Depletion Region Research Articles

Temperature-controlled tunable metamaterial absorber based on vanadium dioxide with ‘switch’ functionality

The performance of traditional absorbers is fixed in a specific frequency or wavelength range, and the actual application often needs to adjust the absorption characteristics according to different scenarios or needs. A THz wave modulator, utilizing temperature-controlled phase change materials, is proposed to address the limitation of absorbers’ inability to adjust to external environments. Tunable absorber is a kind of device with dynamic regulation ability, and its absorption characteristics can be adjusted and optimized according to external conditions. This modulator enables the switch function of metamaterial absorbers, comprising a gold reflector layer, a silicon dioxide depletion layer, and a vanadium dioxide pattern layer. Simulations via finite element method reveal two nearly perfect absorption peaks, up to 99.99%. As temperature rises, absorption rates increase, stabilizing gradually after vanadium dioxide transitions from insulating to metallic phase. With a modulation depth of 98.49%, the absorber achieves adjustability. It enables polarization-independent absorption of electromagnetic waves, exhibiting strong absorption at incident angles from 0° to 50° for TE and TM waves. Leveraging vanadium dioxide’s phase change characteristics, the absorber can switch between ON and OFF states based on temperature changes, promising potential applications in light modulation and THz absorbers.

Wetting Effect Induced Depletion and Adsorption Layers: Diffuse Interface Perspective.

When a multi-component fluid contacts arigid solid substrate, the van der Waals interaction between fluids and substrate induces a depletion/adsorption layer depending on the intrinsic wettability of the system. In this study, we investigate the depletion/adsorption behaviors of A-B fluid system. We derive analytical expressions for the equilibrium layer thickness and the equilibrium composition distribution near the solid wall, based on the theories of de Gennes and Cahn. Our derivation is verified through phase-field simulations, wherein the substrate wettability, A-B interfacial tension, and temperature are systematically varied. Our findings underscore two pivotal mechanisms governing the equilibrium layer thickness. With an increase in the wall free energy, the substrate wettability dominates the layer formation, aligning with de Gennes' theory. When the interfacial tension increases, or temperature rises, the layer formation is determined by the A-B interactions, obeying Cahn's theory. Additionally, we extend our study to non-equilibrium systems where the initial composition deviates from the binodal line. Notably, macroscopic depletion/adsorption layers form on the substrate, which are significantly thicker than the equilibrium microscopic layers. This macroscopic layer formation is attributed to the interplay of phase separation and Ostwald ripening. We anticipate that the present finding could deepen our knowledge on the depletion/adsorption behaviors of immiscible fluids.

DC current–voltage and impedance spectroscopy characterization of nCdS/pZnTe HJ

This paper describes the electrical and dielectric behavior of the nCdS/pZnTe HJ by current–voltage, capacitance–voltage characteristics, and impedance spectroscopy in a temperature interval 220–350 K. A microcrystalline p-ZnTe layer and n-CdS were grown on glass/ZnO substrate by closed space sublimation method. As frontal contact to CdS, the transparent ZnO and as a back contact to ZnTe, silver conductive paste (Ag) treated at 50 °C in vacuum were used. The current–voltage results of nCdS/pZnTe HJ show a rectifying behavior. The junction ideality factor, barrier height, and series resistance values were extracted from the rectifying curves at different temperatures. The built-in voltage, carrier concentration and depletion width were obtained from the capacitance–voltage measurements. Analysis of the J–V–T and C–V–T characteristics shows that the thermionic emission and recombination current flow mechanisms dominate in the nCdS/pZnTe HJ. The dielectric study reveals that the experimental values of the AC conductivity, dielectric constant, dielectric loss, the imaginary part of the electric modulus are found to be very sensitive to frequency and temperature. The dielectric constant and dielectric loss are observed to be high at the low frequency region. The increase in the values of electric modulus with the frequency implies an increase in the interfacial polarization at the interface of nCdS/pZnTe HJ. Jonscher’s universal power law shows that with increasing frequency, AC conductivity increased. The results conductivity show that the ionic conductivity and interfacial polarization are the main parameters affecting the dielectric properties of the device when the temperature changes.

