Hydrogen Evolution Reaction Of Iron Triad Intermetallics In Alkaline Media

Nowadays,with the rapid consumption of fossil coal energy,more serious environmental pollution is produced in the process of use.Countries urgently need to find efficient new energy to replace traditional energy to reduce carbon dioxide emissions.Hydrogen energy has attracted the attention of scientists due to its advantages of high energy density and environmental protection.As an important means of preparing hydrogen gas,electrocatalytic water splitting has always been the key point of scientists’ research.However,the electrocatalysts such as precious metals used for water splitting were more expensive,which once limited the development of the electrocatalytic hydrogen production industry.We therefore prepared a series of low-prize iron triad intermetal compounds for the hydrogen evolution reaction under alkaline conditions and studied the factors affecting the HER activity in three parts.In the first part,firstly we investigated systematically the hydrogen analysis reaction properties of RE2Co17（RE=Y,Pr,Gd,Tb,Ho,Er）and revealed that their HER activities are highly correlated with averaged Co-Co bond length of each compound.The HER performance follows the order as Gd2Co17>Tb2Co17>Pr2Co17>Y2Co17>Ho2Co17>Er2Co17.This suggesting the unique feature of rare-earth metals,lanthanide contraction,can effectively alter the interatomic spacing and impact corresponding HER activity.Additionally,Gd2Fe17 and Gd2Ni17 with different d electron density in the system were synthesized and comparison of their HER activities is also discussed.Gd2Ni17 had the best HER performance in all samples,requiring only an overpotential of 44 mV to obtain a 10 mA/cm2 of current density,and had a lower Tafel slope（32mV/dec）.The theoretical calculation offers a clue that H adsorption energy（GHad）for H atom on Ni is lower than that on Co and Fe due to the high electron population in antibonding state of Ni atom.In the second part,doping foreign elements into transition metal based catalysts can further improve their electrocatalytic activity.Based on this goal,this section was designed to synthesize a series of RENi2 and RERu0.25Ni1.75（RE=Pr,Tb and Er）and explored their electrocatalytic HER activities.Among undoped compounds,PrNi2 exhibits the best performance and requires hydrogen overpotential of 55 mV to reach current density of 10 mA/cm2.Replacing Ni with Ru element（PrRu0.25Ni1.75）,it can greatly reduce overpotential down to 20 mV.Such enhancement was later recognized that belongs to extrinsic property and their intrinsic HER activities after normalize surface area is similar.This result is quite unexpected and further investigation on ScM2 and ScRu0.25M1.75（M=Co and Ni）series suggests doping Ru element in ScCo2 will significantly enhance the antibonding character around Fermi level（EF）and thus weaken Hydrogen adsorption energy.On the other hand,the antibonding population for ScNi2 and ScRu0.25Ni1.75 is similar at EF,which is an important reason for their similar catalytic performance.In the third part,in order to further study the influence of doping foreign elements on transition metal-based catalysts,we designed,synthesized and tested the HER activity of ZrCo2 doped with different types of M（M=Fe,Ni,Ru）metals.The undoped ZrCo2 exhibited poor catalytic activity,with an overpotential of 127 mV at the 10 mA/cm2 current density.After doping with different M metals,its electrochemical activity is improved to varying degrees.Among them,ZrRu0.25Co1.75 has the largest increase,and its overpotential is only 37 mV.Theoretical calculation shows that ZrRu0.25Co1.75 increases the most amount of antibonding state near the Fermi level,thus effectively weakening its adsorption capacity to Hads and eventually achieving efficient water splitting.At the same time,the HER activity and stability of ZrRu0.25Co1.75 was tested in high concentration of KOH solution,which has good performance.