Carbon Nanotube/Magnesium Composite as a Hydrogen Source

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Hydrogen production for proton-exchange-membrane fuel cells (PEMFCs) often relies on steam reforming, which generates impurities like sulfur and carbon monoxide detrimental to platinum catalysts.
• Alternative CO-free hydrogen generation methods include the hydrolysis of aluminum in alkaline water or magnesium in neutral chloride solutions (e.g., seawater).
• The hydrolysis of magnesium exhibits a slow hydrogen generation rate, directly linked to its corrosion rate in chloride-containing water.

Purpose of the Study:

• To develop a fast hydrogen generation source for PEMFCs by fabricating a magnesium-matrix composite.
• To investigate the effect of carbon nanotube (CNT) reinforcement on the hydrogen generation rate from magnesium hydrolysis.
• To understand the underlying mechanism, specifically the role of galvanic corrosion, in enhancing hydrogen production.

Main Methods:

• Fabrication of a carbon nanotube (CNT)-reinforced magnesium-matrix composite using Spark Plasma Sintering.
• Testing the hydrogen generation rate from the hydrolysis of the composite in a neutral chloride solution (NaCl).
• Analysis of the composite's microstructure and the corrosion behavior of magnesium in the presence of CNTs.

Main Results:

• The fabricated 5 vol.% CNT/Mg composite demonstrated a significantly accelerated hydrogen generation rate.
• The hydrogen generation rate from the CNT/Mg composite was found to be 3300 times faster than that of pure magnesium.
• The enhanced hydrogen production is attributed to severe galvanic corrosion induced by CNTs acting as local cathodes within the magnesium matrix.

Conclusions:

• Carbon nanotube reinforcement is an effective strategy to dramatically increase the hydrogen generation rate from magnesium hydrolysis.
• The galvanic corrosion effect between the magnesium matrix and CNTs is the primary driver for the accelerated hydrogen production.
• The CNT/Mg composite presents a promising, fast-acting hydrogen generation source for applications like PEMFCs.