Electrical manipulation of telecom color centers in silicon

Silicon color centers have recently emerged as promising candidates for commercial quantum technology, yet their interaction with electric fields has yet to be investigated. In this paper, we demonstrate electrical manipulation of telecom silicon color centers by implementing novel lateral electrical diodes with an integrated G center ensemble in a commercial silicon on insulator wafer. The ensemble optical response is characterized under application of a reverse-biased DC electric field, observing both 100% modulation of fluorescence signal, and wavelength redshift of approximately 1.24 ± 0.08 GHz/V above a threshold voltage. Finally, we use G center fluorescence to directly image the electric field distribution within the devices, obtaining insight into the spatial and voltage-dependent variation of the junction depletion region and the associated mediating effects on the ensemble. Strong correlation between emitter-field coupling and generated photocurrent is observed. Our demonstration enables electrical control and stabilization of semiconductor quantum emitters.

Plasma sprayed duplex ytterbium disilicate/monosilicate EBCs and the transformation from ytterbia to ytterbium monosilicate during burner rig testing

Environmental Barrier Coating systems (EBCs) were thermally cycled in a burner rig test facility. Yb2Si2O7 (YbDS) layer was deposited by air plasma spraying while two suspension plasma sprayed Yb2SiO5 (YbMS) microstructures were evaluated in duplex (YbDS/YbMS) systems: columnar and segmentation cracked. EBCs underwent 2000 cycles at a surface temperature of 1300 °C without signs of delamination failure. A porous YbMS layer formed at the base of intercolumnar gaps and segmentation cracks in the duplex systems, presumably due to reactions with entrapped water vapor. Furthermore, Yb2O3 depletion zones were evident at both the surface and YbDS/YbMS interface of the duplex EBCs.

Ultraviolet electroluminescence with electrically tunable colour from epitaxial n-(0001)ZnO/p-(0001)GaN light-emitting diodes

Pulsed laser deposition technique is used to grow unintentionally n-type (0001)ZnO layers with high crystalline and morphological qualities on p-type (0001)GaN/sapphire templates. Electroluminescent devices are fabricated on these p–n heterojunctions. Oxygen pressure during growth has been found to influence strongly the crystalline and defect properties of the grown layers, which affect not only the current–voltage characteristics but also the emission properties of the electroluminescent devices. It has been observed that the electroluminescence (EL) spectra have both defects related visible and band-edge related ultraviolet (UV) transition features stemming from both GaN and ZnO sides. The study reveals that UV to visible EL intensity ratio maximizes at an optimum oxygen pressure. The relative contribution of EL originating from ZnO and GaN sides can be tuned by the applied bias, as the bias can control the depletion width and hence the carrier interdiffusion across the junction. This finding thus offers a scope to electrically tune the colour of the emitted light in these devices.

Direct Determination of Carrier Parameters in Indium Tin Oxide Nanocrystals.

We develop here a comprehensive experimental approach to independently determine charge carrier parameters, namely, carrier density and mass, in plasmonic indium tin oxide nanocrystals. Typically, in plasmonic nanocrystals, only the ratio between these two parameters is accessible through optical absorption experiments. The multitechnique methodology proposed here combines single particle and ensemble optical and magneto-optical spectroscopies, also using 119Sn solid-state nuclear magnetic resonance spectroscopy to probe the surface depletion layer. Our methodology overcomes the limitations of standard fitting approaches based on absorption spectroscopy and ultimately gives access to carrier effective mass directly on the NCs, discarding the use of literature value based on bulk or thin film materials. We found that mass values depart appreciably from those measured on thin films; consequently, we found carrier density values that are different from reported literature values for similar systems. The effective mass was found to deviate from the parabolic approximation at a high carrier density. Finally, the dopant activation and defect diagram for ITO NCs for tin doping between 2.5 and 15% are determined. This approach can be generalized to other plasmonic heavily doped semiconductor nanostructures and represents, to the best of our knowledge, the only method to date to characterize the full Drude parameter space of 0-D nanosystems.

