Polysulfone-poly(vinyl alcohol) composite diaphragm doped with boehmite for alkaline water electrolysis

In this study, poly(styrene-co-vinyl benzyl trimethyl ammonium chloride) with different styrene to vinyl benzyl chloride ratio (3:1, 1:1, 1:2) have been synthesized. The formation ofproducts was confirmed by Fourier transform infrared spectrophotometry (FTIR) and nuclear magnetic resonance spectra (1H NMR). Then, anion exchange membranes were prepared by combination of poly(styrene-co-vinyl benzyl trimethyl ammonium hydroxide) and poly (vinyl alcohol) The obtained membranes were evaluated for their own conductivity, anion exchange capacity, and thermal decomposition. The results showed that the anion exchange membrane produced from copolymer with styrene to vinyl benzyl chloride ratio 1: 2 exhibited good hydroxide conductivity of 7 mS/cm, ion exchange capacity was 0.65mmol/g and stability to 200oC.
 Keywords
 Membrane, poly(vinyl alcohol), copolymer, conductivity, fuel cell.
 References
 [1] D. J. Kim, C. H. Park, S. Y. Nam, Characterization of a soluble poly(ether ether ketone) anion exchange membrane for fuel cell application, Int. J. Hydrogen Energy 41 (2016) 7649-7658. https:// doi.org/10.1016/j. ijhydene.2015.12.088[2] J. Fu, J. Qiao, H. Lv, J. Ma, X.-Z. Yuan, H. Wang, Alkali doped poly(vinyl alcohol) (PVA) for anion-exchange membrane fuel cells - Ionic conductivity, chemical stability and FT-IR characterizations, Alkaline Electrochem. Power Sources 25 (2010) 15–23. http://doi.rog/10.1149/ 1.3315169[3] D. L. Zugic, I. M. Perovic, V. M. Nikolic, S. L. Maslovara, M. P. Marceta Kaninski, Enhanced Performance of the Solid Alkaline Fuel Cell Using PVA-KOH Membrane, Int. J. Electrochem. Sci. 8 (2013) 949-957. [4] Jikihara, R. Ohashi, Y. Kakihana, M. Higa, and K. Kobayashi, Electrodialytic transport properties of anion-exchange membranes prepared from poly(vinyl alcohol) and poly(vinyl alcohol-co-methacryloyl aminopropyl trimethyl ammonium chloride), Membranes (Basel) 3 (2013) 1-15. http: //doi.rog/10.3390/membranes3010001[5] S. Vengatesan, S. Santhi, S. Jeevanantham, G. Sozhan, Quaternized poly(styrene-co-vynylbenzyl choloride) anion exchange membranes for alkaline water electrolysers, Journal of Power Sources 84 (2015) 361-368. https://doi.org/10.1016/j.jpowsour. 2015.02.118[6] L. E. Shmukler, N. V. Thuc, and L. P. Safonova, Conductivity and thermal stability of proton-conducting electrolytes at confined geometry of polymeric gel, Ionics 19 (2013) 701-707. https:// doi.org/10.1007/s11581-012-0800-2[7] D//A. Lewandowski, K. Skorupska, J. Malinska, Novel poly(vinyl alcohol)–KOH–H2O alkaline polymer electrolyte, Solid State Ionics 133 (2000) 265-271. https://doi.org/10.1016/S0167-2738(00) 00733-5 [8] Jun F, Y. Wu, Y. Zhang, M. Lyu, J. Zhao, Novel anion exchange membranes based on pyridinium groups and fluoroacrylate for alkaline anion exchange membrane fuel cells, Int. J. Hydrogen Energy 40 (2015) 12392-12399. https://doi.org/10. 1016/j.ijhydene.2015.07.074[9] Géraldine M, M. Wessling, K. Nijmeijer Anion exchange membranes for alkaline fuel cells: A review, Journal of Membrane Science, 377(2011) 1-35. https://doi.org/10.1016/j.memsci.2011.04.043.
 

