Cobalt silicate: critical synthetic conditions affect its electrochemical properties for energy storage and conversion.

Cobalt silicate (CoSi) is a promising electrode material for supercapacitors (SCs) and an electrocatalytic material for the oxygen evolution reaction (OER). How to synthesize cobalt silicate with excellent energy storage and OER properties has not been reported and it is a great challenge for researchers to accomplish it. In this work, we find that the electrochemical properties of CoSi are particularly affected by critical factors during the synthesis process. Three types of CoSi compounds are synthesized using Stöber SiO 2 as the self-sacrificing template via a hydrothermal reaction. The CoSi compounds generated from different reaction systems have obvious differences in the macrostate, microscopic morphology, composition and valence, leading to different electrochemical performances for energy storage and OER properties. The findings reveal that the differences (especially valence) among CoSi are determined by the formation of the metal source in the reaction system. The specific capacitance of CoSi-3 obtained from the system with basic salts as the metal source is eight times higher than that of CoSi-1 obtained from the system with coordination compounds as the metal source, whereas CoSi-1 has a greater advantage in electrocatalytic activity. This work provides insight for the synthesis of cobalt silicates applied to energy storage and conversion.