Directly electrospun copper ferrite CuFe2O4 nanofiber-based for gas classification

The cross-response is a considerable primary challenge of gas sensors based on semiconducting metal oxide (SMO), especially in detecting and classifying gases with comparable properties. In this work, the copper ferrite (CuFe2O4, CFO) nanofibers (NFs)-based sensors were straightforwardly synthesised by electrospinning technique. The morphology of the CFO NFs was observed using scanning electron microscopy (SEM), which revealed a rough surface with a diameter of approximately 80 nm. The composition of the fiber was confirmed by energy dispersive spectroscopy (EDS), which showed the fiber’s chemical elements to include Cu, Fe, and O. The microstructural characteristics of the CFO NFs were analysed using x-ray diffraction (XRD) and Raman spectroscopy, confirming the characteristic peaks of the CFO phase. The gas sensing characteristics of CFO-based sensors have been examined to 25−200 ppm of various gases of (CH3)2CO, CH3CH2OH, NH3, and H2 at a function of working temperature of 350−450 °C. The gas-sensing mechanism of the sensor based on CFO NFs is explained by the surface depletion layer and the grain boundary model. The successful categorisation of these gases into distinct groups was realised, indicating that the issue of cross-response caused by interfering gases was effectively addressed with the aid of an artificial intelligence algorithm.

In-situ growth of vertically stacked 2D SnS2/SnS heterostructure for highly sensitive and rapid room temperature NO2 gas sensor

Construction of 2D heterostructure is a potential strategy to improve the sensing performance of 2D layered materials owing to the high-quality of heterointerfaces. This attributed to the remarkable electronic band alignment between the constituent materials and their distinctive characteristics. Woefully, very limited attempts have been taken to investigate the effect of 2D heterointerface for gas sensing applications. Here, the SnS2/SnS heterostructure is fabricated on a SiO2/Si substrate using a single-step atmospheric chemical vapor deposition technique for room temperature NO2 sensing. The heterostructure has imparted a 1.3 times enhancement in response (S(%)), with ultra-fast response (τres) and recovery time (τrec) of 32 s and 382 s, towards 40 ppm of NO2 at 30 °C. Moreover, the impact of humidity on the sensing performance of SnS2/SnS has also been studied, confirming its negligible effect on relative humidity. Additionally, it also demonstrates a remarkable stability of 93% over a period of 40 days. Besides, due to strong adsorption energy of SnS2 (1914 meV) and SnS (600 meV) towards NO2 endorses the reaction kinetic parameters validated by the gas adsorption/desorption isotherm analysis of heterostructure. The substantial interface contacts between the SnS2/SnS heterostructure facilities the fermi-level mediated charge transfer, contributing significantly towards the improvement in sensing performance. Therefore, the formation of hierarchical 2D heterostructure with electron depletion layer can be considered as a conducive way for the future development low-powered gas sensor.

Photoelectrochemical properties of self-powered corundum-structured Ga2O3 nanorod array/fluorine-doped SnO2 photodetectors modulated by precursor concentrations

