Electronic Structure Modulation By Heterogeneous Interface Constructing For The Design And Application Of Water Splitting Catalyst

Hydrogen(H2),with the advantages of high energy density,carbon-emissionfree characteristic and sustainability,has been considered as one of the most promising green energy sources to replace the dwindling fossil fuels.Hydrogen production from electrochemical overall water splitting driven by renewable energy has been identified as a key technology for generating high-purity H2 gas.However,due to the sluggish kinetics of the cathodic hydrogen evolution reaction(HER)and the anodic oxygen evolution reaction(OER),water splitting often requires high electrical power consumption.Therefore,how to reduce the energy consumption is the key issue to develop electrolytic hydrogen production technology.The use of efficient electrolytic water catalysts can effectively accelerate the reaction kinetics as well as reduce the reaction overpotential.At present,the state-of-the-art catalysts for HER and OER are mainly noble metal materials(Pt for HER and Ru/Ir for OER,respectively),which faces the problems of high cost and low energy conversion efficiency.Therefore,the development of efficient,inexpensive and stable nonprecious metal-based electrocatalysts remains a critical issue to be solved in advancing the industrial application of electrocatalytic hydrogen production.Recently,transition metal-based materials are considered as promising alternatives to the precious metal-based catalysts due to its reasonable electronic structure,excellent electronic conduction properties,superior alkaline electrochemical activity and stability.Nevertheless,the transition metal-based catalysts still exist some problems,such as larger dissociation energy of H2O under alkaline conditions,stronger adsorption of Hads,sluggish kinetics for OER.and poor bifunctional catalytic activity.Based on these problems,interface engineering strategy was adopted in this paper to optimize the active site density,electrical conductivity,adsorption state of reaction intermediates and surface electronic structure of the material.Additionally,based on the experimental and theoretical calculation results,the relationship between material structure and catalytic activity was summarized to investigate the mechanism of heterogeneous interface construction on catalytic performance,which can provide experimental and theoretical basis for the research and development of cheap,efficient,stable and suitable catalysts for electrolytic water in industrial electrolytic cells.The main contents and results are listed as follows:(1)Heterogeneous interfaces modulate the adsorption/desorption state:The interaction between metal/metal oxide heterogeneous interfaces can not only significantly enhance the charge transfer between the interfaces,but also optimize the electronic structure of the active sites,which in turn can regulate the adsorption and desorption of reaction intermediates and promote the reaction kinetics.Based on this,the effect of the interfacial interaction between Pd and CeO2 on the catalytic activity of OER was investigated by constructing heterogeneous interfaces between noble metal Pd nanoparticles and transition metal oxide CeO2 with different morphologies and exposed facets.The experimental results show that the interaction between Pd nanoparticles and CeO2-C support can effectively improve the dispersion and utilization of Pd,promote the adsorption and activation of oxygen-containing species,and optimize their adsorption/desorption balance,thus improving its catalytic activity and reaction rate.The Pd/CeO2-C catalyst exhibits excellent OER performance with an overpotential of 329 mV to achieve the current densities of 10 mA cm-2 and small Tafel slope of 46.5 mV dec-1.(2)Heterogeneous interfaces modulate the reaction barrier:The interaction between semiconductor/conductor heterogeneous interfaces can noy only modulate the electronic structure of the material and promote the adsorption/desorption balance of oxygen-containing species during the OER process,but also reduce the energy barriers of the OER rate-limiting step,thus improving the OER catalytic activity.Based on this,an interface engineering strategy was adopted to construct heterogeneous interfaces between FeNi-LDH and V2C MXene,in order to investigate the effect of MXene on the electronic structure of LDH,and to reveal the mechanism of its interfacial effect on the potentiation of the OER reaction.The results show that the strong interfaces interaction between FeNi-LDHs and V2C MXene can effectively improve the electrical conductivity and electron transfer efficiency of the material,reduce the d-band center thus promoting the adsorption/desorption balance of oxygen-containing species during the OER process,and reduce the energy barrier of the OER rate-limiting step thus improving the OER catalytic activity.The H2PO2-/FeNi-LDH-V2C catalyst exhibits excellent OER performance with an overpotential of 250 mV at 10 mA cm-2 and small Tafel slope of 46.5 mV dec-1 in 1.0 M KOH electrolyte.HER is another important semi-reaction in the process of water splitting.It is also an effective way to improve the HER performance by optimizing the electronic structure through semiconductor/conductor heterogeneous interfaces constructing,which can optimize the dissociation of H2O and the adsorption state of Hads on the catalyst surface.Based on this,an interfacial engineering strategy was adopted to construct heterogeneous interfaces between V2C MXene and Co-doped 1T-MoS2,in order to investigate the mechanism of the effect of Co-doping and V2C coupling on the HER catalytic activity of MoS2.DFT calculations reveal the strong interactions between V2C MXene and Co-doped 1T-MoS2 heterogeneous interfaces,in which the strong interactions and electronic coupling guarantee the improved electrical conductivity,the lower water dissociation energy,the weaker adsorption of the intermediates and the optimal ΔGH*,resulting an improved intrinsic catalytic activity of HER.As a result,the synthesized Co-MoS2/V2C@CC nanohybrid exhibits excellent HER performance with small overpotentials of 70.1 and 296 mV to achieve current densities of 10 and 1000 mA cm-2,respectively,and outstanding stability for 50 h HER test without degradation.Additionally,the overall hydrazineassisted water splitting(OHzS)system catalyzed by Co-MoS2/V2C@CC in both anode and cathode requires only 0.33 V to achieve a current density of 10 mA cm-2 with significant long-term durability.(3)Heterogeneous interfaces modulate the synergistic catalytic effects:The synergistic effects between multi-component interfaces of heterogeneous structures can not only promote the charge transfer and optimize the electronic structure,but also give full play to the physicochemical properties and synergistic catalytic ability of the composite catalysts,thus effectively improving its multifunctional catalytic activity.Based on the study of(1)and(2),CoP2-Mo4P3/NF catalyst with heterogeneous interfaces bctween CoP2 and Mo4P3 was constructed to improve the HER/OER bifunctional catalytic activity.The experimental results show that the synergistic effect between CoP2 and Mo4P3 heterogeneous interfaces can not only effectively improve the electrochemical active area and reduce the surface charge transfer impedance,but also optimize the electronic structure of the active sites,which in turn can reduce the adsorption of H and improve the redox ability,thus improving the bifunctional intrinsic catalytic activity of the composite.The catalyst exhibits excellent HER/OER bifunctional catalytic activity under alkaline conditions,with low overpotentials of 77.6 and 300.3 at 100 mA cm-2 for HER and OER,respectively.Additionally,the CoP2-Mo4P3/NF catalyst also displays excellent catalytic activity and stability for the overall water splitting in a two-electrode system,which can achieve 100 and 500 mA cm-2 at the cell voltages of 1.59 and 1.80 V,indicating that the catalyst can meet the requirements of water splitting with high current density in industrial applications.