Electrolyte Membrane Water Electrolysis Research Articles

In-Situ Analysis of Gas Crossover in PEM Water Electrolysis - the Effect of Membrane Variation

Polymer electrolyte membrane (PEM) water electrolysis is well identified today as a sustainable solution for the production of hydrogen, and of paramount importance when coupled to renewable but intermittent power sources such as wind and solar. PEM water electrolysis is based on a solid polymer electrolyte concept first realized by Grubb in 1960s, where a thin solid sulfonated polystyrene membrane is used as an electrolyte. The polymer electrolyte membrane is responsible for providing high proton conductivity, compact system design, and low gas crossover. However, depending on the power load range, operating temperature, pressure range, membrane thickness, and a number of other parameters diffusion processes of the product gases through the membrane occur. The diffusion of hydrogen into the oxygen compartment for example reduces the efficiency of the electrolyzer, and allows the extensive mixing of gases that must be avoided in order to preserve efficiency and safety. This is particularly severe at a low power load – important when coupling to intermittent power sources – where the oxygen production rate decreases, thus drastically increasing the hydrogen concentration to unwanted and dangerous levels (lower explosion limit > 4 mol-% H2). Nevertheless, PEM water electrolysis can operate at high current densities, capable of achieving values above 4 Acm-2, provided by very low ohmic losses. Though, very high current densities (over 6 Acm-2) can only be achieved if thin membranes (20 – 50 µm) are used which lead to lower cell resistances. In this case unfortunately, the crossover of gases across the membrane is drastically enlarged, if compared to the use of thicker membranes (100 – 200 µm). In any case, PEM electrolysis is recognized for practically covering a wide power density range. However, the practical power operation range of PEM water electrolysis has not been consistently evaluated yet, especially when considering the variation of perfluorosulfonic acid (PFSA) membrane, thickness, and operation pressure. In this study, the in-situ crossover aspect of a series of PFSA Nafion membranes at different operation conditions will be evaluated and compared to a simulation study of the gas permeation pathways. The main message is to clearly define the power load and pressure range for the PEM water electrolysis technology when using different membrane alternatives, providing a road map in order to aid scientists with regards to the R&D of PFSA membranes for PEM water electrolysis.

NSTF Advances for PEM Electrolysis - the Effect of Alloying on Activity of NSTF Electrolyzer Catalysts and Performance of NSTF Based PEM Electrolyzers

