Epitaxially Grown Ru Clusters-Nickel Nitride Heterostructure Advances Water Electrolysis Kinetics in Alkaline and Seawater Media

The epitaxial heterostructure can be rationally designed based on the in situ growth of two compatible phases with lattice similarity,in which the modulated electronic states and tuned adsorption behaviors are conducive to the enhancement of electrocatalytic activity.Herein,theoretical simulations first disclose the charge transfer trend and reinforced inherent electron conduction around the epitaxial heterointerface between Ru clusters and Ni_(3)N substrate(cRu-Ni_(3)N),thus leading to the optimized adsorption behaviors and reduced activation energy barriers.Subsequently,the defectrich nanosheets with the epitaxially grown cRu-Ni_(3)N heterointerface are successfully constructed.Impressively,by virtue of the superiority of intrinsic activity and reaction kinetics,such unique epitaxial heterostructure exhibits remarkable bifunctional catalytic activity toward electrocatalytic OER(226 mV@20 mA cm^(−2))and HER(32 mV@10 mA cm^(−2))in alkaline media.Furthermore,it also shows great application prospect in alkaline freshwater and seawater splitting,as well as solar-to-hydrogen integrated system.This work could provide beneficial enlightenment for the establishment of advanced electrocatalysts with epitaxial heterointerfaces.

Density Functional Theory for Electrocatalysis

It is a considerably promising strategy to produce fuels and high-value chemicals through an electrochemical conversion process in the green and sustainable energy systems.Catalysts for electrocatalytic reactions,including hydrogen evolution reaction(HER),oxygen evolution reaction(OER),oxygen reduction reaction(ORR),nitrogen reduction reaction(NRR),carbon dioxide reduction reaction(CO_(2)RR),play a significant role in the advanced energy conversion technologies,such as water splitting devices,fuel cells,and rechargeable metal-air batteries.Developing low-cost and highly efficient electrocatalysts is closely related to establishing the composition-structure-activity relationships and fundamental understanding of catalytic mechanisms.Density functional theory(DFT)is emerging as an important computational tool that can provide insights into the relationship between the electrochemical performances and physical/chemical properties of catalysts.This article presents a review on the progress of the DFT,and the computational simulations,within the framework of DFT,for the electrocatalytic processes,as well as the computational designs and virtual screenings of new electrocatalysts.Some useful descriptors and analysis tools for evaluating the electrocatalytic performances are highlighted,including formation energies,d-band model,scaling relation,egorbital occupation,and free energies of adsorption.Furthermore,the remaining questions and perspectives for the development of DFT for electrocatalysis are also proposed.

Tuning Active Metal Atomic Spacing by Filling of Light Atoms and Resulting Reversed Hydrogen Adsorption-Distance Relationship for Efficient Catalysis

Precisely tuning the spacing of the active centers on the atomic scale is of great significance to improve the catalytic activity and deepen the understanding of the catalytic mechanism,but still remains a challenge.Here,we develop a strategy to dilute catalytically active metal interatomic spacing(d_(M-M))with light atoms and discover the unusual adsorption patterns.For example,by elevating the content of boron as interstitial atoms,the atomic spacing of osmium(d_(Os-Os))gradually increases from 2.73 to 2.96?.More importantly,we find that,with the increase in dOs-Os,the hydrogen adsorption-distance relationship is reversed via downshifting d-band states,which breaks the traditional cognition,thereby optimizing the H adsorption and H_2O dissociation on the electrode surface during the catalytic process;this finally leads to a nearly linear increase in hydrogen evolution reaction activity.Namely,the maximum dOs-Os of 2.96?presents the optimal HER activity(8 mV@10 mA cm^(-2))in alkaline media as well as suppressed O adsorption and thus promoted stability.It is believed that this novel atomic-level distance modulation strategy of catalytic sites and the reversed hydrogen adsorption-distance relationship can shew new insights for optimal design of highly efficient catalysts.

