Design And Synthesis Of Ordered Mesoporous Cobalt-based Metal Oxides For Electrochemical Applications

Electrochemical sensors are widely used in environmental monitoring,medical diagnostics,public safety and other fields due to their excellent characteristics such as easy operation,high sensitivity,low cost,easy miniaturization,where electrocatalysts with high activities are viewed as one of the most critical factors to determine the performance in these electrochemical sensors with high sensitivity,high selectivity,low detection limit and high stability.There are usually three strategies to enhance the activity of an electrocatalyst system by increasing the number of active sites on the specific electrocatalyst,the intrinsic activity of each active sites and the ability to transfer charges.In this paper,a series of ordered large-mesopore cobalt-based spinel metal oxides with high specific surface area and controllable framework thickness and composition were synthesized,which improved their transport property,catalytic activity and conductivity.The effect of mesoporous structure parameters(specific surface area,pore size distribution,framework thickness and pore volume)and composition on electrochemical sensing performance have been studied.A series of ordered mesoporous nickel cobalt spinel oxides materials were synthesized via hard template method by using ordered mesoporous silica KIT-6 as template,cobalt nitrate hexahydrate and nickel nitrate hexahydrate as mixed precursors.Controlled mesostructural transformation were successfully presented during the replication from KIT-6 to mesoporous NiCo2O4,whose specific surface areas increased from 92 to 181 m2·g-1,accompanied by the reduction of framework thickness from 8.7 to 4.6 nm and the increase of pore sizes from 4.6 nm to 11 nm by decreasing the pore size and interconnectivities of the KIT-6 template.Moreover,the framework composition was regulated by changing the ratio of nickel to cobalt in precursors.Other ordered mesoporous cobalt-based spinel metal oxides MCo2O4(M=Cu.Zn,Mn,Fe)were also synthesized via the similar synthesis strategy by changing the composition of precursors,which have large-mesopores of 10 to 13 nm,high specific surface area of 135 m2·g-1 to 185 m2·g-1 and ultrathin framework of 4.6 to 5 nm.Electrochemical measurements revealed that large mesoporous structure was beneficial to the diffusion and transport of glucose and related reactants,while ultrthin framework can increase the specific surface area and provide more active sites.As a result,the electrocatalytic activity of mesoporous NiCo2O4 for oxiding glucose was significantly improved,resulting in the enhanced glucose sensing proformance.Especially,NiCo2O4 with both large mesopores(11 nm)and high specific surface area(181 m2·g-1)as well as ultrathin framework(4.6 nm)exhibited the fast response towards glucose(less than 2 s)and excellent electrochemical sensing performance with the sensitivity of 4368.8 ?A·mM-1·cm-2(0.01?0.683 mM),superior over other common mesoporous NiCo2O4 replicas.The effect of metal cations M in cobalt-based spinel metal oxide framework on the catalytic activity,conductivity and glucose electrochemical sensing performance have been studied.It was found that mesoporous CuCo2O4 with both large pore(12 nm)and ultrathin framework(5 nm)as well as high specific surface area(135 m2·g-1)exhibited high intrinsic catalytic activity,excellent conductivity and the highest sensitivity of 5871.4 ?A·mM-1·cm-2(0.01?0.977 mM).This work demonstrated the great potential of mesoporous cobalt-based spinel metal oxides as novel electrocatalysts for advanced nonenzymatic glucose biosensor,which will bring more opportunities for designing and developing other electrocatalysts with higher activities.