PEM Electrolysis Cell Research Articles

PEM Fuel cell and electrolysis cell technologies and hydrogen infrastructure development – a review

This review presents the current status of PEM fuel cell & electrolysis cell technologies, along with the H2infrastructure, describes their similarities & differences in structures, materials, and fundamentals, and outlines challenges/opportunities.

H+-Conducting Aromatic Multiblock Copolymer and Blend Membranes and Their Application in PEM Electrolysis.

As an alternative to common perfluorosulfonic acid-based polyelectrolytes, we present the synthesis and characterization of proton exchange membranes based on two different concepts: (i) Covalently bound multiblock-co-ionomers with a nanophase-separated structure exhibit tunable properties depending on hydrophilic and hydrophobic components’ ratios. Here, the blocks were synthesized individually via step-growth polycondensation from either partially fluorinated or sulfonated aromatic monomers. (ii) Ionically crosslinked blend membranes of partially fluorinated polybenzimidazole and pyridine side-chain-modified polysulfones combine the hydrophilic component’s high proton conductivities with high mechanical stability established by the hydrophobic components. In addition to the polymer synthesis, membrane preparation, and thorough characterization of the obtained materials, hydrogen permeability is determined using linear sweep voltammetry. Furthermore, initial in situ tests in a PEM electrolysis cell show promising cell performance, which can be increased by optimizing electrodes with regard to binders for the respective membrane material.

The effect of geometric parameters of PTL on oxygen transport in PEM electrolysis cell

In this study, two-phase flow of oxygen-water is studied by using numerical simulation in the Porous Transport Layer (PTL) of the Polymer Electrolyte Membrane Electrolysis Cell (PEMEC). The effect of thickness, porosity and multi-layer arrangement of PTL on the oxygen flow pattern and its removal from the PTL is investigated. The results showed the increase in the PTL thickness causes to increase the growth of the lateral paths from the inlet to the channel, which leads to increase the oxygen saturation in the PTL. It is also obtained that for PTL with different porosity, number and volume of occupied pores by oxygen in the PTL are the two main factors affecting the oxygen saturation and trade-off between them indicate the proper porosity to be used in different operating conditions. Furthermore, studies showed the use of two-layer PTL instead of single-layer can cause reduction in oxygen saturation in the proximity of reaction sites leading to a better operation of the electrolyzer.

Local Two-Phase Flow and Performance in Polymer Electrolyte Water Electrolysis Cells

