Impedance spectroscopy was used to study proton conductivity changing of pre-dried sulfonated perfluorinated and hydrocarbon (polynaphtoleimide) membranes over time during their hydration. For this purpose, commercial perfluorinated membranes Nafion 212, Nafion 211, Gore 18 and hydrocarbon co-polynaphthoyleneimide (co-PNIS) membranes with different hydrophobicity blocks (ODAS/MDAC and ODAS/MDOT) synthesized in this work were used. It was found that the proton conductivity steady state values of Gore 18 membrane were established faster in humidity atmosphere after its drying than for other membranes studied in this work. This membrane demonstrates also better characteristics with cyclic humidity changes from 35 to 75

The ice rules determine the structure of the proton system of ice and play a fundamental role in ice physics. Usually, the ice rules are viewed as a result of minimizing the Coulomb interaction energy between protons. In this work, we studied the influence of electronic energy on the formation of ice rules. It is shown that the energy of electrons does not break the ice rules but strongly affects the creation energies of ice rules violations and the mechanism of their movement, leading to stronger quantum tunneling of protons along bonds. We also discussed the possibility of a quantum state of ice, which is a superposition of different proton configurations that satisfy the ice rules.

We use 1H and 17O NMR static field gradient diffusometry to measure self-diffusion coefficients of protons (DH) and oxygens (DO) in Nafion 212 with various hydration levels (λ = 4-18). For all samples and both nuclei, we obtain activation energies (Ea) of ≈0.19 eV. Analyzing the hydration-level dependence of DH and DO, we find DO/DH ≈ 1 at λ ≈ 18, resembling the situation in bulk water, while oxygen diffusion becomes faster than proton diffusion when the water content is decreased, leading to DO/DH ≈ 1.2 at λ ≈ 4. A comparison with literature data for acidic bulk solutions implies that faster oxygen than proton diffusion results from the existence of the polymer framework. To rationalize the observed ratios DO/DH ≥ 1, we consider a bimodal dynamical model in which the interactions of H+(H2O)m ions with neighboring SO3- groups lead to slower water dynamics in the vicinity of the polymer framework than in the center of the water nanochannels.

This paper presents research on the technological development of hydrogen-air fuel cells with high output power characteristics using fluorine-free co-polynaphtoyleneimide (co-PNIS) membranes. It is found that the optimal operating temperature of a fuel cell based on a co-PNIS membrane with the hydrophilic/hydrophobic blocks = 70/30 composition is in the range of 60–65 °C. The maximum output power of a membrane-electrode assembly (MEA), created according to the developed technology, is 535 mW/cm2, and the working power (at the cell voltage of 0.6 V) is 415 mW/cm2. A comparison with similar characteristics of MEAs based on a commercial Nafion 212 membrane shows that the values of operating performance are almost the same, and the maximum MEA output power of a fluorine-free membrane is only ~20% lower. It was concluded that the developed technology allows one to create competitive fuel cells based on a fluorine-free, cost-effective co-polynaphthoyleneimide membrane.

Proton diffusion in the co-PNIS85/15 membrane was investigated in the temperature range from 200 to 363 K at different water contents (4 ≤ λ ≤ 21) using 1H SFG NMR diffusometry. At high hydration values, above the threshold value λ0 = 10.5, the ln(DNMR(1/T)) dependences show two different activation modes, separated by a crossover point Tcr ≈ 250–260 K. At temperatures above Tcr, the activation energy is Ea 0.20 eV, which is close to the value for bulk water (Ea 0.17 eV). At temperatures below the crossover point, the ln(DNMR(1/T)) dependences for different water contents merge together into one straight line characterized by a much higher Ea = 0.46 eV. At low hydration values λ < λ0, the activation energies for the high-temperature and low-temperature modes converge, so that at λ = 4, the dependence ln(DNMR(1/T)) is described by one straight line throughout the studied temperature range with Ea = 0.38 eV. A model is proposed that phenomenologically describes the diffusion in the co-PNIS membrane at different moisture contents λ.

