Lanthanum-Promoted Electrocatalyst for the Oxygen Evolution Reaction: Unique Catalyst or Oxide Deconstruction?

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Conventional oxygen evolution reaction (OER) catalyst assessment relies on current density at a set overpotential.
• This metric is unreliable for OER catalysts due to lattice deconstruction and amorphization, which increase active sites under working conditions.

Purpose of the Study:

• To investigate the effect of lanthanum (La3+) incorporation into cobalt oxide (Co3O4) on OER performance.
• To elucidate the structural and chemical changes in La-modified Co3O4 during OER catalysis.

Main Methods:

• Powder X-ray diffraction (PXRD), Raman spectroscopy, and extended X-ray absorption fine structure (EXAFS) to analyze material structure.
• Operando spectroscopies and High-Resolution Transmission Electron Microscopy (HRTEM) to study catalyst behavior under OER conditions.
• X-ray Photoelectron Spectroscopy (XPS) to determine surface chemical states after catalysis.

Main Results:

• La incorporation into Co3O4 leads to decreased domain sizes, reduced long-range order, and increased amorphization.
• Lattice deconstruction is accelerated by La3+ under OER conditions, forming an amorphous overlayer.
• OER overpotential decreases with increasing La3+ concentration, peaking at 17% La incorporation.
• Post-OER XPS reveals loss of lattice oxide and formation of hydroxylated/defective Co(O)(OH) species.

Conclusions:

• Improved OER activity in La-doped Co3O4 is attributed to lattice deconstruction and the formation of more active Co(O)(OH) edge sites.
• The enhanced performance stems from an increased number of active sites, not improved intrinsic catalytic properties.
• This mechanism likely applies to other metal ion dopants in oxide catalysts.