Standard Contact Porosimetry Research Articles

Fast-activating reserve power sources: is lead dead indeed?

The purpose of this research is to improve the performance and reduce the activation time of reserve power sources based on lead-acid systems at lower temperatures, down to –50 °C. Physico-chemical factors affecting the activation speed of reserve power sources based on Pb–HClO4–PbO2 and Zn–HClO4–PbO2 systems are investigated using chronopotentiometry, scanning electron microscopy, and standard contact porosimetry. Two approaches to the improvement of the low-temperature performance of power sources are used. The first one is based on the substitution of lead as anodic material with zinc. This allows the increase in discharge voltage and simultaneous decrease in activation time, but brings about the instability of discharge characteristics and, finally, deteriorates the reliability of power sources. The second approach is based on the use of PbO2 cathode material with enhanced nanoporosity. The chronopotentiometric method in galvanostatic mode is applied to the quality estimation of cathodes. The criterion of applicability of cathodes for reserve power sources consists in the low discharge overvoltage (0.1–0.2 V). Efficient performance of reserve power sources possessing the stable discharge voltage (1.5–1.8 V per cell) and the unprecedentedly short activation time (under 30 ms) even at lower temperatures (down to –50 °C) is achieved. The results are verified by fabrication and testing of pilot batches of miniaturized reserve power sources having microcells’ volume of 0.02 ml. The second approach to the improvement of power sources is transferred into the industrial production.

INFLUENCE OF THE POSITIVE ELECTRODE PROPERTIES ON THE ACTIVATION TIME OF THE RESERVE CHEMICAL POWER SOURCES OF THE SYSTEM LEAD – PERCHLORIC ACID – LEAD DIOXIDE

The influence of the positive electrode properties on the activation time of the reserve chemical power sources of the system lead – perchloric acid – lead dioxide has been studied. Coatings of cathodes with lead dioxide obtained under various conditions are characterized by scanning electron spectroscopy, X-ray spectral microanalysis, X-ray photoelectron spectroscopy, standard contact porosimetry. The improvement of the performance characteristics of power sources including the ensuring of a short time of their activation at a low temperature has been shown to be possible with the use of a nanoporous coating of lead dioxide. To estimate the applicability of cathodes for the manufacture of power sources having minimal activation time a diagnostic principle has been used that it based on testing of cathodes by the method of chronopotentiometric measurements during galvanostatic discharge. Pilot industrial samples of small-sized reserve power sources of the mentioned electrochemical system with unprecedented short activation time (less than 30 ms at temperarure –50°С) were manufactured and tested.

Influence of Heterogeneous Ion-Exchange Membranes Composition on Their Structure and Transport Properties

The physicochemical properties of experimental heterogeneous MK-40 and MA-41 membranes with different ratios of ion-exchange resin and polyethylene binder in their composition are studied. It is shown that the specific electrical conductivity in 0.01–1 M NaCl solution decreases by more than 3 times for cation-exchange membranes and by 2 times for anion-exchange ones with a decrease in the content of ion-exchange resin in the membranes from 69 to 55%. It has been established that the diffusion permeability of anion-exchange membranes is more sensitive to their composition and naturally increases with an increase in the ion-exchange resin proportion in the composition. Information on the influence of the heterogeneous membrane composition on its structure, obtained by method of standard contact porosimetry, is supplemented by the calculation of transport-structural parameters of the microheterogeneous and extended three-wire models of the ion-exchange membrane.

Physico-Chemical Properties and Performance Characteristics of Perfluorined Membranes Bulk Modified with Platinum during Operation in Proton Exchange Membrane Fuel Cell

The results of application of platinum bulk modified perfluorinated membranes in proton exchange membrane fuel cell are presented. The change in physicochemical and transport characteristics of the membranes after modification with platinum and at different stages of their operation in the PEMFC are also discussed. The thickness, radius pore distribution obtained by the standard contact porosimetry method, the concentration dependences of the conductivity, and the current-voltage characteristic are studied. The influence of copper in bimetallic electrocatalyst on the characteristics of the perfluorinated membrane are considered. An increase in the efficiency of PEMFC with both commercial and bimetallic catalysts and platinum bulk modified membranes due to the formation of a self-humidifying structure is found.