N3-butyl imidazolium-based anion exchange membranes blended with Poly(vinyl alcohol) for alkaline water electrolysis

Alkaline ion-solvating membranes, such as those based on polybenzimidazole (PBI), offer high ion conductivity and good gas barrier properties, making them promising for next-generation alkaline water electrolyzers.1 However, the stability of commonly used PBI derivatives is limited due to gradual backbone degradation. Consequently, alternative PBI chemistries and other polymer options like poly(vinyl alcohol),2 and carboxylate functionalized styrene-ethylene-butylene copolymers are being explored to address this inherent stability issue.3 In this study, we present the synthesis and characterization of a novel type of ion-solvating membranes for alkaline water electrolyzers. These membranes are based on tetrazole functionalized polymers derived from poly(styrene-co-acrylonitrile). A one-step click-type [3+2] cycloaddition reaction was utilized to introduce tetrazole pendants by converting acrylonitrile groups in poly(styrene-co-acrylonitrile). The degree of functionalization was controlled by adjusting the content of acrylonitrile units in the polymer. Subsequent treatment in aqueous KOH solution led to the formation of negatively charged tetrazolide pendants with high ionization degrees.The alkaline stability of the tetrazolides was evaluated using both DFT simulations and model compound studies, demonstrating remarkable stability with no degradation observed for over 3000 hours in 25 wt.% KOH at 80 °C. Physicochemical properties such as electrolyte uptake, swelling behavior, thermal stability, and ion conductivity were assessed for the synthesized polymers. The electrolyte-imbibed membranes exhibited high ion conductivity, reaching up to 90 mS cm-1 in 15 wt% KOH at 80 °C. Electrolysis operation using these membranes showed stable performance for 600 hours with no signs of degradation. 1 D. Aili, M. R. Kraglund, S. C. Rajappan, D. Serhiichuk, Y. Xia, V. Deimede, J. Kallitsis, C. Bae, P. Jannasch, D. Henkensmeier, J. O. Jensen, ACS Energy Letters, 2023, 1900–1910. 2 Y. Xia, S. C. Rajappan, D. Serhiichuk, M. R. Kraglund, J. O. Jensen, D. Aili, J Memb Sci 2023, 680, 121719. 3 D. Serhiichuk, D. Tian, M. R. Almind, Z. Ma, Y. Xia, M. R. Kraglund, C. Bae, J. O. Jensen, D. Aili ACS Applied Energy Materials 2024 7 (3), 1080-1091 Figure 1 Tetrazolation of poly(styrene-co-acrylonitrile) and formation of corresponding potassium tetrazolide following equilibration in aqueous KOH. Figure 1

This study evaluates the techno-economic feasibility of solar-based green hydrogen potential for off-grid and utility-scale systems in Niger. The geospatial approach is first employed to identify the area available for green hydrogen production based on environmental and socio-technical constraints. Second, we evaluate the potential of green hydrogen production using a geographic information system (GIS) tool, followed by an economic analysis of the levelized cost of hydrogen (LCOH) for alkaline and proton exchange membrane (PEM) water electrolyzers using fresh and desalinated water. The results show that the electricity generation potential is 311,617 TWh/year and 353,166 TWh/year for off-grid and utility-scale systems. The hydrogen potential using PEM (alkaline) water electrolyzers is calculated to be 5932 Mt/year and 6723 Mt/year (5694 Mt/year and 6454 Mt/year) for off-grid and utility-scale systems, respectively. The LCOH production potential decreases for PEM and alkaline water electrolyzers by 2030, ranging between 4.72–5.99 EUR/kgH2 and 5.05–6.37 EUR/kgH2 for off-grid and 4.09–5.21 EUR/kgH2 and 4.22–5.4 EUR/kgH2 for utility-scale systems.