We use static field gradient (SFG) NMR to determine the self-diffusion coefficients of protons in fluorine-free sulfonated co-polynaphthoyleneimide (co-PNIS) proton exchange membranes with different ratios of hydrophilic to hydrophobic groups. The investigations were carried out in the temperature range from 193 to 355 K. Because there are protons not only in water but also in the polymer framework, H-1 NMR diffusion studies of these membranes may suffer from cross-relaxation effects between the different types of protons. To overcome this problem, different methods for measuring proton diffusion coefficients are compared and a suitable strategy for analysis is proposed. It is found that the proton diffusion is practically isotropic and shows two activation regimes, separated by a crossover near 260 K. The activation energy above the crossover is 0.19 eV, which is close to that of Nafion 212. Below the crossover, all co-PNIS membranes studied have very similar diffusion coefficients and the activation energy amounts to 0.46 eV, which is higher than that of Nafion (0.36 eV). Increasing the ratio of hydrophilic to hydrophobic polymer groups leads to faster diffusion in the temperature range from 273 to 355 K. For the co-PNIS membranes with the highest ratio of hydrophilic to hydrophobic groups, the proton diffusivity is about 2.3 times higher than for the Nafion 212 membrane. Unlike for Nafion-type membranes, the diffusion does not depend on the length scale of the experiment, indicating that the morphology of co-PNIS membranes may differ from the channel-like structure of Nafion membranes.

A model of the proton system in one-dimensional water is proposed, which takes into account the Coulomb interaction between protons, quantum tunneling of protons between the nearest-neighboring positions, and the interaction of protons with the channel walls. Cases of extremely confined channels in a hydrophilic and hydrophobic medium are studied, various approximations of the proposed model are considered, and their analogy with the corresponding electronic systems is indicated. Almost all protons of water molecules are found to be localized on broken bonds near the walls of the hydrophilic channel so that one-dimensional water can be considered as a molecular gas tightly bound to the channel walls. The mechanical motion of such water media and the diffusion of water molecules are determined by the interaction of water molecules with hydrophilic walls. Most likely, the water flow through such channels will be significantly hampered. Conversely, almost all hydrogen bonds at the center of the channel are occupied by protons in the channel with strongly hydrophobic walls, while the bonds with the walls are considerably weakened, and the mechanical behavior of one-dimensional water becomes similar to that of a solid. One-dimensional water in this form moves as a whole medium through the channel, while the hydrodynamic boundary condition on the channel walls (the velocity vanishing at the boundary) will be violated. This leads to a sharp increase of water flow through the channel compared to the classical hydrodynamic calculations of the water flow. It is assumed that one-dimensional water in this case reveals antiferromagnetic behavior.

Field Cycling (FC) 2H nuclear magnetic resonance (NMR) relaxometry was applied to study dynamics in Nafion NR 212 in the temperature range from 300 K to 190 K and water content of λ = 8.2. The sensitive time window of FC was extended up to eight decades using the temperature-frequency superposition principle and master curve. The rotational correlation times obtained from 2H FC NMR coincide with translational correlation times gained from static field 2H NMR diffusometry in the temperature range applied. This fact means that a long-range mass transport in Nafion is coupled to molecular rotations. It is assumed that confined water in Nafion has more ordered oxygen sublattices as compared with bulk water, on a short range is similar to ice. We discuss the possible role of D and L defects, typical for the ordered ice structure and using this concept to describe the processes of self-diffusion of confined water in Nafion, as well as the similarity of temperature and humidity dependence of self-diffusion and proton conductivity.

The diffusion coefficients in proton-exchange perfluorosulfonated membranes fabricated by different techniques have been analyzed in the temperature range from 200 K to 300 K using NMR diffusometry in a static magnetic gradient field. The influence of the water content as well as the effects of the membrane thickness and the side-chain length on the diffusion coefficient was analyzed. It is found that the fabrication by the extrusion cast method leads to faster diffusion as compared to the solution cast fabrication method. Shorter side chains are also preferable for faster diffusion. Both the decrease of the temperature and the water content leads to a reduced diffusion coefficient, affecting the transport micromechanism in a similar way by increasing the role of the water on the pore walls with respect to proton transport. The model of confined water in Nafion pores has been applied to analyze the results. It is proposed that both conductivity and diffusion at low temperatures are determined by protonic transport of the surface water via bond defects in contrast to the bulk water or ice, where the ionic defects are responsible for the mass transport.

