Preparation Of Nover Transition Metal Nanocomposites And Their Application In Water Splitting

With a rapidly growing world population,energy consumption is also increasing significantly.Due to limited oil resources,there is an urgent need to develop new technologies to provide clean,affordable renewable energy.Hydrogen is a green and renewable fuel,which has the potential to replace fossil fuels in the future.Water splitting by electric drive?preferably solar?is one of the most promising methods for producing high purity hydrogen.Efficient water splitting requires a highly active and stable catalyst,which can accelerate the kinetic rate of electrode reactions such as oxygen evolution?OER?,hydrogen evolution?HER?and oxygen reduction?ORR?.Precious metals and their oxides such as Pt,RuO₂ and IrO₂ are currently the most desirable catalysts,but they are extremely limited in large-scale applications due to their high cost and scarcity,which are not suitable for industrial water splitting.Therefore,it is indispensable to develop an economical and excellent catalytic performance electrocatalyst.In this paper,catalysts of different transition metal nanocomposites were prepared.The morphology,structure and composition of the obtained catalysts were studied by a series of characterization techniques,and the catalytic activity and stability of the electrolyzed water were investigated.The main tasks as follows:?1?Ultrathin MoSSe alloy nanosheets array on multiwalled carbon nanotubes?MWCNTs?to form a core shell structure via a simple solvothermal process.This three-dimensional?3D?MoSSe hybrids show a high activity in hydrogen evolution reaction?HER?with a small Tafel slope of 38 mV dec^-1 and a low overpotential of102 mV at 10 mA cm^-2.In addition,their HER activity remains remarkably stable without significant decay after 1h polarization.Such superior catalytic HER activity springs from the 3D hierarchical heterostructure,which is abundant of catalytic edge sites,and the alloy effect between S and Se,which will create huge defects and strain to form vacancy sites on the basal plane.?2?Oxygen evolution reaction?OER?is the rate-controlling step of the electrochemical water splitting.The slow kinetics hinders large-scale H₂ production.Herein,spinel NiFe oxides were prepared by direct pyrolysis of nickel hexacynoferrate precursor in air.The NiFe oxides were presented as mesoporous nanocubes with a specific surface area of 125 m² g^-1.These mesoporous spinel NiFe oxide nanocubes can afford a geometric activity of 10 mA cm^-22 at a low overpotential of a 0.24 V and a small Tafel slope of 41 mV dec^-1 in alkaline solution.The specific activity can reach up to 0.37 mA cm^-22 with a turnover frequency of 0.93 s^-1.The superior OER activity of the NiFe oxide nanocubes?NiFeO NBs?can outperform the state-of-the-art IrO₂ catalyst,and compare favorably with other spinel transition metal oxides reported recently under identical condition.NiFeO NBs also show a long-term durability without significant loss of OER activity.Our works provide the possibility to develop an efficient,robust and earth-abundant spinel NiFe oxide as an advanced OER electrocatalysts used to replace the expensive commercial IrO₂ catalysts for water splitting in the industrial scale.?3?It is still a great challenge to produce cheap,stable and high-performance electrocatalytic electrode materials under a facile approach.The introduction of metallic elements into transition metal phosphatides?TMPs?as catalysts is an effective way to enhance their catalytic activity in alkaline media.Herein,we develop a neotype bimetallic alloy iron-cobalt phosphide nanomaterial,which is synthesized by phosphatating with cobalt-iron nano cubes?CoFe NCs?as precursors and annealing at 350 ^oC.The prepared Co-Fe-P-350 catalysts display superior electrochemical catalytic activity and long-term durability in both Oxygen evolution reaction?OER?and Oxygen reduction reaction?ORR?.In an alkaline solution,for the oxygen evolution reaction and oxygen reduction of Co-Fe-P-350,when the current density is 10 mA cm^-2,the overpotential of OER is 264 mV,and the overpotential of ORR is 230 mV,corresponding to the tafel slopes of 48 mV dec^-1 for OER and 98 mV dec^-1 for ORR in an alkaline solution.This work provides a facile and novel route to prepare Fe-Co-P,which displays superior electrocatalytic activity and can be used in future applications such as water splitting.