Over the past decade, investigations[1-3] have been carried out to better understand the two-phase flow characteristics within a polymer electrolyte water electrolyzer (PEWE) and optimize the porous transport layer (PTL) morphology to improve the system performance and efficiency. Zhang, et al.[3] used a high-speed camera and transparent cell to study the strong influence of temperature and current density on bubble growth rate. Ito, et al. [4] showed that PTL porosity has a minor effect on cell performance while pore diameter greatly influences performance. They categorized the type of two-phase flow experienced by an electrolyzer by using liquid/gas superficial velocity plots. Furthermore, they showed that bubble detachment diameter strongly influenced the two-phase flow regime at any operating point. In a similar direction, Majasan, et al.[5] showed that longer flow path length promotes gas accumulation and results in annular flow at high current density, negatively impacting cell performance. Immerz et al.[6] also suggested that increased local ionic resistance down-the-channel may be attributed to large bubble accumulation. Therefore, the impacts of two-phase flow characteristics on mass transport as well as ohmic losses need to be better understood.Although the serpentine flow-field is very useful to study transport phenomena within a PEWE, it is rarely used as in commercial and large-scale PEWE system; the parallel channel-land configuration is a more conventional flow-field architecture. Through this work we hope to understand how architectural features in the flow field impact local performance to inform next-generation design. Furthermore, this work focuses on characterizing the two-phase flow and bubble accumulation occurring within the PEWE and understanding its relationship with performance. Initial experimental results revealed that the parallel flow-field outperforms the triple serpentine flow-field at high (50 ml/min) flowrates as seen in Figure 1a. This may be caused by the shorter channel lengths that do not exacerbate bubble accumulation near the outlet. Preliminary calculations of the superficial gas/liquid velocities have supported this conclusion (Figure 1c). However, at lower flowrates the parallel flow-field was observed to underperform and exhibit severe mass transport limitations. We believe that the fluid velocity in the channels at these low flowrates (6 ml/min) was insufficient to facilitate proper bubble detachment at the channel/PTL interface. This led to the formation of a large and spread out region of mass transport limited current density as seen in figure 1b. In conclusion, insights into local two-phase flow characteristics and their impact on performance in a PEWE cell will be described in this presentation[1] Lopata, J., et al., Effects of the Transport/Catalyst Layer Interface and Catalyst Loading on Mass and Charge Transport Phenomena in Polymer Electrolyte Membrane Water Electrolysis Devices. Journal of The Electrochemical Society, 2020. 167(6): p. 064507 DOI: 10.1149/1945-7111/ab7f87.[2] Lopata, J.S., et al., Considering Two-Phase Flow in Three-Dimensional Computational Fluid Dynamics Simulations of Proton Exchange Membrane Water Electrolysis Devices. ECS Transactions, 2020. 98(9): p. 653-662 DOI: 10.1149/09809.0653ecst.[3] Li, Y., et al., In-situ investigation of bubble dynamics and two-phase flow in proton exchange membrane electrolyzer cells. International Journal of Hydrogen Energy, 2018. 43(24): p. 11223-11233 DOI: https://doi.org/10.1016/j.ijhydene.2018.05.006.[4] Ito, H., et al., Experimental study on porous current collectors of PEM electrolyzers. International Journal of Hydrogen Energy, 2012. 37(9): p. 7418-7428 DOI: https://doi.org/10.1016/j.ijhydene.2012.01.095.[5] Majasan, J.O., et al., Two-phase flow behaviour and performance of polymer electrolyte membrane electrolysers: Electrochemical and optical characterisation. International Journal of Hydrogen Energy, 2018. 43(33): p. 15659-15672 DOI: https://doi.org/10.1016/j.ijhydene.2018.07.003.[6] Immerz, C., et al., Local Current Density and Electrochemical Impedance Measurements within 50 cm Single-Channel PEM Electrolysis Cell. Journal of The Electrochemical Society, 2018. 165(16): p. F1292-F1299 DOI: 10.1149/2.0411816jes. Figure 1

Capabilities and Limitations of 3D-CFD Simulation of Anode Flow Fields of High-Pressure PEM Water Electrolysis

In this work, single-phase (liquid water) and two-phase (liquid water and gaseous oxygen) 3D-CFD flow analysis of the anode of a high pressure PEM electrolysis cell was conducted. 3D-CFD simulation models of the anode side porous transport layer of a PEM electrolyzer cell were created for the flow analysis. For the geometrical modelling of the PTL, two approaches were used: (a) modelling the exact geometry and (b) modelling a simplified geometry using a porosity model. Before conducting two-phase simulations, the model was validated using a single-phase approach. The Eulerian multiphase and the volume-of-fluid approaches were used for the two-phase modelling and the results were compared. Furthermore, a small section of the PTL was isolated to focus on the gas bubble flow and behaviour in more detail. The results showed plausible tendencies regarding pressure drop, velocity distribution and gas volume fraction distribution. The simplified geometry using the porous model could adequately replicate the results of the exact geometry model with a significant reduction in simulation time. The developed simulation model can be used for further investigations and gives insight into two-phase flow phenomena in the PTL. Additionally, the information obtained from simulation can aid the design and evaluation of new PTL structures.

Influence of the gasket materials on the clamping pressure distribution in a PEM water electrolyzer: Bolt torques and operation mode in pre-conditioning

To keep optimally connected, all electrolysis cell elements is one of the most important design criteria. The optimal distribution of the clamping points is crucial to increasing cell performance. In this work, the compression pressure distribution inside of a 25 cm2 PEM electrolysis cell was evaluated, using different materials: Teflon®, Viton®, ethylene propylene diene monomer rubber (EPDM), and nitrile rubber. Sealing material evaluation was performed taking as performance indicators: total compressed area (%) and compression pressure, for different torques applied. Pressure distribution was obtained by using pressure-sensitive films, analyzing the distribution of pressure points from three-dimensional plots (3D), and quantifying intensities of the images obtained. Results showed that pressure points distribution depends on the stiffness and thickness of the gasket materials. For a tightening torque of 3.70 N m, a pressure of 2.23 MPa is obtained with 85% of the membrane area compressed using nitrile rubber-EPDM gaskets.

