Novel pyrrolidinium-functionalized styrene-b-ethylene-b-butylene-b-styrene copolymer based anion exchange membrane with flexible spacers for water electrolysis

Anion exchange membranes (AEM) are core components for alkaline electrochemical energy technologies, such as water electrolysis and fuel cells. They are regarded as promising alternatives for proton exchange membranes (PEM) due to the possibility of using platinum group metal (PGM)-free electrocatalysts. However, their chemical stability and conductivity are still of great concern, which is appearing to be a major challenge for developing AEM-based energy systems. Herein, we highlight an AEM with styrene-b-ethylene-b-butylene-b-styrene copolymer (SEBS) as a backbone and pyrrolidinium or piperidinium functional groups tethered on flexible ethylene oxide spacer side-chains (SEBS-Py2O6). This membrane reached 27.8 mS cm-1 hydroxide ion conductivity at room temperature, which is higher compared to previously obtained piperidinium-functionalized SEBS reaching up to 10.09 mS cm-1. The SEBS-Py206 combined with PGM-free electrodes in an AWE water electrolysis (AEMWE) cell achieves 520 mA cm-2 at 2 V in 0.1 M KOH and 171 mA cm-2 in ultra-pure water (UPW). This high performance indicates that SEBS-Py2O6 membranes are suitable for application in water electrolysis.EU project NEWELYChinese Scholarship Counci

Elucidating the performance limitations of alkaline electrolyte membrane electrolysis : dominance of anion concentration in membrane electrode assembly

Anion exchange membrane water electrolyzers (AEMWEs) offer a cost‐effective technology for producing green hydrogen. Here, an AEMWE with atmospheric plasma spray non‐precious metal electrodes was tested in 0.1 to 1.0 M KOH solution, correlating performance with KOH concentration systematically. The highest cell performance was achieved at 1.0 M KOH (ca. 0.4 A cm-2 at 1.80 V), which was close to a traditional alkaline electrolysis cell with ≈6.0 M KOH. The cell exhibited 0.13 V improvement in the performance in 0.30 M KOH compared with 0.10 M KOH at 0.5 A cm−2. However, this improvement becomes more limited when further increasing the KOH concentration. Electrochemical impedance and numerical simulation results show that the ohmic resistance from the membrane was the most notable limiting factor to operate in low KOH concentration and the most sensitive to the changes in KOH concentration at 0.5 A cm-2. It is suggested that the effect of activation loss is more dominant at lower current densities; however, the ohmic loss is the most limiting factor at higher current densities, which is a current range of interest for industrial applications.Projekt DEA

A novel advanced test system for polymer electrolyte membrane water electrolysis based on hydraulic cell compression

In this work, a novel polymer electrolyte membrane water electrolyzer (PEMWE) test cell based on hydraulic single-cell compression is described. In this test cell, the current density distribution is almost homogeneous over the active cell area due to hydraulic cell clamping. As the hydraulic medium entirely surrounds the active cell components, it is also used to control cell temperature resulting in even temperature distribution. The PEMWE single-cell test system based on hydraulic compression offers a 25 cm2 active surface area (5.0 × 5.0 cm) and can be operated up to 80◦C and 6.0 A/cm2. Construction details and material selection for the designed test cell are given in this document. Furthermore, findings related to pressure distribution analyzed by utilizing a pressure-sensitive foil, the cell performance indicated by polarization curves, and the reproducibility of results are described. Experimental data indicate the applicability of the presented testing device for relevant PEMWE component testing and material analysi

NdMn1.5Ru0.5O5, a high-performance electrocatalyst with low Ru content for acidic oxygen evolution reaction