Recent resurgence of interest in harnessing energy from renewable sources, and a push to achieve environmental cleanliness in the energy industry has rekindled interest in hydrogen as a clean and environmentally benign energy carrier. This is done with the ultimate goal of supplanting the current hydrocarbon based economy by hydrogen economy as means to achieve environmentally friendly energy industry and energy independence. The rising star of hydrogen enabled mobility i.e. recent accomplishments in (automotive) fuel cells adds further impetus to advance renewable and at the same time economical means to generate hydrogen – i.e., which is the ultimate key to success for hydrogen as fuel in societal everyday transportation solutions. As such, this rekindled interest in the age-old water electrolysis process spawned new approaches to generate hydrogen with increased efficiency and lower cost. Polymer electrolyte membrane (PEM) water electrolysis, while one of those relatively new approaches, has been used for quite a few years now without undergoing any substantial improvements over those years. Solutions based on Nafion 117 and high loadings of Platinum-Group Metals (PGM) worked well enough and were sufficiently durable. Now, however, with the new focus on hydrogen as the energy carrier (as opposed to a chemical reactant, mobile phase, or coolant – its major applications at present), there is much more interest in low cost/high efficiency H2 production. This explains the renewed interest and recent increase in R&D activity in this fertile and promising area. As a matter of fact it is quite possible the success (or lack of) in achieving lower cost of hydrogen production may make or break the success of fuel cell as grid-level energy storage solution and personal transportation technology of choice. There are two main ways to lower the cost of hydrogen production via PEM water electrolysis: to lower the capital expenses (CAPEX) and/or to lower the operating expenses (OPEX). We at 3M have recently addressed reducing the first (high CAPEX ) by widening the range of current densities where electrolyzers can operate from a maximum of about 2.0 A/cm2, as used today in commercial electrolyzers, to as much as 20 A/cm2. While the research on high power density operation of PEM water electrolysis still continues, and many questions remain as yet unanswered, the NSTF catalyst, with its highly conductive, compact, and hydrophilic catalyst layer seems uniquely fitting to the task. Indeed, its hydrophilicity that is a major weakness in fuel cells is a tremendous strength in water electrolysis and one of the features enabling the extremely high mass transport free current densities we reported previously1. Currently, we intend to tackle the second means for reduction of cost of hydrogen production by increasing the intrinsic activity of the catalyst as means to increase the kinetics of oxygen evolution and hence the efficiency of water electrolysis (thus reducing the OPEX). We will show the effect of alloying on the performance of typical PGM based NSTF anode catalysts. One such example will be exploration of the Pt/Ir compositional parameter space (in the NSTF alloy catalyst format) and the compositional effects on fundamental catalyst activity, as determined by RDE measurements. Subsequently, we will correlate this to the in-situ performance measurements in a PEM electrolysis cell. Finally, we will discuss the possibilities in other promising alloying compositions and structures. Krzysztof A. Lewinski, Sean M. Luopa, “High Power Water Electrolysis as a New Paradigm for Operation of PEM Electrolyzer.”, Spring ECS Meeting, Chicago, IL, May 2015.

In-Operando Neutron Radiography Studies of Polymer Electrolyte Membrane Water Electrolyzers

Polymer Electrolyte Membrane Water Electrolysis (PEMWE) is increasingly attracting interest from academia and industry as it offers an option for storing renewable energy from sources such as wind or solar [1]. Further, electrolysis is considered one of the few available pathways to achieve a 100% renewable electricity supply [2]. In PEMWE, water is typically supplied via flow channels and distributed across the catalyst layer through a porous transport layer (PTL). Gas evolution occurs at the catalyst layer, and the gas is transported back through the PTL and discharged into the flow channels where it is then transported out of the cell as a two-phase mixture with the feed water. This evolution of oxygen and hydrogen in the surrounding water leads to distinct two-phase flow phenomena, which are investigated in this study in-operando inside operating PEMWE cells using synchrotron X-ray radiography as well as neutron radiography. In the past, both methods have allowed to visualize processes inside operating fuel cells, elucidating water management issues [3], the formation of liquid water, its accumulation rate and transport in polymer electrolyte membrane fuel cells (PEFC) [4], as well as the carbon dioxide evolution in liquid fed direct methanol fuel cells (DMFC) [5]. PEM water electrolysis systems are currently scaled to the megawatt range, necessitating an increase of the active area of an individual cell. This scale-up goes along with challenges concerning media distribution on large cell areas. Information about the oxygen saturation and distribution inside the PTL at different points of operation but also at different locations a large area PTL is therefore of special interest. In this work, operating PEMWE cells are examined using synchrotron X-ray radiography at BESSY II and using neutron radiography at BER II (both Helmholtz-Zentrum Berlin). In both setups, a synchrotron X-ray beam or a neutron beam is directed at the running cell, and the attenuation dependence of the beam on the elements inside the cell allows visualizing the processes occurring inside the cells. Both methods are to a certain degree complimentary – the synchrotron radiography setup allows inspecting small areas of some mm² with a spatial resolution of a few µm, while the neutron radiography allows inspecting areas of several cm² with a spatial resolution of lower than 100µm. The especially strong neutron attenuation in hydrogen offers the possibility to visualize the gas/water distribution on large areas, while the comparably low neutron attenuation in metals allows using a typical cell setup with only minor adjustments. The PEMWE cells examined using neutron radiography contained different PTLs, which were compared in terms of the gas/water distribution under different operating conditions. On the anode side, an additional injection of oxygen from the bottom of the cell was used to simulate the effects occurring in a scaled cell exhibiting a larger area. This setup allowed examining the dynamics in the transport and quantifying the distribution along the cell area. In the PEMWE cells examined using synchrotron radiography, oscillations in the gas bubble discharge from the PTL into the flow channel were investigated in terms of their frequency and the gas discharge volumes. Furthermore, the implications of this on the gas transport within the PTL are discussed, and the number of gas bubble discharge sites is correlated with the current density. Thereby it is demonstrated that both synchrotron X-ray and neutron radiography represent valuable tools to study transport processes and to gain insights into the gas-water distribution inside running PEMWE cells. These results pose important implications for the design of cell components with facilitated gas removal, for the modeling of two-phase flow in PEMWE cells and for the modeling of mass transport losses in PEMWE.

