Origin of Disparities in Water Oxidation between Amorphous and Crystalline Electrocatalysts

Amorphous catalysts behave differently in oxygen evolution reaction (OER) performance compared with their crystalline counterparts; however, the origin of this disparity is still ambiguous. Herein, amorphous and crystalline CoOOH are invoked as the model catalysts to explore the origin of their difference in the OER performance. Electrochemical measurement results demonstrate that the amorphous CoOOH has more active sites in quantity but lower intrinsic activity per site than the crystalline CoOOH in the initial stage of the OER. Nevertheless, the intrinsic activity per site of the amorphous CoOOH continues to increase until a level close to that of the crystalline CoOOH is achieved when the OER proceeds. On the basis of operando characterizations and electrochemical analysis, a dual-pathway model of reconstruction is proposed to explain the catalytic behaviors of these CoOOH. The intrinsic activity of catalysts is dominated by two reconstruction pathways. The distinction of intrinsic activity between the amorphous and crystalline CoOOH is caused by the different proportions of each pathway included in OER. Moreover, the quenching reaction between Co4+ and the oxygen vacancy in the amorphous catalyst motivates the surface reconstruction and subsequently promotes the crystallinity. This study provides a perspective for understanding the surface reconstruction mechanism in the OER.