Pulsed electrodeposition of iridium catalyst nanoparticles on titanium suboxide supports for application in PEM electrolysis

In this work recent progress on a novel preparation route for iridium-based electrodes applied in PEM-electrolysis cells is communicated. Substoichiometric titanium oxide (TiO2-x) particles have been synthesized to prepare a nano porous coating on top of a titanium electrode substrate. The TiO2-x-material is stabilized on the substrate by laser sintering and utilized as an electrically conductive support for iridium catalyst particles, which were deposited via electrochemical methods. The influence of the deposition current density and iridium concentration in the electrolyte were analyzed, resulting in samples with increased catalytic activity when compared to reference samples in linear sweep voltammetry.

Characterization and electrocatalytic properties of electrospun Pt‐IrO2 nanofiber catalysts for oxygen evolution reaction

SummaryIn this study, novel Pt‐IrO2 nanofiber catalysts for oxygen evolution reaction (OER) were successfully prepared using the electrospinning method with a high‐concentration precursor solution. The composition and structure of catalysts were characterized, and the electrocatalytic performance of the nanofiber catalysts in water electrolysis was investigated from various aspects such as overpotential, charge transfer resistance, and exchange current density. Special attention was paid on the effect of Pt/Ir ratio on the electrocatalytic activity of the electrospun nanofibers. The results showed that the Pt‐IrO2 nanofiber catalysts with average fiber diameters ranging from 10 to 100 nm can be successfully obtained by the electrospinning method, and the average diameter decreased with the increase of Pt content. Since a bigger amount of IrO2 content and a thinner fiber structure are all beneficial to the electrocatalytic performance, the Pt‐IrO2 catalysts with Pt:Ir = 1:9 and Pt:Ir = 9:1 both showed better catalytic performance for OER than the commercial IrO2, which was also demonstrated by the lower charge transfer resistance and higher exchange current density. As a result, the overpotentials of Pt‐IrO2 catalysts with Pt:Ir = 1:9 and Pt:Ir = 9:1 are 50 mV and 32 mV lower than the overpotential of the commercial IrO2 at 30 mA cm−2 in 0.5 M H2SO4, respectively. The electrospun Pt‐IrO2 nanofiber catalyst with proper Pt content seems to be very promising since it can not only improve the catalytic performance and the safety of PEM electrolysis cells, but also reduce the amount of more expensive Ir in catalysts.

Sulfonated and Partially Fluorinated Poly(aryl) Multiblock-Co-Ionomer- and Blend Membranes As Proton Conductors for PEM Electrolysis

