Cathodic Protection System against a Reverse-Current after Shut-Down in Zero-Gap Alkaline Water Electrolysis

Area of Science:

• Electrochemistry
• Materials Science
• Renewable Energy

Background:

• Alkaline water electrolysis is crucial for a hydrogen economy but suffers from instability during intermittent operation.
• Nickel (Ni) cathodes degrade due to irreversible oxidation caused by reverse current during power supply fluctuations.

Purpose of the Study:

• To address the electrode degradation problem in alkaline water electrolysis under transient conditions.
• To propose and validate a cathodic protection strategy to enhance the stability of nickel cathodes.

Main Methods:

• Investigated the degradation mechanism of nickel cathodes under reverse-current conditions.
• Determined the critical potential (0.6 V_RHE) for maintaining nickel cathode stability.
• Implemented a cathodic protection approach using a sacrificial metal anode (lead) to maintain the Ni electrode potential.

Main Results:

• Demonstrated that reverse current irreversibly oxidizes Ni cathodes to β-Ni(OH)₂ or NiO phases.
• Showed that maintaining Ni electrode potential below 0.6 V_RHE prevents degradation.
• Identified lead as a cost-effective and stable sacrificial metal for cathodic protection in accelerated tests.

Conclusions:

• A cathodic protection strategy using a sacrificial anode effectively prevents nickel cathode degradation during intermittent alkaline water electrolysis.
• This method ensures stable and cost-effective hydrogen production, crucial for the growing hydrogen economy.
• The developed system significantly improves the reverse-current stability factor of alkaline electrolyzers.