Mechanistic Insights into Magnetic Field-Induced OER Enhancement via Magnetization Cycle Analysis

Area of Science:

• Electrochemistry and Materials Science
• Catalysis and Magnetism

Background:

• Quantifying magnetic field effects on catalytic reactions like oxygen evolution reaction (OER) is difficult due to challenges in measuring local magnetic flux density.
• Understanding the interplay between a catalyst's intrinsic magnetic properties and its response to external magnetic fields is crucial for optimizing catalytic performance.

Purpose of the Study:

• To disentangle non-spin-dependent and spin-dependent contributions to magnetic field-induced OER enhancement.
• To develop a method for quantifying magnetic field effects on OER by analyzing catalyst magnetization states.

Main Methods:

• Utilized 2:17-type samarium-cobalt (Sm₂Co₁₇) magnets with varying initial magnetization states.
• Employed an electromagnet-integrated flow cell for evaluating catalysts under controlled magnetic fields.
• Performed magnetization cycle analysis, including potential shift (ΔE) measurements, to study magnetic hysteresis and its relation to OER.

Main Results:

• Observed butterfly-shaped hysteresis loops in the potential shift (ΔE) during magnetization cycles, offering mechanistic insights into magnetic field effects.
• Demonstrated that bulk magnetic properties influence hysteresis loop shape via spin-pinning, while surface composition and magnetization state dictate linear ΔE shifts.
• Introduced the slope (κ) of linear ΔE shifts as a descriptor for catalytic surface response to magnetic fields, enabling prediction of OER enhancement.

Conclusions:

• The study provides a novel analytical framework using magnetization cycle characteristics (butterfly loops and slope κ) to quantify magnetic field-induced OER enhancement.
• The findings suggest that surface-specific magnetic properties under OER conditions can be elucidated, opening new avenues for designing advanced magnetic catalysts.