Function of Internal and External Fe in a Ni-Based Precatalyst System Toward Oxygen Evolution Reaction

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Iron impurities significantly impact oxygen evolution reaction (OER) in alkaline electrolytes, particularly for nickel-based electrocatalysts.
• While the role of iron in the active OER phase (M(OH)2/MOOH) is well-studied, its function within precatalyst systems remains largely unexplored.

Purpose of the Study:

• To investigate the distinct roles of internal and external iron in Ni-based precatalysts for OER.
• To elucidate the mechanism by which iron influences phase transformation and OER activity in Ni-Fe phosphide systems.

Main Methods:

• Synthesis and characterization of Ni3-xFexP (x = 0, 0.5, 1) precatalyst series.
• Electrochemical evaluation of OER activity in alkaline media.
• Computational analysis of electronic structures to understand iron's influence on the d-band center.

Main Results:

• Ni-Fe phosphide precatalysts with internal iron (Ni2.5Fe0.5P, Ni2FeP) exhibited superior OER activity compared to iron-free Ni3P.
• The presence of internal iron facilitated the formation of active M(OH)2/MOOH species, indicating a role in phase transformation.
• External iron addition (FeCl2·4H2O) improved OER performance for Ni3P, but Ni2FeP remained significantly more active, highlighting the importance of internal iron.

Conclusions:

• Internal iron in Ni-Fe phosphide precatalysts is crucial for enhancing OER activity by promoting phase transformation.
• The electronic structure, specifically the d-band center of Ni and Fe, plays a key role in the observed OER performance.
• Internal iron offers a more effective strategy for OER enhancement compared to relying solely on external iron impurities.