Characterization of the membrane alkaline water electrolysis stack under operational conditions

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F60461373%3A22310%2F19%3A43918225" target="_blank" >RIV/60461373:22310/19:43918225 - isvavai.cz</a>

Výsledek na webu

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DOI - Digital Object Identifier

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Jazyk výsledku

angličtina

Název v původním jazyce

Characterization of the membrane alkaline water electrolysis stack under operational conditions

Popis výsledku v původním jazyce

Membrane alkaline water electrolysis (MAWE) represents a promising technology for hydrogen production and subsequent storing. In combination with renewable energy sources, it can serve as a clean hydrogen source. The use of non platinum catalysts ensures low capital cost while substitution of an inorganic diaphragm with a membrane enables achieving higher current densities, higher gas purities and asymmetric pressure operation. In diaphragm alkaline water electrolysis, purity of the produced gasses is lower than in membrane (PEM) electrolysis. This can be improved by replacing the porous diaphragm by a dense anion selective membrane. Permeation of the gases through the membrane is an attribute of the membrane independent on the current density. On the other hand, the amount of produced gasses follows the Faraday’s law and it is therefore controlled by current density. Thus, at low current densities, the fraction of hydrogen in the oxygen stream can exceed safety limits. Therefore, the purity of the produced gasses rises with the use of higher current loads. The use of membranes also affects energy demand of the whole process by allowing the so called zero-gap cell setup in which the electrodes are pressed directly to the surface of the membrane and the ohmic resistance between the electrodes is minimized. In this work, we characterized a MAWE stack consisting of three cells with nickel foam electrodes and nickel sheet current collectors. The anion-selective membranes were made of poly(styrene ethylene butylene-styrene) functionalized by 1,4-diazabicyclo[2.2.2]octane (DABCO). The active area of each cell was 78.5 cm2. Potassium hydroxide was used as the electrolyte in different concentrations (1, 5, 10 and 15 wt.%). As for the characterization methods, linear sweep voltammetry was used to obtain the load curves for performance characterization. The current efficiency was evaluated based on produced gas flow rate measurement. Given these results, energy efficiency was calculated. Electrochemical impedance spectroscopy was used to determine the resistance of the stack and gas chromatography was used to find out the gas purities under different operational conditions. In MAWE, gas purities depend mostly on the efficiency of used gas separators. With the rising electrolyte concentration, the stack performance improved due to the higher conductivity. Nevertheless, while remaining required characteristics, anion-selective membranes enabled using lower electrolyte concentration (e.g. 10 wt.% KOH) instead of highly concentrated (25-30 wt.% KOH) electrolyte. This increased ohmic resistance of the distribution channels, thus minimized parasitic currents.

Název v anglickém jazyce

Characterization of the membrane alkaline water electrolysis stack under operational conditions

Popis výsledku anglicky

Membrane alkaline water electrolysis (MAWE) represents a promising technology for hydrogen production and subsequent storing. In combination with renewable energy sources, it can serve as a clean hydrogen source. The use of non platinum catalysts ensures low capital cost while substitution of an inorganic diaphragm with a membrane enables achieving higher current densities, higher gas purities and asymmetric pressure operation. In diaphragm alkaline water electrolysis, purity of the produced gasses is lower than in membrane (PEM) electrolysis. This can be improved by replacing the porous diaphragm by a dense anion selective membrane. Permeation of the gases through the membrane is an attribute of the membrane independent on the current density. On the other hand, the amount of produced gasses follows the Faraday’s law and it is therefore controlled by current density. Thus, at low current densities, the fraction of hydrogen in the oxygen stream can exceed safety limits. Therefore, the purity of the produced gasses rises with the use of higher current loads. The use of membranes also affects energy demand of the whole process by allowing the so called zero-gap cell setup in which the electrodes are pressed directly to the surface of the membrane and the ohmic resistance between the electrodes is minimized. In this work, we characterized a MAWE stack consisting of three cells with nickel foam electrodes and nickel sheet current collectors. The anion-selective membranes were made of poly(styrene ethylene butylene-styrene) functionalized by 1,4-diazabicyclo[2.2.2]octane (DABCO). The active area of each cell was 78.5 cm2. Potassium hydroxide was used as the electrolyte in different concentrations (1, 5, 10 and 15 wt.%). As for the characterization methods, linear sweep voltammetry was used to obtain the load curves for performance characterization. The current efficiency was evaluated based on produced gas flow rate measurement. Given these results, energy efficiency was calculated. Electrochemical impedance spectroscopy was used to determine the resistance of the stack and gas chromatography was used to find out the gas purities under different operational conditions. In MAWE, gas purities depend mostly on the efficiency of used gas separators. With the rising electrolyte concentration, the stack performance improved due to the higher conductivity. Nevertheless, while remaining required characteristics, anion-selective membranes enabled using lower electrolyte concentration (e.g. 10 wt.% KOH) instead of highly concentrated (25-30 wt.% KOH) electrolyte. This increased ohmic resistance of the distribution channels, thus minimized parasitic currents.

Druh

O - Ostatní výsledky

CEP obor

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OECD FORD obor

10405 - Electrochemistry (dry cells, batteries, fuel cells, corrosion metals, electrolysis)

Projekt

<a href="/cs/project/FV10529" target="_blank" >FV10529: Pokročilá elektrolytická výroba vodíku z OZE</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2019

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů