Hydrolysis of MgH₂ in MgCl₂ solutions as an effective way for hydrogen generation

V. Berezovets¹,

A. Kytsya¹,

Yu. Verbovytskyy¹,

I. Zavaliy²,

V. Yartys³

¹ Фізико-механічний інститут ім. Г.В. Карпенка НАНУ, Львів, Україна
² Фізико-технологічний інститут металів та сплавів НАН України, Київ
³ Institute for Energy Technology, Kjeller NO-2027 , Норвегія

ВОДНЕВІ ТЕХНОЛОГІЇ ЗБЕРІГАННЯ ЕНЕРГІЇ: СТАН ТА ПЕРСПЕКТИВИ РОЗВИТКУ - Львів: Простір-М, 2021
https://doi.org/10.15407/materials2021.038

Анотація

Magnesium hydride (MgH2) has a high hydrogen storage capacity (7.6 wt%) and the Mg element is abundant on the earth. Due to its strong reduction ability, even at room temperature it can provide the hydrogen yield reaching 15.2 wt% H (1703 mL/g) when interacting with water, which makes it very attractive for the application in supplying hydrogen for autonomous H energy systems. However, the hydrolysis reaction is rapidly inhibited by the Mg(OH)2 passivation layer formed on the surface of MgH2. In order to remove the passivation film and improve the efficiency of the MgH2 hydrolysis process, several methods including alloying, ball milling, changing the aqueous solution, have been successfully utilized. In this paper the process of hydrolysis of magnesium hydride in aqueous solutions of MgCl2 used as a promotor of the interaction has been studied in detail. It was found that the initial hydrolysis rate, pH of the reaction mixture, and overall reaction yield are all linearly dependent of the logarithm of MgCl2 concentration. It has been shown that pH of the reaction mixture in the presence of MgCl2 is well described by considering a system “weak base and its salt with strong acid” type buffer solution. Reference data for this hydrolysis reaction were also carefully analyzed. The mechanism and the kinetic model of the process of MgH2 hydrolysis in water solutions involved passivation of the MgH2 surface by the formed Mg(OH)2 precipitate followed by its repassivation have been proposed. The obtained after the hydrolysis reactions precipitates were studied using XRD and EDS. It was found also that the final products of reaction consist of Mg(OH)2 (brucsite type) and remaining MgH2. This fact shows that the formation of solid species such as MgCl2 xMgO yH2O at the studied conditions is unlikely and decreasing of pH the reaction mixture has a different nature.

Завантажити повний текст

ГІДРИД МАГНІЮ, ГІДРОЛІЗ, КИСЛОТНО-ЛУЖНА РІВНОВАГА, КІНЕТИКА, ХЛОРИД МАГНІЮ

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