Two relatively simple synthetic procedures were developed for the synthesis of Pt-HxMoO3 composites. The obtained materials may be of interest as CO-tolerant catalysts for hydrogen-air fuel cells with proton-exchange membranes (PEMFCs). The first step of both syntheses was to prepare hydrogen molybdenum bronzes (HxMoO3) through the addition of Zn powder to acidic solutions containing Mo(VI) species. Two types of hydrogen-containing molybdenum bronzes were synthesized, namely, red bronze (x approximate to 1.55) and green bronze (x approximate to 2.0). The next step was the Pt deposition in a redox reaction between HxMoO3 and potassium tetrachloroplatinate (K2PtCl4) under open-circuit conditions that resulted in composite materials defined by aPt.b(HxMoO3). Numerous physical methods, including XRD, STEM, SEM, and XPS, were used to determine both the composition and structure of the catalysts. Platinum clusters were distributed over the surface of catalytically active support (HxMoO3) in both cases; however, the type of molybdenum bronze used for synthesis affects the size of Pt particles. Linear sweep voltammetry (LSV) was used to determine the regularities of both adsorbed carbon monoxide electrodesorption and dissolved CO electrooxidation. CO-tolerance of prepared composites was estimated using H-2/100 ppm CO mixture under conditions of both an electrochemical cell and a membrane electrode assembly (MEA). The results of this work are promising, as they provide a relatively simple method for the synthesis of CO-tolerant catalysts. The understanding of the origin of the CO-tolerance is essential for the development of electrode materials that could be used in the real fuel cells.

Proton-conducting membranes were fabricated from a new short-side chain ionomer Inion (Russian analogue of Aquivion) by solution casting method. A series of temperature treatment experiments was conducted to show that annealing of Inion membranes at the temperature range from 160 °C to 170 °C leads to a significant increase of specific proton conductivity to values even higher than those of commercial membrane Nafion NR212. An explanation of this fact can be given by considering the membranes’ proton transport mechanism and water behavior models in nanopores. Matching the proton conductivity mechanism of the membranes, which is realized in nanostructured channels with the diameter of about several nanometers according to the Grotthuss proton hopping mechanism, and the model of water and ice states in nanopores leads to the comprehensive understanding for the further optimization of the membranes to achieve high transport characteristic. For example, it can be improved by increasing the number of side-chain branches of the polymer.

The isotope effect H → D on diffusion in proton-exchange membrane Nafion 212 is investigated using 1H and 2H nuclear magnetic resonance (NMR) diffusometry in a static magnetic field gradient in the temperature range from 200 to 332 K for proton and from 245 to 332 K for deuteron transport. The diffusion coefficients of both isotopes have identical temperature dependence, while proton diffusion is 1.4 times faster than deuteron diffusion at the same humidity. This difference indicates a significant influence of the mass of the diffusing particle and allows us to conclude that the Grotthuss mechanism or relay diffusion of H+ or D+ ions prevails over the vehicular mechanism involving H2O molecules or H3O+ ions.

The pressure dependence of the proton conductivity of water ice is studied theoretically. It is shown that the decrease in the hydrogen bond length leads to the decrease in the formation energy of ionic defects and to the increase in the formation energy of bond defects. As a result, the partial conductivity of ionic defects, which determines the static conductivity of ice, increases, while the partial conductivity of bond defects, which determines the high-frequency conductivity of ice, decreases. At a certain pressure, a crossover of majority and minority carriers occurs, and the partial conductivities of ionic and bond defects become equal, while the static conductivity of ice reaches a maximum, and the permittivity of ice reaches a minimum. At the further pressure increase, the static conductivity of ice is determined by the partial conductivity of bond defects and decreases, while the high-frequency conductivity is determined by the partial conductivity of ionic defects and increases. The pressure at which the crossover occurs, as well as the maximum proton conductivity and the minimum permittivity, is estimated, and the comparison with experimental results is discussed.

The sulfonated polynaphthoyleneimide polymer (co-PNIS70/30) was prepared by copolymerization of 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODAS) and 4,4’-methylenebisanthranilic acid (MDAC) with ODAS/MDAC molar ratio 0.7/0.3. High molecular weight co-PNIS70/30 polymers were synthesized either in phenol or in DMSO by catalytic polyheterocyclization in the presence of benzoic acid and triethylamine. The titration reveals the ion-exchange capacity of the polymer equal to 2.13 meq/g. The membrane films were prepared by casting polymer solution. Conductivities of the polymer films were determined using both in- and through-plane geometries and reached ~96 and ~60 mS/cm, respectively. The anisotropy of the conductivity is ascribed to high hydration of the surface layer compared to the bulk. SFG NMR diffusometry shows that, in the temperature range from 213 to 353 K, the 1H self-diffusion coefficient of the co-PNIS70/30 membrane is about one third of the diffusion coefficient of Nafion® at the same humidity. However, temperature dependences of proton conductivities of Nafion® and of co-PNIS70/30 membranes are nearly identical. Membrane–electrode assemblies (MEAs) based on co-PNIS70/30 were fabricated by different procedures. The optimal MEAs with co-PNIS70/30 membranes are characterized by maximum output power of ~370 mW/cm2 at 80 °C. It allows considering sulfonated co-PNIS70/30 polynaphthoyleneimides membrane attractive for practical applications.

