The Preparation Of Noble-Metal Alloyed Nanomaterials And Their Applications In Energy Electrocatalysis

Electrochemical energy conversion and storage is one of the important ways for human to solve the problems of energy shortage and environmental pollution in the future.However,the electrochemical technologies often suffer from low efficiency,poor selectivity and high energy consumption in practical implementation.The development of electrocatalytic materials with excellent performance can effectively improve the rate and efficiency of electrochemical reactions,which is the most efficient strategy at present.Noble-metal materials are of good application potential in the electrocatalytic reactions,but there are still many limitations for the catalytic properties of the single metal due to fixed intrinsic electronic structure.Alloying is a common strategy to improve the catalytic performance of single-metal materials.By adding another metal to form alloys,it can effectively alter the electronic structure of noble metals,so as to optimize the interaction between the key intermediate and materials’surface and improve the activity,selectivity as well as stability during the electrocatalysis.The introduction of the second metal can also decrease the amount of precious metals,which,to a certain extent,reduces the cost when applied in practical applications.In this essay,we explored the solution synthesis of several noble-metal alloyed nanomaterials,characterized their structure information in detail,carried out electrochemical measurements systematically,and analyzed the possible mechanism by theoretical calculations,which proved alloying is an effective strategy for the design of noble-metal catalysts.The main contents and conclusions are listed as the following three aspects:1.In Chapter 3,the chemically homogeneous palladium-silver alloyed nanospheres with a diameter of about 50 nm are successfully prepared by co-reduction method in the low-temperature solution.This alloyed nanomaterial has a threedimensional mesoporous structure with uniform pore size,which effectively increases the electrochemical surface area and active sites of the catalyst.Compared with conventional pure Pd,PdAg shows excellent formate selectivity(90%)and long-term stability(10000 s)during the electrochemical CO2 reduction towards formate.Through controlled experiments and theoretical calculations,it is proved that the introduction of Ag could effectively alter the electronic structure of Pd and lower the position of dband center of Pd,thus reducing the binding energy of CO on surface and improving the stability of PdAg during electrocatalysis.2.In Chapter 4,palladium-copper alloys with uniform morphology and size are synthesized by co-reduction method in the low-temperature solution.Due to the low reaction temperature and suitable surfactants,this alloy could selectively grow in plane to form two-dimensional nanodendrites with a thickness of～7nm.Compared with pure Pd nanoparticles,the unique two-dimensional nanodendrites have a higher specific surface area and abundant undercoordinated sites,which provides more active sites and improves the active current density during the electrochemical CO2 reduction.In addition,PdCu alloys could realize the stable adsorption of formate intermediates.Compared with pure Pd,PdCu nanodendrites could not only maintain high formate selectivity at a wider potential window(0～-0.4 V vs.RHE),but also keep a stable operation at-0.3 V for a long time(8 h).3.In Chapter 5,two different synthetic methods are tried to prepare nickel-iridium alloyed catalysts.The first method is to selectively grow Ir nanoparticles on the Ni(OH)2 nanosheets substrate.They are then transformed into NiIr alloys by annealing under H2 atmosphere;The second method is to prepare NiIr alloyed nanoparticles by solvothermal synthesis.Preliminary electrochemical tests show that both two NiIr nanomaterials have good activity in alkaline hydrogen oxidation reaction.In particular,NiIr alloys from solvothermal method achieve a high current density of 2.2 mA/cm2 at 50 mV,which is close to the performance of commercial platinum-carbon catalysts.