Design Of Oxygen Electrocatalysts Based On Biomass/MOF Derived Carbon Frameworks

Electrochemical energy devices have been considered as an alternative to solve the current global energy crisis.These devices are driven by various reactions which include ORR,OER,and HER.ORR and OER have been the challenge these devices have faced due to the 4 electron-proton coupled reaction processes.To achieve the widespread application of these devices,the synthesis of cheap and abundant electrocatalysts which can effectively drive oxygen reactions(ORR and OER)is imperative.Electrocatalysts designed for enhanced oxygen reduction reactions(ORR)and oxygen evolution reactions(OER)are essential for energy conversion systems like fuel cells,water splitting,and metal-air battery devices.In the first study,an earthly abundant and cheap biomass of tobacco-stem was used to prepare a novel porous carbon framework(NiCo@N-C)by incorporating transition metal alloy and nitrogen-rich small molecules.The resultant catalysts afforded an onset potential of 0.92 V and a half-wave potential of 0.86 V for oxygen reduction reaction in alkaline media,which is better than commercial Pt/C.Besides,the catalysts also exhibited good oxygen evolution reaction performance with a low overpotential of 280 mV@10 mA cm-2,and the potential gap between ORR and OER is only 0.65 V.The incorporated NiCo alloy and N heteroatom modulated the electronic structure of the prepared carbon frameworks,created abundant active sites,and improved charge redistribution,thus resulting in faster ORR and OER reaction kinetics.The applicability of the prepared NiCo@N-C is fully harnessed as an air-cathode for a Zn-air battery.This work creates a platform for developing efficient porous and functionalized biomass-derived oxygen electrocatalysts for energy applications.In the second project,Co and Ni ions were embedded into the framework of UiO-66 MOF through ultrasonic impregnation and calcined at 300℃ in the air to form a unique CoOx/UiO66-300 and NiO/UiO-66-300 heterostructures with inherent UiO-66 framework for efficient OER.Among the prepared materials,a lower overpotential was recorded for CoOx/UiO-66-300(η10=283.6 mV)compared to NiO/UiO-66-300 and UiO-66 that gave 291.6 mV and 416.6 mV.At increased thermal treatment of the UiO-66 and impregnated ions under 550℃ the UiO-66 framework collapsed,leading to a decrease in the OER performance of the heterostructures.This work provides a new way to improve the OER performance of Co and Ni-based materials by rational design of heterostructures.