The core of a PEM water electrolyzer is represented by the proton conductive membrane. While nowadays PFSA-based materials such as Nafion are state of the art in large scale energy applications, there is a strong need for development of cost efficient alternatives, which exhibit reduced gas crossover, high ionic conductivity and durability.Here, we present proton exchange membranes based on two different concepts: Blends of partially fluorinated polybenzimidazole and pyridine side-chain-modified polysulfones (3K-BM) as well as arylene main-chain multiblock co-ionomers (MB-O).The 3K-BM ionomer membranes represent a blend of hydrophilic partially fluorinated and sulfonated aromatic polyethers with two hydrophobic components: F6-PBI and pyridine-modified PSU [1]. Proton conductivity is achieved by the hydrophilic parts of the material whereas the hydrophobic components ensure stability and enable adjustment of mechanical properties.MB-O consists of hydrophobic and hydrophilic building blocks, which are synthesized via step-growth polycondensation. The former blocks are partially fluorinated aromatics, whereas the latter ones are based on sulfonated nonfluorinated aromatics [2].Multiblock-co-ionomers are capable of forming nanophase-separated structures [2,3], which are tunable by varying the ratio of hydrophilic and hydrophobic proportions. In addition to the polymer synthesis and membrane preparation, ex-situ characterization including NMR spectroscopy, gel permeation chromatography, thermogravimetric analysis, H2-crossover analysis via linear-sweep-voltammetry and AC impedance spectroscopy have been performed with our novel materials. First preliminary in-situ tests in a PEM electrolysis cell have already yielded high performances, which can potentially be increased further by optimization of electrodes with respect to binders for the respective membrane material. Acknowledgements This work has been funded by the German Federal Ministry of Education and Research (BMBF) as part of the project: “Increasing Lifespan and Power of Polymer Electrolyte Membrane Electrolysers through High Power Membrane Electrode Assemblies (POWER-MEE)“ References [1] J. Kerres, A. Ullrich, M. Hein, J. Polym. Sci.: Part A: Polym. Chem. 39 (2001) 2874–2888[2] F. Schönberger, J. Kerres, J.Polym. Sci. Part A: Polym. Chem. 45 (2007) 5237–5255.[3] H. Ghassemi, J. E. McGrath, T. A. Zawodzinski, Polymer 47 (2006) 4132-4139

Enhanced performance of a PtCo recombination catalyst for reducing the H2 concentration in the O2 stream of a PEM electrolysis cell in the presence of a thin membrane and a high differential pressure

High electrochemical efficiency at elevated current densities and low H2 concentration in O2 can be achieved in PEM electrolysis using thin membrane and integrated recombination catalyst. An enhanced PtCo alloy recombination catalyst was synthesized and used at the anode of a membrane-electrode assembly (MEA). This allowed reducing the H2 concentration in the oxygen stream during electrolysis operation with a thin 50 μm perfluorosulfonic acid (PFSA) Aquivion® membrane. Both dual-layer and composite anode configurations (PtCo/IrRuOx) were investigated. The electrochemical performance of the MEAs containing the recombination catalyst was better than a bare MEA while producing a decrease of the H2 content at the anode. This allowed extending the partial load operation down to 5% at 55 °C under a differential pressure of 20 bar. The effects of the cathodic pressure and cell temperature (including evaluation of intermediate temperature operation at 140 °C) on both electrochemical performance and H2 concentration in the anode stream were investigated. An excellent performance of 4 A cm−2 at 1.75 V, at 140 °C, 20 bar cathode pressure, 5.5 bar anode pressure, with 0.6 mg cm−2 overall precious metal catalysts content was recorded. At 140 °C, the MEA also showed a moderate H2 concentration in O2 of about 2.3%, almost constant through most of the current density range.

Analysis of oxygen evolving catalyst coated membranes with different current collectors using a new modified rotating disk electrode technique

For the first time, the oxygen evolution reaction (OER) behavior of commercial catalyst-coated membranes (CCMs) has been studied using an in-house modified rotating disk electrode (MRDE) tip capable of reaching current densities of up to 2 A cm−2. The electrochemical results are comparable with a full PEM electrolysis cell. The kinetic analysis reveals Tafel slopes of about 50 and 60 mV dec−1 for all temperatures with the PEM electrolysis hardware and the MRDE, respectively. The activation energy of the OER obtained with the MRDE and the PEM electrolysis cell are 75 and 68 kJ mol−1, respectively. Detailed cyclic voltammetric measurements of Ir-based CCMs were performed to examine the influence of operating temperature, Ti-based current collectors, the scan rate on the adsorbed charge, and the electro kinetics of the OER. Six different expanded metal Ti current collectors were analyzed in sulfuric acid and their impact on the CCM charging at various temperatures were examined in order to calculate the electrode's inner and outer charge. It was observed that the voltammetric charge is proportional to the coverage of the CCM by the current collector. The MRDE tool presented here is an ideal tool for electrochemical characterization of CCMs and current collectors and allows for an economical and accelerated screening of these important PEM electrolyzer components without the requirement of full cell testing.

