Valence State Of Ions Research Articles

Strong spin-lattice entanglement in cobaltites

Strongly correlated electronic system contains strong coupling among multi-order parameters and is easy to efficiently tune by external field. Cobaltite (LaCoO<sub>3</sub>) is a typical multiferroic (ferroelastic and ferromagnetic) material, which has been extensively investigated over decades. Conventional research on cobaltites has focused on the ferroelastic phase transition and structure modulation under stress. Recently, researchers have discovered that cobaltite thin films undergo a paramagnetic-to-ferromagnetic phase transition under tensile strain, however, its origin has been controversial over decades. Some experimental evidence shows that stress leads the valence state of cobalt ions to decrease, and thus producing spin state transition. Other researchers believe that the stress-induced nano-domain structure will present a long-range ordered arrangement of high spin states, which is the main reason for producing the ferromagnetism of cobalt oxide films. In this paper, we review a series of recent researches of the strong correlation between spin and lattice degrees of freedom in cobalt oxide thin films and heterojunctions. The reversible spin state transition in cobalt oxide film is induced by structural factors such as thin-film thickness, lattice mismatch stress, crystal symmetry, surface morphology, interfacial oxygen ion coordination, and oxygen octahedral tilting while the valence state of cobalt ions is kept unchanged, and thus forming highly adjustable macroscopic magnetism. Furthermore, the atomic-level precision controllable film growth technology is utilized to construct single cell layer cobaltite superlattices, thereby achieving ultra-thin two-dimensional magnetic oxide materials through efficient structure regulation. These advances not only clarified the strong coupling between lattice and spin order parameters in the strongly correlated electronic system, but also provided excellent candidate for the realization of ultra-thin room temperature ferromagnets that are required by oxide spintronic devices.

Magnetic transitions and different valence states of manganese ions in solid solutions (Ni,Cu,Mn)-=SUB=-3-=/SUB=-BO-=SUB=-5-=/SUB=-

The content of metal ions and their valence state for three NixCuyMn3-x-yBO5 compositions were estimated by EXAFS and XANES spectroscopy methods. In all three compositions, the copper y content did not exceed 0.25; in the third composition, some manganese ions entered the compound not only in the trivalent, but also in the divalent state. A detailed study of the magnetic properties showed that two magnetic transitions are observed in all compositions: one in the region of 60-75 K, and the second in the region of 10 K. Based on the exchange interactions calculated within the framework of the empirical model, the magnetic ordering temperatures for two- and three-lattice magnets were determined and it was assumed that the magnetic transition in the region of 60-75 K is associated with the ordering of magnetic moments in positions 2 and 3. Keywords: ludwigites, magnetic phase transition, indirect exchange interactions.

Evolution of the valence state of Ru metal ions in correlation with the structural and electronic properties of double perovskite ruthenates; A2SmRuO6 (where A = Ba & Sr)

This novel study is crucial in understanding the intriguing electronic, structural and chemical properties of special double perovskite compounds, Ba2SmRuO6 and Sr2SmRuO6, for their applications as “Spintronics based devices”.

Promotional effects of cerium in ytterbium doped fibers on proton irradiation damage.

This paper investigated the defect generation mechanism of two self-made ytterbium-doped fibers (a Yb-doped fiber and a Yb/Ce-doped fiber) under proton irradiation and the influence of Ce-doping on proton radiation defects. The macroscopic damage of different optical fibers caused by proton irradiation energy and irradiation doses was further studied. Fluorescence spectroscopy, EPR electron paramagnetic resonance and SEM experiments were used to characterize the micro defects and macro damage of the fibers. The following conclusions are drawn: the damage on the surface of optical fibers increases continuously with the increase of irradiation dose, and does not change significantly with the increase of proton energy. The main defect in the irradiated fibers is proved to be the Al-OHC defect which leads to energy loss in the visible light region and a photon darkening effect. After Ce doping, the change trend of the amount of Al-OHC defect is greatly suppressed, while it shows little effect on the oxygen defect (intrinsic), and basically does not change this trend. On the other hand, Ce doping can also effectively reduce the generation of Si-E' defects in the irradiated fibers according to the EPR electron paramagnetic resonance experiment. In conclusion, due to the presence of two valence states of Ce ions, Ce doping prominently improves the performance of high-power Yb-doped fibers under proton irradiation.