A series of poly(vinyl alcohol-co-vinyl acetal) gel electrolytes was synthesized, characterized and assessed as electrode separators in alkaline water electrolysis. The copolymers were prepared by reacting poly(vinyl alcohol) with benzaldehyde or 4-formylbenzoic acid under acidic conditions at different ratios, and visually homogenous and water-insoluble membranes were subsequently obtained by solution casting. The physicochemical characteristics in terms of electrolyte uptake, swelling behavior, and ion conductivity could be tuned by varying the degree of functionalization. At a moderate vinyl acetal content of 5%, the membrane combined mechanical robustness with ion conductivity reaching 36 mS cm−1 in 30 wt% aqueous KOH at room temperature. Current densities of up to 1000 mA cm−2 were reached with uncatalyzed Ni-foam electrodes at a cell voltage of less than 2.6 V in alkaline water electrolysis tests, while the membrane effectively prevented hydrogen crossover. Although apparent membrane degradation was observed after a few days of electrolysis operation, the strategies presented in this work to tune membrane properties are of general relevance to the field towards the development of new ion-solvating membrane systems based on more alkaline stable and robust backbone chemistries.

Introduction In order to solve depletion of fossil fuels and global warming by CO2emission, the introduction of renewable energies such as solar and wind power has been promoted. Here, these renewable energies are fluctuated with uneven distribution. So the technologies of the energy conversion from renewable electric power to hydrogen by water electrolysis and the energy storage and transportation with hydrogen have been paid attention. With a perspective of practice use, alkaline and polymer electrolyte water electrolysis have potential to these applications. Especially, alkaline water electrolysis has advantage in large-scale energy system due to lower plant costs with common materials. In a bipolar type alkaline water electrolysis, electrolyte is fed via manifolds to anode or cathode chambers. Then leak circuits through ionic conduction are formed and it leads to several problems. During electrolysis, leak current flows through electrolyte in the manifolds, and decreases current efficiency. After electrolysis, reverse current, which flows through the bipolar plates in the opposite direction to that during electrolysis, leads to the degradation of electrodes1) - 3). However its mechanism has not been understood enough. Therefore, the mechanism should be understood to reduce these currents. In this study, we have investigated the relationship among the operating conditions of alkaline water electrolyzer, the cell voltage and leak or reverse current to clarify the mechanism. Experimental The electrolyzer consisted of two cells connected in a series with external manifold. The anodes and the cathodes were Ni mesh, and Nafion membranes (NRE212CS) were used as the separator. Projected area of the electrodes was 27.8 cm2. The electrolyte of 7.0 M (=mol・dm-3) NaOH solution was fed to electrode chambers at 25 ml・min-1. The temperature of the electrolyte was controlled at 25 ℃. Leak current was measured during electrolysis in the current density region from 100 to 600 mA・cm-2 for 60 min. Electrolysis was stopped by opening the external circuit, and reverse current was measured. The electronic current through external circuit, the ionic currents through manifolds, and the cell voltages were measured to determine leak and reverse currents. Here, U 1 and U 2were the cell voltages of the anode terminal side cell and the cathode terminal side cell, respectively. The ionic current was measured by DC milliampere clamp meter (KEW 2500). Results and discussion Figure 1 shows ionic currents through manifold (a) and the cell voltages (b) during and after electrolysis as a function of time. The leak current, during electrolysis over the first 60 min, increased with loading current density. Since the potential difference between the ends of the manifold increased with the terminal voltage of the electrolyzer, the leak current increased following Ohm’s law. At this time, the ratio of leak current to the loading current increased with the decrease of the loading current. Even if each cell voltage is lower than theoretical decomposition voltage, the sum of the cell voltages of the electrolyzer will be able to be larger than theoretical decomposition voltage. This moment, most of current flows through manifold, and the ratio of leak current is very large. After electrolysis, the reverse current flowed around 80 min for all loading current, and the current increased with loading current. The U 2 was about 1.3 V for 80 min while reverse current was observed, and then decreased to about 0.3 V regardless of loading current density while on the other hand U 1 was almost constant around 1.3 V. Since the state of the terminal electrodes could not change after electrolysis with open circuit, the decrease of the reverse current and the U 2 should result from the anode on the bipolar plate. Considering the electromotive force for reverse current, the possible redox should be reduction of the oxidized anode surface of NiOOH to Ni(OH)2 or dissolved oxygen to OH- and oxidation of the reduced surface of Ni to Ni(OH)2 or dissolved hydrogen to OH-. In these couples, only the combination of [NiOOH/Ni(OH)2] and [H2/OH-] should show 1.3 V. Therefore these reactions should be the electromotive force for the reverse current. Figure 2 shows electric charge of the reverse current as a function of the loading current density during electrolysis. The electric charge increased with loading current density. Since both U 1 and U 2were independent from loading current density, the amount of oxide on the anode of bipolar plate increased with loading current density. References 1) WO 2013/141211 A1. 2) J. Divisek, J. Appl. Electrochem., 20, 186, (1990). 3) F. Hine, Handbook of Chlor-Alkari Technology, vol.2, p.394 (2005). Figure 1

