the ERGO-GP as both negative and positive electrode of VRFBs were better than the common carbon felts (CF) and GP electrode system (CF-GP) due to the lower polarization. The obtained results also indicated the great promise of this material for application in other flow redox batteries and helped us to improve the design of carbon-based porous electrodes.

Sal wood sawdust derived highly mesoporous carbon as prospective electrode material for vanadium redox flow batteries

This work reports the development of a prospective electrode material for the use in vanadium redox flow batteries. The developed electrode material was a high surface area activated carbon (1857m2g−1) with a large mesoporosity (1280m2g−1) that was derived using biomass residues, Sal wood sawdust (Shorea robusta), as a feedstock. The physico-chemical and electrochemical properties of Sal wood sawdust activated carbon were extensively characterized applying cyclic voltammetry and electrochemical impedance spectroscopy. The graphite plate electrode based on Sal wood sawdust activated carbon exhibited higher electro-catalytic activity and lower charge transfer resistance towards both positive and negative redox couples than when applying pristine graphite plate electrode. Further investigations on the application of static cell at higher current densities (20–80mAcm2) revealed higher efficiencies for the Sal wood sawdust activated carbon modified graphite plate electrode in comparison with the pristine graphite plate electrode. Thus, the Sal wood sawdust can be suitable as carbon precursor for preparation of electrodes to be utilized in practical applications, such as in vanadium redox flow batteries.

Investigation on Lithium Isotope Fractionation with Diffusion, Electrochemical Migration, and Electrochemical Isotope Effect in PEO-PC Based Gel Electrolyte

Lithium isotope fractionation, based on the difference of the diffusion coefficients, migration mobility, as well as the electrochemical isotope effect, can be achieved in the appropriate solvents. The Propylene Carbonate-Polyethylene Oxide gel electrolyte was utilized to separate Li isotopes by eliminating the fluid flow mixing and part of the solvation shell around Li ions. A higher Li isotope fractionation (△7Li = −4.53‰) was achieved with the effects of both diffusion and electrochemical migration in a long 10-cm cell test. Also, a short 2-cm cell gel electrolyte short duration test yielded a very high separation factor of 1.033, which is a very promising separation factor for Li isotope separation. Similarly, the electrochemical intercalation test into the graphite plate electrode associated with the diffusion and migration assisted separation shows a separation factor of 1.033. Influence of the electrochemical cell length was studied with an electrochemical model, and results show that an appropriate cell length needs to be determined by considering both the separation time and the separation factor.

Algal biomass derived biochar anode for efficient extracellular electron uptake from Shewanella oneidensis MR-1

The development of cost-effective and highly efficient anode materials for extracellular electron uptake is important to improve the electricity generation of bioelectrochemical systems. An effective approach to mitigate harmful algal bloom (HAB) is mechanical harvesting of algal biomass, thus subsequent processing for the collected algal biomass is desired. In this study, a low-cost biochar derived from algal biomass via pyrolysis was utilized as an anode material for efficient electron uptake. Electrochemical properties of the algal biochar and graphite plate electrodes were characterized in a bioelectrochemical system (BES). Compared with graphite plate electrode, the algal biochar electrode could effectively utilize both indirect and direct electron transfer pathways for current production, and showed stronger electrochemical response and better adsorption of redox mediators. The maximum current density of algal biochar anode was about 4.1 times higher than graphite plate anode in BES. This work provides an application potential for collected HAB to develop a cost-effective anode material for efficient extracellular electron uptake in BES and to achieve waste resource utilization.

Improvement of the Borohydride Oxidation Reaction by Electrocatalysis on Pt/[TaOPO4/VC