Impact of Cathode Current Collector on High Temperature PEM Water Electrolysis

1. Introduction Polymer Electrolyte Membrane Water Electrolysis (PEMWE) is a hydrogen production method, which has advantages on conversion efficiency, compactness and gas purity. Also, PEMWE is expected to be applied to load leveling of electricity between consumer demands and supply from renewable energies [1]. Higher conversion efficiency has been realized in two strategies: higher temperature operation with new composite electrolyte membranes and development of current collector. The new membrane can endure high temperature up to 120°C, and a high temperature operation can reduce overpotentials, leading to further performance[2]. Developing the current collector is concentrated on anode side, major source of overpotentials exist. Optimizations of current collector on its hydrophobicity and stricture play a key role on water/gas management and improve performance[3]. This study evaluates the current collector in cathode if it changes the performance of PEMWE especially under high temperature condition. As well know, high temperature tends to dehydrate PEM and results in low performance, although temperature dependence of non-leaner overvoltages predicts their reduction. This study aims to suppress the dehydration with possible candidates of current collector in cathode. Impact of hydrophobicity in cathode current collector on the dehydration is experimentally evaluated through IV characteristic and high frequency resistance. 2. Experimental apparatus and method The PEMWE cell consists of a CCM, porous current collectors, and separators with flow channels. The CCM was fabricated by spraying catalyst ink on Nafion® 117 membrane and hot-pressing. Iridium oxide (IrO2powder, type IV, Tokuriki Co., Japan) was used for anode catalyst, and a commercial 46% Pt/C (Tanaka Kikinzoku Japan) was for cathode catalyst. As for cathode current collector, carbon paper (SGL Co., Germany, 20BA, thickness 0.2mm) or SUS316L sheet (Nikko Techno, fiber diameter 35μm, thickness 0.3mm) was selected. The two collectors have different hydrophobicity. The carbon paper indicates rather hydrophobic characteristic. On the other hand, The SUS sheet shows opposite characteristic. In the case of carbon paper, two layers of it was built in the cell considering the thickness of seal material and contact resistances. Ti mesh (Nikko Techno Co., Japan, fiber diameter 20μm) was used for anode current collector. 3. Results and discussion Fig.1 and Fig.2 show the measured I-HFR and I-V characteristics during PEM electrolysis with different cathode current collectors at 80°C and 100°C. The HFR in the case of carbon paper had lower value, suggesting lower ohmic resistance. Corresponding to I-HFR characteristic, the I-V characteristic in the carbon paper case indicated lower cell voltage. The cell voltage in the case of carbon paper is smaller than that in the case of SUS sheet. As expected, the carbon paper, which has rather hydrophobic property, hydrates the PEM and make its ionic resistance low. The hydrophobic carbon paper placed in cathode may work to block the water transport driven by electro-osmosis from anode to cathode. It also enhances the back diffusion of water, resulting in the hydration of PEM and lower resistance. However, this mechanism, in which PEM is hydrated with hydrophobic carbon paper, is not enough to explain the cell voltage difference by 110 mV at 2 A/cm2appeared in Fig. 2. The ohmic resistance difference of 10 Ω*cm2 at 2 A/cm2 appeared in Fig.1 predicts a cell voltage difference 20 mV, which is 90 mV smaller than that in I-V characteristic. A possible explanation to the gap of 90 mV is the overvoltage reduction in anode. Generally, the overvoltage in anode is larger than that in cathode. Also, the water content in anode catalyst layer impacts the overvoltage in anode. These concern and the water back diffusion with carbon paper in cathode, above mentioned, can suggests that the water back diffusion from cathode may reach to the anode catalyst layer and hydrate the ionomer in the anode catalyst layer even though cell is operated at high temperature. This mechanism may explain the gap of 90 mV, where the water back diffusion reduces the overvoltage in anode.

