Internal Electric Field Contructed By Charge Seperation For Enhanced Manganese Dioxide Kinetics And Its Capacitive Deionization

In recent years,the water resource pollution problem and its associated water shortage have gradually attracted people’s attention,and become a problem that countries must be accelerating to solve.Seawater desalination has become a new idea of water production.Capacitive deionization（CDI）technology has become a new technology which takes advantage of environmental protection and low energy consumption.However,the traditional CDI technology has poor deionization performance due to the co-ion effect of carbon materials.As a pseudocapacitor material with a high theoretical specific capacitance value,manganese dioxide（MnO₂）can be used as a hybrid capacitive deionization（HCDI）material.Unfortunately,due to its semiconductor properties,manganese dioxide has low ionic and electronic conductivity,which makes it difficult to reach the theoretical value.Therefore,it is the key through the modification of MnO₂to enhance its kinetic properties and improve its conductivity of ions and electrons for HCDI application.In this paper,the local electronic structure is regulated to induce internal electric field by superexchange and heterostructure construction,leading to enhanced kinetics of manganese dioxide,and then improve its HCDI performance.The main works are as follows:（1）MnO₂doped with nickel（Ni-MnO₂）was prepared by hydrothermal method,and the Mn⁴⁺-O^2--Ni²⁺coordination structure unit was formed.Subsequently,it induced an uneven charge distribution via superexchange interaction,leading to the construction of an intensive IEF and thus a significantly enhanced charge transfer process during HCDI.Both soft X-ray absorption spectroscopy（s XAS）and density functional theory（DFT）results demonstrate that electrons transfer from the 2p orbital of O^2-to the e_gorbital of TM sites(Ni²⁺and Mn⁴⁺)via superexchange interactions within the basic coordination structure unit of Mn⁴⁺-O^2--Ni²⁺in Ni-MnO₂.The resulting charge separation induces the formation of IEF in Ni-MnO₂,facilitating the electron and ion transfer processes during HCDI.As a result,Ni-MnO₂exhibits an obviously enhanced HCDI performance with a SRC of 72.9 mg g^-1and a SRR of 3.79 mg g^-1min^-1at 1.2 V operation voltage in 500 mg L^-1Na Cl solution.（2）The material was successfully prepared by hydrothermal method and formed a heterojunction MoS₂@MnO₂.The formation of S-O bond at the interface promotes charge transfer from MoS₂to MnO₂based on the difference in work function between MoS₂and MnO₂,resulting in uneven charge distribution.This uneven charge distribution induces the formation of an internal electric field at the interface,which in turn enhances the charge transfer process MoS₂@MnO₂during the HCDI process.Both theory and practice indicate that electrons shift from MoS₂to MnO₂.The results showed that MoS₂@MnO₂exhibited better HCDI performance in 500 mg L^-1Na Cl solution.In conclusion,based on the principle of charge separation,high performance Ni-MnO₂and MoS₂@MnO₂electrode materials for HCDI electrode materials are synthesized by superexchange and the construction of heterojunction to form internal electric field.The experimental and theoretical results show that the formed internal electric field improves the electron configuration of MnO₂and the kinetics of adsorption of Na⁺ions in HCDI application.This paper provides a strong support through solid data for the application of modified manganese dioxide to catalysis,energy storage and other fields.