Fe Incorporation in Ni-Based Layered Hydroxides: Implications for Oxygen Evolution Electrocatalysis.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Alkaline water electrolysis (AWE) for hydrogen production is hindered by the oxygen evolution reaction (OER) requiring high voltages.
• Nickel-based layered hydroxides (LHs) are earth-abundant OER catalysts, but their performance is significantly enhanced by iron (Fe) impurities.
• Understanding Fe incorporation mechanisms is crucial for optimizing AWE catalyst efficiency.

Purpose of the Study:

• To systematically investigate Fe impurity incorporation into different Ni-based layered hydroxide (LH) and layered double hydroxide (LDH) phases.
• To compare the effectiveness of standard electrolyte purification versus electrochemical activation for Fe incorporation.
• To elucidate the structural and catalytic implications of Fe incorporation in Ni-based materials for AWE.

Main Methods:

• Systematic examination of Fe impurity incorporation in α-Ni-LH, β-Ni-LH, NiAl-LDH, and NiFe-LDH phases.
• Comparison of Fe incorporation using a standard electrolyte purification process and an electrochemical activation approach.
• Characterization using spectroscopical techniques to analyze Fe incorporation and structural changes.

Main Results:

• Electrochemical activation proved more effective for Fe incorporation than standard purification, particularly in expanded LH phases.
• Fe incorporation induced a partial transformation of NiAl-LDH into a NiFe-like LDH, resulting in superior electrocatalytic performance for OER.
• Spectroscopic analysis indicated structural Fe incorporation in NiAl-LDH, potentially linked to Al leaching, while NiFe-LDH showed limited response to treatment.

Conclusions:

• The initial layered hydroxide phase critically influences structural Fe incorporation and subsequent catalytic performance in AWE.
• Electrochemical activation is a promising strategy for enhancing OER catalysts via Fe impurity incorporation in specific Ni-based materials.
• Strict control over electrolyte Fe concentration and phase selection is essential for optimizing catalyst design and performance in AWE.