Regulation Of Electrostatic Potential At The Mott-schottky Heterojunction Interface And The Activation Mechanism Of Small Molecules

The electrostatic potential at Mott-Schottky heterojunction interface electrostatic potential as formed by the electron transfer between metal and semiconductor solid materials has led to the development of rising conceptual metal/semiconductor Mott-Schottky catalysts.The efficient charge separation induced by the electrostatic potential at both sides of metal and semiconductor solid materials immensely promotes the potential applications of Mott-Schottky catalysts for the related reactions in photocatalysis and organic synthesis.Based on the controllable electrostatic potential at the Mott-Schottky heterojunction interface,the design and synthesis of more catalysts and further investigation of their catalytic activity in more and important catalytic systems（e.g.gas-solid heterogeneous catalysis,electrocatalysis）will help us to discover the intrinsic connotation of the facilitation of electrostatic potential at the Mott-Schottky heterojunction interface for molecules adsorption and activation,and thereby to construct the valid relationships amongst the fabrication of catalysts,modulation of electrostatic potential at the interface,and the actual efficacy.This will inevitably impulse the construction and further large-scale preparation of Mott-Schottky catalysts and other solid catalysts,and expand their applications in major catalysis projects（e.g.catalytic hydrogen evolution,nitrogen fixation）,thus providing the practical and theoretical basis for exploring broader application prospects of Mott-Schottky catalyst and constructing important and efficient heterogeneous catalytic systems.Based on the above considerations,a series of metal/semiconductor heterojunction catalysts have been synthesized via the Mott-Schottky effect and applied to various typical catalytic activation of small molecules（e.g.gas-phase methanol dehydrogenation,electrochemical water splitting,and electrochemical nitrogen reduction）in this dissertation.We have studied the effects of charge transfer and electrostatic potential at the interface of heterojunction structure on the active center of the catalysts,and most importantly,confirmed the mechanism of adsorption and further activation of small molecules by the electrostatic potential at the Mott-Schottky heterojunction interface.The major findings are as follows:First,we developed an overall solid-state self-assembly method to construct a Mott-Schottky catalyst composed of Ni nanoparticles and tailorable nitrogen-doped carbon-foam（Ni/NCF）.The Ni/NCF catalyst could achieve an efficient dehydrogenation of gas-phase methanol to hydrogen and CO with a constant selectivity between 91-95%under varied weight hourly space velocity from 15 to 105 h^-1.Both theoretical and experimental results reveal the role of the Schottky rectifying contact and the electrostatic potential at the Ni/NCF interface in activating the methanol molecules and further accelerating methanol dehydrogenation via enhancing the absorption energies.The typical Mott-Schottky catalyst exhibited a remarkably high turnover frequency（TOF）value(356 mol methanol mol^-1Ni h^-1)for methanol dehydrogenation in such a gas-solid heterogeneous catalytic system,10-fold outpacing the state-of-the-art transition-metal-based catalysts in the literature.Meanwhile,the Ni/NCF catalysts also showed excellent long-term stability.Second,a sulfate radical(SO₄^2?)induced propagation method was developed to increase the exposed density of Ni/nitrogen-doped carbon（NC）boundaries.The solid-state self-assembly of Ni sheet and nitrogen-carbon molecules was directly converted into the Mott-Schottky Ni/NC catalysts with tunable content of Ni nanoparticles and fixed and stable electronic structure of nitrogen-carbon support in the presence of SO₄^2?.The typical Ni/NC with the highest Ni content（35 wt%）could be efficient electrocatalysts to achieve a nearly 100%selectively（as indicated by the Faradaic efficiency）for 8-electron process of electrochemical reduction of nitrate into ammonia.Third,based on the different electrostatic potentials between Ni/nitrogen-doped carbon（NC）and Au/NC,we present a powerful method to significantly boost the Faradaic efficiency of Au electrocatalysts to 67.8%for the nitrogen reduction reaction（NRR）by increasing their electron density through the construction of inorganic donor-acceptor couples of Ni and Au nanoparticles.The unique role of the electron-rich Au centers formed by the electron transfer from Ni nanoparticles（donor）to Au nanoparticles（acceptor）in facilitating the fixation and polarization-activation of N₂was also been investigated via theoretical simulation methods and then confirmed by experimental results.The highly coupled Au and Ni nanoparticles supported on NC were stable for reuse and long-term performance of the NRR,making the electrochemical process more sustainable for practical application.Finally,a controllable vacuum-diffusion method was developed for gradual phosphidation of carbon coated metallic Co nanoparticles into Co/CoP Janus nanoparticles within heterojunction structure between metallic Co and n-type semiconductive CoP.The redox capacities of both sides of semiconductor and metal were enhanced by the Mott-Schottky effect between CoP and Co.Janus Co/CoP nanoparticles,as typical Mott-Schottky electrocatalysts,exhibit excellent HER and OER performance in various electrolytes across wide p H range along with high durability.The Mott-Schottky Co/CoP catalyst could work as bifunctional electrode materials for overall water splitting in wide p H range and could achieve a current density of 10 m A cm^–2 in neutral electrolyte at only 1.51 V.