Flammability reduction in a pressurised water electrolyser based on a thin polymer electrolyte membrane through a Pt-alloy catalytic approach

Various Pt-based materials (unsupported Pt, PtRu, PtCo) were investigated as catalysts for recombining hydrogen and oxygen back into water. The recombination performance correlated well with the surface Pt metallic state. Alloying cobalt to platinum was observed to produce an electron transfer favouring the occurrence of a large fraction of the Pt metallic state on the catalyst surface. Unsupported PtCo showed both excellent recombination performance and dynamic behaviour. In a packed bed catalytic reactor, when hydrogen was fed at 4% vol. in the oxygen stream (flammability limit), 99.5% of the total H 2 content was immediately converted to water in the presence of PtCo thus avoiding safety issues. The PtCo catalyst was thus integrated in the anode of the membrane-electrode assembly of a polymer electrolyte membrane electrolysis cell. This catalyst showed good capability to reduce the concentration of hydrogen in the oxygen stream under differential pressure operation (1-20 bar), in the presence of a thin (90 µm) Aquivion® membrane. The modified system showed lower hydrogen concentration in the oxygen flow than electrolysis cells based on state-of-the-art thick polymer electrolyte membranes and allowed to expand the minimum current density load down to 0.15 A cm -2 . The electrolysis cell equipped with a dual layer PtCo/IrRuOx oxidation catalyst achieved a high operating current density (3 A cm -2 ) as requested to decrease the system capital costs, under high efficiency conditions (about 77% efficiency at 55°C and 20 bar). Moreover, the electrolysis system showed reduced probability to reach the flammability limit under both high differential pressure (20 bar) and partial load operation (5%), as needed to properly address grid-balancing service

L’avvocato Leonida Casali e la difesa dei partigiani emiliani

Il lavoro si propone di analizzare il ruolo e le caratteristiche dell’avvocatura militante del legale bolognese Leonida Casali, esponente di spicco sia del Partito Comunista Italiano, sia del Comitato di Solidarietà Democratica nel secondo dopoguerra. Attraverso lo studio di vari casi particolari, quali i processi contro ex partigiani e militanti politici, si è puntato a far emergere l’intrinseca politicità dell’operato dell’avvocato, mostrandone, da una parte l’autorevolezza e l’autonomia operativa, dall’altra lo stretto rapporto che lo legava al PCI e al CSD. Tali aspetti permettono di delineare la figura dell’avvocato Casali come un unicum nel panorama della giustizia italiana dell’immediato dopoguerra.This paper aims to analyze the role and the pattern of the militant lawyering of Leonida Casali, one of the leading members of Bologna section of the Italian Communist Party and of the Democratic Solidarity Committee during the postwar period. By construing some specifical cases, as the trials against partisans and political activists, the focus has been pointed on demonstrating the intrinsic political nature of Casali’s behavior, showing on the one hand his mastership and the operational independence, on the other the strict relationship he had with the Communist Party and the Democratic Solidarity Committee. These issues allow to trace Casali’s role as a unique in the panorama of Italian justice immediately after the Second World War

Enhanced performance of a PtCo recombination catalyst for reducing the H 2 concentration in the O 2 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 H 2 concentration in O 2 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 H 2 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 H 2 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 H 2 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 H 2 concentration in O 2 of about 2.3 %, almost constant through most of the current density range

Chemically stabilised extruded and recast short side chain Aquivion proton exchange membranes for high current density operation in water electrolysis

