Fig. 8: Schematic diagram showing surface reconstruction and transformation of CoCr2O4 and Co2CrO4 during OER. | Nature Communications

Fig. 8: Schematic diagram showing surface reconstruction and transformation of CoCr2O4 and Co2CrO4 during OER.

From: Atomic-scale insights into surface reconstruction and transformation in Co-Cr spinel oxides during the oxygen evolution reaction

Fig. 8: Schematic diagram showing surface reconstruction and transformation of CoCr2O4 and Co2CrO4 during OER.

a Cr dissolves substantially across nearly the entire CoCr2O4 nanoparticles, leading the formation of Cr and O vacancies that promote the hydroxide ion incorporation; b the gradual hydroxide ion incorporation potentially facilitates reversible (CoII, CrIII)(OH)2 ↔ (CoIII, CrIII)OOH transformation, giving rise to high activity and stability of CoCr2O4; as OER proceeds, c the (oxy)hydroxides are gradually exfoliated from CoCr2O4 surfaces. In contrast, d pristine Co2CrO4 surface is covered by rock-salt structured (Co,Cr)O which does not assist transformation of Co-based oxyhydroxide. Instead, e amorphous Cr(OH)3 layer is formed on the Co2CrO4 surfaces, serving as active species for OER. Such self-limiting amorphous layer is gradually depleted from Co2CrO4 surfaces, decreasing the activity.

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