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Water recycling and the production of drinking water have recently become a very actual topic. Pressure membrane processes make it possible to produce water with a quality higher than or comparable to the product of conventionally used processes such as sand filtration and flotation. The operation of membrane technologies requires specialist knowledge. By correctly analysing the input parameters of the water and controlling the operating parameters of the process, the technology is capable of achieving a very high recovery with a very high product quality while simultaneously using low energy. The IQ‑MINT intelligent software can analyze these parameters in real time and is able to immediately change the operating parameters of the technology with an emphasis on obtaining the highest possible recovery with regard to operational safety and membrane life. The software was validated on the example of cleaning real surface water in the UF60-MINT unit. When switched on, the software adjusted the operating parameters of the technology in such a way that – to the expense of the recovery – the lifetime of the membrane was extended and the consumption of chemicals and energy was reduced, with an emphasis on operational safety. The use of the IQ-MINT software thus enables the autonomous function of the technology with any type of incoming water without the need for a constant control and regulation by the operator.

Electrolytes utilized in solid oxide cells (SOCs) are based on oxide ion-conductive ceramic materials. The conductivity occurs via oxygen vacancies in the crystal lattice, which are created by the introduction of dopant into the material. Fast and simple preparation of electrolytes using variable dopant content is of great importance for SOCs development. ZrO2 doped by Y2O3 (YSZ) is still considered to be a state-of-the-art material due to its conductivity and thermomechanical compatibility with electrodes. Therefore, a detailed procedure to fabricate YSZ electrolytes with desired dopant content is of significant importance. Each prepared electrolyte was examined by means of spectroscopic methods in combination with electrochemical ones. The results obtained allows to understand connection between electrolyte composition and structural properties.

In this work, a combined approach, utilising both experimental cyclic voltammetry and mathematical modelling, was adopted in order to determine the kinetics of Pt oxidation to PtO and chemical dissolution of PtO to Pt2+ in concentrated H3PO4 at elevated temperatures. Experimental cyclic voltammograms were corrected for chemical dissolution of PtO based on a charge balance calculation and the corresponding kinetic constant was evaluated. The corrected voltammograms were compared with the results of a 0-dimensional dynamic model of electrochemical Pt oxidation and the kinetic parameters of this reaction were evaluated. Finally, the two surface reactions were integrated into a mathematical model. This model is able to simulate cyclic voltammograms of Pt in concentrated H3PO4 electrolyte within the temperature range of 120–160 °C. It was shown that Pt electrochemical oxidation is the dominating reaction on the Pt surface, based on total recorded charge. However, the chemical dissolution of PtO is by no means negligible, since as much as 10% of the PtO monolayer formed can chemically dissolve under specific conditions.

The article contains examples about hydrogen research and development progress in different countries: Czech Republic, Poland, Romania, Russia and Ukraine. Each chapter describes a specific situation for a country and one of them describes some aspects from Germany for comparison with one of international leaders. The examples described into articles are not aleatory. The intention of the authors is to give to the reader the possibility to understand the concrete examples about what means the state of hydrogen and fuel cell research and innovation in the Central and Eastern European countries. The chapters dedicated to Czech Republic, Poland, and Romania, reveal the commitment of these countries in this adventure, often viewed today as a subject of very advanced countries. The specific situation in the Russia Federation describes a strong background, an uncertain present and a questionable future for the hydrogen and fuel cell technology. Development of hydrogen technologies and fuel cells in Ukraine have a long history, also. All of that, in the EU context, by voice of the main stakeholders, considered the hydrogen and fuel cell a decisive issue, with economic and societal ramifications.

A stable, platinum-free catalyst-coated anion-exchange membrane with a promising performance for alkaline water electrolysis as an energy conversion technology was prepared and tested. A hot plate spraying technique used to deposit electrodes 35 or 120 μm thick on the surface of an anion-selective polymer electrolyte membrane. These thicknesses of 35 and 120 μm corresponding to the catalyst load of 2.5 and 10 mg cm−2. The platinum free catalysts based on NiCo2O4 for anode and NiFe2O4 for cathode were used together with anion selective polymer binder in the catalyst/binder ratio equal to 9:1. The performance of the prepared membrane-electrode assembly was verified under conditions of alkaline water electrolysis using different concentrations of liquid electrolyte ranging from 1 to 15 wt% KOH. The electrolyser performance was compared to a cell utilizing a catalyst-coated Ni foam as the electrodes. The prepared membrane-electrode assembly stability at a current load of 0.25 A cm−2 was verified by a 72-hour electrolysis test. The results of the experiments indicated the possibility of a significant reduction of the catalyst loading compared to a catalyst-coated substrate approach.

Nanocrystalline Fe60Co20Si10B10, prepared by ball milling atomised powder, was studied as a hydrogen evolution reaction catalyst for alkaline water electrolysis. Two application-oriented aspects of this material were studied: (i) Surface activation of the catalyst (cyclic voltammetry and leaching in 1 mol dm−3 potassium hydroxide) and (ii) the composition of a catalyst layer (ratio of the amount of catalyst to the polymer binder). Polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene with DABCO functional groups (PSEBS-CM-DABCO) was used as an anion-selective binder. The catalytic activity of the material was evaluated by means of Tafel analysis and by recording load curves under alkaline water electrolysis conditions. The results revealed that both activation procedures increase the activity of the Fe60Co20Si10B10 catalyst by almost 50% compared to as-received material. The most suitable ratio of catalyst to binder was determined as 70:30. The catalyst remained stable and active in the stability test performed.

Transformation of energy sector to carbon dioxide neutrality is one of the main goals of governments around the globe. This is closely connected with propagation of Hydrogen Economy scheme, where excess electric energy from renewable sources is stored in the form of hydrogen. Hydrogen is a valuable commodity and promising energy vector with numerous applications not only directly in industry, but also as a fuel for mobility sector. Water electrolyser with polymer electrolyte membrane (PEMWE) represents a key component for hydrogen production within Hydrogen Economy scheme. Among its principal advantages is use of water as a feed, option of operation at elevated pressure, flexibility of operation suitable for pairing with renewable electric sources and very high power to volume ratio, critical for delocalised hydrogen production. Despite these outstanding properties of PEMWE, several shortcomings still limit its application on industrial scale. The main constraint is a high loading of precious metals, especially on the anode, where IrO2 is the state-of-the-art catalyst and anode itself is a component most susceptible to degradation due to highly oxidative, acidic environment. In general, the anode consists of unsupported catalyst nanoparticles based on IrO2 and Ti porous transport layer (PTL), which is often coated with Pt, Au or Ir to prevent its passivation during electrolyser operation. The absence of catalyst support and microporous layer (MPL) on the top of Ti PTL decreases utilisation of catalyst, leading to the use of high catalyst loadings. Despite the significant progress in development of catalyst supports and Ti PTLs with gradient porosity in recent years, the issue of high Ir content and PTL without precious meatal coating passivation is still far from being solved. This presents a bottleneck for further PEMWE application. The goal of this work is to optimise anodic PTL for PEMWE in an efficient and economically feasible way, avoiding coating of PTL by precious metals and decreasing catalyst loading by its better utilisation. This was achieved by preparation of microporous layer on the top of commercially available PTLs, based on Ti felts and sintered Ti. From the materials potentially applicable for MPL, TiH2 was chosen due to its good electron conductivity and material compatibility with PTL. TiH2 is inherently thermodynamically unstable in presence of water and O2, forming non-stoichiometric Ti oxides with significantly lower electron conductivity. However, the rate of TiH2 oxidation at PEMWE operating conditions and impact of this process on cell Ohmic resistance was not yet investigated. MPL based on TiH2 powder was deposited on the surface of Ti PTLs by means of ultrasonically assisted spray deposition from ink. TiH2 was bonded in MPL by ionomer based on perfluorinated-sulfonated polymer. Stability of treated PTLs with and without MPL was investigated by single cell tests performed with in-house made membrane-electrode assembly in catalyst-coated membrane arrangement, consisting of commercial state-of-the-art materials at temperature of 80 °C and constant voltage of 2 V for 120 h. During single cell operation, its performance was periodically investigated by polarisation curves and impedance spectroscopy, performed at selected voltages. Impact of MPL of PEMWE performance is discussed in term of cell performance, Ohmic resistance and polarisation resistances. This study was supported by the Grant Agency of the Czech Republic under project no. GC20–06422J.