Impact of Mechanical Operation Conditions on PEM Water Electrolyzer Performance

Hydrogen can be generated by means of PEM water electrolysis that makes use of renewably-produced electricity. To improve and maintain good performance of PEM electrolysis cells and stacks, research has been carried out mostly in the field of operation conditions, catalyst loading reduction and substitution of precious metals, two-phase flow investigation and analysing degradation effects. However, understanding mechanical interactions in the cell can additionally help to improve performance and lower investment costs [1]. In the electrolysis cell, the components are clamped against each other to ensure a good electrical contact. Excessive clamping pressure, however, leads to damage of the components. Studies on PEM fuel cells found that high clamping pressures reduces GDL porosity and leads to mass transport limitation [2]. In this work the influence of clamping pressure on the performance of different PEM electrolysis cell designs has been studied. Therefore, a test cell was designed that allows applying pressure directly on the active cell area. Polarisation curves and ohmic resistances were measured at different clamping pressures. Electrochemical impedance spectroscopy (EIS) was used to show the effect of compression on ohmic losses and mass transfer limitations. Furthermore, the pressure change within the cell over time was investigated. For all cell designs, optimal clamping pressure was found to be approximately 2.3 – 3 MPa. The impedance data show no higher mass transfer losses for higher pressures on the active area. However, the ohmic losses rise above a critical pressure. The results indicate that for PEM electrolysis, not mass transport limitations but protonic ohmic losses are crucial for a worse performance at high clamping pressures. Also it was found that stress relaxation of the membrane lead to pressure loss and thus to a worse performance over time. Borgardt, E., et al., Mechanical characterization and durability of sintered porous transport layers for polymer electrolyte membrane electrolysis. Journal of Power Sources, 2018. 374: p. 84-91.Mason, T.J., et al., A study of the effect of compression on the performance of polymer electrolyte fuel cells using electrochemical impedance spectroscopy and dimensional change analysis. International Journal of Hydrogen Energy, 2013. 38(18): p. 7414-7422.

Cr- and Ti-Based Spinels As Materials for Anodic Catalyst Support in PEM Electrolysis Cells: Assessing Corrosion Stability and Support Role in Catalyst Activity of Corrosion Stable Ceramics

PEM electrolysis is an efficient and robust technology for conversion of power-to-H2 for energy storage [1]. However, the cost of the components is still too high for large scale applications. Corrosion resistant catalyst supports with high conductivity have continuously been researched in order to provide a better catalyst utilization and current collection eliminating the need of Pt coated Ti components [2,3]. Spinel-structured chromites are stable toward corrosion. They are the passivating layer on the surface of stainless steels as a product of the oxidation of the surface [4,5]. On the other hand, Ti-based spinels are conductive at room temperature and they are reported to reversibly exchange H+ on Li+ sites [6], which might enable proton conductivity throughout the support. MCr2O4 (M = Mg, Zn, Mn, Ni, NiFe) compounds were synthesized by solid state route to form a single phase of the cubic spinel compound. In order to increase the overall conductivity of the best performing ceramic support, nitrate combustion synthesis was used to prepare MDxCr2-xO4 (where M=Ni, Mn, and D=Cu, Li) with x=0.25, 0.5.While NiCr2O4 showed limited ability to be doped, single phase spinels were obtained in the case of doped MnCr2O4. MTi2O4 (with M=Li, Mg, Mn) were also prepared by solid state synthesis. LiTi2O4 pellets were prepared by wrapping cylindrical pellets of the raw materials with Cu foil and firing them in 5% H2/Ar. MnTi2O4, and MgTi2O4 pellets were wrapped in Mo foil, and fired in vacuum in quartz tubes. For all the materials, tiny amount of secondary phases were detected after the synthesis. The conductivity of the materials was measured on sintered rectangular bars using a 4-probe DC measurement, revealing insulating characteristics of the materials. The conductivity of doped MnCr2O4 showed an increase of several orders of magnitude, reaching 10-4 S/cm at 70°C. In the case of Ti-based spinels, the conductivity was measured on disks using a Van der Pauw set up. The measured conductivities were of the order of 102, 101.5 and 10 S/cm for LiTi2O4, MnTi2O4 and MgTi2O4 respectively. All the materials were tested chemically for 24 h at 85°C in a 1:1 H2SO4:HNO3 1 M mixture under continuous agitation and electrochemically by repeated cycling of an ink-drop casted layer between 0.5 and 2.0 V vs RHE in 1 M H2SO4 in a RDE setup. The activity test was conducted on physical mixtures with IrO2 and support by CV between 0.5 and 2.0 V vs RHE in 0.5 M H2SO4 in a RDE setup. The chemical testing of undoped Cr-based spinels showed negligible corrosion. The test did not show any negative effect of doping to the corrosion stability of the compound. Ti-based spinels showed to undergo sensible mass loss after chemical corrosion testing, together with loss of the spinel crystal structure. Electrochemical characterization of the best performing materials, Cu-MnCr2O4 and LiTi2O4, revealed that the materials are redox active in the potential window under analysis. Both the materials present distinctive oxidation peaks, coupled to reduction peaks in the case of Cu-MnCr2O4. To establish the effect of doping, also the undoped MnCr2O4 was tested. The integrated areas of the voltammetry curves are consistent with the complete oxidation of the deposited material, in the case of MnCr2O4 and LiTi2O4. Interestingly, Cu-MnCr2O4 does not show the same electrochemical activity in the potential window under study. Activity test were conducted on pure IrO2 and on the physical mixtures IrO2/Cu-MnCr2O4 and IrO2/LiTi2O4. The absolute value of current density at 2.0 V showed an increase of 10% in the case of IrO2/Cu-MnCr2O4 compared with pure IrO2.