Developing high-Q × f value MgNb2–xTaxO6(0≤x≤0.8) columbite ceramics and clarifying the impact mechanism of dielectric loss: Crystal structure, Raman vibrations, microstructure, lattice defects, chemical bond characteristics, structural parameters, and microwave dielectric properties in-depth studies

With the increasing frequency of wireless mobile communication, dielectric materials with higher Q × f are required to enhance the signal strength of microwave passive devices and thus compensate for the rapid attenuation of high-frequency signals during propagation. In order to improve the Q × f of the MgNb2O6 system and study the internal mechanism between the structure and microwave dielectric properties, Ta5+ ion is introduced to design and fabricate MgNb2−xTaxO6 (0 ≤ x ≤ 0.8) ceramics by the solid-state reaction method. The single columbite phase and dense structure are observed throughout the entire composition range. All elements (Mg, Nb, Ta, and O) can be detected by X-ray photoelectron spectroscopy. Insights from the Raman spectroscopy and group theoretical analysis reveal that the Ag(2) and Ag(3) modes located at ∼ 905 cm−1 dominate the Raman vibration. In addition, the ɛr depends on the polarizability reflected by the C–M equation and Raman shift. The τf closely relates to the bond energy of the Nb/Ta–O bond and restoring force characterized by average octahedral distortion of [Nb/TaO6]. Notably, the crucial factors for the huge improvement of Q × f are clarified deeply, in terms of the lower internal strain, the reduced ordering-induced domain size, and the chemical bond valence closer to the ionic valence state, which promotes the stability of crystal structure. Moreover, the introduction of lower electronegative ions enhances the ability of electrons to compensate for oxygen vacancies, thereby reducing the dielectric loss caused by the conductance. Excellent microwave properties (ɛr = 19.2, Q × f = 170,000 GHz, and τf = −55.6 ppm °C–1) are achieved in MgNb1.4Ta0.6O6 ceramic, specifically a nearly 40% increase in the Q × f. This work has enriched the theory associated with low dielectric loss and provided the MgNb1.4Ta0.6O6 ceramic with a pretty high-Q × f for the application in the design of the 5G/6G wireless communication devices.

High Verdet Constant Glass for Magnetic Field Sensors

Due to the high transparency, high Verdet constant, as well as easy processing properties, rare-earth ion-doped glasses have demonstrated great potential in magneto-optical (MO) applications. However, the variation in the valence state of rare-earth ions (Tb3+ to Tb4+) resulted in the decreased effective concentration of the paramagnetic ions and thus degraded MO performance. Here, a strategy was proposed to inhibit the oxidation of Tb3+ into Tb4+ as well as improve the thermal stability by tuning the optical basicity of glass networks. Moreover, the depolymerization of the glass network was modulated to accommodate more Tb ions. Thus, a record high effective concentration (14.19 × 1021/cm3) of Tb ions in glass was achieved, generating a high Verdet constant of 113 rad/(T·m) at 650 nm. Lastly, the first application of MO glass for magnetic field sensors was demonstrated, achieving a sensitivity of 0.139 rad/T. We hope our work provides guidance for the fabrication of MO glass with high performance and thermal stability and could push MO glass one step further for magnetic sensing applications.

Effects of Mg-doping on distorted structure and enhanced electrochemical performance of V1-Mg O2 nanorods

In this work, a series of V1-xMgxO2 samples (x = 0–0.030) were synthesized by hydrothermal method. The corresponding laws of Mg2+ doping concentration on the microstructures and electrochemical performance of V1-xMgxO2 were studied in detail. The XRD results indicated that the prepared V1-xMgxO2 samples showed monoclinic crystal phase and Mg2+ doping caused lattice distortion in the experimental doping range. The SEM and TEM results showed that all the V1-xMgxO2 samples were nanorods and well-crystallized. The positron lifetime spectra showed that the main defects in the V1-xMgxO2 samples were vacancy clusters. The concentration and size of the defects were affected by the combined action of ion radius and valence state of doped Mg2+. The electrochemical results revealed that the samples showed better electrochemical properties when the Mg2+ doping concentration x is 0.015. The high discharge capacitance of the x = 0.015 sample reached 140.6 F/g and the capacitor retention of this sample was still about 90 % after 1000 cycles.