Supercapacitor Properties of rGO-TiO2 Nanocomposite in Two-component Acidic Electrolyte

The electrochemical properties of the highly porous reduced graphene oxide/titanium dioxide (rGO/TiO2) nanocomposite were studied to estimate the possibility of using it as a supercapacitor electrode. Granular aerogel rGO/TiO2 was used as an initial material for the first time of manufacturing the electrode. For the aerogel synthesis, industrial TiO2 Hombikat UV100 with a high specific surface area and anatase structure was used, and the aerogel was carried out with hydrazine vapor. Porous structure and hydrophilic-hydrophobic properties of the nanocomposite were studied with a method of standard contact porosimetry. This is important for a supercapacitor containing an aqueous electrolyte. It was found that the hydrophilic specific surface area of the nanocomposite was approximately half of the total surface area. As a result of electrochemical hydrogenation in the region of zero potential according to the scale of a standard hydrogen electrode, a reversible Faraday reaction with high recharge rate (exchange currents) was observed. The characteristic charging time of the indicated Faraday reaction does not exceed several tens of seconds, which makes it possible to consider the use of this pseudocapacitance in the systems of fast energy storage such as hybrid supercapacitors. Sufficiently high limiting pseudo-capacitance (about 1200 C/g TiO2) of the reaction was obtained.

Influence of secondary carbon fiber on the mechanical behaviour and microstructure of alkali-activated granulated blast furnace slag-based composites

This study aimed to investigate the mechanical behaviour and microstructure of an environmentally friendly fibre-reinforce alkali-activated composites. The composites were obtained from alkali-activated granulated blast furnace slag reinforced with chopped secondary carbon fibres (SCFs) coming from the aircraft industry carbon fiber reinforced plastics waste. Three types of surfactants and two concentrations of SCFs were investigated. The compressive and bending strengths were measured to evaluate the mechanical behaviour of specimens. Moreover, the polycondensation products, pore structure, and microscopic morphology of the composites were analyzed using X-ray diffraction (XRD), method of standard contact porosimetry (MSCP), and scanning electron microscopy (SEM). It was found that tetraethylammonium bromide and a superplasticizer agent Glenium-51® increase compressive strength for reference granulated blast furnace slag-based alkali-activated matrix approximately by 60 % and lead to lower open porosity from 16 to 5 %. The experimental results showed that the incorporation of 0.7 vol. % SCFs had an optimal influence on mechanical behaviour and microstructure of composite. Based on the test results, it can be clearly said that using of Glenium-51® is improving the compressive strength of slag based alkali-activated composites reinforced SCFs.

Increasing the efficiency of carbon coating on olivine-structured cathodes by choosing a carbon precursor

• LiFe 0.5 Mn 0.5 PO 4 /C is obtained by mechanochemically assisted solid-state synthesis. • Carbon black, citric acid and polyvinylpyrrolidon are used as carbon precursors. • Carbon coating formation is studied using FTIR spectroscopy of adsorbed probe molecules. • The properties of carbon coating are studied by Raman spectroscopy, MSCP and EIS. Carbon-coated LiFe 0.5 Mn 0.5 PO 4 (C-LFMP) cathode materials were obtained by two-step mechanochemically assisted solid-state synthesis. After mechanical activation and heat treatment of the reagent mixture at 400 °C, the pre-prepared carbon-free LFMP-400 was obtained, which was then ball milled with three different carbon precursors: carbon black (CB), citric acid (CA) and polyvinylpyrrolidon (PVP) and subsequently annealed at 700 °C. FTIR spectroscopy of adsorbed probe molecules (pyridine) was used to detect the presence of Brønsted acid centers on the surface of LFMP-400. The mechanism of their interaction with functional groups of carbon precursors during joint ball milling and heating up to 700 °C was investigated using FTIR spectroscopy. The properties of carbon coatings were studied by Raman spectroscopy, standard contact porosimetry, and electrochemical impedance spectroscopy, and their effect on electrochemistry of the C-LFMP composites was studied by galvanostatic cycling. It is shown that the LFMP/PVP composite is characterized by higher capacity and better high-rate capability due to the formation of well-graphitized carbon coating tightly bound to the surface of LFMP and having an optimal porous structure.

