Amorphous Co(OH)2 nanosheet electrocatalyst and the physical mechanism for its high activity and long-term cycle stability

Abstract

Good conductivity is conventionally considered as a typical reference standard in terms of selecting water electrolysis catalysts. Cobalt hydroxide (Co(OH)2) has received extensive attention for its exceptional properties as a promising electrocatalysis catalyst. However, research on Co(OH)2 so far prefers to its crystal phase instead of amorphous phase because the former generally exhibits better conductivity. Here, we have demonstrated that the amorphous Co(OH)2 electrocatalyst synthesized via a simple, facile, green, and low-cost electrochemistry technique possesses high activity and long-term cycle stability in the oxygen evolution reaction (OER). The as-synthesized Co(OH)2 electrode was found to be a promising electrocatalyst for mediating OER in alkaline media, as evidenced by the overpotential of 0.38 V at a current density of 10 mA cm−2 and a Tafel slope of 68 mV dec−1. The amorphous Co(OH)2 also presented outstanding durability and its stability was just as well as that of crystalline Co(OH)2. Generally, the integrated electrochemical performances of the amorphous Co(OH)2 in the OER process were much superior to that of the crystalline Co(OH)2 materials. We also established that the short-range order, i.e., nanophase, of amorphous Co(OH)2 creates a lot of active sites for OER which can greatly promote the electrocatalysis performance of amorphous catalysts. These findings showed that the conventional understanding of selecting electrocatalysts with conductivity as a typical reference standard seems out of date for developing new catalysts at the nanometer, which actually open a door to applications of amorphous nanomaterials as an advanced electrocatalyst in the field of water oxidation.

Earth-abundant amorphous catalysts for electrolysis of water

“…The as-synthesized Co(OH)2 electrode exhibited an overpotential of 0.38 V at a current density of 10 mA/cm 2 and a Tafel slope of 68 mV/dec. The amorphous Ni(OH)2 afforded a better performance with a current density of 10 mA/cm 2 at an overpotential of 0.344 V and a Tafel slope of 46 mV/dec [87,88].…”

Earth‐Abundant Amorphous Electrocatalysts for Electrochemical Hydrogen Production: A Review

“…[ 23 ] In electrochemical studies, an electrocatalyst material is categorized as crystalline or amorphous depending on its atomic arrangement, being either ordered or disordered (i.e., no long range periodicity), respectively. This classification remains true whether the material is in the bulk [ 24 ] or nanosized [ 25 ] form. Meanwhile, amorphous shell–crystalline core type electrocatalyst variants have also been studied, with the amorphous shell playing a significant role in enhancing the overall electrochemical performance.…”

High Density and Unit Activity Integrated in Amorphous Catalysts for Electrochemical Water Splitting

“…4) An amorphous structure, with its high density of coordinatively unsaturated sites and high surface energy is metastable. [ 29–34 ] These make the amorphous catalyst superior to its crystalline counterpart as shown in Figure a. For example, Wang and co‐workers [ 35 ] explained that the amorphous glassy electrocatalyst (MG) is more effective to drive HER than crystalline catalysts revealed in Figure 1b.…”