Solid oxide cells (SOCs) show high potential in applications related to sustainable society. The substantial contribution of the SOCs is their high efficiency in terms of the electric energy utilization due to the operating temperature up to 800 °C. The effect of high operation temperature is favorable in two ways. Firstly, it accelerates the kinetics of electrochemical reactions preventing the need of the use of Pt-based catalysts. Secondly, the high temperature offers favorable thermodynamic conditions decreasing the equilibrium potential for water splitting. This makes the SOCs technology a direct competitor to low-temperature technologies, such as alkaline or PEM electrolysis. The SOCs are composed of electrolyte, fuel electrode and oxygen electrode. The electrolyte allows transport of oxygen ions between the electrodes due to its high ionic conductivity. Yttria-stabilized zirconia (YSZ) represents a typical example of such a material. The oxygen electrode is where the oxygen reduction reaction or the oxygen evolution reaction takes place according to the operation mode of the SOC. Lanthanum strontium manganite (LSM) has been the state-of-the-art oxygen electrode material for almost 25 years and is considered as a pure electron conductor. Lack of ionic conductivity of the LSM leads to limitation of the overall reaction rate to the amount of triple phase boundary (TPB) where gaseous phase, electron-conducting phase and ion-conducting are in simultaneous contact. According to the literature it is optimal for the electrode material to be mixed in the 50:50 ratio with YSZ to increase the amount of the TPB. Thus, the active zone is extended further from the electrolyte surface into the volume of the electrode body. Even though the mixed electrode material exhibits great performance, information on the optimal thickness of the electrode is scarce in the literature. The electrode thickness is a crucial parameter since not all of the electrode volume is electrochemically active and represents just surplus resistance for the electric current impairing the overall electrode performance. The goal of our research is to determine of the extent of the active zone that we can estimate the optimal thickness of the LSM—YSZ electrode for various operation conditions. A macrohomogenous 1D model was developed to simulate the active electrode zone extent. Initial parametric study has shown that the extent of the active region of the electrode is influenced by many factors including the kinetics of the occurring reactions, the ionic and electronic conductivity of the respective domains and working conditions, such as temperature and operating current density. Even though the literature offers data on the conductivity of bulk the LSM and YSZ, the data of the respective conductivities in the LSM—YSZ are not applicable due to the electrode structure. The conductivity of the structure consisting of packed particles with a small contact area is limited by the contact resistance. This study targets to determine the electronic conductivity of the LSM phase and the ionic conductivity of the YSZ phase in the LSM—YSZ electrode framework. The LSM conductivity in the electrode framework was determined by resistance measurement of the casted layers of the LSM—YSZ using electrochemical impedance spectroscopy (EIS). The results show an exponential decrease of the LSM conductivity with decreasing LSM content. Furthermore, the 50:50 LSM—YSZ exhibits conductivity comparable to that of the bulk YSZ electrolyte. This result proves that the energy losses due to the electrical resistance of the LSM—YSZ electrode cannot be neglected in the terms of SOC performance. The determination of the ionic conductivity of YSZ in the electrode framework required the substitution of LSM with an inert material. The material of choice was CaSO4 due to its availability and its melting point being relatively close to that of the LSM. Similarly to the LSM, YSZ exhibited an exponential decrease of ionic conductivity with a decrease in YSZ volume fraction in the samples. Furthermore, the trend was compared to the Koh-Fortini relationship, showing that grain boundaries have a strong influence on the total conductivity of the material. The results of the experiments helped us to determine the extent of the active electrode zone leading to the estimation of optimal thickness of the LSM—YSZ oxygen electrode thickness. The authors acknowledge the financial support of the Czech Science Foundation (GACR), contract No: 19-142-44-J and by the Technology Agency of the Czech Republic under project no. TK04030143.

High-temperature solid oxide water electrolysis cells have become the center of attention of the research community owing to several advantages over traditional water electrolysis technologies. Among others, solid oxide water electrolysis represents highly efficient technology with the possibility to operate in a reversible regime (fuel cell/steam electrolysis). Despite the fast reaction kinetics due to the high operating temperature (600-900 °C). A more detailed understanding of the reaction mechanism is of critical importance to further develop this technology. Lanthanum-strontium-manganite La1-xSrxMnO3-δ is still considered a viable material for an oxygen electrode due to its high electrical conductivity, good chemical stability, and thermomechanical compatibility with various solid electrolytes. However, its negligible ionic conductivity is frequently reported in the literature. Although, La1-xSrxMnO3-δ is utilized as an oxygen electrode for several decades and its properties are reported in the literature, the reaction mechanism occurring on this oxygen electrode is insufficiently described, with multiple discrepancies occurring between the individual authors. The open literature almost exclusively considers the oxygen reduction reaction. Here La1-xSrxMnO3-δ is described exclusively as a pure electron conductor. In the case of the oxygen evolution reaction, only the mechanism reversed to the oxygen reduction is considered, which is clearly an oversimplification. Recent articles tend to connect the defect chemistry of La1-xSrxMnO3-δ and electrochemistry to disapprove the generally accepted description of reaction mechanisms, owing to the rather low agreement between theory and experimental data. In the framework of this study, a series of experiments was conducted, both under current-less as well as current-load conditions using laboratory button cells. Oxygen electrodes based on various mixtures of La0.8Sr0.2MnO3-δ-ZrO2:Y2O3 were tested to prove that La1-xSrxMnO3-δ may become a mixed ionic-electron conductor under specific conditions. The obtained data showed that conditions, such as oxygen partial pressure, temperature and, in particular, the polarization history, could result in a partial reduction of Mn4+ to Mn2+ in the crystal lattice of La1-xSrxMnO3-δ. The change of valence is of a great importance because it creates oxygen vacancies through which oxide ions can be transported. Therefore, under such conditions La1-xSrxMnO3-δ becomes a partial mixed ionic-electron conductor, significantly increasing the number of active reaction sites in the three-dimensional structure of the electrode. The most recent articles reported this behavior; however, only during the oxygen reduction reaction owing to the most suitable conditions for the Mn oxidation state transition. Within the framework of this study, the aim is to expand this concept also to the conditions of the oxygen evolution reaction, which has been completely omitted in the literature. The presented results significantly contribute to the understanding of solid oxide cells and represent a solid base for further modelling of the electrolysis cell, and optimization of its construction as well as operational conditions. This work was supported by the Technology Agency of the Czech Republic under project no. TK04030143.