Insights over the in-situ grown copper sulfide/NiFe-LDH composites for alkaline and urea water electrolysis

The future of energy conversion and storage is expected to rely on the production and storage of hydrogen via water electrolysis1. In this scenario, water electrolyzers will play a key role to the establishment of an energy matrix based on renewable but intermittent power sources (e.g. wind turbines and photovoltaics). Other technologies could also be used to store the surplus of energy, such as pumped hydro, geo thermal, batteries, air compression, and the like2. However, none of those have the same value proposition as hydrogen. Hydrogen has the advantage of being able to drive multiple revenue streams like transportation, chemicals, green production of fertilizers, regeneration of electricity through fuel cells, and also initially supplement the energy gap through methanation, when coupling with CO2 sequestration1. Moreover, the production, storage, or distribution can be chosen to be centralized or decentralized and it is the only option with a multi-GWh storage capacity1. To date, only alkaline and polymer electrolyte membrane (PEM) water electrolyzers are commercially available1,3. In order to meet the future demand for water electrolyzers, investment and operational costs still have to be reduced. Moreover, it is fundamental to develop electrolyzers that are able to operate at high current densities, variable partial load, overload, and on/off conditions. These requirements usually place PEM water electrolysis as the best alternative to couple with intermittent power sources. In any case the high costs of PEM water electrolysis components (based on Pt, Ir, and Ti materials) still hamper its large-scale commercial application3. Though consistent R&D one can pursue to considerably reduce the costs of PEM water electrolyzers, so that the loading of the expensive based materials can be reduced or even to the point of being completely substituted3. On the other side, alkaline water electrolysis stays as a long-established, well matured, and comparatively low cost available technology and another approach could be pursued by improving the performance and operational characteristics of this KOH based system. The hydroxide transport across the diaphragm inside alkaline electrolyzers promoted by the KOH responds very slowly to the power input, limiting the efficiency of the electrochemical reaction, and consequently resulting in low current densities1,3. Moreover, the porous structure of the diaphragm allows the diffusion and extensive mixture of the produced hydrogen and oxygen gases when operating at low current densities, limiting the safety range for its operation. Conventional electrodes used in alkaline electrolyzer also tend to possess low active surface area, poor catalyst utilization, and many associated voltage losses1,3. When conventional diaphragms or separators are replaced by thin polymer based separators or anion exchange membranes (AEM), the performance of the alkaline electrolyzers can be substantially enhanced. These are the so-called advanced alkaline electrolyzer units and are already expected to reach performance levels close to that of PEM water electrolyzers. The direct comparison between those three presented alternatives is absolutely not trivial and yet cannot be avoided. It is therefore essential to establish a fair performance range comparison when using standard and available materials for classic alkaline, alkaline PEM, and PEM water electrolysis. As an example for the performance behavior in PEM water electrolysis, by using thin PFSA based membranes (< 50 µm), performances reaching up to 10 Acm-2 are obtained. Due to the low ohmic losses when using thin membranes, lower cell voltages are also found, mitigating the voltage inducing corrosion, allowing the use of less expensive material. Nonetheless, the thinner membrane shall increase the hydrogen permeation to the oxygen side limiting its partial load and differential pressure operation4. Another important point is the loading of noble metals used in the catalyst layer. To date, Ir loadings range between 2 and 3 mgIrcm-2, Pt loadings range between 0.8 and 1.5 mgPtcm-2.1,3By using advanced methods for the membrane electrode assembly (MEA) fabrication, loadings were dramatically reduced without statistically affecting the performance. In conclusion, a new, robust and efficient benchmark study is presented showing the up-to-date performance behavior of classic alkaline, alkaline PEM, and PEM water electrolysis. This study shall be able to contribute to validate the R&D potential for each technology and its future incorporation into our energy matrix for energy storage and conversion. [1] J. Mergel, M. Carmo and D. Fritz. in Transition to Renewable Energy, D. Stolten, V. Scherer, Editors, p. 423-450, Wiley-VCH (2013) [2] W.F. Pickard et al Energy Reviews; 13(8), 1934 (2009). [3] M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901 (2013) [4] M. Schalenbach, M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 14921 (2013) Figure 1