Herein, corundum-structured Ga2O3 (α-Ga2O3) nanorod array/fluorine-doped SnO2 (FTO) structures have been fabricated by hydrothermal and thermal annealing processes with different precursor concentrations from 0.01 to 0.06 M. The diameter and length of the nanorod arrays are much larger with increasing precursor concentrations due to more nucleation sites and precursor ions participating in the reaction procedures. The optical bandgap decreases from 4.75 to 4.47 eV because of the tensile stress relieving with increasing the precursor concentrations. Based on self-powered photoelectrochemical (PEC) photodetectors, the peak responsivity is improved from ∼0.33 mA W−1 for 0.06 M to ∼1.51 mA W−1 for 0.02 M. Schottky junctions can be formed in PEC cells. More photogenerated carriers can be produced in wider depletion region. From Mott–Schottky plots, the depletion regions become much wider with decreasing the precursor concentrations. Therefore, the enhance responsivity is owing to the wider depletion regions. Due to the reduced possibility of photogenerated holes captured by traps ascribed from fewer green and yellow luminescence defects, smaller charge transfer resistance, and shorter transportation route, the decay time becomes much faster through decreasing the precursor concentrations. Compared with the other self-powered α-Ga2O3-nanorod-array-based PEC photodetectors, it shows the fastest response time (decay time of 0.005 s/0.026 s) simply modulated by precursor concentrations for the first time without employing complex precursors, seed layers or special device designs. Compared with other high-responsivity monoclinic Ga2O3 (β-Ga2O3) self-powered photodetectors, our devices also show comparable response speed with simple control and design. This work provides the realization of fast-speed self-powered Ga2O3 based solar-blind ultraviolet photodetectors by simple modulation processes and design, which is a significant guidance for their applications in warnings, imaging, computing, communication and logic circuit, in the future.

One-dimensional hierarchical core-shell metal oxide semiconductor@WO3 nanocomposites for Ppb-level acetone sensing

Detecting acetone is vital for both environmental safety and human health. However, many existing detection methods suffer from bulky equipment, complex processes, and limited efficiency. Metal oxide semiconductor (MOS) based gas sensors, particularly WO3, have gained attention due to their portability, cost-effectiveness, and sensitivity. In this study, we successfully synthesize a series of 1D hierarchical core-shell metal oxide semiconductor MOS@WO3 structures (MOS: TiO2, WO3, and SnO2) via a hydrothermal method employing self-assembly. Notably, the TiO2@WO3 sensor exhibits an exceptional response value (Ra/Rg = 23.6) at a concentration of 50 ppm for acetone. It also demonstrates a rapid response recovery time (12/35.5 s) and a remarkably low detection limit, as low as 10 ppb (Ra/Rg = 1.29). This exceptional sensing performance is attributed to the large specific surface area, abundant oxygen vacancy, narrow bandgap, additional depletion layer of the heterostructure, and the main conduction channel in the shell of TiO2@WO3 NCs. This study not only promotes acetone sensor development but also contributes to innovative layered core-shell material fabrication methodologies.

Study of drain-induced channel effects in vertical GaN junction field-effect transistors

A normally-off vertical gallium nitride (GaN) junction field-effect transistor (JFET) is demonstrated in this work. The device shows an on/off current ratio of 3.6 × 1010, a threshold voltage (V TH) of 1.64 V, and a specific on-resistance (R ON,SP) of 1.87 mΩ·cm2. Drain-induced channel effects were proposed to explain the change in the gate current at different drain voltages. Drain current decline in the output characteristics and the reverse turn-on between drain and source can be explained by effects. A technological computer-aided design was used to simulate the change of the depletion region and confirm the explanation. Detailed analyses of the channel effects provide a reference for the design of novel structures. The characteristics at different temperatures demonstrated the stability of threshold voltage and specific on-resistance, thus indicating the great potential of applications in switching power circuits of vertical GaN JFETs.