Hydrogen is an efficient energy carrier with numerous applications in various areas as industry, energetics, and transport. Its potential depends also on the origin of the energy used to produce the hydrogen with respect to its environmental impact. Where the standard production of hydrogen from fossil fuels (methane steam reforming, etc.) doesn’t bring any benefit to decarbonisation of society. The most ecological approach involves water electrolysis using ‘green’ electricity, such as renewable power sources. Such hydrogen thus stores energy which can be used later. Hydrogen, used in the transport sector, can minimize its environmental impact together with preserving the driving range and decrease the recharge/refill time in comparison with a pure battery-powered vehicle. For transportation the hydrogen filling stations network is required. Local production of hydrogen is one of proposed scenarios. The combination of electrolyser and renewable power source is the most viable local source of hydrogen. It is important to know the possible amount of hydrogen produced with respect to local environmental and economic conditions. Hydrogen production by water electrolysis is an extensively studied topic. Among the three most prominent types, which are the alkaline water electrolysis (AWE), proton-exchange membrane (PEM) electrolysis and high-temperature solid-oxide electrolysis, AWE is the technology which is widely used in the industry for the longest time. In the recent development, AWE is being modified by incorporation of anion-selective membranes (ASMs) to replace the diaphragm used as the cell separator. In comparison with the diaphragm, ASMs perform acceptably in environment with lower temperatures and lower concentrations of the liquid electrolyte, thus, allowing for very flexible operation similarly to the PEM electrolysers. On the other hand, ASMs are not yet in a development level where they could outperform the diaphragm and PEM in long-term stability. Renewable sources of energy, predominantly photovoltaic (PV) plants and wind turbines, operate with non-stable output of electricity. Considering their proposed connection to the water electrolysis, flexibility of such electrolyser is of the essence for maximizing hydrogen production. The aim of this work is to consider a connection of a PV plant with an AWE. Power output data from a real PV plant are taken as a source of electricity for a model AWE. The input data for the electrolyser were taken from a laboratory AWE. The AWE data were measured using a single-cell electrolyser using Zirfon Perl® cell separator with nickel-foam electrodes. Operation including ion-selective membranes was also taken into consideration. Data from literature were used to set possible operation range and other electrolyser parameters. Small-scale operation was then upscaled to match dimensions of a real AWE operation. Using the before mentioned data, a hydrogen production model was made. The model takes the power output of the PV plant in time and decides whether to use the power for preheating of the electrolyser or for electrolytic hydrogen production. Temperature of the electrolyser is influenced by the preheating, thermal-energy loss of the electrolytic reactions, or cooling to maintain optimal conditions. The advantage of the created model is its variability for both energy output of the power plant or other instable power source and the properties of the electrolyser. It can be used to predict hydrogen production in time with respect to the electrolyser and PV power plant size. The difference between standard AWE and AWE with ion exchange membrane is mainly shown during start-up time where membrane based electrolyser shows better efficiency. Frequency of start-stop operation modes thus influences the choice of suitable electrolyser type. Another output is to optimize design of an electrolyser to fit the scale of an existing plant from economical point of view. This knowledge is an important input into the plan which is set to introduce hydrogen-powered transport options where fossil-fuel powered vehicles is often the only option, such as unelectrified low-traffic railroad networks. Acknowledgment: This project is financed by the Technology Agency of the Czech Republic under grant TO01000324, in the frame of the KAPPA programme, with funding from EEA Grants and Norway Grants.

Alkaline fuel cell (AFC) is historically 1st successfully applied fuel cell type. The main benefit of AFC is still possibility to use non platinum based catalysts at ambient conditions. With increase of demand for platinum metals for PEM water electrolysis and fuel cell this benefit would become more significant. Therefore it has sense to focus on AFC development. Gas diffusion electrodes (GDE) are crucial part in numerous technologies. Its main function is to enable contact of gaseous reactant with electron conductor and ionic conductor. Enlargement of contact area of mentioned three phase boundary lead to increase of electrode performance. In the case of liquid electrolyte like potassium hydroxide in AFC it is crucial to balance penetration of liquid into pores of electrode and to keep part of electrode unflooded. It must be realized in catalytic layer of GDE. Variation of temperature change electrolyte viscosity and vapor pressure both influences flooding of electrode. Beside suitable structure GDE for AFC must be stable in strong alkaline solutions. Standard GDE construction is based on combination of hydrophilic a hydrophobic materials to reach desired wettability. Also, the preparation method influences the porosity of the catalytic layer. GDE consist of three layers: catalytic, diffusion and supporting. The gas/liquid interface must be realized in catalytic layer. It is usually composed of catalyst and binder. Catalyst is chosen with respect to electrochemical reaction running on electrode thus binder must deliver desired hydrophobicity. Most typical binders are perfluorinated polymers like PTFE polytetrafluoroethylene (PTFE) with excellent chemical resistivity. Nickel, manganese, platinum, silver etc. are widely used in alkaline systems like catalysts. The most important property of the catalytic layer is the ratio of catalyst to PTFE which provides suitable hydrophobicity. The diffusion layer (GDL) is usually made of a mixture of carbon blacks/graphite and PTFE. The support layer is typically made of nickel foam or carbon paper. This work aims to optimize the ratio of PTFE to platinum catalyst in the catalytic layer. The commercial catalyst HiSPEC 40 wt. % Pt/C was used and Pt load was set to 0.5 mg/cm2. Electrodes were prepared by ink spraying technique on commercial GDL Sigracet® BC28. The ink with different ratios of PTFE to catalyst was applied to prepare GDE with PTFE content from 5 wt. % to 40 wt. %. Electrode baking under inert atmosphere was the last preparation step to increase mechanical stability. As the first characteristic the contact angle was measured. The droplet of water was placed on catalyst layer surface. The contact angle of droplet to GDE surface represents the level of hydrophobicity. A high level of hydrophobicity brings about low inundation GDE and bad contact between liquid, gas and catalyst. On the other hand, if GDE has low hydrophobicity, liquid can inundate the catalytic layer easily. As it was found already 5% of PTFE makes GDE surface hydrophobic. Higher loading of PTFE lead only to small angle increase. But significant decrease was found after GDE operation and PTFE loading over 15% is necessary to prevent further hydrophobicity decrease. In the second step prepared GDE were tested in the laboratory AFC. Pure hydrogen and pure oxygen were dosed to GDE chambers. 25% KOH solution was used as electrolyte. The I-V curve at the beginning of cell assembly, performance in time and I-V curve at the end of experiment was measure. The power of AFC with prepared electrodes improves if the hydrophobicity of GDE decreases. However, the penetration of liquid through the GDE was observed in low hydrophobic GDE in a long time testing alkaline fuel cell. Also the gradual decrease of cell performance was observed due to the flooding of the catalytic layer. After stop of operation and repeated start the performance of the cell again improved but no to the origin level. Only if the PTFE content was over 40% the performance was identical for several repeated experiments. The importance of PTFE loading in catalyst layer composition was demonstrated and its influence on AFC performance. The low loading of PTFE in GDE shows the highest performance but with fast drop. For longtime operation it is necessary to use PTFE leading at least 40%. Acknowledgment Financial support of this research by the Technological Agency of the Czech Republic under the project No TK02030001 “Research and development of advanced flow energy storage technologies” is gratefully acknowledged.

