Hexafluorophosphate additive enables durable seawater oxidation at ampere-level current density

Area of Science:

• Electrochemistry
• Materials Science
• Sustainable Energy

Background:

• Direct seawater electrolysis offers a sustainable route for hydrogen production using renewable energy.
• Chloride ions in seawater cause significant anode degradation, limiting operational stability and efficiency.

Purpose of the Study:

• To investigate the use of hexafluorophosphate (PF₆⁻) as an electrolyte additive to mitigate chloride-induced anode degradation.
• To enhance the long-term stability and efficiency of anodes in direct seawater electrolysis.

Main Methods:

• Electrochemical testing of nickel-iron layered double hydroxide (NiFe LDH) anodes in seawater with PF₆⁻ additive.
• Long-term stability tests at high current densities (1-2 A cm⁻²).
• Constant-potential molecular dynamics simulations to elucidate the mechanism of chloride exclusion.

Main Results:

• Achieved prolonged operation exceeding 5,000 hours at 1 A cm⁻² and 2,300 hours at 2 A cm⁻².
• PF₆⁻ intercalates into LDH interlayers and adsorbs onto the surface, blocking chloride ions (Cl⁻) and stabilizing the anode.
• Molecular dynamics simulations confirmed high surface concentrations of PF₆⁻ effectively exclude Cl⁻, mitigating corrosion.

Conclusions:

• Hexafluorophosphate (PF₆⁻) additive effectively prevents chloride-induced anode degradation in seawater electrolysis.
• Synchronous interlayer and surface engineering by PF₆⁻ enables efficient Cl⁻ rejection, crucial for stable hydrogen production.
• This approach represents a significant advancement for practical seawater electrolysis powered by renewables.