Modified Carbon Nanotubes: Surface Properties and Activity in Oxygen Reduction Reaction

In order to develop highly efficient and stable catalysts for oxygen reduction reaction (ORR) that do not contain precious metals, it is necessary to modify carbon nanotubes (CNT) and define the effect of the modification on their activity in the ORR. In this work, the modification of CNTs included functionalization by treatment in NaOH or HNO3 (soft and hard conditions, respectively) and subsequent doping with nitrogen (melamine was used as a precursor). The main parameters that determine the efficiency of modified CNT in ORR are composition and surface area (XPS, BET), hydrophilic–hydrophobic surface properties (method of standard contact porosimetry (MSP)) and zeta potential (dynamic light scattering method). The activity of CNT in ORR was assessed following half-wave potential, current density within kinetic potential range and the electrochemically active surface area (SEAS). The obtained results show that the modification of CNT with oxygen-containing groups leads to an increase in hydrophilicity and, consequently, SEAS, as well as the total (overall) current. Subsequent doping with nitrogen ensures further increase in SEAS, higher zeta potential and specific activity in ORR, reflected in the shift of the half-wave potential by 150 mV for CNTNaOH-N and 110 mV for CNTHNO3-N relative to CNTNaOH and CNTHNO3, respectively. Moreover, the introduction of N into the structure of CNTHNO3 increases their corrosion stability.

Optimization of the cathode porosity via mechanochemical synthesis with carbon black

Nanostructured carbon–coated composite cathode materials LiFe0.5Mn0.5PO4/C (LFMP/C) are prepared by the mechanochemically assisted solid-state synthesis using different reagent mixtures and carbon as reducing and covering agent. The effect of the precursors, gas release during the solid-state reaction, and of the intensity of high-energy ball milling on the porous structure and electrochemistry of LFMP/C is studied using DSC/TG/MS, XRD, SEM, TEM, standard contact porosimetry (MSCP), EIS, CV, and GVC. It is shown that the particle size and porosity of LFMP/C strongly depend on the chosen precursors and intensity of mechanical impact. The higher the intensity, the more effective incorporation of carbon black in the pores formed in LFMP, which leads to improved electronic conductivity and better access of the electrolyte to the surface of the electrode, while smaller particles provide improved Li diffusion in the bulk of LFMP. As a result, the cyclability and high-rate performance of the LFMP/C composites are improved.

Activated Carbons as Nanoporous Electron-Ion-Exchangers

The electrochemical, ion-exchange, sorption, hydrophilic-hydrophobic properties of several types of electrodes based on activated carbon (AC) and its porous structure are studied. By the method of standard contact porosimetry it is found that AC exhibits both hydrophilic and hydrophobic porosity and has the high specific surface area (600–2600 m2/g) which explains its use in supercapacitors and for capacitive deionization (CDI) of water. A new phenomenon of superhydrophilicity caused by swelling of surface groups (SG) in water is observed. The measurements of the AC surface conductivity show that even in pure water AC exhibits considerable ionic conductivity, which makes possible its use in the production of pure water by CDI. AC is shown to be an electron-ion-exchanger which is its unique feature. It is found that in addition to the electric double layer capacitance, the pseudocapacitance of redox-reactions of surface groups makes a substantial contribution into its total capacitance. The deep cathodic charging to negative potentials vs. reversible hydrogen electrode (RHE) in concentrated H2SO4 allows reaching the specific preudocapacitance of AC of 1100 F/g mainly due to the high pseudocapacitance of the reaction of hydrogen intercalation into carbon. This corresponds to the formation of a new compound C6H. In pure water, the specific capacitance of AC reaches 66 F/g and does not increase with the increase in KCl concentration, which suggests that this capacitance is associated with surface groups.

