Application Of Transition Metal Nanomaterials In Electrocatalysis

Oxygen electrocatalysis(including oxygen reduction reaction or ORR and oxygen evolution reaction or OER)plays vital roles in many energy conversion devices such as fuel cells,metal-air batteries and artificial photosynthetic cell.However,they involve multi-step proton-coupled electron transfer,and are highly sluggish in nature.At the same time,the development of a low-cost,high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode(HOR).Electrocatalysts are often required to accelerate their reaction rates for practical applications.Two works are introduced as followed:1)Layered double hydroxides have great promise,and to fulfill their full potentials requires effective strategies to engineer and stabilize their structures at the nanoscale.In this study,we report the scalable preparation and delamination of atomic-thick CoNi layered double hydroxide nanosheets,and the subsequent flocculation from their colloidal dispersion upon the introduction of negatively charged graphene oxide nanosheets.Thanks to the large electrochemical surface areas of CoNi layered double hydroxide monolayers and the high electrical conductivity of reduced graphene oxide support,the thus-formed composite exhibits bifunctional activity and stability far more superior to its close competitors for oxygen reduction and oxygen evolution in both 1 M and 6 M KOH.For the cathodic half reaction,its ORR half-wave potential was measured to be 0.85 V;for the anodic half reaction,an OER current density of 10 mA/cm2 was sustained at 1.56 V.It could also be used as the oxygen electrocatalyst of rechargeable Zn-air batteries to enable remarkable discharge peak power density and stable cycling stability2)The development of a low-cost,high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode.Herein,we report a composite catalyst of np-Ni3N which exhibits exceptional HER/HOR activities in aqueous electrolytes,including high mass activity(18.95 mA/mgNi),high jk,0.05v(4.17 mA/cm2)and excellent CO tolerance.At the same time,an HER current density of 10 mA/cm2 was sustained at 0.064 V.Owing to its high activity and low cost,our catalyst shows significant potential for use in low-cost,high-performance fuel cells.