Development of electrodeposited IrO2 electrodes as anodes in polymer electrolyte membrane water electrolysis

Abstract To reduce the use of noble metals, iridium oxide (IrO2) catalysts are prepared on carbon paper (CP) by electrodeposition for use as the anodes in polymer electrolyte membrane water electrolysis (PEMWE). The activities of the fabricated electrodes toward the oxygen evolution reaction are evaluated. The loading amount and morphology of the IrO2 deposits are varied by controlling the electrodeposition potential (Edep) and time (tdep). When electrodeposited at 0.7 V, the IrO2 loading ranges from 0.007 to 0.464 mg cm−2 (tdep: 1 ∼ 30 min). In the PEMWE test at 90 °C, the IrO2/CP electrode with an IrO2 loading of 0.1 mg cm−2 shows the highest performance (1.92 A cm−2 at 1.8 V) in which high IrO2 utilization is achieved without significant exposure of the substrate carbon surface. The developed IrO2/CP electrodes provide cell performances comparable to those in previous reports with a higher IrO2 loading, indicating markedly enhanced mass activity.

Development of the Anion Exchange Membrane Water Electrolysis

Water electrolysis is an established method to produce hydrogen from the surplus power of renewable energy sources1. There are two technologies considered to be the most suitable when connected to intermittent power sources: polymer electrolyte membrane (PEM) water electrolysis and alkaline electrolysis with a liquid electrolyte2. Both technologies are linked to certain advantages and limitations. High current densities for example are achieved with PEM electrolysis but the acidic regime requires scarce and expensive platinum-group-metal (PGM) catalysts and Ti-based stack components3. On the other hand alkaline electrolysis is regarded as a mature and less expensive technology but is limited to low current densities4. In order to combine the benefits of both technologies while simultaneously overcoming their drawbacks, a thin anion exchange membrane (AEM) is used as the electrolyte, allowing the use of low-cost transition-metal catalysts and stack material5. In this study we developed membrane electrode assemblies (MEAs) for the AEM water electrolysis that closely match the performance of state-of-the-art PEM water electrolysis. Furthermore we have assessed commercial AEMs to determine the ionic conductivity and ion-exchange capacity. To precisely measure the hydrogen permeability of the membranes at different temperatures, an electrochemical monitoring technique was developed. Best results were achieved with Tokuyama´s A201 AEM as the ionic conductivity reached 0.4 S/cm and a hydrogen permeability of only 10-16 mol/(cm·s·Pa) at 70 °C. A screening method was also developed to identify and characterize the most active set of electrocatalysts. Nickel nanoparticles were found to have an overpotential of about 0.4 V towards HER and OER at 10 mA/cm2 and was thus chosen for the development of MEAs. Single cells exhibited a current density of 220 mA/cm2 at 2.2 V and 50 °C in deionized-water. We suppose that the low current density originates from the poor ionic conductivity of the AS4 ionomer used in the electrode layer. Nevertheless the use of 1 M KOH solution as an additional electrolyte led to an improved ionic conductivity. This optimization resulted in single cells reaching current densities of 1.5 A/cm2 at 2.2 V and 50 °C. Long-term experiments were additionally conducted to gain information on the impact of both operational modes on the ionomer stability. Our results clearly show the potential of AEM water electrolysis to meet the performance of state-of-the-art PEM electrolyzers without using scarce and expensive electrocatalysts and stack components. Figure 1: Polarization curves of a MEA containing Nickel nanoparticles on anode and cathode electrode. Tokuyama AS4 was used as ionomer and A201 as AEM. A 25 cm2 single cell was measured at 50 °C in deionized water and 1M KOH solution. Current density ranges after [1].

