Preparation And Water Electrosis Performance Of Trasition Metal Phosphides Nanosheets

Nowadays,humanity are facing the great chanllenges of environment problem and energy crisis.To establish a renewable system is priority for increasing depletion of fossil energy and the environmental degradation.Water electrolysis to produce hydrogen and oxygen is an important way of energy conversion and energy storage.The biggest obstacle to electrolytic water technology is to find cheap and efficient catalysts.Based on this,noble metal free based catalytic materials have become a hot topic in current research.Transition metal phosphides have great potential in water electrolysis due to their good conductivity and stability in acidic and alkaline solutions.Our study is focused on the preparation of two-dimensional transition metal phosphides and 'their electrochemical performance.The research is divided into the following two parts:(1)With MO3 nanosheets and red phosphorus as precursor and phosphorus resource respectively,MoP2 nanosheets were synthesized by high temperature solid phase method successfully.On the one hand,the two-dimension structure increased the specific surface area of MoP2 and exposed more active sites.On the other hand,the structure is also conducive to electron transfer and enhanced reaction kinetics.The electrochemical test results showed that the two-dimensional MoP2 nanosheets performed better HER activity and electrochemical stability than bulk MoP2.The overpotential of the MoP2 nanosheets was about 78 mV lower than that of bulk MoP2 at 10 mA cm-2.We further studied HER performance of different sizes of two-dimensional MoP2 nanosheets obtained by centrifuged under different rotate rates.We found that as the horizontal size and thickness of nanosheets becaming smaller,a more regular enhancement trend is shown for HER performance.Probably the reason is that more active sites were exposed with the thickness of nanosheets became smaller.(2)With NiCo2O4 nanosheets and sodium hypophosphite as precursors and phosphorus source,bimetallic phosphide NiCo2P2.5 nanosheets were synthesized successfully through a gas-solid reaction under mild temperature(300 ?).Compared with bulk NiCo2P2.5,NiCo2P2.5 nanosheets showed more prominent HER and OER catalytic activity.The overpotentials of NiCo2P2.5 nanosheets for HER and OER are about 30 mV and 70 mV lower than that of bulk NiCo2P2.5 respectively.Besides,compared with CoP and Ni2P nanosheets,we found that bimetallic NiCo2P2.5 nanosheets showed more prominent activity.The reason may be that there is a synergistic effect between Ni and Co,resulting in the change of the electronic structure and the reduction of hydrogen adsorption energy on the surface of the materials.