Preparation And Electrocatalytic Properties Of Carbon-based Mo,Co Composites

Since the 21st century,the rapid development of the world economy has been accompanied by serious energy consumption.The development of traditional fossil fuels has been limited by their non-renewability and environmental pollution.Therefore,the development and utilization of new energy has become a new focus in the field of scientific research.Hydrogen energy is a kind of economic and environment-friendly energy.Hydrogen production from electrolytic water splitting is a good channel to obtain hydrogen fuel.Hydrogen production from electrolytic water involves two important processes:hydrogen evolution(HER)and oxygen evolution(OER).Metal-air battery is a new and environmentally friendly energy storage carrier.Oxygen reduction(ORR)and oxygen evolution(OER)are two key processes in metal-air batteries.In order to improve the efficiency of these reactions,electrocatalysts play an important role.Therefore,the search for suitable and efficient electrocatalysts has become the primary issue in the research of hydrogen production from electrolytic water and metal-air batteries.In this paper,three kinds of carbon-based Mo and Co electrocatalysts were designed and prepared,and their structures were characterized.Their HERs,OERs and ORRs were also studied.In the first part:Mo2C-based electrocatalyst(Mo2C@SNC)with sunflower seed hulls derived N,S-co-doped carbon as matrix has been synthesized.In Mo2C@SNC,Mo2C particles with the size about 5 to 8 nm distribute uniformly in N,S-co-doped carbon.In addition,Mo2C@SNC has a large specific surface area.These special structural characteristics lead to good electrocatalytic activity of Mo2C@SNC for hydrogen evolution reaction(HER).In 1M KOH,to obtain 10 mA·cm-2 current,it overpotential is only 60 mV.Mo2C@SNC also has good stability.After 2000 cycles of scanning,LSV did not change significantly.The hydrogen evolution rate is 90.2 umol·h-1,and the Faraday efficiency is almost 100%.Under acidic condition,the electrocatalytic hydrogen production performance of Mo2C@SNC is also excellent.We anticipate that Mo2C@SNC will become a new material in hydrogen energy exploration.In the second part,in order to explore efficient and inexpensive electrocatalysts for hydrogen evolution(HER),Na2MoO4 and carbonated beverages were used as precursors to successfully load Mo2C nanoparticles with the size about 8 to 10 nm on N-P co-doped mesoporous carbon substrates.The dimension of the obtained Mo2C@NPC is only 200 to 300 nm.Mo2C@NPC exhibits excellent HER activity in 1 M KOH with overpotential 60 mV and slope of 63 mV·dec-1.In order to realize the overall Water splitting,a new electrocatalyst Co/Mo2C@NPC was obtained by doping Co into the structure of Mo2C@NPC.Co/Mo2C@NPC shows excellent OER activity.To obtain 10 mA·cm-2 current,it only needs overpotential of 360 mV.The electrocatalysts also shows excellent durability.After 1000 cycles and 10 hours of long-term HER and OER tests,the current remains stable.To achieve overall water splitting,electrolytic cells were constructed with Mo2C@NPC and Co/Mo2C@NPC as cathodes and anodes.In order to obtain a current density of 10 mA·cm-2,only 1.60 V of voltage is required.We expect that Mo2C@NPC and Co/Mo2C@NPC can be used as electrocatalysts for practical overall water splitting.As a promising energy storage device,zinc-air battery has the advantages of higher energy density,lighter weight and more compact structure than other rechargeable batteries.It is an ideal choice for electric vehicles.For zinc-air battery,the activity of air cathode plays an important role in its performance.With filter paper derived three-dimensional mesoporous carbon as matrix,a Co3O4 based electrode was synthesized.The electrode exhibits excellent activity and durability in oxygen reduction(ORR)and oxygen evolution reaction(OER)processes.In ORR and OER,its has small half-wave potential(ORR1/2=0.811 V)and overpotential(OER10=1.518 V).The chargeable zinc-air battery was successfully assembled with this electrode as air cathode.In the discharge process,the maximum power density of the zinc-air battery reaches 71 mW·cm-2.In addition,it has high specific capacity(828 mAh·g-1,20 mA·cm-2,544 mAh·g-1,50 mA·cm-2)and small voltage gap(0.91 mV,10 mA·cm-2)during charge and discharge process.As a rechargeable battery,after a long period of charge and discharge experiments,it also shows good stability.Therefore,we have found a simple and convenient method to manufacture rechargeable zinc-air batteries with low cost and effective dual-function air cathode.