Research progress of manganese-based layered oxides as cathode materials for potassium-ion batteries

In this paper, the research progress of K x MnO 2 as cathode material for potassium-ion batteries is reviewed, and a series of doping modification (low valence substitution) of this material is summarized. Finally, the future optimization measures of K x MnO 2 are proposed. • The research progress and challenges of monobasic K x MnO 2 as cathode materials for potassium-ion batteries are summarized. • The advantages of doped binary ferromanganese-based and manganese-magnesium-based materials as cathode materials for potassium-ion batteries are summarized. • The future improvement measures of K x MnO 2 material are proposed. Potassium is inexpensive, abundant, and evenly distributed in the Earth’s crust. It has similar physical and chemical properties to those of lithium. Therefore, the use of potassium-ion batteries is expected to be realized. Cathode materials are important components of potassium-ion batteries. In addition to potassium-containing compounds, other cathode materials should be actively explored. Manganese-based oxides are widely used as cathode materials in various batteries because of their multiple ion valence states, abundant mineral reserves, low cost, and convenient synthesis methods. Among these various cathode materials manganese dioxide with a layered structure has a large interlayer spacing, which can be used for the insertion and extraction of potassium ions with a large ionic radius between the layers. Therefore, layered K x MnO 2 (KMO) cathode materials have significant potential for development. This paper reviews the research status of manganese-, ferromanganese-, manganese magnesium-, nickel manganese-, nickel cobalt manganese-, and iron titanium manganese-based metal oxides as cathode materials for potassium-ion batteries. Additionally, the obstacles and opportunities faced by KMO materials as cathode materials for potassium-ion batteries are comprehensively discussed.

Electron transfer by ion conductance in a soil bioelectric field

The efficacy of electron transfer determines the performance of soil microbial electrochemical systems (MESs). Ion conductance is an important endogenous route of electron transfer for the soil, yet its efficacy is unclear. Under the bioelectric field force generated in situ by indigenous soil microorganisms, dominant cations (Na+ and Mg2+) and anions (Cl− and SO42−) were all transported to the cathode in soil MESs. Furthermore, the same valence state of ions exhibited different and even opposite effects on ion conductance according to the work done by the bioelectric field force over time, e.g., Na+ and K+. Based on charges carried by migrated ions, we demonstrated that ion conductance was the main route of electron transfer in a soil MES, even for treatments with conductive magnetite and haematite. In contrast, electron shuttles contributed predominantly to electron transfer in ferrihydrite treatment. This was also supported by the characteristics of the charge transfer resistance and ohmic resistance according to the redundancy analysis with interpretation degrees of 93.96–94.25 %. Overall, this study provides profound insight into electron transfer by ion conductance in soil bioelectrochemical technology.

Conversion of the valence states of europium ions in reduced SrTiO3 based on the photoluminescence spectra

The photoluminescence (PL) of Eu ions and their modulation with oxygen vacancy amount were investigated in SrTiO3 with site substitution (A-site vs. B-site in ABO3-type perovskite) dependence, aiming at obtaining the color tunability by the change in the valence states of Eu ions. The samples, which were synthesized in air using a solid state reaction method, exhibited strong orange-red emissions near 600 nm, which is a characteristic of Eu3+. We annealed our samples in H2 atmosphere to increase the oxygen vacancies, and we established that the orange-red emissions of the Eu ions were suppressed. However, surprisingly, new emissions of Eu2+ emerged near 400 nm, which has not been reported. More interestingly, this behavior was more robust in the B-site-doped sample than in the A-site-doped sample. In the samples with O2-ambient annealing to decrease oxygen vacancies, the PL intensities returned to the initial states for both site substitutions, indicating the reversible change in the valence states (+2/+3) of Eu ions. Our new finding of the tunable emission property of Eu ions in SrTiO3 could be explained in terms of the substitution sites and the related charge compensations with regulating oxygen vacancies.

Chemical-substitution dependence of magnetization strength in room- temperature ferromagnetism of dilute magnetic oxides: Valence and spin state of slightly doped cobalt in (In,Al)2O3

This study investigates the valence and spin states of cobalt ions and the magnitude of room-temperature ferromagnetic magnetization in In1.9−xAlxCo0.1O3 (0≤x≤0.3) prepared by a chemical solution method. According to X-ray photoelectron spectroscopy, the Co ions in the Al-free sample (x=0) existed in a mixed state of trivalent Co3+ and divalent Co2+. The abundance ratio of Co2+ increased with Al content, and only divalent ions were present at x=0.3. A magnetic susceptibility analysis showed that both the spin and orbital degrees of freedom were magnetized in Co2+, whereas Co3+ was in a low-spin state. Co3+ was converted to Co2+ by vacuum annealing. The higher the conversion ratio of Co3+ to Co2+, the stronger was the room-temperature ferromagnetism.