Tunable Ru-Ru2P heterostructures with charge redistribution for efficient pH-universal hydrogen evolution

Designing synergistic heterogeneous catalytic interfaces is the key to developing highly compatible pH-universal electrocatalysts for complex chemical environments.Our theoretical calculation results demonstrate that the Ru-Ru2P heterointerface can not only promote the redistribution of charges,but also reduce the d-band center,and then enhances the adsorption capacity of the key intermediate.However,in situ and facile synthesis of Ru-Ru2P heterostructures is severely limited by thermodynamic obstacles.Herein,we propose a molten salt-assisted catalytic synthesis scheme,and successfully build a series of homologous metallic Ru-Ru2P heterostructure catalysts with different molar ratios of Ru to P under atmospheric pressure and low-temperature(400C).The resultant Ru-Ru2P with rich heterostructures show the Pt-like HER performance in different pH media.Particularly,it is prominent under alkaline conditions(18 mV@10 mA cm^(2)),which outperforms the Pt catalyst(37 mV@10 mA cm^(2)).Furthermore,Ru-Ru2P heterostructures also show certain potential in the electrolysis of seawater to produce hydrogen.This work represents a significant supplement of high-efficiency pH-universal HER catalysts,and provides a new light on interface engineering in energy technology fields and beyond.

Micropore-confined Ru nanoclusters catalyst for efficient pHuniversal hydrogen evolution reaction

Pt-based catalysts are used commercially for the hydrogen evolution reaction(HER),even though the low earth abundance and high cost of platinum hinder scale-up applications.Ru metal is a promising alternative catalyst for HER owing to its lower cost but similar metal-hydrogen bond strength to Pt.However,designing an efficient and robust Ru-based electrocatalyst for pHuniversal HER is challenging.Herein,we successfully synthesized N-doped carbon(NC)supported ruthenium catalysts with different Ru sizes(single-atoms,nanoclusters and nanoparticles),and then systematically evaluated their performance for HER.Among these catalysts,the Ru nanocluster catalyst(Ru NCs/NC)displayed optimal catalytic performance with overpotentials of only 14,30,and 32 mV(at 10 mA·cm^(-2))in 1 M KOH,1 M phosphate buffer saline(PBS),and 0.5 M H_(2)SO_(4),respectively.The corresponding mass activities were 32.2,12.1 and 8.1 times higher than those of 20 wt.%Pt/C,and also much better than those of the Ru single-atoms(Ru SAs/NC)and Ru nanoparticle(Ru NPs/NC)catalysts,at an overpotential of 100 mV under alkaline,neutral and acidic conditions,respectively.Density functional theory(DFT)calculations revealed that the outstanding HER performance of the Ru NCs/NC catalyst resulted from a strong interaction between the Ru nanoclusters and the N-doped carbon support,which downshifted the d-band center and thus weakened the*H adsorption ability of Ru sites.

Tailoring the microenvironment in Fe–N–C electrocatalysts for optimal oxygen reduction reaction performance

Fe-N-C electrocatalysts,comprising FeN_(4) single atom sites immobilized on N-doped carbon supports,offer excellent activity in the oxygen reduction reaction(ORR),especially in alkaline solution.Herein,we report a simple synthetic strategy for improving the accessibility of FeN_(4) sites during ORR and simultaneously fine-tuning the microenvironment of FeN_(4) sites,thus enhancing the ORR activity.Our approach involved a simple one-step pyrolysis of a Fe-containing zeolitic imidazolate framework in the presence of NaCl,yielding a hierarchically porous Fe-N-C electrocatalyst containing tailored FeN_(4) sites with slightly elongated Fe-N bond distances and reduced Fe charge.The porous carbon structure improved mass transport during ORR,whilst the microenvironment optimized FeN_(4) sites benefitted the adsorption/desorption of ORR intermediates.Accordingly,the developed electrocatalyst,possessing a high FeN_(4) site density(9.9×10^(19) sites g^(-1))and turnover frequency(2.26 s^(-1)),delivered remarkable ORR performance with a low overpotential(a half-wave potential of 0.90 V vs.reversible hydrogen electrode)in 0.1 mol L^(-1) KOH.

