Water-surface reconstruction of sulfurized spinel-structured oxide oxygen catalysts for alkaline water electrolysis

Abstract

Slow kinetics related to oxygen evolution reactions (OERs) are currently the main obstacle in developing effective and extremely stable oxygen electrocatalysts for alkaline water electrolysis cells. Catalysts based on spinel-structured cobalt ferrites (CoFe₂O₄), which have remarkable catalytic activity and quick kinetics, are highly promising OER electrocatalysts. Here, sulfur-doped cobalt ferrites nanoarrays on iron foam (S-CoFe₂O₄/IF) are made using an effective and simple technique based on anion–exchange reactions in order to create effective OER catalysts. These S-CoFe₂O₄/IF catalysts demonstrate exceptional OER activity via a topotactical transformation, wherein their Co oxide undergoes continuous cyclic voltammetry scanning to evolve into active Co oxyhydroxide (CoOOH) nanoplates while the Fe stays stable within the Fe–O component. This sulfidation, as evidenced by its electronic density of states, can induce surface reconstruction, leading to the formation of active CoOOH under OER conditions by elevating the O 2p energy level as a result of cation substitution. When sulfidation is applied to the spinel-structured CoFe₂O₄/IF, the total catalytic activity is greatly increased. This leads to a smaller Tafel slope and overpotential (42 mV dec⁻¹ and 286 mV) at 0.1 A cm⁻² than when CoFe₂O₄/IF is used as the catalyst (51 mV dec⁻¹ and 304 mV). The relationship between activity and structure in spinel structures is explained by this work.