Elucidating the Multisite and Multivalence Nature of Mn Ions in Solids and Predicting Their Optical Transition Properties: A Case Study on a Series of Garnet Hosts.

The abundant site occupancy and optical transitions of multivalence Mn dopants in luminescent materials have attracted much attention. Here, detailed first-principles calculations based on density functional theory have been carried out to clarify the multisite and multivalence nature of Mn ions in solids and predict their optical transition properties by using garnets as prototype systems. The formation energies of dodecahedral, octahedral, and tetrahedral coordinated Mn dopants are evaluated with chemical potential environments, and the preferable site occupancy and valence state of Mn ions in three garnet systems are clarified. The results show that even in a fixed atmosphere, taking Ca3Al2Ge3O12 in air as an example, not only can the preference of Mn ions switch between dodecahedral and octahedral sites, but also can the valence state change from Mn2+ to Mn3+ and Mn4+. Furthermore, for all of the three garnet systems, the calculation results of the energy-level structure and photoluminescence of Mn ions at different sites in the different valence states provide a reliable interpretation of the available spectroscopic data. The proposed first-principles scheme, with general applicability and encouraging predictive power, provides an effective approach for elucidating and characterizing the site occupancy, valence state, and optical transition of Mn activators in insulators, and will greatly benefit the design and optimization of related materials.

Optimized Solid-State Synthesis of Sr2Fe1.5Mo0.5O6−δ Perovskite: Implications for Efficient Synthesis of Mo-Containing SOFC Electrodes

Sr2Fe1.5Mo0.5O6−δ (SFMO) perovskite has been considered as a promising anode candidate for solid oxide fuel cells. However, the significant inconsistency in the conductivity properties of SFMO perovskite has been reported in the literature through various synthesis procedures, highlighting the necessity of a standard and unified synthesis process. In this work, we propose an optimized solid-state synthesis process of SFMO perovskite based on the thermal properties of the precursors. Our TG analysis indicates that the evaporation of MoO3 during sintering over 752 °C may affect the synthesis of the expected SFMO perovskite. The presence of Fe2O3 has a trap effect on MoO3, based on the TG analysis of the binary mixture. A cubically structured SFMO perovskite without a secondary phase is obtained from the as-proposed stepwise sintering program while an impurity phase of SrMoO4 is observed when adopting a direct sintering program. The as-synthesized SFMO perovskite exhibits high stability in a reducing atmosphere, which is attributed to the self-adjustment of the overall valence states of molybdenum ions and iron ions. Many pure cubically structured perovskites have been successfully synthesized using the as-proposed solid-state synthesis process, suggesting its universality for the synthesis of other Mo-containing SOFC perovskite electrodes.

Effect of annealing temperature on the structural, electronic and magnetic properties of Co doped TiO2 nanoparticles: An investigation by synchrotron-based experimental techniques

The present study examines the effect of annealing temperature on the structural, electronic and magnetic properties of Co-doped TiO2 (TCO) nanoparticles (NPs) synthesized by the sol-gel method. X-ray powder diffractograms of TCO NPs annealed at 400, 600 and 800 °C exhibited the monophasic anatase, diphase (anatase and rutile) and monophasic rutile structures respectively. A morphological investigation using high-resolution scanning electron microscopy (HR-SEM) reveals the presence of nanoparticles with diameters ranging from ∼11 to ∼51 nm. The widening and shifting of the most intense Eg peak in Raman studies and SEM images of TCO NPs suggest Co incorporation in the TiO2 matrix and the formation of oxygen vacancies. Magnetic measurements of TCO at room temperature demonstrate ferromagnetic behaviour which is caused by the existence of oxygen vacancies and the doped Co content. Element specific technique, soft X-ray magnetic circular dichroism (XMCD) was used to study the magnetism in Co doped TiO2 samples. The estimated total magnetic moment by XMCD was in the range of ∼1.3 ± 0.1–2.3 ± 0.2 μB/Co. This huge magnetization was first time observed by the surface-sensitive Total Electron Yield (TEY) mode. The estimated saturation magnetic moment is in the range of 1.0–1.5 μB/Co, also consistent with XMCD analysis and cluster model calculation. The results obtained by XMCD recommend an intrinsic behaviour of ferromagnetism. The X-ray absorption spectra (XAS) of Co-doped TiO2 nanoparticles at Ti L2,3 and Co L2,3 -edge in TEY mode concludes that the valence states of Co and Ti ions are in 2 + and 4 + respectively. Cluster model calculation also confirmed that Co ions are in a 2 + valence state with D2 h high spin crystal-field symmetry at the surface while a random crystal field symmetry in bulk has been observed which is well consistent with experimental data.