Cr- and Ti-Based Spinels as Materials for Anodic Catalyst Support in PEM Electrolysis Cells: Assessing Corrosion Stability and Support Role in Catalyst Activity of Corrosion Stable Ceramics

This work aims to determine the stability of Cr- and Ti- based spinels as catalyst supports for oxygen evolution reaction (OER) catalyst in PEM electrolyzers (PEMECs). Different compositions of MCr2O4 (M=Ni, NiFe, Zn, Mg) and MTi2O4 (Li, Mg, Mn) have been synthesized by solid state synthesis. Pure and doped Cr-based spinels exhibit low conductivities at the operating temperatures of PEMECs (<10-4 S cm-1), while Ti-based spinels showed very high conductivities at room temperature (~10-100 S cm-1). Cr-spinels proved to be very stable to chemical corrosion testing, while Ti-spinels manifested substantial weight loss. The most promising materials (LiTi2O4, MnCr2O4, Cu-MnCr2O4) showed redox activity at potentials >1.5 V vs SHE. LiTi2O4 is completely oxidized upon cycling up to 2.0 V vs SHE. Mixtures of IrO2/oxide support deposited on glassy carbon were tested toward OER, which showed a 10% higher absolute current at 2.0 V vs SHE in the case of IrO2/Cu-MnCr2O4 compared with pure IrO2.

Hydrogen from electrochemical reforming of ethanol assisted by sulfuric acid addition

The addition of H2SO4 to the anolyte feeding solution for the electrochemical reforming of ethanol has been studied in terms of activity and stability for hydrogen production in a PEM electrolysis cell. Five equivalent MEAs based on commercial Pt-Sn/C and Pt/C as anode and cathode materials, respectively, and a Nafion membrane, have been prepared and tested to optimize the addition of the H2SO4. Results demonstrated that the addition of an optimal H2SO4 concentration (ethanol 4 mol L−1 and 0.01 mol L−1 H2SO4) enhances the electrocatalytic activity and stability of the MEA by decreasing the energy requirements for hydrogen production. According to impedance spectroscopy experiments, this improvement is caused by a decrease in the anodic charge transfer resistance, probably due to an increase in the number of contact triple points (electrolyte/catalyst particles/electronic support). However, the addition of a higher H2SO4 concentration (0.05 mol L−1) induced the dissolution of the Pt-Sn/C anodic catalyst causing a severe degradation of the MEA. Therefore, the optimal addition of H2SO4, which is not consumed during the electrochemical reforming experiments, may be of great practical importance for using this technology for the renewable hydrogen production from real bioethanol streams.