Ebonex supported iridium as anode catalyst for PEM water electrolysis

The work presents a research on the preparation and properties of iridium dispersed on Magnelli phase titania by sol gel method. The material is characterised in regard to morphology, surface structure and electronic state, electrochemical performance, and catalytic activity toward the oxygen evolution reaction in view of its application as anode in polymer electrolyte membrane water electrolysis. The results obtained are discussed in comparison to the previously studied magnetron sputtered iridium oxide anodes. They show a need for improvements concerning the Ir/Ebonex active surface area and catalyst utilisation. At the same time, the performed accelerated durability tests demonstrate excellent stability of the synthesized composite catalyst and enhanced resistance to corrosion.

In operando synchrotron X-ray radiography studies of polymer electrolyte membrane water electrolyzers

Abstract Polymer electrolyte membrane water electrolysis (PEL) cells are studied in-operando by synchrotron X-ray radiography. Two-phase flow phenomena associated with the evolution of oxygen and hydrogen in the surrounding water are investigated on a running electrolyzer cell. We examine the gas bubble discharge from the porous transport layer (PTL) into the flow channel and discuss the transport of bubbles in the flow channel. The transport of gas inside the PTL and the number of gas bubble discharge sites is examined and correlated with current density.

Ceria 첨가에 따른 수전해용 공유가교 CL-SPEEK/Silane 4wt%/Cs-MoPA/Ceria 복합막의 특성 연구

Ceria (CeO 2) was used to increase the durability of the membrane in the polymer electrolyte membrane water electrolysis (PEMWE) circumstance. The sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ket one (PEEK) to improve electrochemical characteristics. After sulfonation reaction, the organic-inorganic blended composite membranes were prepared by means of sol-gel casting method with loading the highly dispersed CeO 2 and Cs-substituted molybdophosphoric acid (Cs-MoPA) with cross-linking agent (tetrapropyl orthosilicate). Co nsequently, the composite membrane CL-SPEEK/Silane 4wt%/Cs-MoPA/Ceria(1%) showed the improved characteristics such as 82% of water content, 0.11136 S/cm of proton conductivity at 80 , 55.50 MPa of tensile strength and 4.37% of breeding out of MoPA. Ai

Failure of PEM water electrolysis cells: Case study involving anode dissolution and membrane thinning

Polymer electrolyte membrane (PEM) water electrolysis is an efficient and environmental friendly method that can be used for the production of molecular hydrogen of electrolytic grade using zero-carbon power sources such as renewable and nuclear. However, market applications are asking for cost reduction and performances improvement. This can be achieved by increasing operating current density and lifetime of operation. Concerning performance, safety, reliability and durability issues, the membrane-electrode assembly (MEA) is the weakest cell component. Most performance losses and most accidents occurring during PEM water electrolysis are usually due to the MEA. The purpose of this communication is to report on some specific degradation mechanisms that have been identified as a potential source of performance loss and membrane failure. An accelerated degradation test has been performed on a MEA by applying galvanostatic pulses. Platinum has been used as electrocatalyst at both anode and cathode in order to accelerate degradation rate by maintaining higher cell voltage and higher anodic potential that otherwise would have occurred if conventional Ir/IrOx catalysts had been used. Experimental evidence of degradation mechanisms have been obtained by post-mortem analysis of the MEA using microscopy and chemical analysis. Details of these degradation processes are presented and discussed.

Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis.