Possibility of operation a water electrolysis technology using cost-effective components for current collectors or porous transport layers and non-platinum group metal catalysts with fast response to intermittent loads from renewable energy sources makes membrane alkaline water electrolysis (MAWE) an attractive technology for producing low cost “green” hydrogen. MAWE represents a technology combining the advantages of the already established electrolyser technologies, i.e. proton exchange membrane water electrolysis (PEMWE) and alkaline water electrolysis (AWE). It combines the relatively low-cost materials of AWE with utilisation of the ion-selective polymer electrolyte as separator of the electrode compartments which is commonly used in PEMWE. In the case of the utilisation of the ion-selective polymer electrolyte the electrodes can be pressed directly to its surface thus creating the membrane-electrode assembly (MEA). Reduction of the gap between the electrodes and separator to zero lowers the ohmic drop on the cell. This positively affects the efficiency of the water electrolysis. In MAWE the anion-selective materials are still facing some limitations in terms of poorer chemical stability in high pH environments and at elevated temperatures due to degradation of the anion exchange groups either by Hoffman elimination or nucleophilic attack by OH- ions, or lower ionic conductivity. Primarily two different MEA fabrication methods are recognized in literature [1]: catalyst-coated substrate (CCS) and catalyst-coated membrane (CCM). In the CCS method, catalyst ink, consisting of a binder/ionomer, catalyst particles and solvent, is applied to one side of the porous transport layer whereas in CCM method the catalyst ink is applied to the ion-selective membrane. The CCM approach is established in the PEMWE technology, but in MAWE the above-mentioned problem with stability of anion-selective materials limits the research. From PEMWE we know that CCM approach provides several advantages, including close contact between the catalyst layer and membrane resulting in better utilization of the catalyst compared to CCS. This advantage allows the MEA to maintain the overall performance with lower catalyst loading. Also, the catalyst layer thickness is reduced, which lowers ohmic losses on the MEA. However, the CCM method can also cause poor electrical contact between the MEA and current collector or within the catalyst layer itself. In this work, we first compare the CCS and CCM approaches and study the possibility of catalyst loading reduction. Then, with CCM we further optimize the composition of the catalyst layer, study the effect of method of preparation and compare two different membranes – non-commercial with 2 different thicknesses and commercial one As anion-selective material we use chloromethylated block copolymer polystyrene-ethylene-butylene-styrene (PSEBS-CM) functionalized with 1,4-diazabicyclo[2.2.2]octane (DABCO) groups. The solution of PSEBS-CM is used also as a binder of the catalyst layer. This material showed good ionic conductivity, ion exchange capacity and stability at elevated temperature. For comparison reason, Fumapem® FAA-3-50 membrane is tested. NiCo2O4 and NiFe2O4 are used as anode and cathode catalysts, respectively. Air-brush or computer controlled ultrasonic dispersion of catalyst ink are used to prepare MEA. As many operating conditions have been reported to significantly affect MAWE performance, including membrane thickness, electrolyte type, and operating temperature we decided to test the performance of the prepared CCSs and CCMs by mean of the load curves in in the range 1.5 – 2.0 V in different concentrations of KOH (1 – 15 wt.%) at 50 °C. To identify the influence of membrane thickness, we use membrane with thickness of 250 or 60 µm. To have deeper insight on the system, electrochemical impedance spectroscopy is used under the MAWE conditions at voltage of 0, 1.5 and 1.8 V in frequency range 100 kHz – 0.1 Hz with amplitude of 10 mV. Scanning electron microscopy is used to observe the morphology of the layers. The chosen CCMs undergo the stability test measured at 50 °C in 10 wt.% KOH at current density of 250 mA cm-2 for 160 hours. The obtained results show the possibility of: 1) replacing the CCS with CCM, 2) reduction of the catalyst load by 75%, 3) improvement of performance with optimized catalyst/binder ratio and 4) improvement of performance with reduction of the membranes thickness. Acknowledgments: This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 875118. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe research. Financial support by the Technology agency of the Czech Republic within the framework of the project No. TK 02030001 is gratefully acknowledged. Huah, L.B., et al., Chinese Journal of Chemical Engineering, 2020.

Alkaline water electrolysis utilising porous diaphragm type separator of the electrode compartments represents industrially well-established technology of hydrogen production. This is due to the durable and stable operation utilizing abundant materials as iron, nickel, or stainless steel. However, many of the designs, construction solutions and approaches originate in the historical demands on the process (like mentioned durability rather than flexibility) and do not reflect up to date demands. Current demands on water electrolysis are given by the expected connection of water electrolysis technology with renewable sources of energy. The role of the water electrolysis is to use the surplus electrical energy in periods of the high output and/or low need for production of hydrogen. Hydrogen in such scheme represents an energy vector, which can be stored and used for electricity production in periods of the insufficient output of the renewable sources and/or high demand. Alternatively, hydrogen can be used as a fuel in fuel cell-based cars or as feedstock in industry. Due to connection with unpredictable renewable source, it is necessary for water electrolysis technologies to be flexible, highly efficient and be able to produce hydrogen of high purity. Current alkaline water electrolysis failed in several of these demands. Nowadays demands on water electrolysis are met by process utilizing proton exchange membrane (PEM) as separator of the electrode compartments. Unfortunately, PEM water electrolysis is limited by the need of the materials like titanium, platinum and iridium, which are rare, to be involved as electrodes, or catalysts of electrode reactions. The significant effort is paid to the possibility to combine advantages of both, alkaline and PEM processes by replacing porous diaphragm by dense anion-selective polymer membrane (ASM). Such change would allow to reduce the interelectrode distance to the thickness of the ASM used as separator of the electrode compartments, which would increase the performance of the membrane alkaline water electrolysis process. Utilisation of the ASM would also allow to decrease concentration of circulating electrolyte from commonly used 25 – 30 wt.% KOH to 1 – 5 wt.% KOH, increasing thus safety and flexibility. Another important beneficial impacts of ASM application are related to the improved current efficiency at low current densities and purity of the produced gasses, again especially at low current densities. Significant development was achieved in ASM synthesis in last decade and first promising materials are being commercially available. Despite the fact that many of the novel materials are tested in single cells under conditions of the membrane alkaline water electrolysis, the information on the stack behaviour are rare. In our work, we focused on the comparison of the porous diaphragm type and ASM separators in short stack comprising of 3 cells and geometrical area of the separator 78.5 cm2 under different operational conditions in terms of performance achieved. Besides the performance characterisation by mean of the load curve measurement, the complementary information on the gas purity, current efficiency and long-term stability were gathered for ASM separator. Zirfon Perl UTP 500 (Agfa, Belgium) was used as diaphragm type separator, meanwhile chloromethylated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene backbone functionalized by DABCO groups was used as ASM (TailorMem s.r.o., Czech Republic). Different concentrations of the liquid electrolyte represented by KOH solution were used in the range 1 – 15 wt.%. The temperature effect was verified at the same time by using the temperature of 25 and 40 °C. Load curves were measured galvanostically up to current density of 600 mA cm-2. The current efficiency was calculated based on the Faradays law by measuring the real oxygen production and comparing with theoretical value. The gas purity was measured for oxygen stream as the penetration of hydrogen into the oxygen stream is more important. Gas chromatography was used to measure the oxygen stream composition. The long-term stability was measured in 10 wt.% KOH solution at 40 °C at 240 mA cm-2. The results obtained indicate that at low KOH concentrations the performance of membrane alkaline water electrolysis is significantly better when compare to application of the diaphragm type separator. The differences in performance mitigated at increasing concentration. The characterisation of the membrane alkaline water electrolysis short-stack showed possibility to achieve high purity of the produced gasses and current efficiency even at low current densities. The long-term test showed excellent stability of the used ASM. Acknowledgement: This project has received funding from the European Union‘s Horizon 2020 Research and innovation action under grant agreement No 862509. Financial support by the Technology agency of the Czech Republic within the framework of the project No. TK02030103 is gratefully acknowledged.