Local Current Density and Electrochemical Impedance Measurements within 50 cm Single-Channel PEM Electrolysis Cell

The present analysis shows the local distribution of current density and EIS measurements along a 50 cm single-channel proton exchange membrane water electrolysis (PEMWE) cell. Measurements for operating modes with one sufficiently high and one insufficiently low stoichiometric water ratio (λ) were carried out to observe effects on the current density distribution. Furthermore, global and local EIS measurements were performed to distinguish between the cell voltage loss differences in the two cases. The mass transport losses ηmtx and the Ohmic voltage losses ηΩ show a strong increase, when the stoichiometric water ratio falls below a level of λ ≈ 5. The reduction of the inlet water flux of the anode reduces both the proton conductivity of the ionomer within the catalyst layer and the membrane, increasing transport and Ohmic resistances, respectively. The local analysis has shown that the level of membrane and catalyst hydration under low stoichiometric conditions can be distributed highly non-homogeneous in along-the-channel direction, with the most pronounced dehydration toward the end of the channel.

Generation of Pure Hydrogen by the Electrocatalytic Oxidation of Methane-Derived Liquid Fuels in a PEM Electrolysis Cell

The development of clean power sources and the reduction of the emission of greenhouse gases (e.g. CO2) have led to many investigations on Low Temperature Fuel Cells, such as the Proton Exchange Membrane Fuel Cell (PEMFC), fed either with pure hydrogen or with other fuels, particularly liquid fuels such as methanol or ethanol. Steam Methane Reforming (SMR) is the main process to produce hydrogen but it occurs at elevated temperatures (200 to 600°C) and produces a lot of CO2. In addition the reformate gas must be cleaned-up to reduce the content of CO to an acceptable amount (< 5 ppm), in order to avoid poisoning of the Pt-based catalysts of the PEMFC. Water electrolysis is a mature process, leading to very pure hydrogen. However, due to the high overvoltage encountered at the catalytic anode, where oxygen evolution does occur, the hydrogen production cost remains actually not competitive with the SMR. Therefore, instead of using water, other hydrogen containing compounds (particularly organic compounds) can be considered as hydrogen sources leading to pure hydrogen by their electro-oxidation at the anode of a Proton Exchange Membrane Electrolysis Cell (PEMEC) [1- 3]. This is a very challenging approach, since the theoretical cell voltage for their electrolysis (≈ a few tens mV) is much lower than the theoretical cell voltage of water electrolysis (1.23 V under standard conditions). Several organic compounds can be used as H2sources, such as carboxylic acids, alcohols, sugars, e.g. formic acid, methanol, ethanol, etc. Other organic compounds can be interesting for producing very pure hydrogen by their electrochemical decomposition, particularly those derived from methane (natural gas, shale gases, etc.) or from methanol (which is mainly produced by the conversion of “Syngas”, a mixture of CO and H2), such as dimethyl ether DME (CH3OCH3), dimethoxymethane DMM [CH2(OCH3)2] and trimethoxymethane TMM [CH(OCH3)3]. Like methanol these ethers and poly-ethers can be easily oxidized at the Pt-Ru anode of a DMFC hardware since they do not contain a C-C bond (conversely to ethanol). Moreover they have an energy density (≈ 7 to 9 kWh kg-1) higher than that of methanol (≈ 6 kWh kg-1) so that they have been considered as alternative fuels for a Direct Oxidation Fuel Cell [4, 5]. Their complete oxidation to carbon dioxide in an acid electrolyte (like a PEM) involves 12 to 20 electrons, respectively, as follows: CH3OCH3 + 3 H2O → 2 CO2 + 12 H+ + 12 e-for DME CH2(OCH3)2 + 4 H2O → 3 CO2 + 16 H+ + 16 e-for DMM CH(OCH3)3 + 5 H2O → 4 CO2 + 20 H+ + 20 e-for TMM. Then the protons produced at the anode cross-over the protonic membrane and reach the cathodic compartment of the PEMEC, where they are reduced to hydrogen, 2 H+ + 2 e- → H2, leading to pure H2 by the electrochemical decomposition of these organic compounds, as follows: CH3OCH3 + 3 H2O → 2 CO2 + 6 H2 for DMECH2(OCH3)2 + 4 H2O → 3 CO2 + 8 H2 for DMM CH(OCH3)3 + 5 H2O → 4 CO2 + 10 H2 for TMM. In this communication the electro-reactivity of several methane-derived liquid fuels, such as poly-ethers, including HCHO and CH3OH (which can result from the hydrolysis of ethers in acidic media), was compared by cyclic voltammetry. Then the electrochemical decomposition of methanol and DMM for the production of clean hydrogen was investigated in a Direct Methanol Fuel Cell (DMFC) hardware of 5 cm2 geometric surface area (with a Pt-Ru/C anode and a Pt/C cathode) working as a PEMEC. The anodic compartment was fed with an acidic solution (0.5 M H2SO4) containing the organic compound (with concentrations from 0.1 M to 10 M) whereas the cathodic compartment was fed with a pure 0.5 M H2SO4 solution. The electrolysis cell, thermostated at several controlled temperatures (25 to 85°C), was polarized at a constant current density j (from 1 to 100 mA cm-2). Both the cell voltage of the electrolysis cell and the volume of hydrogen produced were recorded as a function of time t and current density j. [1] C. Coutanceau, S. Baranton, WIREs Energy Envirion. 5 (2016) 388-400. [2] B. Guenot, M. Cretin, C. Lamy, J. Appl. Electrochem. 45 (2015) 973-981. [3] C. Lamy, T. Jaubert, S. Baranton, C. Coutanceau, J. Power Sources 245 (2014) 927-936. [4] N. Wakabayashi, K. Takeuchi, H. Uchida, M. Watanabe, J. Electrochem. Soc. 151 (2004) A1636-A1640. [5] G.K.S. Prakash, M.C. Smart, G.A. Olah, S.R. Narayanan, W. Chun, S. Surampudi, G. Halpert, J. Power Sources 173 (2007) 102-109.