The Effect of the Stabilization and Carbonization Temperatures on the Properties of Microporous Carbon Nanofiber Cathodes for Fuel Cells on Polybenzimidazole Membrane

Materials based on pyrolyzed electrospun nanofiber polyacrylonitrile were studied by the method of standard contact porosimetry. An influence of oxidation and pyrolysis temperatures on specific surface area. It was shown that an increase of oxidation temperature from 300 to 350°C and of pyrolysis temperature from 900 to 1000°C leads to a decrease of pore specific surface area and to a decrease of a part of micropore specific surface area. Platinated samples showed sufficient values of electrochemically active platinum surface area (12‒35 m2 g $$_{{{\text{Pt}}}}^{{ - 1}}$$ ) and were tested as cathodes for high temperature polymer electrolyte membrane fuel cell. An increase in power density was found when a part of electrode micropore specific surface area was decreasing.

Porous structure optimization of electrospun carbon materials

According to standard contact porosimetry data, treatment of electrospun pyropolymer mats based on pyrolyzed polyacrylonitrile and polybenzimidazole (PBI) nanofibers with a mixture of sulfuric and nitric acids causes a drastic increase in the specific surface area of macro- and mesopores and complete disappearance of micropores. Acid treatment is followed by hydrophilization of pores with radii r < 10 nm. Taken altogether, these effects lead to higher performance of the membrane-electrode assembly of a high-temperature polymer electrolyte membrane fuel cell based on PBI membrane with the cathode made of the platinized acid-treated material.

Electrochemical, Structural, and Thermogravimetric Studies of Activated Supercapacitor Electrodes Based on Carbonized Cellulose Cloth

The high–temperature reagentless activation of carbonized cellulose cloth is used to manufacture supercapacitor (SC) electrodes with different fast times of activation t. It is established by means of the standard contact porosimetry that an increase in t raises both the degree of electrode hydrophilicity and the specific surface area. Thermogravimetry shows that the mass–temperature curves have two steps in the temperature ranges of 25 to 100 and 500 to 650°C, and a plateau in the range of 200 to 400°C. For symmetric supercapacitors (SCs), the potentiodynamic approach provides the voltage–capacity curves characteristic of double–layer SCs. An increase in t raises the electrode capacity from 130 to 170 F/g in 30% KOH solution, due probably to the growing influence of surface groups. It is found that the self–discharge current grows upon an increase in t. The maximum energy density for pulse SCs can be obtained at a charging voltage of 1.4 V. Life cycle tests are performed for a pulse symmetrical SC based on activated carbon electrodes with t = 60 s. It is shown that such SCs can withstand long–term cycling (at least several thousands of cycles) with no noticeable degradation and a negligible reduction in capacity.

The Influence of Porous Structure on the Electrochemical Properties of LiFe0.5Mn0.5PO4 Cathode Material Prepared by Mechanochemically Assisted Solid-State Synthesis

Carbon-free LiFe0.5Mn0.5PO4 and carbon-coated LiFe0.5Mn0.5PO4/C cathode materials were prepared by the mechanochemically assisted solid-state synthesis. The influence of the carbon coating on the porous structure, morphology, conductivity, and electrochemical characteristics of the cathode materials was analyzed using scanning electron microscopy (SEM), standard contact porosimetry (MSCP), electrochemical impedance spectroscopy (EIS), galvanostatic cycling, and galvanostatic intermittent titration technique (GITT). It has been shown that the specific surface area of LiFe0.5Mn0.5PO4/C is twice as high as that of LiFe0.5Mn0.5PO4 despite the very low content of carbon (3%). This was explained by a non-additive contribution of carbon and the active cathode material to the total specific surface area of the composite due to an introduction of carbon in the pores of the cathode material. Among the two key characteristics of a porous structure—specific surface area and volumetric porosity—specific surface area has the greatest impact on electrochemistry of LiFe0.5Mn0.5PO4/C. Mathematical modeling of the discharge profiles of LiFe0.5Mn0.5PO4/C was carried out and compared with the experiment. The cathode heating at high currents was evidenced. The temperatures and coefficients of solid-state diffusion were estimated at different currents. The calculated diffusion coefficient corresponds to the experimental one obtained by GITT at room temperature.