The effect of membrane properties on the vanadium-oxygen fuel cell performance was studied on a series of commercially available ion exchange membranes of different thickness and ion exchange capacity by selected characterization techniques including electrochemical impedance spectroscopy (ohmic and charge transfer resistance), steady load curves (performance stability) and galvanostatic charge-discharge cycles (efficiencies and capacity decay). Performance stability of the fuel cell was studied under defined conditions (state of charge, temperature, air flow rate) using continuous charging of vanadium electrolyte. In contrast to the previous studies, our results revealed that the membrane affects the fuel cell performance mainly via water management in the catalytic layer of gas diffusion cathode, while vanadium permeation across the membrane has only a minor impact. Generally, the fuel cell shows improved performance stability for more conductive membranes (thinner and with higher ion-exchange capacity), partially due to reduced ohmic losses, but more significantly due to the better ability of the membrane to drain water from the cathode via osmosis, which prevents the flooding of the cathodic catalytic layer. With the optimized membrane, we achieved stable fuel cell performance at the highest current and power density values reported (75 mA cm−2 and 57 mW cm−2 in 50% state of charge).

The paper presents a generalized Poisson-Nernst-Planck model of an yttria-stabilized zirconia electrolyte developed from first principles of nonequilibrium thermodynamics which allows for spatial resolution of the space charge layer. It takes into account limitations in oxide ion concentrations due to the limited availability of oxygen vacancies. The electrolyte model is coupled with a reaction kinetic model describing the triple phase boundary with electron conducting lanthanum strontium manganite and gaseous phase oxygen. By comparing the outcome of numerical simulations based on different formulations of the kinetic Eqs. with the results of EIS and CV measurements we attempt to discern the existence of separate surface lattice sites for oxygen adatoms and surface oxides from the assumption of shared ones. Moreover, we show that the mass-action kinetics model is sensitive to oxygen partial pressure unlike exponential kinetics models. The resulting model is fitted to a dataset of EIS and CVs spanning multiple temperatures and pressures, using various relative weights of EIS and CV data in the fitness function. The model successfully describes the physics of the interface around the OCV.

Today the search for new energy resources is a crucial topic for materials science. The development of new effective catalysts for the oxygen reduction reaction can significantly improve the performance of fuel cells as well as electrocatalytic hydrogen production. This study presents the scalable synthesis of nitrogen-doped graphene oxide for the oxygen reduction reaction. The combination of an ab initio theoretical investigation of the oxygen reduction reaction (ORR) mechanism and detailed electrochemical characterization allowed the identification of electrocatalytically active nitrogen functionalities. The dominant effect on electrocatalytic activity is the presence of graphitic and pyridinic nitrogen and also N-oxide functionalities. The overpotential of ORR for nitrogen-doped graphene oxide prepared by microwave-assisted synthesis outperformed the metal-doped graphene materials.

Proton exchange membrane water electrolysis (PEM WE) suffers from several issues, such as the high cost and low stability of the electrolyser unit components. This is especially evident for an anode polarised to a high potential and in contact with an acidic membrane. Such a combination is detrimental to the vast majority of electron-conducting materials. Nowadays Ti (possessing a protective passive layer on its surface) is used as the construction material of an anode gas diffusion layer. Since the passivation layer itself is non-/semiconducting, an excessive degree of passivation leads to high surface contact resistance and to energy losses during PEM WE operation. This problem is usually solved by coating the Ti surface with precious metals. This leads to a further increase of the already very high cell investment costs. In this work an alternative method based on appropriate Ti etching (in acid) is presented. The (surface) composition of the samples treated was investigated using SEM, X-ray fluorescence and diffraction and photoelectron spectroscopy. TiHx was found in the subsurface layer. This was responsible for preventing excessive passivation of the Ti metal. The superior performance of the etched Ti gas diffusion layer (compared to non-etched) in a PEM water electrolyser was confirmed during an (> 100 h) experiment with current densities of up to 1 A cm− 2. Using the described treatment the surface contact resistance was substantially reduced and its increase during PEM WE operation was largely suppressed. As this method is very simple and cheap, it has tremendous potential for improving PEM WE process efficiency.

This review summarizes recent progress in understanding the oxygen reduction and evolution (OER) reactions at the lanthanum strontium manganite electrode of a high-temperature solid oxide cell. Information provided here is put into the perspective of the defect chemistry of lanthanum strontium manganite and its impact on the electrode reaction mechanisms itself. After summarizing recent views on the oxygen reduction reaction mechanism, the focus turns to the OER, which is significantly less treated in the literature. A combination of the information in the literature on both reactions was the basis for modified reaction mechanism of the OER to be proposed under consideration of recent experimental observations and theoretical findings.

In this study the behaviour and structure of a Nafion® 117 membrane exposed to liquid water at temperatures and pressures of up to 150 °C and 700 kPa, respectively, were investigated. The results clearly showed that, as the temperature of the environment approaches or exceeds the glass transition temperature of the membrane, it undergoes extensive swelling. This is connected with several changes in the membrane structure which have a predominantly detrimental influence on the functional properties of the membrane, such as ionic conductivity and ionic exchange capacity. The extent and rate of the changes increase with both rising temperature and pressure. While the changes at 150 °C and 700 kPa take place in the order of tens of minutes, at 110 °C and 500 kPa several hundreds of hours are required. The changes are enabled by amorphisation of pseudo-crystalline domains which are responsible for keeping the membrane structure intact. The changes in the internal structure were followed using small-angle X-ray scattering and visualised by current-sensing atomic force microscopy.