The energetic convenience of electrolytic water splitting is limited by thermodynamics. Consequently, significant levels of hydrogen production can only be obtained with an electrical energy consumption exceeding 45 kWh kg(-1)H2. Electrochemical reforming allows the overcoming of such thermodynamic limitations by replacing oxygen evolution with the oxidation of biomass-derived alcohols. Here we show that the use of an original anode material consisting of palladium nanoparticles deposited on to a three-dimensional architecture of titania nanotubes allows electrical energy savings up to 26.5 kWh kg(-1)H2 as compared with proton electrolyte membrane water electrolysis. A net energy analysis shows that for bio-ethanol with energy return of the invested energy larger than 5.1 (for example, cellulose), the electrochemical reforming energy balance is advantageous over proton electrolyte membrane water electrolysis.

PEMWE를 위한 Cs치환에 따른 공유가교 SPEEK/Cs(x)-TPA/Ceria막의 합성 및 특성 연구

CL-SPEEK/Cs-TPA/CeO2 composite membrane was prepared for polymer electrolyte membrane water electrolysis (PEMWE). In order to improve the electrochemical, mechanical, durabilities and electrocatalytic characteristics, engineering plastic of polyether ether ketone (PEEK) as polymer matrix was sulfonated and the organic-inorganic blend composite membranes was prepared by loading cesium-substituted tungstophosphoric acid (Cs-TPA) by titration method with cross-linking agent contents of 0.01mL. Ceria (CeO2) was used to scavenge free radicals which attack the membrane in the PEMWE circumstance and to increase the duration of the membrane. In conclusion, CL-SPEEK/Cs(1)-TPA/Ceria 1% membrane showed the optimum results such as 0.119 S/cm at 80°C of proton conductivity and 62MPa of tensile strength.

High-Pressure PEM Water Electrolysis: in-Situ Measurement of Hydrogen Crossover

To ensure safe and efficient operation of polymer electrolyte membrane (PEM) water electrolyzers the determination of hydrogen crossover through the membrane-electrode-assemblies (MEA) is an important issue. Hydrogen crossover leads to a contamination of the oxygen product stream with the risk of the formation of explosive atmospheres within the anode channels. Additionally, the crossover flux represents a loss of product hydrogen, leading to an increase of the specific energy demand for the electrolysis. Especially under asymmetric (also named unbalanced or differential) pressure conditions (e.g. discussed by [1]), these losses can easily exceed the benefits connected with the electrochemical co-compression of the produced hydrogen [2].The present contribution proposes an experimental method for the in-situ determination of hydrogen crossover in polymer electrolyte membrane water electrolysis cells [3]. The measurement concept is based on the electrochemical compensation of the hydrogen crossover flux, which translates the mass flux determination into an electric current measurement. The proposed method is based on a very simple set-up and measurement procedure, as well as high accuracy. It allows for measurement with a fully assembled electrolysis cell at standard water electrolysis conditions by use of standard equipment, also installed in industrial electrolyzer plants. The technique is especially suitable for high-pressure PEM electrolyzers operated under asymmetric pressure conditions.In Fig. 1(a) schematic of the employed set-up is shown. The anode side of the electrolyzer under investigation is operated throughout the whole experiment under the same conditions as during normal operation. The cathode side is equipped with a pressure transmitter and is disconnected from the rest of the plant, e.g. by means of a cutoff valve.The measurement principle is as follows: a small current is applied to the set-up described above. On the anode side, water is consumed and oxygen evolves. In the sealed cathode compartment hydrogen is evolved, which leads to a pressure increase over time. The cathode pressure reaches a steady-state value when the hydrogen loss, which is driven by the increasing pressure difference, levels out the hydrogen evolution (Eq. 1).dp cathode /dt = 0 <-> 0 = -G H2,crossover + i/2/F (1)Fig. 1(b),(c) illustrates one application of the described basic measurement principle. If the experiment is carried out repeatedly at different currents, it allows for a quick and simple characterization of MEA materials under electrolysis, since a relation between the cathode pressure and the hydrogen crossover flux can be obtained.The applicability of the suggested method for a broad pressure range is briefly illustrated with a laboratory scale electrolyzer plant and by comparison of the measured data with available literature values (Fig. 2) by use of the membrane permeability coefficient K p,H2 (Eq. 2): G H2,crossover = K p,H2 Δp H2 /tm (2)[1.] F. Marangio, M. Santarelli, M. Cali, International Journal of Hydrogen Energy 34 (2009) 1143–1158.[2.] B. Bensmann, R. Hanke-Rauschenbach, I. K. Pena Arias, K. Sundmacher, Electrochimica Acta 110 (2013), pp. 570-580[3.] B. Bensmann, R. Hanke-Rauschenbach, K. Sundmacher, International Journal of Hydrogen Energy, In press. DOI 10.1016/j.ijhydene.2013.10.085