Thermal analysis and multi-analytical comparison of samples of Neolithic ceramics from Dnepr–Dvina and Low Don regions

Two kinds of samples of Early and Late Neolithic ceramic sherds of pots from excavations of sites located in Dnepr–Dvina and Low Don region (Serteya II and Rakushechny Yar) were investigated for multi-analytical comparison. The methods include thermogravimetric analysis, X-ray powder diffraction, X-ray photoelectron spectroscopy and method of standard contact porosimetry. The pottery manufactured in Serteya II and Rakushechny Yar has different clay sources, but close mineral composition. Inner sides of sherds are less thermally durable as a result of the contact with cooking meal or boiling water in ancient times: They lose more mass during thermogravimetric measurements. At the same time, the minerals in outer sides of the samples are partly destroyed because of contact with fire in the past. According to differential scanning calorimetry curves, there are thermal effects above 1000 °C in all sherds due to mullite formation. There are organic C–F bonds and sharp endothermic peaks at 600–750 °C in samples from Serteya II site. In addition to elevated level of nitrogen and phosphorus and carbon black layer on the inner side, it allows to propose that the pot from Serteya II was used for cooking. The sherds from both sites have close overall porosity, but in case of Serteya II size of mesopore is more isotropic.

Ionic Transport in Sol-Gel Derived Organic-Inorganic Composites

This chapter is devoted to organic-inorganic composite ion exchange resins and membranes. We ascertain interrelation between composition, morphology and porous structure of the materials on the one hand and ion transport through them on the other hand. The composites for different practical application (fuel cells, ion exchange columns, electrodialysis) are in a focus of attention. Porosity of a polymer constituent of the composite was determined with a method of standard contact porosimetry, which gives information about pores in a very wide diapason (from 2 nm to 200 μm). In this context, pore formation in ion exchange polymers during swelling is considered. A number of parameters, which are obtained from porosimetric measurements, can be used for interpretation of ion transport regularities, particularly evolution of electrical conductivity. Embedded non-aggregated nanoparticles, their aggregates and agglomerates affect differently porosity of the polymer constituent: they are able to block, stretch and squeeze pores, As a result, the composites demonstrates different rate of ion transport depending on amount and size of the inorganic particles. The approach to purposeful formation of one or other types of particles has been proposed.

Modeling and experimental verification of operation of supercapacitors with carbon electrodes in non-aqueous electrolytes. The energy efficiency

Charge-discharge processes of supercapacitor with carbon black KJEC 600/Li in non-aqueous electrolyte: 1 M LiPF6 in a mixture of ethylene carbonate (1/3), diethyl carbonate (1/3), dimethyl carbonate (1/3) are investigated. Galvanostatic cycling was carried out in the range from 1 to 4 V with currents from 100 to 5000 mA/g of carbon black. The maximum discharge capacity of 196 F/g has been reached. The porous structure and hydrophilic-hydrophobic properties of carbon black KJEC 600 were investigated by the standard contact porosimetry method (MSCP). The following values were obtained: total specific surface area of 2500 m2/g, total porosity of 7.8 cm3/g, hydrophilic porosity of 4.9 cm3/g, hydrophobic porosity of 2.9 cm3/g. The obtained experimental dependence of the energy efficiency has a maximum (80%) at a current of 250 mA/g. Mathematical modeling of charge-discharge processes of the supercapacitor is developed with taking into account the charging of the double electric layer (EDL) and adsorption of lithium ions according to the Butler-Volmer equation and the Frumkin isotherm for the carbon electrode are taken into account. From the comparison of the calculated and measured charge-discharge curves it follows that these curves are satisfactorily consistent with each other, which indicates the correctness of the model. The density of the exchange current and the specific capacitance of the EDL refereed to the true surface found by the fitting are equal to i0,ad = 2.8 × 10−29A/сm2 and Cdl = 3.5 μF/сm2 respectively.On the basis of the developed model for different specific currents the energy efficiency dependences on the exchange current density of the adsorption reaction were calculated. Interestingly, these dependencies have a minimum. Based on the model, the profiles of the potential the surface coverage of lithium ions were also calculated.