Deterioration of Li-doped phenanthroline-based charge generation layer for tandem organic light-emitting diodes

Understanding the deterioration of the charge generation layer (CGL) is an uprising issue for efficient and stable tandem organic light-emitting diodes. Here, we comprehensively investigated the change in the electrical characteristics of Li-doped CGLs according to different stress conditions and compared the stability of Li diffusion in two phenanthroline-based electron transport materials. Through current density–voltage and capacitance-frequency measurements, it was revealed that electrical stress and thermal stress affect CGL’s electrical properties differently. Moreover, the exponential trap distribution model analysis informed that the Li diffusion is expedited toward narrowing depletion width in the CGL. Diffusion of Li and thermal effect to the diffusion was experimentally observed by X-ray photoelectron spectroscopy (XPS) depth profiling. We also evaluated variations in the operating voltage of tandem devices that differed only in nCGL. Overall, Li diffusion occurs more favorably in sparse Bphen film with weak binding energy rather than closely packed BPPB film with strong binding energy, which highlights that atomic geometry and morphological characteristics are crucial for the stability of tandem devices.

Machine learning techniques for estimation of Pc5 geomagnetic pulsations observed at geostationary orbits during solar cycle 23

Pc5 geomagnetic pulsations can accelerate electrons in the radiation belts, which can pose adverse threats to both astronauts and satellites in space. The estimation of Pc5 waves in space is crucial to radiation belt dynamics studies and will help mitigate these challenges. Here, we explore the advantages of the Feed-forward Neural Network (FFNN) and Random Forest (RF) algorithm for effective estimation of Pc5 geomagnetic pulsations observed in space at geostationary orbit during solar cycle 23. The dataset used in this study is the vector magnetic field measurements retrieved from the Geostationary Operational Environmental Satellite-10 (GOES-10) and the solar wind parameters: Bz and Vx component of the solar wind in the Geocentric Solar Ecliptic (GSE) coordinate system, proton density, flow pressure, and plasma beta obtained from the OMNI Web database during part of solar cycle 23. Pc5 geomagnetic pulsations were extracted from the toroidal component of the magnetic field time series using a bandpass Butterworth filter. The continuous wavelet transform (CWT) was utilized to study the characteristics of the extracted wave in the time-frequency domain for its validation. The validated Pc5 events were used as the target in the model's development, with the solar wind parameters as the inputs. In addition to the solar wind parameters, we included an attribute of the magnetic field time series as an input variable in the model. The dataset is carefully divided to ensure effective training and testing of the models. Finally, we trained both models using the same inputs and targets and explored their estimation abilities. The model was tested during the maximum, descending, and minimum phases of solar cycle 23. Both the FFNN and RF models have a similar estimation, with average cross-correlation score (R) values of 0.74 and 0.73 and corresponding average root mean squared error (RMSEs) of 0.16 nT and 0.67 nT, respectively. The model was deployed to investigate the response of Pc5 waves during three storm days in each testing year. The machine learning (ML) model outputs showed good coherence with the observed Pc5 waves. To validate the models, we studied the correlation between the estimated Pc5 events with the Kp index, and a good correlation was seen to exist between both events. This validates the good performance of the developed models. This work will aid in the study of radiation belt dynamics and the construction of electron depletion regions in the radiation belt.

Heterojunction polarization enhancement and shielding for AlGaN-based solar-blind ultraviolet avalanche detectors.

AlGaN-based solar-blind ultraviolet avalanche detectors have huge potentials in the fields of corona discharge monitoring, biological imaging, etc. Here, we study the impact of the heterojunction polarization-related effects on the AlGaN-based solar-blind ultraviolet avalanche detectors. Our work confirms that the polarization heterojunction is beneficial to reducing avalanche bias and lifting avalanche gain by improving the electric field in the depletion region, while the polarization-induced fixed charges will lead to a redistribution of the electrons, in turn shielding the charges and weakening the electric field enhancement effect. This shielding effect will need external bias to eliminate, and that is why the polarization heterojunction cannot work at relatively low bias but has an enhancement effect at high bias. Controlling the doping level between the hetero-interface can affect the shielding effect. An unintentionally doped polarization heterojunction can effectively reduce the shielding effect, thus reducing the avalanche bias. The conclusions also hold true for the negative polarization regime. We believe our findings can provide some useful insights for the design of the AlGaN-based solar-blind ultraviolet detectors.