Cs 치환에 따른 수전해용 공유가교 SPEEK/Cs(n)-MoPA/Ceria 1%(n = 1~3) 복합막의 특성 연구

Ceria (<TEX>$CeO_2$</TEX>) was used to scavenge free radicals which attack the membrane in the polymer electrolyte membrane water electrolysis (PEMWE) circumstance and to increase the duration of the membrane. In order to improve the electrochemical, mechanical and electrocatalytic characteristics, engineering plastic of the sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ketone (PEEK) and the organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted phophomolybdic acid(Cs-MoPA) with cross-linking agent contents of 0.01mL. In conclusion, CL-SPEEK/<TEX>$Cs_{(2.5)}$</TEX>-MoPA/ceria(1%) membrane showed the optimum results such as 0.1095S/cm of proton conductivity at <TEX>$80^{\circ}C$</TEX>, 2.906meq./g-dry-membrane of ion exchange capacity and mechanical characteristics, and 49.73MPa of tensile strength which were better than Nafion 117 membrane.

In situ diagnostic techniques for characterisation of polymer electrolyte membrane water electrolysers – Flow visualisation and electrochemical impedance spectroscopy

An optically transparent polymer electrolyte membrane (PEM) water electrolysis cell was studied using a high-speed camera, thermal imaging and electrochemical impedance spectroscopy to examine the relationship between flow and electrochemical performance. The flow regime spans bubble and slug flow, depending on the rate of gas formation (current density) and water feed rate. Electrochemical impedance spectroscopy (EIS) shows that there is a reduction in mass transport limitation associated with the transition to slug flow.

Electrochemical characterization of Polymer Electrolyte Membrane Water Electrolysis Cells

The purpose of this paper is to report on the electrochemical characterization of Polymer Electrolyte Membrane (PEM) water electrolysis cells. Results were obtained using membrane-electrode assemblies containing unsupported IrO2 catalyst at anode for the oxygen evolution reaction (OER) and carbon-supported platinum nano-particles at the cathode for the hydrogen evolution reaction (HER). Roughness factors of anodes and cathodes have been determined using an internal reference electrode. Individual cell voltage contributions have also been measured as a function of operating current density. Cell impedance spectra have been measured at different cell voltages along the polarization curve. It is shown that charge transfer processes are major cell impedance contributors at voltages up to 1.8-1.9V. At higher cell voltages, cell impedances are mainly resistive. It is shown that the impedance associated with the HER is negligible and that the two time-constants observed on experimental impedance spectra can both be attributed to the OER. Possible mechanism options are discussed. Finally, some results related to the EIS characterization of PEM water electrolysis stacks are also reported.

