Amorphous Co(OH)_2 nanosheet electrocatalyst and the physical mechanism for its high activity and long-term cycle stability

摘要

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., nano-phase, 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the conventional understanding of selecting electrocatalysts with conductivity as a typical reference standard seems out of date for developing new catalysts at the nanometer, which actually open a door to applications of amorphous nanomaterials as an advanced electrocatalyst in the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.