A deep catalogue of protein-coding variation in 983,578 individuals.

Rare coding variants that significantly impact function provide insights into the biology of a gene1-3. However, ascertaining their frequency requires large sample sizes4-8. Here, we present a catalogue of human protein-coding variation, derived from exome sequencing of 983,578 individuals across diverse populations. 23% of the Regeneron Genetics Center Million Exome data (RGC-ME) comes from non-European individuals of African, East Asian, Indigenous American, Middle Eastern, and South Asian ancestry. This catalogue includes over 10.4 million missense and 1.1 million predicted loss-of-function (pLOF) variants. We identify individuals with rare biallelic pLOF variants in 4,848 genes, 1,751 of which have not been previously reported. From precise quantitative estimates of selection against heterozygous loss-of-function, we identify 3,988 loss-of-function intolerant genes, including 86 that were previously assessed as tolerant and 1,153 lacking established disease annotation. We also define regions of missense depletion at high resolution. Notably, 1,482 genes have regions depleted of missense variants despite being tolerant to pLOF variants. Finally, we estimate that 3% of individuals have a clinically actionable genetic variant, and that 11,773 variants reported in ClinVar with unknown significance are likely to be deleterious cryptic splice sites. To facilitate variant interpretation and genetics-informed precision medicine, we make this important resource of coding variation from the RGC-ME accessible via a public variant allele frequency browser.

On-Chip Annealing Using Embedded Micro-Heater for Highly Sensitive and Selective Gas Detection.

The demand for gas sensing systems that enable fast and precise gas recognition is growing rapidly. However, substantial challenges arise from the complex fabrication process of sensor arrays, time-consuming data transmission to an external processor, and high energy consumption in multi-stage data processing. In this study, a gas sensing system using on-chip annealing for fast and power-efficient gas detection is proposed. By utilizing a micro-heater embedded in the gas sensor, the sensing material of adjacent sensors in the same substrate can be easily varied without further fabrication steps. The response to oxidizing gas is constrained in metal oxide (MOX) sensing material with small grain sizes, as the depletion width of grain cannot extend beyond the grain size during the gas reaction. On the other hand, the response to reducing gases and humidity, which decrease the depletion width, is less affected by grain sizes. A readout circuit integrating a differential amplifier and dual FET-type gas sensors effectively emphasizes the response to oxidizing gases by canceling the response to reducing gases and humidity. The selective on-chip annealing method is applicable to various MOX sensing materials, demonstrating its potential for application in commercial fields due to its simplicity and expandability.

Rare-earth element (REE) remobilization and fractionation in bauxite zones from sedimentary kaolin deposits, western Georgia (USA), Upper Coastal Plain

Rare-earth elements (REE) are critical minerals that are indispensable for high-tech products and technologies. Significant efforts have been focused on the exploration and identification of new and domestic reserves of REE. This study reports geochemical and mineralogical occurrences of accumulated REE with significant fractions of ion-adsorption clays (IAC) within bauxite-kaolin ore, hosted within sedimentary strata. This deposit type can be found throughout portions of Georgia and eastern Alabama (USA) in the Southeast Upper Coastal Plain. These deposits were developed by high degrees of chemical weathering of older, kaolinite-rich sedimentary strata. Several major changes in whole rock mineralogy and geochemistry occurred, leading to the development of zones of REE depletion, fractionation, and accumulation. Depletions of REE in the bauxite zone were significant, with whole rock contents of ∼50% ΣREE relative to average upper continental crust (UCC). Fractionated REE were observed by low La/YbN values (La/YbN = 0.2) due to depletion in LREE (<40% UCC) with concomitant HREE retention (∼1.1–1.3 times UCC). Strongly positive Ce/Ce* anomalies (Ce/Ce* = 1.3), very low ion-exchangeable Ce contents (Ce/LREE = 0.1), and low solubility of Ce (0.9–1.2%) under reducing conditions compared to all other LREE (4.5–9.9%) were further observed. These characteristics were strong indications of REE fractionation that occurred during formation of the bauxite zone. Underlying the bauxite zone, accumulations of the remobilized REE were substantial. At the base of the lower kaolin zone, elevated ion-exchangeable REE contents were notable (11–33% for total REE), and more specifically 11–12% for LREE, ∼28% for ΣTb-Lu, and ∼ 33% for Y. The elevated ion-exchangeable contents coincided with whole rock contents that were ∼ 250% ΣREE relative to UCC. These REE accumulations occurred within organic-rich strata at the base of the section. This setting represents a significant difference relative to the REE accumulations in profiles for the granite-regolith deposit type. These findings highlighted the movement of dissolved REE, accumulation as sorbed species, as well as the potential role that organic ligands play during REE precipitation and sorption processes. These results permit consideration for further research into REE occurrences in clay deposits of sedimentary origin, which have been underexplored compared to granite-regolith REE deposits.