Direct borohydride fuel cells (DBFCs) are a possible high energy source because a complete borohydride oxidation reaction (BOR) can provide up to 8 electrons per BH4 - anion that may result in high energy density. However, complete electrooxidation in a DBFC is challenging to achieve for a number of reasons. The BOR (BO2 -(aq) + 6H2O + 8e- ↔ BH4 -(aq) 8OH-, Eo=-1.24 vs. SHE) has a complex reaction mechanism that can result in a number of intermediate species (BHx­,ads or BHx­OH, x = 1 to 3), hydrogen gas (H2), adsorbed hydrogen (Hads) and solid borates.1 Hydrolysis of BH4 - (BH4 -(aq) + 2H2O → BO2 -(aq) + 4H2) can occur, reducing the availability of BH4 - for complete oxidation and the resulting H2 may compete with intermediate species for electrooxidation. The escape of reaction species, including unutilized H2, from the electrocatalyst surface prior to complete electrooxidation results in incomplete BOR and varied concentrations as the fuel proceeds along the flow field towards the outlet.2 It is therefore desirable to have catalyst layers capable of utilizing all reaction species and intermediates that need to be oxidized along with having a limited affinity for heterogeneous hydrolysis of BH4 -­. To date, no single electrocatalyst has been found to effectively utilize all BOR species alone and any cell design will likely require variable and/or graded catalyst compositions along the flow channel as well as electrocatalysts capable of H2 electrooxidation. In this study, we examine single and graded catalyst compositions in a well-characterized liquid flow hydrogen peroxide DBFC (H2O2-DBFC) design.3 Either a single carbon-supported catalyst, mixture or in-plane gradient of catalysts are deposited directly onto bipolar graphite plate (BGP) electrodes at the anode by ultrasonic spray deposition. Linear single flow channels are used at the cathode and anode separated by a Nafion® 117 membrane prepared for Na+ exchange. Performance and reaction mechanisms of the electrocatalysts are tested under variable experimental conditions using chronoamperometry (CA), rotating disk electrode (RDE) voltammetry, electrochemical impedance spectroscopy (EIS) and H2 escape measurements. The polarization curves of the DBFC with anodes composed of carbon supported Pt (Pt/C) and/or Pd (Pd/C) can be improved by creating a gradient of the electrocatalysts (Figure 1, for ~22 ºC and a low BH4 - concentration (10mM)).4 Pt/C has the best performance at high cell potentials (low overpotentials), while Pd/C has superior performance at lower cell potentials (high overpotentials). Cell performance improves at lower cell potentials when catalysts are graded, where a mixture of the catalysts perform similarly to Pt/C alone. The experiments carried out at varied cell conditions give further insight into BOR mechanisms at the anode catalyst layer using this DBFC configuration. This presentation will discuss the performance of such graded electrodes under more relevant fuel cell conditions of 60 ºC and 100 mM NaBH4.Figure 1: Polarization curves of Pd/C (a, black), Pt/C (a, red), mixed Pt/C and Pd/C (b, blue) and graded Pd/C to Pt/C (b, gold).4 References P.-Y. Olu, A. Bonnefont, M. Rouhet, S. Bozdech, N. Job, M. Chatenet and E. Savinova, Electrochemica Acta, 179, 637 (2015).R. O. Stroman and G. S. Jackson, Journal of Power Sources, 247, 756 (2014).R. O. Stroman, G. S. Jackson, Y. Garsany and K. Swider-Lyons, Journal of Power Sources, 271, 421 (2014).R. M. E. Hjelm, Y. Garsany, R. W. Atkinson III, R. O. Stroman, K. Swider-Lyons, C. Lafforgue and M. Chatenet, ECS Transactions, 2017. 80(8): p. 1033-1042. Figure 1

Decolorization of Reactive Black 5 and Reactive Blue 4 Dyes in Microbial Fuel Cells.

Microbial fuel cells (MFCs) have potential to treat industrial wastewater containing organic compounds and simultaneously generate power. Organic compounds include textile dyes with various chromophore groups, which can be decolorized reductively by microorganisms under anaerobic conditions. In the present study, we examined the decolorization of Reactive Black 5 (RB5) azo dye and Reactive Blue 4 (RBL4) anthraquinone dye under open circuit potential in MFCs with graphite plate and graphite felt electrodes and a microbial consortium originally derived from bovine rumen fluid. RB5 dye was more than 90% decolorized in 120, 165, and 225min at 50, 100, and 200mgL-1 concentrations, respectively. RBL4 dye at 50 and 100mgL-1 took 225 and 300min to decolorize, while 200mgL-1 RBL4 dye was not decolorized at all. Under closed circuit conditions, decolorization increased with decrease in external load, whereas current generation increased with external resistance. The results demonstrate that the reductive cleavage of the chromophore was more rapid with RB5 than with RBL4.

