Anions Regulation Strategy for Seawater Hydrolysis Medium: A Green and Efficient Mg Alloy Waste-Seawater On-Site Hydrogen Generation System

Abstract

Generating hydrogen via Mg alloy waste hydrolysis in clean medium, and achieving a large-scale and on-site process is demonstrated as a significant trend for developing ‘Green hydrogen’. Seawater is the most promising hydrolysis medium, however, there is still lack of regulation strategy for anions in seawater to efficiently generate hydrogen. This work explores a novel ‘residuary waste AZ91D alloy (Rw-AZ91D)-seawater’ system under regulating seawater with various types and concentrations of anions. The results demonstrate that Rw-AZ91D can achieve best H2 capacity (727.0 mL·g-1) in 0.5 M NaCl solution at 298 K. The hydrolysis induction period is demonstrated to be 0.42 min and activation energy is calculated to be 27.8 kJ·mol-1. Furthermore, employing oxygenated acid anions into NaCl solution greatly reduces the hydrolysis kinetics and capacity of Rw-AZ91D. On the basis of results in micro-hydrolysis morphology and thermodynamic investigation, the effect of anions is attributed to ionic volume, chemical property, solution acidity and solubility of metallic compound formed by anions with Mg2+. The anions competitive adsorption hydrolysis H2 generation mechanism in multi-anions solution is proposed. Our research provides a cost-effective and green regulation strategy of anions in H2 generation process, which is approach to satisfy the demand on portable hydrogen generators.

Keywords: Hydrogen generation, hydrolysis, residual waste AZ91D alloy, seawater, anions regulation