Ion Diffusion Research Articles

Oxidation behavior and corrosion resistance of CoCrFeNi high entropy alloy compared with FeCoNi medium entropy alloy

The entropy-based alloy with excellent oxidation and corrosion resistance is of great significance for practical applications in high-temperature environments. Thus, the difference in anti-oxidation property and corrosion behavior of FeCoNi MEA and CoCrFeNi HEA in a simulated marine environment was studied via a series of measurements. The results reveal that the HEA possesses superior oxidation and corrosion resistance in comparison with the MEA, which can be demonstrated by comparing the oxidation rate and thickness of oxide layer, corrosion current density (icorr) as well as corrosion morphology after polarization. The microstructure and composition of the oxide layer are the primary reasons resulting in the difference of oxidation and corrosion behaviors of the two alloys. The oxide layer with a compact, even and intact structure is produced on the HEA surface, which hinders the diffusion of detrimental ions and oxygen, whereas the loose, porous and cracked oxide layer consisting of inner Fe3O4 and outer CoO exhibits poor protection against corrosion and oxidation of the MEA. For the HEA, the preferential combination of Cr and O elements forms the protective oxide of Cr2O3, effectively enhancing corrosion resistance and inhibiting oxidation. However, the low protective CoO and relatively active Fe3O4 grow on the MEA surface, which cannot provide a good barrier to restrain oxidation and corrosion.

Novel self-healing glass-like CexOY film on a Flash-PEO coated AZ31B Mg alloy.

The aim of this work is to develop a glass-like CexOy coating to seal the pores of a Flash-PEO coated AZ31B Mg alloy and simultaneously provide smart self-healing corrosion protection. The cerium sol was synthesized using cerium acetate as main precursor by sol-gel method. SEM micrographs revealed that upon cerium sol deposition, the pores of the oxide coating were effectively sealed, resulting in a double-layer coating system and thereby in a big reservoir of cerium ions (Ce3+/Ce4+). The glassy character of the cerium coating, confirmed by X-Ray diffraction, implies that cerium exists in Ce3+ and Ce4+ ionic states enclosed in a high internal energy structure which facilitate the diffusion of cerium ions to active cathodic zone. Electrochemical Impedance Spectroscopy (EIS), X-Ray Diffraction (XRD), and Raman spectroscopy were used to explore the active corrosion protection of the CexOy sol-gel coating. The corrosion inhibition mechanism involves the migration of cerium ions and the precipitation of insoluble-crystalline cerium compounds (CeO2). The coating demonstrated self-healing properties, presenting a promising alternative to traditional chrome conversion coatings (CCC).

A PEDOT based graft copolymer with enhanced electronic stability.

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) remains the most investigated conjugated polymer in bioelectronics, due to its biocompatibility, high conductivity, and commercial availability. Despite these advantages, it suffers from structural and electronic instability, associated with the PSS component. Here, a graft copolymer based on ionised sulfonic modified PEDOT, poly(EDOTS-g-EDOT), was electrochemically synthesised with demonstrated structural and electronic stability and enhanced electrochemical performance. The graft copolymer was insoluble in water without crosslinking, and exhibited enhanced ion diffusion upon electrochemical switching, as revealed by its volumetric capacitance (159 ± 8 F cm-3), which was significantly higher than that of spin-coated PEDOT:PSS films (41 ± 5 F cm-3). Similarly, its performance as an active channel material in organic electrochemical transistors (OECTs) was superior to the spin-coated PEDOT:PSS, as shown for instance by its high normalised transconductance (273 ± 79 S cm-1) and a significantly high ION/IOFF ratio (19 345 ± 1205). Its short- and long-term electronic stability were also confirmed with no drop in its output drain current, despite its high swelling degree. In contrast, the spin-coated PEDOT:PSS experienced a significant deterioration in its performance over the same operational time. The facile synthesis and improved performance of poly(EDOTS-g-EDOT) highlight the importance of innovative material design in overcoming existing operational shortcomings in electronic devices.