Nanoclay Modulates Cation Occupancy in Manganese Ferrite for Catalytic Antibacterial Treatment.

Controllable preparation is the current frontier in the field of inorganic nanomaterial-based artificial enzymes (nanozymes). For ferrites, the factors affecting cation occupancy are very complex, making the modulation of cation occupancy extremely challenging. Herein, we report a new strategy to modulate the cation occupancy of manganese ferrite (MFO) based on the structural properties of nanoclay (i.e., montmorillonite K10). It demonstrates that montmorillonite K10 mainly changes the valence state and occupancy of manganese ions in manganese ferrite and not iron ions. K10 increases the proportion of Mn (II) in manganese ferrite and causes more manganese ions to migrate to the tetrahedral sites. As expected, the prepared new inorganic compound possesses excellent enzyme-like catalytic activities and antibacterial functional properties, which are attributed to Mn (II) accelerating Fe (III) reduction and hydroxyl radical formation. Furthermore, steady-state kinetic assays are used to study the reaction mechanism in detail. In vitro and in vivo antibacterial experiments show that the synthesized inorganic compounds exhibit satisfactory disinfection and wound skin recovery efficiencies. This work emphasizes the controllable preparation of new inorganic compounds with biomimetic activity and provides novel insight into the biological effects of inorganic nanomaterials.

Influence of MnO2 addition on the dielectric properties of 0.95MgTiO3-0.05CaTiO3 ceramics sintered in a reducing atmosphere

The increasing cost of palladium has demonstrated the significant value of using inexpensive base metals as inner electrodes for RF/microwave multilayer ceramic capacitors. However, solving the co-sintering problem of dielectric ceramics with base metals such as copper is highly challenging, as sintering in a reducing atmosphere is required to prevent the oxidation of the base metals. In this work, the feasibility of sintering nonreducible MnO2-doped 0.95MgTiO3-0.05CaTiO3 (95MCT) ceramics in a reducing atmosphere (H2-N2, pO2=1×10−10∼1×10−11MPa) at 1000 °C was investigated. The effects of the MnO2 additive (1.6–2.4 mol%) on the phase structures, dielectric properties, and thermal stability were studied. Thermally stimulated depolarization current (TSDC) analysis and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the oxygen vacancies and Mn ion valence state in MnO2-doped ceramics, indicating that Mn plays an important role in the dielectric properties, especially the extrinsic dielectric loss. With the optimized addition of 2.0 mol% MnO2, due to the decrease in oxygen vacancy concentration, the samples with εr=20.22 exhibited the attractive properties of a high insulation resistivity of IR =3.65×1014 Ω∙cm and a low dielectric loss of tanδ=0.036%, meeting the C0G specifications. The results show that the 2.0 mol% MnO2-doped 0.95MgTiO3-0.05CaTiO3 ceramic is an outstanding nonreducible dielectric material for base-metal electrode RF/microwave multilayer ceramic capacitor applications with low cost, excellent dielectric properties, and high reliability.

Stabilization of oxidation state in ZnO decorated-CeO2 for enhanced formation of CO in CO2 electroreduction

Electrochemical CO2 reduction (ECR) is regarded as a potential approach to generate renewable fuel and realize carbon cycling. Zn-based materials have been considered as effective catalysts to reduce CO2 into CO. Unfortunately, low selectivity for CO and Zn metallization impede the development of Zn-based materials. Herein, we propose a strategy in utilizing the changeable valence state of Ce ions to stabilize oxidation state of ZnO, in which the Zn-O-Ce model is constructed by CeO2-modified ZnO nanofibers through electrospinning technique. The effective stabilization of ZnO oxidation state during electroreduction has been verified via operando Raman spectra and other characterizations. Besides, we also find that the introduction of trace amount of inactive CeO2 can not only suppress the hydrogen evolution reaction (HER), but also greatly enlarge active sites. The catalyst with optimized molar ratio of CeO2 to ZnO exhibits high Faradaic efficiency (FE) of 90.00 % for CO at −0.69 V vs reversible hydrogen electrode (RHE) in a flow cell. This work suggests stabilization of oxidation state via introduction of secondary metal-oxide by strong interactions between atoms can be improved.