Model Parameters and Degradation Mechanism Analysis of Indium Phosphide Hetero-Junction Bipolar Transistors Exposed to Proton Irradiation

The degradation properties of Indium phosphide hetero-junction bipolar transistors (InP HBTs) under proton irradiation are studied and modelled using a compact model for pre-irradiation, post-irradiation, and post-annealing. The variation rates of the model parameters, such as the base–emitter saturation current (ISE) and ideality factor in the ideal region (NE) in the forward Gummel characteristics, the zero-biased capacitance (Cje) and the grading factor (Mjer) in the BE junction capacitance, and the transit time parameter in the base region (Tfb), are analysed to delve into the degradation mechanism induced by proton irradiation. The displacement damage, induced by proton irradiation in the space charge region of the base–emitter junction and in the quasi-neutral bulk base region, is found to be responsible for the decrease in current gain and cut-off frequency. After annealing, the variation rates of the parameters decrease significantly compared to post-irradiation. This suggests that the recombination of unstable defects leads to a slight recovery in the degradation characteristics of InP HBTs after a period of annealing.

Mesoporous Electrocatalysts with p-n Heterojunctions for Efficient Electroreduction of CO2 and N2 to Urea.

The electrocatalytic synthesis of high-value-added urea by activating N2 and CO2 is a green synthesis technology that has achieved carbon neutrality. However, the chemical adsorption and C-N coupling ability of N2 and CO2 on the surface of the catalyst are generally poor, greatly limiting the improvement of electrocatalytic activity and selectivity in electrocatalytic urea synthesis. Herein, novel hierarchical mesoporous CeO2/Co3O4 heterostructures are fabricated, and at an ultralow applied voltage of -0.2 V, the urea yield rate reaches 5.81 mmol g-1 h-1, with a corresponding Faraday efficiency of 30.05%. The hierarchical mesoporous material effectively reduces the mass transfer resistance of reactants and intermediates, making it easier for them to access active centers. The emerging space-charge regions at the heterointerface generate local electrophilic and nucleophilic regions, facilitating CO2 targeted adsorption in the electrophilic region and activation to produce *CO intermediates and N2 targeted adsorption in the nucleophilic region and activation to generate *N ═ N* intermediates. Then, the electrons in the σ orbitals of *N ═ N* intermediates can be easily accepted by the empty eg orbitals of Co3+ in CeO2/Co3O4, which presents a low-spin state (LS: t2g6eg0). Subsequently, *CO couples with *N ═ N* to produce the key intermediate *NCON*. Interestingly, it was discovered through in situ Raman spectroscopy that the CeO2/Co3O4 catalyst has a reversible spinel structure before and after the electrocatalytic reaction, which is due to the surface reconstruction of the catalyst during the electrocatalytic reaction process, producing amorphous active cobalt oxides, which is beneficial for improving electrocatalytic activity.