Establishing a theoretical insight for penta-coordinated ironnitrogen-carbon catalysts toward oxygen reaction

Developing highly active iron-nitrogen-carbon catalysts for electrocatalytic oxygen reduction reactions(ORR)is pivotal to future energy technology.The penta-coordinated Fe-N-C with an augmented activity toward the oxygen reduction has been regarded as one of the promising candidates to replace platinum-based ORR catalysts.However,the lack of pertinent fundamental understanding hinders further optimizing the catalytic activity of such catalysts.Herein,through density functional theory(DFT)calculations,we systematically investigated the catalytic activity and ligand/metal coordination effects of 17 penta-coordinated FeN-C catalysts(labeled as FeNC-Xs,X denotes axial ligand).Our results not only show the theoretical overpotential of FeNC-Xs is lower than that of conventional tetra-coordinated Fe-N-C catalysts(labeled as FeNC),verifying the preeminent performance of FeNC-Xs,but also further indicate that the axial coordination effect of X ligands can decrease the orbital hybridization of Fe active center with ORR-relevant intermediates,sequentially accelerating the ORR.More importantly,we reveal that the catalytic activity of FeNC-Xs increases with a decreased electronegativity of X ligands,which can be utilized to describe the axial coordination effect for FeNC-Xs.These findings can deeply advance the understanding of penta-coordinated iron-nitrogencarbon catalysts,which provide timely guidelines for designing optimum Fe-N-C based catalysts.

Coordination environments tune the activity of oxygen catalysis on single atom catalysts:A computational study

Designing highly efficient bifunctional electrocatalysts for oxygen reduction and evolution reaction(ORR/OER)is extremely important for developing regenerative fuel cells and metal-air batteries.Single-atom catalysts(SACs)have gained considerable attention in recent years because of their maximum atom utilization efficiency and tunable coordination environments.Herein,through density functional theory(DFT)calculations,we systematically explored the ORR/OER performances of nitrogencoordinated transition metal carbon materials(TM-N_(x)-C(TM=Mn,Fe,Co,Ni,Cu,Pd,and Pt;x=3,4))through tailoring the coordination environment.Our results demonstrate that compared to conventional tetra-coordinated(TM-N_(4)-C)catalysts,the asymmetric tri-coordinated(TM-N_(3)-C)catalysts exhibit stronger adsorption capacity of catalytic intermediates.Among them,Ni-N_(3)-C possesses optimal adsorption energy and the lowest overpotential of 0.29 and 0.28 V for ORR and OER,respectively,making it a highly efficient bifunctional catalyst for oxygen catalysis.Furthermore,we find this enhanced effect stems from the additional orbital interaction between newly uncoordinated d-orbitals and p-orbitals of oxygenated species,which is evidently testified via the change of d-band center and integral crystal orbital Hamilton population(ICOHP).This work not only provides a potential bifunctional oxygen catalyst,but also enriches the knowledge of coordination engineering for tailoring the activity of SACs,which may pave the way to design and discover more promising bifunctional electrocatalysts for oxygen catalysis.

Dynamic reconstruction of Ni-Zn alloy solid-electrolyte interface for highly stable Zn anode

Aqueous zinc ion batteries(AZIBs)are ideal candidates for large-scale battery storage,with a high theoretical specific capacity,ecological friendliness,and extremely low cost but are strongly hindered by zinc dendrite growth.Herein,Ni-Zn alloy is artificially constructed as a solid-electrolyte interface(SEI)for Zn anodes by electrodeposition and annealing.The Ni-Zn alloy layer acts as a dynamic shield at the electrode/electrolyte interface.Interestingly,the zinc atoms migrate out of the electrode body during zinc stripping while merging into the electrode body during the plating.In this way,the Ni-Zn alloy is able to guide the zinc deposition in the horizontal direction,thereby suppressing the formation of dendrite.Benefiting from those,the Ni-Zn alloy symmetric cell shows a greatly improved cycle life and is able to operate stably for 1,900 h at a current density of 0.5 mA·cm^(−2).The present study is a strategy for negative electrode protection of AZIBs.