Iron ions induced self-assembly of graphene oxide lubricating coating with self-adapting low friction characteristics

Graphene oxide (GO) is a promising solid lubricant for moving mechanical systems to implement reliable and effective lubrication due to its easy modification and excellent tribological properties. However, obtaining highly dense GO coatings simultaneously with high hardness and extensibility is still a challenge for available self-assembly techniques, and these characteristics are beneficial to tribological properties. Inspired by the advanced abrasion resistance system of mussel byssus threads, a surprisingly simple and versatile metal ions (namely Fe2+ and Fe3+ ions) directed self-assembly strategy has been developed to rapidly fabricate GO coatings. GO as a solid lubricant is highly sensitive to the interface structure and test environment. Consequently, the influence of the valence state of iron ions on the macroscopic tribological properties of GO-based coatings in air, nitrogen gas and vacuum environments are comparatively investigated. The results show that the GO-Fe3+ coating with a highly compact characteristic and unique granular microarchitecture resulting in higher hardness and strain capacity displays a lower friction coefficient and remarkable wear resistance than the GO-Fe2+ coating. Additionally, because water molecules generate strong hydrogen bonding gradually disrupting the ordered layered structure, both GO-Fe2+ and GO-Fe3+ coatings exhibit a higher friction coefficient in air than in nitrogen gas and vacuum.

Magnetic properties of CaCu3-xTi4-yFex+yO12 solid solutions: Valence state of iron ions and metamagnetic phase transitions

CaCu3-xTi4-yFex+yO12 (1 or 3%) solid solutions were synthesized using a solid state method, while 1 or 3 mas. % of iron (natural abundance of isotopes) was added to the stoichiometric amount of CaO, CuO and TiO oxides. CaCu3-xTi4-y57Fex+yO12 (3%) sample with a higher 57Fe isotope content was synthesized using the same technology for the detailed investigation by the Mӧssbauer spectroscopy. The structural and microstructural characteristics of calcium copper titanate samples were studied by X-ray diffraction, X-ray fluorescence analysis and scanning electron microscopy techniques. The magnetic properties were studied by Mӧssbauer spectroscopy, electron spin resonance and magnetometry methods. Based on all experimental data we can conclude that Fe ions substitute Ti4+ and Cu2+ positions in octahedral and planar oxygen environment, respectively. Such type of substitution leads to the appearance of three types of iron magnetic centers: divalent Fe2+ in the planar environment and trivalent Fe3+ in the symmetrical and distorted octahedral positions that strongly effects to the magnetic properties of the investigated samples. Most unique magnetic properties including the metamagnetic phase transitions are observed in CaCu3-xTi4-yFex+yO12 (3%) sample where both the significant amount of Fe3+ ions in distorted octahedral position together with Fe2+ are present.

General Strategies to Construct Highly Efficient Sensing Interfaces for Metal Ions Detection from the Perspective of Catalysis.

Constructing high-effective electrode sensing interfaces has been considered an effective method for electrochemical detection toward heavy metal ions (HMIs). However, most research has been devoted to enhancing the stripping currents of HMIs by simply improving the adsorptive capacity and conductivity of the electrode modified materials, while lacking theoretical guidelines in fabricating catalytic sensing interfaces. Besides, the understanding of detection mechanisms is quite unscientific from the perspective of catalysis. This perspective summarizes five general strategies in designing highly efficient sensing interfaces in the recent five years, including modulating crystal phases, orientations and planes, defect engineering, ionic valence state cycle engineering, adsorption in situ catalysis strategy, and construction of atomic level catalytic active sites. What's more, the catalytic mechanisms for improving the signals of HMIs, such as boosting the electron transfer rates and conversion rates, lowering the energy barriers, etc., are introduced and emphasized. This study has a great significance in directionally controlling functionalized electrochemical sensors to achieve excellent sensitivity and selectivity in detecting environmental pollutants from the view of catalysis, and it also brings enlightenments and guidance to develop new electroanalytical methods.