Core–shell CoFe₂O₄@Co–Fe–Bi nanoarray: a surface-amorphization water oxidation catalyst operating at near-neutral pH

The exploration of high-performance and earth-abundant water oxidation catalysts operating under mild conditions is highly attractive and challenging. In this communication, core-shell CoFe₂O₄@Co-Fe-Bi nanoarray on carbon cloth (CoFe₂O₄@Co-Fe-Bi/CC) was successfully fabricated by in situ surface amorphization of CoFe₂O₄ nanoarray on CC (CoFe₂O₄/CC). As a 3D water oxidation electrode, CoFe₂O₄@Co-Fe-Bi/CC shows outstanding activity with an overpotential of 460 mV to drive a geometrical catalytic current density of 10 mA cm^-2 in 0.1 M potassium borate (pH 9.2). Notably, it also demonstrates superior long-term durability for at least 20 h with 96% Faradic efficiency. Density functional theory calculations indicate that the conversion from OOH* to O₂ is the rate-limiting step and the high water oxidation activity of CoFe₂O₄@Co-Fe-Bi/CC is associated with the lower free energy of 1.84 eV on a Co-Fe-Bi shell.