Within this contribution an experimental analysis of a 50 cm long single-channel polymer electrolyte membrane water electrolysis cell is presented. The current density and the temperature distribution along the channel coordinate is measured with a printed circuit board setup that enables a very fine resolution of 252 independent measurement segments. After first cell testings in a steady state mode, effects of changed amounts of feed water flux on the cell voltage, the distribution of current density and the temperature profile were investigated. Although the water feed did not significantly influence the current density distribution over a wide range of water fluxes, very low water fluxes lead to a massive drop in the current density in the rear part of the active area and a moderate increase at the inlet. This growing heterogeneity influenced the temperature distribution as well as the cell voltage.

In this study a novel alkaline polymer electrolyte membrane is presented, based on polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PSEBS) functionalized by the 1,4-diazabicyclo[2.2.2]octane (DABCO) to be used as an electrode compartment separator as well as a catalytic layer binder in the alkaline water electrolysis process with the aim to reduce the concentration of KOH in the liquid electrolyte and to allow the construction of an efficient zero gap-type cell. This material was selected due to the promising properties of both individual components resulting from their molecular structure. The prepared membrane was thoroughly characterized with regard to its stability in an alkaline environment. The prepared membrane showed an ion-exchange capacity value of 0.76 mmol g −1 dry membrane and ionic conductivity of 7.5 S m −1 at 30 °C. Excellent membrane durability was confirmed for a KOH concentration range up to 10 wt.% and temperature up to 50 °C. Subsequently, the polymer electrolyte was tested in a laboratory alkaline water electrolyser using 10 wt.% KOH as a circulating medium showing promising current density of 150 mA cm −2 at 40 °C. In a 150-hour experiment the PSEBS functionalized by DABCO manifested very good stability and high potential for optimization for this process as it showed no signs of chemical degradation.

A microporous layer represents an important element of the gas diffusion electrodes used in polymer electrolyte membrane (PEM) fuel cells and water electrolysers. It forms an interface between the nanostructured catalyst layer and the macrostructured electrode body. In the case of PEM water electrolysis such a layer has only been applied to the cathode to date. On the other hand, it is typically absent on the anode side of the cell. In the present study, such a layer was integrated into the anode of a PEM water electrolyser. It was based on antimony-doped tin oxide placed on titanium felt forming the electrode backing. Using an in-house synthesised IrO2, gas diffusion anodes were manufactured with and without the microporous layer and their performance compared in a laboratory PEM water electrolyser. Current–voltage curves and electrochemical impedance spectra were recorded. The results revealed that the microporous layer is only advantageous in a range of low current densities, while at higher current densities the ohmic resistance of the microporous layer significantly reduces the efficiency of electrolysis.

In this paper, a rotating rod electrode disk is introduced as a hydrodynamic electrode and both the electrolyte flow hydrodynamics as well as mass transport towards the disk were investigated and compared with the rotating disk electrode. The main difference to the rotating disk is the absence of disk insulation leading to slightly enhanced mass transport towards the disk surface. Based on a combination of experiments and mathematical modelling for a broad range of kinematic viscosity values of the electrolyte solution, a correction of the Levich equation was introduced. This enables recalculation of the data determined using the rotating rod disk electrode so that they are equivalent to those of the rotating disk electrode. Although glassy carbon was used as the material of the rotating rod electrode in this work, in principle any other suitable material can be used. Thus, it can be concluded that the rotating rod electrode disk represents a cheap and effective tool easily applicable for measurements with controlled electrolyte convection in systems that are hardly manageable using a conventionally constructed rotating disk electrode. Good examples are melts or electrolyte solutions at temperatures above 80 °C. The applicability of the rotating rod electrode disk was successfully tested in the continuation (Part II) of this study. There, the thin-film modified (activated) rotating rod electrode disk was used for determining the mass transport properties of the oxygen and kinetic constants of the oxygen reduction reaction in concentrated phosphoric acid at 160 °C.

In this paper a novel and simple method to determine the O 2 reduction reaction activity of Pt/C in 99% H 3 PO 4 at a temperature of 160 °C using a well-established thin film procedure is reported. It utilizes a disk of rotating rod made of glassy carbon as a working hydrodynamic electrode. By introducing polybenzimidazole as a thin film polymer binder, a modified rotating rod electrode disk (the cylindrical part is electrochemically inactive under the conditions used) suitable for measurements in hot concentrated H 3 PO 4 was obtained. Using this electrode together with the Koutecky-Levich equation modified for rotating rod electrode hydrodynamics, the kinetics of the oxygen reduction reaction and mass transfer parameters of O 2 in 99% H 3 PO 4 at 160 °C were successfully determined. The presented method can be easily used to determine the activity of various catalysts under conditions which preclude the use of a conventional rotating disk electrode.

In this work, the Ni-Co spinel oxides are synthesized via different methods and using different calcination temperatures. Properties of the prepared materials are compared. The best route is selected and used to prepare a Ni1+xCo2−xO4 (−1 ≤ x ≤ 1) series of materials in order to investigate their catalytic activity towards the oxygen evolution reaction (OER). The results show that hydroxide preparation yields NiCo2O4 oxide with the highest activity. 325 °C is identified as the optimum calcination temperature. Subsequently, the catalysts are tested in an electrolysis cell. To prepare an anode catalyst layer based on NiCo2O4 catalyst on top of a nickel foam substrate for membrane electrode assembly (MEA) construction, following polymer binders are used: anion-selective quaternized polyphenylene oxide (qPPO), inert polytetrafluoroethylene (PTFE®), and cation-selective Nafion®. qPPO ionomer containing MEA exhibited highest OER activity. The current density obtained using a MEA containing qPPO binder attains a value of 135 mA cm−2 at a cell voltage of 1.85 V. After 7 h chronopotentiometric experiment at a constant current density of 225 mA cm−2, the MEA employing PTFE® binder shows higher stability than the other binders in alkaline water electrolysis at 50 °C. Under similar conditions, stability of the PTFE®-binding MEA is examined for 135 h.

This chapter deals with hydrogen production by water electrolysis. It first presents a history of the development of water electrolysis technology. In the next part the focus is on the fundamentals of water electrolysis thermodynamics and the kinetic aspects of this process. Engineering aspects concerning the design of the electrolysis stack and the selection of system components are covered in a later part. The final part of this chapter provides a detailed description of water electrolysis technologies. Beside traditional technologies, that is, alkaline, and emerging water electrolysis technologies, that is, polymer electrolyte and high-temperature processes, chlor-alkali electrolysis of brine is also addressed. Although, in the latter case, hydrogen only represents a side product, it now produces the majority of hydrogen originating from water decomposition by electrolysis.