A simple model has been proposed for water confined in nanochannels of a porous material, where the proton conductivity is six orders of magnitude higher than the value for bulk water. The key concept of the model is topological inconsistency of the ice rules with ordering of interface molecules, which results in the formation of excess charge carriers near the interface and in a sharp increase in the proton conductivity of water confined in channels with diameters of about several nanometers as compared to bulk water. Numerical estimates within our model are in quantitative agreement with measured proton conductivities of nanoporous materials with different chemical compositions, degrees of crystallinity, and morphologies of the structure. The model gives a useful scheme for the interpretation of proton transport in confined water and provides recommendations for the fabrication of nanoporous materials with a high proton conductivity.

We have developed the stand for the practical hydrogen power engineering course. This stand consists of hydrogen-air fuel cell, electronic system control, control of functional parameters and hydrogen source based on metal hydride cylinder. The specially manufactured 40 W stack is used in the stand as a fuel cell consisting of 22 membraneelectrode assemblies (MEA). We have investigated the current-voltage characteristics of the stack. Hydrogen fluxes of more than 0.7 l/min are shown to be required for the efficient operation of the fuel cell used in the stand 30 W under a current load of 3 A. We have studied the distribution of the temperature of the stack outer surface at different load currents, and establish that the maximum temperature does not exceed 45 ºC at the operating working load used in the stand. The paper describes the station hydrogen refueling metal hydride cylinders in detail. The station allows one to refuel metal-hydride cylinders with different form factors and volumes from 50 ml to 15 l. The connecting elements of the station withstand pressure drops from 0.1 Pa up to 1.5 MPa. The hydrides of La0.9Се0.1Ni5 and La 0.8 Се 0.2 Ni 5 alloys are used as a source of hydrogen. We have studied the P–C dependences cycles of hydrogen absorption and desorption for La 0.9 Ce 0.1 Ni 5 and La 0.8 Ce 0.2 Ni 5 alloys utilizing in metal hydride cylinders at temperatures of 25 ºC and 45 ºC. The paper gives a description of hydrogen filling procedure of these cylinders in detail. The developed stand allows one in real time to measure and stabilize the temperature of the fuel cell for two sensors with the edge and in the center of the fuel cell; to control the temperature of the metal hydride cylinder; to measure voltage and current on the fuel cell, and current through a connected external load irrespective of the internal electronic load of the stand; to measure the hydrogen flow. This stand can be applied to demonstrate the work of alternative energy sources, as well as for the training of personnel working in the field of energy.

AbstractThe influence of pulsed activation on the electrochemical characteristics of fuel cells based on the Nafion proton-conducting membrane is studied. The activation was a repeated pulsed operation of the membrane–electrode assembly (MEA), which was characterized by alternating a constant load of the MEA near a short-circuit current at voltage U _L = 0.1 V and its “idle time” corresponding to the open circuit voltage of the MEA, U _OCV ≈ 0.95 V. It is shown that there is an optimal ratio of the time parameters of the pulsed load at which the activation is much more efficient than in the case of constant potentiostatic or galvanostatic regimes often used in practice.

The influence of pulsed activation on the electrochemical characteristics of fuel cells based on the Nafion proton-conducting membrane is studied. The activation was a repeated pulsed operation of the membrane–electrode assembly (MEA), which was characterized by alternating a constant load of the MEA near a short-circuit current at voltage UL = 0.1 V and its “idle time” corresponding to the open circuit voltage of the MEA, UOCV ≈ 0.95 V. It is shown that there is an optimal ratio of the time parameters of the pulsed load at which the activation is much more efficient than in the case of constant potentiostatic or galvanostatic regimes often used in practice.