Assessment of the importance and catalytic role of chromium oxide and chromium carbide for hydrogen generation via hydrolysis of magnesium†

Abstract

Increasing energy demands and low-carbon emission energy carriers are global challenges for renewable energy resources. Regarding the aforementioned issues, magnesium-based composites are promising candidates for energy carriers. However, rapid initial hydrolysis kinetics and higher hydrogen yields are the objectives for practical applications. In this study, chromium-based catalysts (Cr₂O₃ and Cr₃C₂) were employed via ball milling to activate Mg. Finally, we used Mg-X wt% Y (X = 1, 3, 5, and 10; Y = Cr₂O₃ and Cr₃C₂) composites to produce hydrogen. Mg-10 wt% Cr₂O₃ can produce 798 and 812 mL g⁻¹ hydrogen, while Mg-10 wt% Cr₃C₂ can produce 821 and 831.6 mL g⁻¹ hydrogen in seawater and 0.5 M MgCl₂ solutions, respectively. Additionally, Cr₂O₃ and Cr₃C₂ significantly improve the Mg hydrolysis activation energies. However, by incorporating Cr₂O₃ and Cr₃C₂, the activation energies for the hydrolysis of Mg with seawater achieved were 19.5 kJ mol⁻¹ and 17.3 kJ mol⁻¹, while they reduced to 15.7 kJ mol⁻¹ and 14.4 kJ mol⁻¹ with 0.5 M MgCl₂ solutions, respectively. In comparison, Mg-10 wt% Cr₃C₂ composite exhibits superior performance, which is attributed to the higher anode potential value of Cr₃C₂. This work accelerates the hydrolysis kinetics and provides a sufficient technique to produce hydrogen from Mg composites for application in portable devices.