Polybenzimidazole-type polymer doped with H3PO4 is commonly used as the proton-conductive phase in high-temperature proton-exchange membrane fuel cells. However, H3PO4 is not stable during fuel cell operation and undergoes reduction by hydrogen on a Pt surface to phosphorus compounds in a lower oxidation state, such as H3PO3. In this work the kinetics of H3PO3 oxidation on Pt electrode was studied, including an investigation of H4P2O6 as a possible oxidation intermediate. H3PO3 adsorption in hydrogen underpotential deposition region was described by a triple Langmuir isotherm corresponding to adsorption on specific Pt crystalline planes. Co-adsorption of hydrogen as well as SO42−, HSO4− ions decreased the total amount of adsorbed H3PO3. The determined apparent charge transfer coefficients of H3PO3 anodic oxidation on a metallic Pt surface were found to be concentration and temperature-dependent, indicating that the nature of the anodic process is complex. From chronopotentiometric measurements of H3PO3 and H4P2O6 oxidation on a preoxidised Pt surface it was concluded that, while H3PO3 is oxidised by means of a chemical reaction with PtOx, H4P2O6 undegoes anodic oxidation on the PtOx surface. According to voltammetry and bulk electrolysis experiments H4P2O6 is not formed as an intermediate product during electrochemical oxidation of H3PO3 on a metallic Pt surface.

Despite the advantages of high temperature polymer electrolyte fuel cells (HT-PEM FCs) over low temperature PEM-FC, like higher tolerances against CO, degradation rates are higher in comparison to LT-PEM fuel cells. The best published degradation rates, achieved with HT-PEM FCs so far, constitute 4.9 µV/h under pure hydrogen and air supply and an operating temperature of 160 °C [1-2]. Low temperature PEM fuel cells under optimal conditions and a working temperature of 75 °C show very low degradation rates of 1-2 µV/h [3]. Therefore, one of the most important tasks within the European project CISTEM (Construction of Improved HT-PEM MEAs and Stacks for Long Term Stable Modular CHP Units, GA-No. 325262) is, next to the development of a new HT-PEM fuel cell based Combined Heat and Power (CHP) technology, to realize degradation rates with values less than 4 µV/h. The test conditions have been defined by the FCH JU: Single cell test with 25 cm²-MEAs Constant current density: 0.3 A/cm² Hydrogen and air supply (λ=1.5/2) Temperature: 160 °C Min. test duration: 2,000 hours The tests have been performed with Dapozol®-G55 MEAs with thermally cured polybenzimidazole (PBI) membrane and Pt/C based electrodes (BoA1-MEAs), developed and provided by Danish Power Systems and delivered to the facilities of different partners. The distribution of new MEAs and testing at three different lab facilities under agreed identical operating conditions support and verify achieved degradation results perfectly. Electrochemical investigation with polarization curves have been performed at Begin of Life (BoL), every 1,000 hours of operation and at the End of Test (EoT). The characterization has been completed with ante- and post-mortem micro-computed tomography (µ-CT). Several tests have been performed, three representatives are shown in Figure 1 and the corresponding degradation rates are listed in Table 1. The average degradation rate of the long term tests presented in this work results in 1.7 µV/h and this value correlates with the average degradation rate of LT-PEM fuel cells [3]. To verify the influence of different test conditions on the degradation rates, these experiments have been compared with constant load (0.3 A/cm²) long term tests under different fuel and oxidant compositions, with different flow field designs (serpentine and grid flow fields) and performed with complete in-situ electrochemical characterization procedures (polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry). These investigations enable the determination of the best possible operating conditions for HT-PEM fuel cells to achieve ultralow degradation rates. Figure 1:Voltage changes as function of time under hydrogen and air supply (λ=1.5/2.0) and degradation rates, 160°C, 0.3 A/cm², Dapozol®-G55-MEAs. Test at UCTP still in progress. References: 1. S. Yu, L. Xiao, B.C. Benicewicz, Fuel Cells, 08, 3-4, 165-174 (2008). 2. T.J. Schmidt, J. Baurmeister, ECS Transactions 3, 1, 861-869 (2006). 3. F.A. de Bruijn, V.A.T. Dam, G.J.M. Janssen, Fuel Cells, 08, 1, 3-22 (2008). Figure 1

The present study deals with the development and characterisation of a carbon electrode for the process of capacitive deionisation (CDI). Special attention was paid to an analysis of the decline in electrode performance over time and to a more detailed understanding of the related degradation processes. Besides electrode blockage by Ca2+ and Mg2+ precipitates, an additional degradation process, resulting in an irreversible electrode surface modification reducing its salt adsorption capacity, was identified. The mechanism of electrode surface modification based on the anodic oxygen evolution reaction, as well as the interaction of the surface modified by on this way formed oxygen containing functional groups with charged species present in the treated water, were discovered. A method of preventing or at least reducing the above-mentioned degradation process is proposed.

Degradace Pt katalyzátoru je jedním z největších problémů ve vysokoteplotních palivových článcích s PEM membránami (HT PEM FC). Přestože na toto téma bylo napsáno mnoho publikací, nebyl doposud jasně objasněn vztah mezi růstem velikosti nanočástic Pt a provozními podmínkami HT PEM FC. Cílem předkládané práce je určit závislost růstu nanočástic Pt na provozním napětí HT PEM FC pomocí experimenálních pokusů s individuálními palovovými články (single cell) s následnou post-mortem analýzou katalytických vrstev na obou elektrodách. Dlouhodobé experimenty za dobře definovaných podmínek prováděné za konstatního napětí v kombinaci s několika post-mortem instrumentálními metodami umožnily předpověď vývoje distribuce nanočástic Pt v čase. Při vyšších napětích byl růst velikosti nanočástic Pt méně výrazný než při napětích nižších. To je pravděpodobně způsobeno změnou rychlost určujícího kroku při růstu velikosti nanočástic Pt. Degradation of the Pt catalyst is one of the most serious problems related to the high-temperature fuel cell with a proton-exchange membrane (HT PEM FC). Despite many publications on this topic, no clear relationship between Pt nanoparticle growth and HT PEM FC operating conditions has been formulated yet. The goal of the presented study is to determine the dependence of Pt nanoparticle growth on the operational voltage of the HT PEM FC by means of experimental single-cell testing with subsequent post mortem analysis of the catalyst layers on the two electrodes. Well-defined, long-term tests performed at constant voltage in combination with several post mortem instrumental methods enabled the prediction of the development of Pt nanoparticle distribution. At higher voltages, Pt nanoparticle growth was less pronounced than at low voltages. This was likely caused by the change in the rate-limiting step in Pt nanoparticle growth.

In this work a systematic study of the behaviour of a Nafion 117 membrane under conditions of elevated temperatures (up to 150 °C) and pressure (up to 0.7 MPa) was carried out. Attention focused primarily on the ionic conductivity of the membrane in the proton form with exposure to the conditions under study for up to 800 h. The ion-exchange capacity, morphology, FTIR and NMR spectra of the membrane were determined to explain the decline in conductivity observed over time. The techniques used did not reveal any chemical degradation of the membrane polymer. The morphological changes to the membrane connected with excessive expansion of the internal structure of the polymer are assumed to be the reason for the phenomenon observed. Finally, to confirm the conclusions derived, the membrane behaviour in a laboratory-scale water electrolysis cell was studied under operating conditions corresponding to its prior characterization.