Membrane-electrode assemblies based on chemically stabilised short-side-chain proton exchange Aquivion® membranes, prepared by extrusion or recast methods, have been investigated for operation at high current density (3-4 A cm -2 ) in water electrolysis cells. A thickness of 90 µm was selected for these perfluorosulfonic acid membranes in order to provide proper resilience to hydrogen crossover under differential pressure operation while allowing operation at high currents. The membranes showed proper mechanical strength for high-pressure operation and suitable conductivity to reduce ohmic losses at high current densities. Both membranes showed excellent performance in electrolysis cells by achieving a voltage efficiency better than 85% and 80% (1.85 V) at 3 and 4 A cm -2 , respectively, in polarisation curves at 90 °C. A smaller surface roughness was observed from atomic force microscopy for the recast membrane compared to the extruded one. This may affect the intimate contact between the ionic clusters of the membrane and the catalyst agglomerate at the interface producing a catalytic enhancement in the activation region of the polarisation curves in the case of the recast membrane. At high cell voltages, the polarisation resistance was instead slightly lower for the cell based on the extruded membrane. Interestingly, the different characteristics of the membrane-electrodes interface produced lower recoverable losses in durability studies for the recast membrane-based electrolyser allowing stable operation at both 3 and 4 A cm -2 . Hydrogen crossover analysis at a differential pressure of 20 bar showed low gas permeation through both membranes allowing for a wide load range (15-100 %) and high faradaic efficiency >99% at practical current densities (1-4 A cm -2 )

L\u2019avvocato Leonida Casali e la difesa dei partigiani emiliani

Il lavoro si propone di analizzare il ruolo e le caratteristiche dell\u2019avvocatura militante del legale bolognese Leonida Casali, esponente di spicco sia del Partito Comunista Italiano, sia del Comitato di Solidariet\ue0 Democratica nel secondo dopoguerra. Attraverso lo studio di vari casi particolari, quali i processi contro ex partigiani e militanti politici, si \ue8 puntato a far emergere l\u2019intrinseca politicit\ue0 dell\u2019operato dell\u2019avvocato, mostrandone, da una parte l\u2019autorevolezza e l\u2019autonomia operativa, dall\u2019altra lo stretto rapporto che lo legava al PCI e al CSD. Tali aspetti permettono di delineare la figura dell\u2019avvocato Casali come un unicum nel panorama della giustizia italiana dell\u2019immediato dopoguerra

Electrochemical Impedance Spectroscopy as a Diagnostic Tool in Polymer Electrolyte Membrane Electrolysis

Membrane–electrode assemblies (MEAs) designed for a polymer electrolyte membrane (PEM) water electrolyser based on a short-side chain (SSC) perfluorosulfonic acid (PFSA) membrane, Aquivion®, and an advanced Ir-Ru oxide anode electro-catalyst, with various cathode and anode noble metal loadings, were investigated. Electrochemical impedance spectroscopy (EIS), in combination with performance and durability tests, provided useful information to identify rate-determining steps and to quantify the impact of the different phenomena on the electrolysis efficiency and stability characteristics as a function of the MEA properties. This technique appears to be a useful diagnostic tool to individuate different phenomena and to quantify their effect on the performance and degradation of PEM electrolysis cells

Analysis of performance degradation during steady-state and load-thermal cycles of proton exchange membrane water electrolysis cells

A membrane-electrode assembly based on a 90 μ m short-side-chain Aquivion ® proton exchange membrane and containing low catalyst loadings, 0.4 mg IrRuOx cm 2 and 0.1 mg Pt cm 2 at anode and cathode, respectively, is investigated for combined thermal and load cycling at high current density (3 A cm 2) in water electrolysis cell. Durability tests under steady-state and load-thermal cycles are compared to evaluate the efficiency losses under specific operating conditions. Ac-impedance spectra and post-operation analyses are carried out to investigate the degradation mechanism. Catalyst degradation occurs more rapidly under cycled operation whereas mass transfer issues are relevant especially under steady-state mode. Membrane thinning appears to be affected by the uptime hours at high current density. The overall cell voltage increase is slightly larger for the cycled operation compared to the steady-state mode. However, this is essentially related to a compensation effect associated to a larger decrease of series resistance during the steady-state durability test. The dynamic electrolysis mode at high current density does not exacerbate significantly the degradation issues of low catalyst loading MEAs compared to a steady-state operation. This confirms the proper dynamic characteristics of the polymer electrolyte membrane electrolyser