A mixed oxide with the crystal structure of the DyMn2O5 family, namely NdMn1.5Ru0.5O5, is reported active for the oxygen evolution reaction (OER) in acidic media. NdMn1.5Ru0.5O5 displays high OER activity of 500 A gRu-1 at 1.5 V. Moreover, is more stable than most Ru oxides reported to date, remaining active for more than 500 cycles between 1.1. and 1.7 V at low scan rate of 10 mV s-1. The high activity and stability are attributed to the Ru cations, as NdMn2O5 exhibits very low OER activity. NdMn1.5Ru0.5O5 has particularly short Ru-Ru distances of 2.60Å, a value close to the Ru-Ru metallic distances around 2.642 Å. The high activity and durability of NdMn1.5Ru0.5O5 for the OER are also demonstrated in a proton exchange membrane water electrolysis cell by producing a low-loaded anode electrode with 0.5 mgRucm-2. The cell achieves 1.97 V at 0.5 A cm-2, consistent with the performances reported for Ru-based catalysts but with lower Ru loading. This performance is maintained during 100 h of operation. Additionally, NdMn1.5Ru0.5O5 displays visible ORR activity in acidic media, recording an onset potential of 0.85 V at 0.1 mA cm-2. It is noteworthy to highlight the extreme rarity of bifunctional ORR/OER catalysts acidic media

Développement de systèmes et matériaux pour la conversion de l'énergie chimique et lumineuse

Plusieurs matériaux et systèmes, pour la conversion de l'énergie chimique et lumineuse ont été mis au point. Dans un premier temps, des amas métalliques nanostructurés, à base du chalcogénure, RuxSey, ont été synthétisés en milieu aqueux. La cinétique de la réaction de réduction du dioxygène en présence de l'acide formique, sur ces catalyseurs, a été systématiquement étudiée. En outre, des piles à combustible à écoulement laminaire (LFFC), de géométrie différente, ont été développées. Ainsi, les chalcogénures à base de PtxSy, RuxSey et CoSe2, supportés sur carbone, ont été évalués à la cathode de ces systèmes microfluidiques. Les résultats obtenus montrent que les matériaux étudiés ont de bonnes perspectives pour être utilisés comme cathodes des piles à combustible où l'entrecroisement de combustibles organiques est un défi à relever. Dans un deuxième temps, des couches minces à base de dioxyde de titane dopé au tungstène (Ti1-xWxO2) ont été synthétisés par la technique de pulvérisation magnétron PVD. La structure cristallographique et les propriétés photoélectrochimiques des ces matériaux ont été analysées. Les résultats montrent que ces matériaux peuvent être un substrat prometteur de nanoparticules métalliques. Pour finir, les propriétés photoélectrochimiques des couches à base de TiO2 ont été déterminées en vue de son évaluation dans un microréacteur photocatalytique. Ce dernier, permet de suivre insitu la décoloration photocatalytique sur le TiO2, ainsi que l évolution du potentiel et le photocourant généré sous illumination UV-Vis. En outre, le microréacteur photocatalytique peut servir à simuler un système pilote pour la dépollution de l'eau à l'échelle industrielle.In this work, various materials and systems for the conversion of chemical and light energy were developed. First of all, chalcogenide nanoclusters of RuxSey were synthesized in aqueous medium. The kinetics of the oxygen reduction reaction in presence of formic acid was systematically studied. Furthermore, different laminar flow fuel cells (LFFC) were fabricated. Thus, the chalcogenides PtxSy, RuxSey, CoSe2 supported on carbon, were evaluated as cathodes for these microfluidic systems. The obtained results show that the studied materials have good perspectives to be used, as cathode of fuel cells were fuel crossover is relevant. Secondly, thin films of tungsten-doped titanium dioxide (Ti1-xWxO2) were synthesized by PVD magnetron sputtering. The crystallographic structure and the photoelectrochemical properties of these materials were analyzed. The results showed that these materials can be a promising substrate for metallic nanoparticles, to perform the electrocatalytic fuel cell reactions. Finally, the photoelectrochemical properties of TiO2 films were determined and evaluated in a photocatalytic microreactor. This later allows studying in-situ the photocatalytic discoloration of a dye, as well as the effect of electrode potential and the photocurrent generated under UV-Vis illumination. Additionally, the photocatalytic microreactor can be used to simulate a pilot system for water decontamination at industrial level.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Photohole Trapping Induced Platinum Cluster Nucleation on the Surface of TiO2 Nanoparticles