Coordination and diffusion in glyoxal-based electrolytes for potassium-ion batteries.

Glyoxal-based electrolytes have been identified as promising for potassium-ion batteries (PIBs). Here we investigate the properties of electrolytes containing bis(fluorosulfonyl)imide (KFSI) in 1,1,2,2-tetra-ethoxy-ethane (tetra-ethyl-glyoxal, TEG) using density functional theory (DFT) calculations, Raman spectroscopy, and impedance spectroscopy. The coordination and configuration of the complexes possible to arise from coordination of the K+ ions by FSI and TEG were investigated both from an energetic point of view as well as qualitatively determined via comparing experimental and artificial Raman spectra. Overall, the K+ coordination depends heavily on the electrolyte composition with contributions both from FSI and TEG. Energetically the coordination by both the trans FSI anion conformer and the TEG solvent with four z-chain conformation is preferrable. From the spectroscopy we find that at lower concentrations, the predominant coordination is by TEG, whereas at higher concentrations, K+ is coordinated mostly by FSI. Concerning the diffusion of ions, investigated by impedance spectroscopy, show that the diffusion of the potassium salt is faster as compared to lithium and sodium salts in comparable electrolytes.

Multifunctional Power Generators beyond Moisture Limitation

AbstractThe moisture‐enabled electricity generators (MEGs) represent an appealing clean power strategy within the realm of hydrovoltaic technology. However, their stable operation under all‐weather conditions is still challengeable due to the effect of ambient humidity. Herein, a self‐water‐storage MEGs with multifunctionality was developed. Gel textiles are employed as the proton‐release layer, while graphite fibers loaded with tin‐bismuth alloy liquid metal serve as water‐storing electrode. The gel textiles absorb water permeating down from the electrodes, releasing protons, which then react with the active electrode to enhance output performance. The experiment demonstrates that a device can generate a voltage of 0.55 V and a current of 7.08 μA after water storage, with a maximum power density of 1.14 μW·cm‐². The device's performance output can remain stable within a wide temperature range. The experiment confirms that the electrical output of the device originates from ionic diffusion, while density functional theory (DFT) and molecular dynamics (MD) calculations reveal the importance of the strong hydrolysis ability of the polymer and the high adsorption energy of the liquid metal for H3O+ on the output performance of the device. Furthermore, the integrated device has demonstrated effective applications in driving microelectronic devices, charging capacitors and, self‐powered health monitoring.

Current‐Adaptive Li‐Ion Storage Mechanism in High‐Rate Conversion‐Alloying Metal Chalcogenides

AbstractBeyond the high theoretical capacity, conversion‐alloying metal chalcogenides (CAMCs) exhibit exceptional high‐rate performance as Li‐ion battery electrodes. However, the inherent origin of the high‐rate performance remains elusive, especially given the lower intrinsic conductivity of CAMCs. Here, the correlation between phase evolution and charge transport dynamics in fully activated CAMCs is systematically investigated, elucidating a current‐adaptive Li‐ion storage mechanism to explain the anomalous high‐rate performance. Briefly, the deconversion reaction manipulated by ion diffusion acts as a “regulator” to adaptively modulate the transition from metal (high electronic conductivity) and lithium chalcogenides (high ionic conductivity) to CAMCs, thus removing the charge transport bottleneck without affecting the formation of the metal feedstock required for the alloying reaction. On this basis, the high capacity can be maintained at high rates through a “fading‐free” alloying reaction. This study offers a novel perspective for the design of high‐rate electrode materials.

Ultrafast and Reversible Superwettability Switching of 3D Graphene Foams via Solvent-Exclusive Plasma Treatments.

