Anions regulation strategy in simulated seawater: A sustainable and efficient approach for on-site hydrolysis hydrogen generation from Mg alloy waste

Abstract

This innovative study addresses a critical gap in ‘Green hydrogen’ technology by examining the impact of anions on the hydrolysis of residuary waste AZ91D alloy (Rw-AZ91D) in simulated seawater. Despite seawater's potential as an abundant resource for hydrogen production, its complex anionic composition presents efficiency challenges. Through meticulous regulation of anion types and concentrations, the results demonstrate that under ideal conditions (0.5 M NaCl at 298 K), Rw-AZ91D yields a remarkable hydrolysis capacity of 727.0 mL g−1, with a rapid onset (0.42 min) and low activation energy (27.8 kJ mol−1). Intriguingly, oxygenated acid anions notably impede both kinetics and yield. In 0.5 M NaCl solution respectively mixed with 0.1 M Na2SO4, Na2CO3 and NaNO3 solution, the hydrolysis capacities of Rw-AZ91D increase to 409.5, 514.4 and 118.6 mL g−1. When the concentration of employed anions decreases to 0.02 M, 516.5, 621.0 and 480.5 mL g−1 H2 can be obtained. Microstructural and thermodynamic assessments indicate that anions affect hydrolysis via their ionic size, chemistry, induced acidity, and solubility of Mg2+-complexed metallic compounds. This work introduces a cost-effective and eco-friendly method to manage anions during hydrogen production, thereby bolstering the feasibility of portable hydrogen generators and advancing sustainable seawater utilization in Mg alloy waste-based hydrogen generation systems.