NiFe 2 O 4 electrocatalyst for the hydrogen evolution reaction (HER) has been synthesized using the co-precipitation method of the respective metal ions from water solution. After calcination of the precipitate, the resulting electrocatalyst was characterized by a broad range of techniques to obtain information on its crystallographic structure, specific surface area, morphology and chemical composition. The electrocatalytic activity towards HER in alkaline water electrolysis was investigated by means of linear sweep voltammetry. The catalyst showed promising electrocatalytic properties. Subsequently three types of binders were used to prepare a cathode catalytic layer based on a catalyst synthesized on top of a nickel foam support, namely an anion-selective quaternized poly(phenylene oxide) (qPPO) ionomer, an electroneutral polymer polytetrafluoroethylene and cation-selective Nafion ® . The resulting membrane-electrode assemblies (MEAs), based on an anion-selective membrane, were tested in an alkaline water electrolyzer. In a single-cell test the MEA with a qPPO ionomer exhibited higher HER activity compared to the remaining binders tested. The current density obtained using a MEA containing qPPO binder attained a value of 125 mA cm −2 at a cell voltage of 1.85 V. The stability of the MEA containing qPPO binder was examined by continuous operation for 143 h, followed by 55 h intermittent electrolysis.

In the field of polymer electrolyte membrane water electrolysis (PEMWE), a significant amount of excellent scientific results has been generated during the past decades. However, the comparability and reproducibility of these results between different cell types and different laboratories is not always straightforward. In this contribution, an exemplary ring experiment on the single-cell level compares the performances of three cell types: the differential cell ($${4}{\text { cm}^{2}}$$) and two integral cells: an elongated cell ($${50.4}{\text { cm}}\times {0.45}{\text { cm}}$$) and a circular cell ($${63.5}{\text { cm}^{2}}$$). Therefore bi- and trilateral experiments were carried out with differently prepared catalyst-coated membranes (CCMs) and porous transport layers (PTLs) as well as with an alternative catalyst-coated electrode (CCE) concept in three laboratories. This contribution aims to evaluate the grade of systemic inequality, which still permits a comparison of individual parameters. The comparison of CCM preparation methods showed no significant influence on the initial electrochemical characteristics. An HCl etching of the anode PTLs in two different cells confirmed to be a useful treatment for the reduction of Ohmic losses in PEMWE cells. Self-made CCEs could not serve as an alternative concept, owing to their inadequate contact between the electrode and the membrane, which was observed in three laboratories as well. The general compatibility between the different cells was proven by the observation of a phenomenon in one laboratory that could be reproduced in one or two other laboratories. In this context, the size and geometry of the single cells did not influence the performance, indicating that up to the present measuring range and with sufficient water feed rates, the different single cells were functioning comparably.

To find cheap, efficient and durable hydrogen evolution reaction catalysts is one of the major challenges when developing an alkaline water electrolysis system. In this paper we describe an electrochemically reduced graphene oxide (RGO)-modified Ni electrode, which could be used as a pre-eminent candidate for such a system. The experimentally determined characteristics of this electrode showing superior electrocatalytic activity were complemented by density functional theory calculations. Thermodynamic considerations led to the conclusion that H atoms, formed upon H2O discharge on Ni, spill onto the RGO, which serves as an H adatom acceptor, enabling continuous cleaning of Ni-active sites and an alternative pathway for H2 production. This mode of action is rendered by the unique reactivity of RGO, which arises due to the presence of O surface groups within the graphene structure. The significant electrocatalytic activity and life time (>35 days) of the RGO towards the HER under conditions of alkaline water electrolysis are demonstrated.

Reverse electrodialysis (RED) is one of the most promising membrane-based processes for renewable energy generation from mixing two solutions of different salinity. However, the presence of Mg2+ in natural water has been shown to drastically reduce open circuit voltage (OCV) and output power of RED. To alleviate this challenge, commercial cation exchange membranes (CEM) supplied by Fujifilm Manufacturing Europe B.V. (The Netherlands) were chemically modified by polypyrrole (PPy)/chitosan (CS) composites under controlled Pyrrole (Py) concentration (0.025–1 M) and polymerization time (0–8 h). The modified membranes were physically characterized by FTIR, SEM and EDX along with the determination of key electrochemical properties like ion exchange capacity, ionic conductivity, monovalent selectivity and swelling degree. The monovalent selectivity (Na+ vs Mg2+) of the modified membranes, evaluated based on flux of ions by diffusion dialysis, indicated up to 3-fold improvement compared to pristine membranes inline with the enhanced OCV (up to 20%) during RED test in multi-ion solution. This was obtained without significant change in membrane and interface resistances as depicted by electrochemical impedance spectroscopy. The modified membranes displayed power densities in the range of 0.6–1.5 W/m2MP (MP: membrane pair) with more than 42% improvement compared to pristine membranes during RED test with multi-ion solutions. Although there is a gap for further improvement, these findings highlight a promising use of conducting polymers to design a highly selective and conductive membrane for RED.

Poly(vinylphosphonic acid-co-acrylonitrile) with various concentrations of vinylphosphonic acid polymer units were prepared by free radical solution polymerization. The membranes were prepared by casting polymer solutions in N,N′-dimethylformamide and evaporating the solvent. Thermogravimetric analysis showed the stability of prepared membranes up to 175°C, and membranes were stable in oxidative Fenton reagent for 1 h at 70°C. The membranes of polymers containing more than 16 mol% of units with phosphonic acid group swelled excessively in water. The ionic conductivity of membranes increased with the increasing concentration of polymer units with a phosphonic acid group in the polymer chain and with temperature. The conductivity of a membrane with 15.5 mol% of polymer units with a phosphonic acid group was 5.15 S m−1 at 35°C. Membrane containing 15.5 mol% phosphonic acid units in polymer was tested in fuel cell.

Within the framework of this work, spinel-type ternary transition metal oxides of nickel, cobalt and iron with the composition FexNi1−xCo2O4 (0 ≤ x ≤ 1) were prepared and tested as promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline water electrolysis. The hydroxide precipitation method was used for the synthesis. The morphology, structure and specific surface area of the prepared electrocatalysts were determined by means of scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, the Brunauer Emmet Teller method and X-ray photo electron spectroscopy. The electrochemical properties were tested by thin-film technique on a rotating disk electrode and in a single-cell laboratory water electrolyzer coupled with electrochemical impedance spectroscopy. The OER studies indicate that substitution of Ni by Fe increases the electrocatalytic activity of the resulting material significantly. The highest activity was achieved for x = 0.1. Whereas the current density obtained using a pure nickel anode in the water electrolysis test was 54 mA cm−2 at a cell voltage of 1.85 V, in the case of the anode modified with NiCo2O4 catalyst the value was 87 mA cm−2. Using ternary transition metal oxides in the water electrolysis test and under identical conditions, the catalyst with the highest activity displayed a current density of 115 mA cm−2.