Performance of a PEM water electrolyser using a TaC-supported iridium oxide electrocatalyst

Polymer electrolyte membrane (PEM) water electrolysis is an attractive way of producing carbon-free hydrogen. One of the drawbacks of this method is the need for precious metal-based electrocatalysts. This calls for a highly efficient utilization of the precious metal, which can be obtained by dispersing the precious metal compound onto a catalyst support. Electrocatalysts with 50, 70 and 90 wt.% of IrO2 on a TaC support were tested in a laboratory PEM water electrolyser and compared with pure IrO2. The temperature was set at 90, 110, 120 and 130 °C respectively and the cell voltage was varied between 1.4 and 1.8 V. The load characteristics and electrochemical impedance spectra were obtained and compared for a range of electrocatalysts. The highest current densities and the lowest charge transfer and cell resistances were found for the 70 wt.% IrO2 electrocatalyst. By contrast, the pure IrO2 electrocatalyst showed the lowest current densities and the highest charge transfer and cell resistance. For example, the relative difference in current densities between the 70 wt.% IrO2 and the pure IrO2 electrocatalyst attained 36% at 130 °C and 1.7 V. All of the supported electrocatalysts showed a higher efficiency of utilization of the precious metal than the pure IrO2.

In-situ measurement of hydrogen crossover in polymer electrolyte membrane water electrolysis

An in-situ method for determination of hydrogen crossover in polymer electrolyte membrane (PEM) water electrolysis cells is discussed. The measurement principle is based on the electrochemical compensation of the crossover flux, which translates the mass flux determination into an electric current measurement. The proposed method features an extremely simple set-up and measurement procedure, as well as high accuracy. It allows for measurement with a fully assembled cell at normal water electrolysis conditions by use of standard equipment, also installed in industrial electrolyzer plants. The technique is especially suitable for high-pressure PEM electrolyzers operated under asymmetric pressure conditions. The applicability of the suggested method for a broad pressure range is briefly illustrated with a laboratory scale electrolyzer plant and by comparison of the measured data with available literature values.

Pressurized PEM water electrolysis: Efficiency and gas crossover

In this study the influence of cathodic and anodic pressures during polymer electrolyte membrane water electrolysis on the gas crossover is simulated and compared to in-situ measurements of the anodic hydrogen content at differential and balanced pressure operation. The efficiency losses due to the reduced Faraday efficiency caused by crossover, ohmic loss of the membrane and pressurized hydrogen and oxygen evolution are estimated. Therefore, the correlated dependencies on the current density, membrane thickness, anodic and cathodic pressures, membrane conductivity and permeabilities are quantified. In addition, pressurized electrolysis is compared to adiabatic and isothermal subsequent compression in focus of efficiency. The outcome of this study can be utilized as a powerful computational tool to optimize the membrane thickness with respect to the operating pressures.

Development and characterization of covalently cross-linked SPEEK/Cs-TPA/CeO2 composite membrane and membrane electrode assembly for water electrolysis

Covalently cross-linked SPEEK/Cs-TPA/CeO2 composite membrane was prepared for the polymer electrolyte membrane water electrolysis. Tungstophosphoric acid (TPA) with a cesium was added to the SPEEK to increase proton conductivity. CeO2 was used to scavenge free radicals which attack the membrane in the water electrolysis and to improve the durability of the membrane. The composite membrane featured the electrochemical characteristics, such as 0.130 S/cm of proton conductivity at 80 °C, and 2.324 meq./g-dry-memb. of ion-exchange capacity. Pt(NH3)4Cl2, Pd(NH3)4Cl2, RhCl3 and Co(NH6)4Cl3 were used to prepare a variety of the membrane electrode assemblies (MEAs) as electrocatalytic precursors. Electrochemical activity surface area (ESA) of the Pt–Pd electrode prepared with 2 mM Pt(NH3)4Cl2 and 2 mM Pd(NH3)4Cl2 showed the best properties of 26.2 m2/g with CL-SPEEK/Cs-TPA/CeO2 membrane. In water electrolysis performance, the cell voltage of Pd/PEM/Pt–Pd MEA with CL-SPEEK/Cs-TPA/CeO2(1%) composite membrane showed cell property of 1.82 V at 1 A cm−2 and 80 °C.