Study of ethanol electrooxidation onto expanded graphite supported Pt

In this paper two types of electrode materials, graphite and expanded graphite as support material have been used. The graphite plate electrode was expanded by doping with potassium (K)-vapour using vapour incorporation technique. After that the expanded graphite and normal graphite electrodes were platinised by simple galvanostatic electro-deposition technique. In this article catalytic activities of the electrodes towards ethanol have been measured using cyclicvoltammetry technique at different scan rates and amperometry technique. It is observed that anodic peak potentials as well as the corresponding peak currents changed with scan rate. It is also found that oxidation current of the alcohol using the expanded graphite as the support material are higher. Amperometry studies shows that expanded support electrocatalyst is more durable than unexpanded support electrocatalyst. So Pt deposited on potassium expanded graphite acts as a better electrocatalyst.

In situ formation of graphene layers on graphite surfaces for efficient anodes of microbial fuel cells.

Graphene can be used to improve the performance of the anode in a microbial fuel cell (MFC) due to its good biocompatibility, high electrical conductivity and large surface area. However, the chemical production and modification of the graphene on the anode are environmentally hazardous because of the use of various harmful chemicals. This study reports a novel method based on the electrochemical exfoliation of a graphite plate (GP) for the in situ formation of graphene layers on the surface of a graphite electrode. When the resultant graphene-layer-based graphite plate electrode (GL/GP) was used as an anode in an MFC, a maximum power density of 0.67 ± 0.034 W/m(2) was achieved. This value corresponds to 1.72-, 1.56- and 1.26-times the maximum power densities of the original GP, exfoliated-graphene-modified GP (EG/GP) and chemically-reduced-graphene-modified GP (rGO/GP) anodes, respectively. Electrochemical measurements revealed that the high performance of the GL/GP anode was attributable to its macroporous structure, improved electron transfer and high electrochemical capacitance. The results demonstrated that the proposed method is a facile and environmentally friendly synthesis technique for the fabrication of high-performance graphene-based electrodes for use in microbial energy harvesting.

Electricity Generation and Biofilm Formation in Microbial Fuel Cells Using Plate Anodes Constructed from Various Grades of Graphite

Construction materials as well as the electrode configuration are major factors affecting electricity generation in microbial fuel cells (MFCs). Three graphite plateelectrodes(HK06,G347andPOCO3)withdifferentcharacteristics(specificresistance,grainsizeandspecificgravity)wereusedtoevaluateelectricity generation and biofilm formation in MFCs. The electrodes were assessed by operating duplicate MFCs under the same conditions. Electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry were used to evaluate the performance of the electrodes. The data indicated the grade of electrode played a critical role in the MFCs performance. Higher power density was observed for the graphite electrode designated as POCO3. The trend for increasing electricity generation was as follows: POCO3 > G347 > HK06. Distinct microbial populations were detected in the biofilm community when comparing the different electrodes. Selecting electrodes for optimum electricity generation is important in the development of laboratory scale and full-scale MFCs.

Experimental and theoretical characterization of microbial bioanodes formed in pulp and paper mill effluent in electrochemically controlled conditions

Microbial bioanodes were formed in pulp and paper effluent on graphite plate electrodes under constant polarization at -0.3 V/SCE, without any addition of nutriment or substrate. The bioanodes were characterized in 3-electrode set-ups, in continuous mode, with hydraulic retention times from 6 to 48 h and inlet COD from 500 to 5200 mg/L. Current densities around 4A/m(2) were obtained and voltammetry curves indicated that 6A/m(2) could be reached at +0.1 V/SCE. A theoretical model was designed, which allowed the effects of HRT and COD to be distinguished in the complex experimental data obtained with concomitant variations of the two parameters. COD removal due to the electrochemical process was proportional to the hydraulic retention time and obeyed a Michaelis-Menten law with respect to the COD of the outlet flow, with a Michaelis constant KCOD of 400mg/L. An inhibition effect occurred above inlet COD of around 3000 mg/L.