International audienceThe photocurrent response of TiO2 nanoparticles synthesized via the sol-gel process was studied in the presence of methanol, ethanol, and isopropanol. The nanocrystalline nature of photoelectrodes showed an important photocurrent in the presence of alcohol following the order methanol approximate to ethanol > isopropanol > H2O. This process mimics the photoelectrochemical response, and therefore a correlation of the photo-deposition process of platinum nanoclusters on TiO2 particles in the presence of alcohol molecules was devised. The photodeposition mechanism of platinum nanoislands at the surface of a nanocrystalline TiO2 powder is discussed in the light of the photoelectrochemical results

Comprehensive investigation of novel pore-graded gas diffusion layers for high-performance and costeffective proton exchange membrane electrolyzers

Hydrogen produced by water electrolysis is a promising storage medium for renewable energy. Reducing the capital cost of proton exchange membrane (PEM) electrolyzers without losing efficiency is one of its most pressing challenges. Gas diffusion layers (GDL), such as felts, foams, meshes and sintered plates, are key stack components, but these are either inefficient or expensive. This study presents a new type of GDL produced via vacuum plasma spraying (VPS), which offers a large potential for cost reduction. With this technology, it is possible to introduce a gradient in the pore-size distribution along the thickness of the GDL by varying the plasma parameters and titanium powder particle sizes. This feature was confirmed by cross-section scanning electron microscopy (SEM). X-ray computed tomography (CT) and mercury intrusion porosimetry allowed determining the porosity, pore radii distribution, and pore entry distribution. Pore radii of ca. 10 mm could be achieved in the layers of the GDL close to the bipolar plate, while those in contact with the electrodes were in the range of 5 mm. The thermally sprayed Ti-GDLs allowed achieving PEM electrolyzer performances comparable to those of the state-of-the-art sintered plates and far superior than those of meshes. Moreover, a numerical model showed that the reduced capillary pressure and tortuosity eliminates mass transport limitations at 2 A cm-2. The results presented herein demonstrate a promising solution to reduce the cost of one of the most expensive components of the stack

Tolerant Chalcogenide Cathodes of Membraneless Micro Fuel Cells.

International audienceThe most critical issues to overcome in micro direct methanol fuel cells (μDMFCs) are the lack of tolerance of the platinum cathode and fuel crossover through the polymer membrane. Thus, two novel tolerant cathodes of a membraneless microlaminar-flow fuel cell (μLFFC), Pt(x) S(y) and CoSe(2) , were developed. The multichannel structure of the system was microfabricated in SU-8 polymer. A commercial platinum cathode served for comparison. When using 5 M CH(3) OH as the fuel, maximum power densities of 6.5, 4, and 0.23 mW cm(-2) were achieved for the μLFFC with Pt, Pt(x) S(y) , and CoSe(2) cathodes, respectively. The Pt(x) S(y) cathode outperformed Pt in the same fuel cell when using CH(3) OH at concentrations above 10 M. In a situation where fuel crossover is 100 %, that is, mixing the fuel with the reactant, the maximum power density of the micro fuel cell with Pt decreased by 80 %. However, for Pt(x) S(y) this decrease corresponded to 35 % and for CoSe(2) there was no change in performance. This result is the consequence of the high tolerance of the chalcogenide-based cathodes. When using 10 M HCOOH and a palladium-based anode, the μLFFC with a CoSe(2) cathode achieved a maxiumum power density of 1.04 mW cm(-2) . This micro fuel cell does not contain either Nafion membrane or platinum. We report, for the first time, the evaluation of Pt(x) S(y) - and CoSe(2) -based cathodes in membraneless micro fuel cells. The results suggest the development of a novel system that is not size restricted and its operation is mainly based on the selectivity of its electrodes