Construction And Electrocatalytic Performance Of Ni-Based Nano-Heterogeneous Catalysts

Hydrogen energy,as an important energy carrier in the third energy revolution,has attracted more and more attention.Electrochemical water splitting is considered to be one of the most promising methods for hydrogen production.It consists of a semi-reactive hydrogen evolution reaction（HER）at the cathode and an oxygen evolution reaction（OER）at the anode.However,the high activation barrier and kinetics of both reactions make the process inefficient and require active electrocatalysts to reduce overpotential.In order to reduce the reaction barrier during electrochemical water splitting techniques,recent papers have found that the OER occurring at the anode can be replaced by small organic molecular oxidation reactions,which have lower theoretical oxidation potential such as urea oxidation reaction（UOR）compared to OER.Currently,commercially available electrocatalysts are precious metal based materials such as Ir/Ru oxides and Pt group materials for OER,UOR and HER,respectively.However,the low abundance and high cost of Pt and Ir/Ru-based nanocatalysts remain a key obstacle in practical application.Therefore,reducing the content of precious metals,or finding low-cost alternatives abundant on Earth with high catalytic activity and significant durability,is the key to overcoming electrolytic water bottlenecks.Nickel-based electrocatalysts are widely concerned because of their abundant reserves,low cost,high corrosion resistance,strong strength and good ductility.In order to give full play to the advantages of each component,it is a feasible method to construct Nibased nano-heterogeneous catalysts by forming different interfaces from different materials.The catalytic activity of two or more composite materials connected by physical or chemical interactions is enhanced due to the addition of active sites,unique physical/electronic structure and strong interfacial effects.According to the above background,this paper takes the transition metal Ni-based electrocatalytic material as the main object of study,and uses interface engineering to form nick-based nano-heterogeneous catalyst.A series of characterization analyses are carried out on its morphology,phase and electron transfer,and its electrocatalytic performance is tested as follows:（1）High density NiFe-LDH nanoclusters（NiFe NCs/GO）nanoheterogeneous catalysts anchored on GO surface were prepared by ultra-fast one-step method using the strong interaction between graphene oxide（GO）and LDH surface charges.Smaller NiFe-LDH nanoclusters can have larger specific surface area.The combination with GO can not only reduce the aggregation of nanoclusters and increase the number of active sites,but also increase the conductivity and mass transfer rate of materials.The electrocatalytic activity of NiFe NCs/GO is also enhanced by the strong interaction at the heterogeneous interface between NiFe-LDH and GO.The strict electrochemical test shows that when current density is 10 m A·cm^-2,NiFe NCs/GO heterogeneous nanometer catalyst has the lowest potential,and has the lowest Tafel slope,which show that the catalyst has excellent OER and UOR catalytic performance.The stability tests show that NiFe NCs/GO heterogeneous nano-catalysts have excellent OER and UOR stability and long-term cycling.（2）On the basis of the first experimental system,we selected Ni₂P and NiSe₂components which are active to both HER and UOR to construct heterojunction catalyst.Firstly,Ni（OH）₂/CFC nanosheet arrays were prepared on carbon cloth by hydrothermal method.NiSe₂/Ni₂P/CFC heterogeneous nanosheet array catalysts were successfully prepared by in situ phosphatizing and low temperature partial selenization using Na H₂PO₂ and Se powders as phosphorus and selenium sources under inert atmosphere.Through a series of characterization of the phase and chemical composition of the compound,we found that due to the synergistic effect of NiSe₂ and Ni₂P and the strong electron interaction between the two interfaces,the electron cloud density around Ni₂P was optimized,which greatly improved the catalytic performance of NiSe₂/Ni₂P/CFC.The best NiSe₂/Ni₂P/CFC heterogeneous nanosheet arrays showed excellent HER and UOR catalytic performance and stability in alkaline media and urea oxidation in alkaline media containing urea.In the double electrode urea assisted water electrolytic cell with NiSe₂/Ni₂P/CFC as anode and cathode catalysts,under the same applied voltage,the LSV curve shows that urea assisted hydrolysis has a higher current density than traditional hydrolysis.The results of long-term stability tests show the remarkable durability of NiSe₂/Ni₂P/CFC heterogeneous nanosheet array catalysts...