Nowadays hydrogen, which is required in huge quantities for many important industrial processes such as ammonia synthesis, is still being produced through inexpensive, but greenhouse gas emitting processes like steam reforming and coal gasification. In the course of the energy turnaround hydrogen is often seen as the fuel of the future. Within the framework of the power-to-gas concept (PtG), particularly water electrolysis is often discussed as the key technology for future synthesis of hydrogen. Alkaline water electrolysis has been applied in the industry for decades, but no further research activities have been undertaken for quite some time. For realization and improvement of the PtG concept precise knowledge, especially about the dynamic behavior of the electrolysis process, is indispensable. Usually the acceptable part-load operation of an alkaline water electrolyzer is limited to about 10 % - 40 % of the nominal load. Below this working range the hydrogen quality is significantly reduced through contamination with oxygen, which is also being produced in the process. The increasing hydrogen impurity is mainly based on two aspects. Firstly, the product gases diffuse through the separator into the opposite half-cell to a certain extent. Secondly, the mixing of the hydrogen and oxygen saturated electrolyte leads to a decrease of the product gas quality in the part-load regime as the saturation of the electrolyte is approximately independent of the electrolyzer load. The mixing of the catholyte and anolyte cycle is necessary to compensate an electrolyte concentration gradient which is caused by the occurring half-cell reactions. Particularly through the use of renewable energy sources an intermitting operation of the process may lead to a safety plant shutdown at around 2 vol% H2 in O2 in the lower working range. In addition, the current development of alkaline water electrolysis focuses on the increase of the electrolysis pressure to avoid the need of additional mechanical hydrogen compression, which further intensifies the problem of product gas contamination. In this study, classical mixing of catholyte and anolyte as well as several other electrolyte management concepts are examined with respect to the resulting gas purity. Next to the classical strategy, the complete electrolyte separation or the application of periodic separation-mixing-sequences are conceivable, which promise a reduction of the product gas contamination. In order to investigate these concepts, experiments are carried out in a custom-built laboratory electrolyzer under industrially relevant conditions, which allow an evaluation of the influence of various process parameters and the quantification of the prevailing crossover mechanisms. In addition, a model is being developed that can be used for the support of the experiments and for the optimization of the process. The results show that a reduction of the electrolyte flow rate and system pressure, an increase of the electrolyte temperature, and an increase of the electrolyte concentration lead to a reduced contamination of the products when the electrolyzer is operated with mixed electrolyte cycles. The analysis of the results further reveals that the main source of contamination is not the permeation of the gases through the separator, but the dissolution in the electrolyte and transport to the other half-cell by electrolyte recycling. Consequently, a significant reduction of gas crossover can be achieved by the separation of the cycles or a dynamic process strategy, which involves a continuous alternation between merged and separated electrolyte cycles. This process management provides an almost constant electrolyte concentration while improving the product gas quality simultaneously.