Generation of Pure Hydrogen by the Electrocatalytic Oxidation of Methane-Derived Liquid Fuels in a PEM Electrolysis Cell

The electrocatalytic oxidation of dimethoxymethane (DMM), to produce clean hydrogen, was carried out at the Pt-Ru anode of a Direct Methanol Fuel Cell hardware at several concentrations and different temperatures. At given concentrations of DMM (0.1 to 4 M) and cell temperatures (25 to 85°C) the quantity of produced hydrogen and the voltage of the electrolysis cell were recorded as a function of time for any current intensity used (from 5 to 800 mA). The cell voltage stabilizes after 15 min and never exceeds 0.50 V corresponding to electrical energy consumption lower than 1.1 kWh (Nm3)-1. The quantity of hydrogen produced is a linear function of the current density and of the electrolysis time, i.e. of the quantity of electricity consumed in the electro-oxidation reaction. Moreover the quantity of hydrogen produced at a given electrolysis time is independent of the DMM concentration, the cell voltage and its temperature.

Investigation on PEM water electrolysis cell design and components for a HyCon solar hydrogen generator

Hydrogen as a secondary energy carrier promises a large potential as a long term storage for fluctuating renewable energies. In this sense a highly efficient solar hydrogen generation is of great interest especially in southern countries having high solar irradiation. The patented Hydrogen Concentrator (HyCon) concept yields high efficiencies combining multi-junction solar cells with proton exchange (PEM) membrane water electrolysis. In this work, a special PEM electrolysis cell for the HyCon concept was developed and investigated. It is shown that the purpose-made PEM cell shows a high performance using a titanium hybrid fiber sinter function both as a porous transport layer and flow field. The electrolysis cell shows a high performance with 1.83 V at 1 A/cm2 and 24 °C working under natural convection with a commercially available catalyst coated membrane. A theoretical examination predicts a total efficiency for the HyCon module from sunlight to hydrogen of approximately 19.5% according to the higher heating value.

Durability and Degradation Issues in PEM Electrolysis Cells and its Components

Durability and Degradation Issues in PEM Electrolysis Cells and its Components