Decolorization Treatment of Copper Phthalocyanine Textile Dye Wastewater by Electrochemical Methods

Electrochemical decolorization and degradation treatment of aqueous copper phthalocyanine reactive dye solutions was comparatively studied by electrocoagulation, electrooxidation and electro-Fenton processes. In the electrocoagulation process with aluminum electrodes the colored aqueous solutions of initial pH 6.4 containing 50 mg L-1 copper phthalocyanine and 6 g L-1 NaCl were treated at applied current densities of 2.5 and 5 mA cm-2. Fast and 100% decolorization was achieved in 4 and 2 minutes of electroprocessing respectively. The indirect electrooxidation process was conducted in acidic electrolyte solutions containing 50 mg L-1 copper phthalocyanine and 6 g L-1 NaCl with Ti/Pt and graphite plate electrodes at the applied current density of 10 mA cm-2. Even after 90 minutes of electrolysis time the dye remained by 23 and 18.8 % respectively undegradable. By the direct and indirect electrooxidation with the same amount of Na2SO4 electrolyte and added H2O2 respectively and using the same electrodes, the copper phthalocyanine dye was not or was only barely degraded respectively. In the electro-Fenton process with Fe electrodes and added amounts of H2O2 at pH 3 and an applied current density of 5 mA/cm2 complete degradation of copper phthalocyanine occurred in 15 minutes.

Lowering the applied potential during successive scratching/re-inoculation improves the performance of microbial anodes for microbial fuel cells

Microbial anodes were formed under polarisation at −0.2V/SCE on smooth graphite plate electrodes with paper mill effluents. Primary, secondary and tertiary biofilms were formed by a successive scratching and re-inoculation procedure. The secondary and tertiary biofilms formed while decreasing the polarisation potential allowed the anodes to provide current density of 6A/m2 at −0.4V/SCE. In contrast, applying −0.4V/SCE initially to form the primary biofilms did not lead to the production of current. Consequently, the scratching/re-inoculation procedure combined with progressive lowering of the applied potential revealed an efficient new procedure that gave efficient microbial anodes able to work at low potential. The observed progressive pH drift to alkaline values above 9 explained the open circuit potentials as low as −0.6V/SCE. The remarkable performance of the electrode at alkaline pH was attributed to the presence of Desulfuromonas acetexigens as the single dominant species in the tertiary microbial anodes.

Photoelectro-Fenton/nanophotocatalysis decolorization of three textile dyes mixture: Response surface modeling and multivariate calibration procedure for simultaneous determination

In this paper, we studied treatment of mixture of three azo dyes using homogeneous photoelectro-Fenton (PEF) combined with heterogeneous photocatalytic process (UV/TiO2). Carbon nanotube immobilized onto graphite plate (CNT/graphite) electrode was used as cathode. The investigated photocatalyst was TiO2 nanoparticles (Degussa P25) immobilized on glass plates. A rapid analytical methodology based on recording UV–Vis spectra during the photoelectro-Fenton/photocatalytic decolorization process and the data treatment using multivariate calibration methods such as partial least square (PLS) was developed. The three textile dyes (C.I. Acid Yellow 36 (AY36), C.I. Acid Red 14 (AR14) and C.I. Basic Yellow 28 (BY28)) were quantified simultaneously despite the overlap of their spectra. Also, the central composite design has been employed to the optimization of photoelectro-Fenton/photocatalytic decolorization of the dye solution containing three dyes using combined process. The factors (variables) investigated were the initial concentration of three dyes, initial amount of Fe3+ and reaction time. Results indicated that the optimum Fe3+ concentration was 0.15mM for decolorization process. Analysis of variance (ANOVA) showed that predicted values match the experimental values reasonably well with R2 of 0.965, 0.943 and 0.947 for AY36, AR14 and BY28, respectively. Three-dimensional surface plots have been used to present the relation between independent variables and dependent variable (response).

Electrosynthesis of SER-Active Silver Nanopillar Electrode Arrays

Here we report a one step electrochemical method for the deposition of pillar-like silver nanostructures on graphite plate electrodes. The devices were tested as SER-active electrode arrays using covalently attached hemin. The nanopillar arrays provide reproducible surface enhanced resonance Raman (SERR) signals within 6% standard deviation and Raman enhancement factors of 1 × 105. They also show good electrochemical performance, as verified by potential-dependent SERR spectroscopy and cyclic voltammetry. Furthermore, the hemin-coated arrays display mediatorless electrocatalytic activity toward NO2−. Thus, the Ag nanopillar arrays present good prospects for their application in sensing devices and for SER/SERR based spectroelectrochemical applications in general.