Synthesis And Activity Trends Of Intermetallic Boride Electrocatalysts For Hydrogen Evolution Reaction

Electrocatalytic water splitting technology is a main strategy for converting renewable energy such as wind and solar energy into green hydrogen,which can effectively solve the instability and discontinuity of renewable energy,so as to realize the storage and transportation of renewable energy.However,the two half-reactions involving electrocatalytic water splitting are difficult to proceed spontaneously in terms of thermodynamics and kinetics,and usually require noble metal materials(e.g.Pt,Ir O_x)as efficient catalysts,which are not economically competitive.Therefore,in order to minimize costs,researchers are committed to developing efficient,inexpensive and stable catalysts for water electrolysis.In recent years,intermetallic boride has become a new type of catalytic material for electrocatalytic water splitting reaction due to their excellent intrinsic conductivity,chemical resistance and potential multifunctional catalytic activity.Compared with other transition metal-based catalysts(e.g.sulfides,carbides),intermetallic borides show more complex diversity in synthetic chemistry,element composition,crystal structure and chemical bonding,resulting in a relatively slow development of intermetallic borides.In addition,the lack of enough knowledge about the structure-bonding-catalytic performance correlation has also restricted the development of intermetallic boride catalysts.Understanding the catalytic trends can provide rational guidance toward the prediction and design of advanced catalysts.In this paper,we have selectively synthesized a series of intermetallic borides through solid-state metathesis reactions to study their catalytic activity trends.Combined with DFT calculations and experiments,we explain the relationship between the crystal structures,electronic structures and catalytic performances of intermetallic borides.The main contents of this paper are as follows:1.Combining DFT calculations and experiments,we have systematically studied the electronic structures and electrocatalytic activities of a family of 12 intermetallic diborides containing"borophene"subunits,revealing the periodic trends in electrocatalytic activities for the hydrogen evolution reaction(HER)from Group IV B to Group VIII intermetallic diborides.Theoretical results demonstrate a general linear relationship between the catalytic activity and d?band center of intermetallic diboride,meaning that the latter can serve as a reliable descriptor of activity.And theoretical results also predict Ru B₂ as the most competitive,nonplatinum candidate among intermetallic diborides for HER because this material has a suitable d?band center and a high density of efficient active sites.Furthermore,we synthesized and tested these 12 intermetallic diborides through a solid-state metathesis reaction.The experimental results validated the theoretical activity trends,i.e.VIII>VII B>VI B>V B>IV B interstitial diborides,and identified Ru B₂ as an efficient,p H-universal electrocatalyst with Pt-like activity for HER.Ru B₂ can reach the current density of 10 m A cm^-2 with only 18 m V overpotential under acidic media,and even has a better HER activity than Pt under alkaline media,which can be catalyzed stably for more than 50 hours.2.WB₂ is identified as the highest active,nonprecious metal diborides material,and the W-B intermetallic borides contain multiple crystal phases with different boron subunit structures.Considering the unique advantages of nonprecious WB₂,a deeper study on the W-B intermetallic borides as electrocatalysts for HER is important.On the basis of the solid-state metathesis reaction,we added an appropriate amount of magnesium powder to selectively synthesize four multiple crystal phases of W-B intermetallic borides,including W₂B,WB,WB₂ and WB₃.We compared the crystal structures,electronic structures and hydrogen evolution catalytic activities of W-B intermetallic borides with multiple crystal phases.The crystal structure analysis shows that with the increase of boron content,the covalent linkage patterns of boron atoms in W-B intermetallic borides evolves from isolated boron to one-dimensional boron chains and two-dimensional boron layers.The electrocatalytic results show that these W-B intermetallic borides with multiple crystal phases have a phase-dependent hydrogen evolution activity trend in both acidic and alkaline medias,i.e.WB₂>WB>W₂B>WB₃.This activity trend is mainly attributed to the changes in the electronic structure caused by the different degrees of hybridization between W d orbitals and B sp orbitals,which affects the surface catalytic behaviors of W-B intermetallic borides.