Membraneless Electrolyzers for Low-Cost Hydrogen Production in a Renewable Energy Future

Green hydrogen from water electrolysis coupled with renewable energy is important to overcome the climate change crisis and drives the energy paradigm shift from fossil fuels to eco-friendly energy. Water electrolysis technology was first discovered in the 19th century, and hydrogen for ammonia synthesis was produced in a 165 MW water electrolysis system linked to the Aswan Dam in Egypt in the early 20th century. Currently, research is being actively conducted to implement a water electrolysis system using wind and solar power generation. Among water electrolysis technologies, alkaline water electrolysis has a high technological maturity based on its long history and has the advantage of being highly economical as it does not use precious metal catalysts. However renewable energy has intermittent and irregular power production characteristics, the water electrolysis system must include load-following technology that can follow load changes when connected to renewable energy.Most electrode materials used in alkaline water electrolysis are Ni-based catalysts, and Raney-Ni is an advanced catalyst through the enlarged specific surface area by forming an intermetallic compound layer such as combined with Ni, Al, and Zn on the surface of the Ni electrode. Complex structural electrodes including many pores are generally used in order to realize a zero-gap design in alkaline water electrolysis. VPS (vacuum plasma spraying), PVD (physical vapor deposition), and electroplating are generally used to form Raney-Ni on the surface of a complex structural substrate. However, above mentioned methods have a technical issue for scaling up the area of the electrode because certain conditions must be established in the vacuum chamber or plating bath.In this study, high-performance Raney-Ni electrode was manufactured using a dip-coating method which is to soak the Ni substrate in the slurry consisted of Al powder and polymeric binder. Heat treatment condition was adjusted to find the optimal temperature range for forming suitable Ni-Al intermetallic compounds on the Ni foam (NF) surface. As a result, the appropriate heat treatment temperature was 700 oC, and the prepared electrode was evaluated by linear sweep voltammetry (LSV) to confirm the hydrogen generation reaction performance. The ratio of polymer binder and Al was adjusted to confirm the optimal slurry viscosity to determine the optimal Al loading conditions on the surface of the complex structural NF. LSV, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were conducted to measure HER performance of prepared Raney-Ni electrodes. Fig. 1a. shows a comparison of HER performance between conventional NF and prepared electrode, and the Raney Ni/NF is achieved for low overpotential of more than 170 mV at the current density of -0.3 A/cm2. In addition, the outstanding kinetics of Raney-Ni were confirmed on the Tafel slope (Fig. 1b). Performance improvement was investigated through CV analysis by improving the electrochemically active area due to the Ni-Al intermetallic compound layer formed on the Ni surface. As shown in 1c, the improvement in surface roughness was confirmed through SEM analysis (Fig. 1c).It is important to respond to load fluctuations from renewable energy and the durability of components in electrolytic stack because the value of alkaline water electrolysis lies in high economy for utilizing surplus energy from renewable energy. Durability and responsiveness were confirmed by repeatedly applying currents from -0.03 to -0.3 mA/cm2 of electrolytic cell equipped with the manufactured Raney-Ni electrode for 100 cycles. The excellent HER performance of the Raney-Ni electrode, which was already confirmed through the previous electrochemical analysis, was also confirmed in repeated current application experiments, and excellent responsiveness and durability were also confirmed (Fig. 1d). It was confirmed that the prepared Raney-Ni electrode showed high responsiveness, with voltage appearing immediately according to the applied current (Fig. 1e). Additionally, there was small or no changes of performance despite repeated load fluctuations during 100 cycles (Fig. 1f).In the previous experiment, HER performance, responsiveness, and durability were confirmed through a half-cell experiment. The water electrolysis efficiency of the prepared electrode was confirmed through in-situ analysis, and durability was confirmed for over 100 hours in a constant current condition. In addition, the electrode corrosion resistance caused by shunt current, which is important in the alkaline water electrolysis stack, was confirmed through the alkaline water electrolysis stack equipped with the prepared electrode and stack was performed on/off test over 100 cycles. As a result, the electrode showed only low performance degradation. Finally, an m2 electrode was manufactured by dip-coating method, and to conduct performance evaluation through the sample which is at a random location with a size of 25 cm2. Samples achieved uniform performance, although efficiency difference was observed. Figure 1

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.

