Rare-Earth-Induced Intermediate-Spin Co Centers in MnCo₂O_4.5 for Sustainable Acidic Water Oxidation

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Developing stable and active oxygen evolution reaction (OER) catalysts for proton exchange membrane water electrolysis (PEMWE) in acidic media is challenging due to activity-stability trade-offs.
• Non-noble metal catalysts often suffer from structural degradation and insufficient activity under acidic conditions.

Purpose of the Study:

• To resolve the activity-stability dilemma in acidic OER by employing a spin-state engineering strategy.
• To investigate the effects of rare-earth doping on the electronic and structural properties of MnCo2O4.5 catalysts.

Main Methods:

• Rare-earth cations (Sm3+, Nd3+, Ho3+) were incorporated into MnCo2O4.5 spinel structure.
• Spin-state modulation, lattice distortion, and oxygen vacancy formation were induced and analyzed.
• Electrochemical performance and long-term stability were evaluated for OER in acidic media and in a PEM electrolyzer.

Main Results:

• Rare-earth doping enhanced Co-O covalency and 4f-3d coupling, shifting the Co sublattice towards a mixed-spin state.
• Spin-state modulation stabilized the spinel framework, mitigating Co overoxidation and structural reconstruction.
• The optimized Sm-MnCo2O4.5 catalyst showed a low OER overpotential (212 mV at 10 mA cm-2) and excellent stability (1200 h).
• The catalyst achieved 0.5 A cm-2 at 1.73 V for over 300 h in a PEM electrolyzer.

Conclusions:

• Rare-earth-mediated spin-state modulation is a viable strategy for designing robust non-noble metal acidic OER catalysts.
• This approach effectively addresses the intrinsic activity-stability trade-off in PEMWE.
• The findings provide a fundamental design principle for sustainable electrocatalysts.