Influence of Electric Field during the Chemical Synthesis of Polyaniline on the Surface of Heterogeneous Sulfonated Cation-Exchange Membranes on the Their Structure and Properties

The influence of electric field in the chemical synthesis of polyaniline on the surface of sulfonated cation-exchange membranes on their structure and properties has been investigated. By using standard contact porosimetry, it has been found that surface modification of heterogeneous membranes with polyaniline, both in static conditions and in an external electric field, does not significantly affect the distribution of water over the effective pore radii and binding energies. It has been shown that the structural heterogeneity of the ion-exchange membrane, rather than the aniline polymerization conditions, has a more significant effect on the morphology of the polyaniline layer on its surface and, hence, on the electrotransport properties. A decrease in the electrical conductivity of the composites obtained with an increase in the quantity of electricity passed during the synthesis of polyaniline on their surface has been revealed. Based on the analysis of the current–voltage characteristics of the samples and their electrical conductivity, the conditions for obtaining materials with the most pronounced asymmetry of the electrotransport properties have been determined.

Electrochemical and Structural Studies of Nanodiamond Composites

The method of detonation synthesis is used to obtain nanodiamond composites (NDCs), and electrochemical and porosimetric studies are carried out for some NDC samples containing both a nanodiamond powder fraction and a nondiamond carbon fraction. Samples of untreated detonation soot (NDC-1) and products of its gas-phase purification (NDC-2 and NDC-3) with different ratio of nanodiamond and nondiamond carbon are studied. The content of the latter in the NDC-1, NDC-2, and NDC-3 samples is 48, 24, and 1 wt %, respectively. It is shown that the intensity of Raman bands of crystalline graphite (1580 cm–1) and disordered graphite phase (1360 cm–1) is higher in the initial detonation soot, as compared to samples partially or completely purified from nondiamond carbon. Here, the specific resistance of the samples increases in the series NDC-1 < NDC-2 < NDC-3, i.e., at an increase in the share of the nanodiamond fraction. The method of standard contact porosimetry shows that samples are characterized by high values of both overall specific (1040–1290 m2 g–1) and hydrophilic specific surface area and that the degree of NDC hydrophilicity decreases at an increase in the nanodiamond concentration. The CV curves of NDC samples have a shape typical for double electric layer charging complicated by ohmic losses growing at an increase in the nanodiamond fraction. Nanodiamond boration results in a decrease in its specific resistance and in its significant hydrophilization. The data of impedance measurements for NDC-1 and NDC-2 samples show that a decrease in the fraction of conducting carbon is accompanied by a significant decrease in capacitance. Studies of oxygen electroreduction on the Pt/NDC-1 catalytic system demonstrate its stability in time, which is probably related to a decrease in the aggregation degree of platinum particles due to the lower corrosion rate of the nanodiamond powder support as compared to standard carbon blacks. Thus, some of the studied NDC samples are promising as supports of oxygen reduction catalysts.

New Gas-Diffusion Electrode Based on Heterocyclic Microporous Polymer PIM-1 for High-Temperature Polymer Electrolyte Membrane Fuel Cell

Polymer of intrinsic microporosity PIM-1 was used for electrospun polymer nanofiber producing. After pyrolysis, the obtained nanofibers, in a form of entire mat, were used as a support for cathode electrocatalyst for high-temperature polymer electrolyte membrane fuel cell on polymer polybenzimidazole membrane. The material was characterized by the methods of standard contact porosimetry, Raman spectroscopy and scanning electron microscopy. The I-V curves for membrane-electrode assembly suggest a possibility of using the carbon material for electrodes in a fuel cell on polymer membrane.