There are two main industrial techniques of water electrolysis operating under near-ambient temperature and pressure conditions: alkaline water electrolysis which uses a liquid electrolyte based on an aqueous solution of potassium hydroxide [1] and PEM water electrolysis [2] which uses a solid electrolyte made of a proton-conducting polymer. Both technologies present a set of strengths and weaknesses in view of practical application in the industry sector. The objective of this communication is to highlight the differences and similarities in terms of design (cell and stack) and balance-of-plant, and to present in a critical way what are these advantages and disadvantages, from a scientific viewpoint (that of materials science, especially for the selection of electrocatalysts), from a technological viewpoint (stack design and balance-of-plant) and from an economic viewpoint (comparative analysis of capex and opex). The discussion will take into account the situation which prevails on machines at the MW-scale. Particular attention will be paid to the ability of these machines to operate under transient conditions, in particular with a view to providing services to the electricity network. Several performance indicators such as the flexibility and reactivity of machines to the demands of network operators will be used to carry out this comparison. A detailed analysis of the existing limitations will make it possible to define a set of development perspectives highlighting possible complementarities.[1] N. Guillet and P. Millet, in : Hydrogen Production: by Water Electrolysis’, chapter 4, Alkaline Water electrolysis, A. Godula-Jopek, D. Stolten Editors, Wiley-VCH (2015).[2] D. Bessarabov and P. Millet in: PEM water electrolysis, “Hydrogen and Fuel Cells Primers”, B.G. Pollet Editor, 1st Edition, Elsevier (2018).

We report semi-interpenetrating polymer network (semi-IPN) membranes prepared easily from a cross-linked network using poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) with interpenetrated Nafion for both proton-exchange membrane fuel cell (PEMFC) and proton-exchange membrane water electrolyzer (PEMWE) applications. Thermal esterification between PAA and PVA induced three-dimensional cross-linking to improve mechanical toughness and reduce hydrogen crossover, while the hydrophilic nature of the PAA-PVA-based cross-linked matrix still enhanced the water uptake (WU) and hence conductivity of the Nafion penetrant. The semi-IPN membrane (NPP-95) composed of Nafion, PAA, and PVA with a ratio of 95:2.5:2.5 showed a hexagonal cylindrical morphology and improved thermal, mechanical, and dimensional stability compared to a recast Nafion membrane (re-Nafion). The membrane was also highly effective at managing water due to its low WU and high conductivity. Furthermore, its hydrogen permeability was 49.6% lower than that of re-Nafion under the actual fuel cell operating conditions (at 100% RH and 80 °C). NPP-95 exhibited significantly improved conductivity and PEMFC performance compared to re-Nafion with a current density of 1561 mA/cm2 at a potential of 0.6 V and a peak power density of 1179 mW/cm2. Furthermore, in the PEMWE performances, NPP-95 displayed about a 1.5-fold higher current density of 4310 mA/cm2 at 2.0 V and much lower ohmic resistance than re-Nafion between 60 and 80 °C.

Energy is crucial to the cycle of existence in the universe and plays an important role in achieving sustainable growth. Considering the traits of the conventional approach and challenges dealing with conventional energy technologies, water electrolysis is reflected to be simple, sustainable, and green energy tool. Alkaline water electrolysis (AWE) process is mature technology of the last century for industrial hydrogen production. AWE uses asbestos as the separator medium. However, asbestos allows crossover of the produced gases therefore, low purity gas is obtained, and with limited stability. In the present study, a novel composite diaphragm separator has been synthesized using Zirconium oxide (ZrO2) with aqueous acrylic solution in different compositions and optimized for enhanced performance. The prepared composite is initially stabilized through sonication and applied on the medium with a uniform thickness using a doctor blade film applicator. The study aims to optimize the composite diaphragm to withstand the severe chemical and thermal conditions of the electrolyzer. Zirconium oxide-based diaphragms offer several advantages over other types of diaphragms, including excellent corrosion resistance, high chemical and thermal stability, and long service life. These coated separator diaphragms showed good electrolysis performance and stability in an alkaline medium.