For highly active electron transfer and ion diffusion, controlling the surface wettability of electrically and thermally conductive 3D graphene foams (3D GFs) is required. Here, we present ultrasimple and rapid superwettability switching of 3D GFs in a reversible and reproducible manner, mediated by solvent-exclusive microwave arcs. As the 3D GFs are prepared with vapors of nonpolar acetone or polar water exclusively, short microwave radiation (≤10 s) leads to plasma hotspot-mediated production of methyl and hydroxyl radicals, respectively. Upon immediate radical chemisorption, the 3D surfaces become either superhydrophobic (water contact angle = ∼170°) or superhydrophilic (∼0°), and interestingly, the wettability transition can be repeated many times due to the facile exchange between previously chemisorbed and newly introduced radicals via the formation of methanol-like intermediates. When 3D GFs of different surficial polarities are incorporated into electric double-layer capacitors with nonpolar ionic liquids or polar aqueous electrolytes, the polarity matching between graphene surfaces and electrolytes results in ≥548.0 times higher capacitance compared to its mismatching at ≥0.5 A g-1, demonstrating the significance of wettability-controlled 3D GFs.

MXene Supported Electrodeposition Engineering of Layer Double Hydroxide for Alkaline Zinc Batteries.

The main challenges faced by aqueous rechargeable nickel-zinc batteries are their comparatively low energy density and poor cycling stability. Moreover, the preparation procedures of these cathodes are complex and not easily scalable. Herein, we utilized MXenetoimprove the electrodeposition preparation of NiCo layered double hydroxides (LDH). Benefiting from the improved interfacial contact between nickel foam (NF) and platting solution and the enhanced ionic conductivity of platting product based on MXene additives, the resulting binder-free NiCo LDH electrode can achieve ultrahigh areal loading (~65 mg cm-2) with abundant active surface for redox reactions and maintained short transport pathway for ion diffusion and charge transfer. Furthermore, the as-fabricated alkaline NiCo LDH-based battery delivers high discharge capacity, up to 20.2 mAh cm-2 (311 mAh g-1), accompanied by remarkable rate performance (9.6 mAh cm-2 or 148 mAh g-1 at 120 mA cm-2). Due to the high structural and chemical stability of MXenes/LDH-based electrode, excellent cycling life can also be achieved with 88.6% capacity retention after 10000 cycles. In addition, ultrahigh areal energy density (31.2 mWh cm-2) and gravimetric energy density (465 Wh kg-1) can be simultaneously achieved. This work has inspired the design of advanced cathode materials to develop high-performance aqueous zinc batteries.

MXene Supported Electrodeposition Engineering of Layer Double Hydroxide for Alkaline Zinc Batteries

The main challenges faced by aqueous rechargeable nickel‐zinc batteries are their comparatively low energy density and poor cycling stability. Moreover, the preparation procedures of these cathodes are complex and not easily scalable. Herein, we utilized MXene to improve the electrodeposition preparation of NiCo layered double hydroxides (LDH). Benefiting from the improved interfacial contact between nickel foam (NF) and platting solution and the enhanced ionic conductivity of platting product based on MXene additives, the resulting binder‐free NiCo LDH electrode can achieve ultrahigh areal loading (~65 mg cm‐2) with abundant active surface for redox reactions and maintained short transport pathway for ion diffusion and charge transfer. Furthermore, the as‐fabricated alkaline NiCo LDH‐based battery delivers high discharge capacity, up to 20.2 mAh cm‐2 (311 mAh g‐1), accompanied by remarkable rate performance (9.6 mAh cm‐2 or 148 mAh g‐1 at 120 mA cm‐2). Due to the high structural and chemical stability of MXenes/LDH‐based electrode, excellent cycling life can also be achieved with 88.6% capacity retention after 10000 cycles. In addition, ultrahigh areal energy density (31.2 mWh cm‐2) and gravimetric energy density (465 Wh kg‐1) can be simultaneously achieved. This work has inspired the design of advanced cathode materials to develop high‐performance aqueous zinc batteries.

Effects of MgO on the fibre spinnability, mechanical properties and acid resistance of simulated Martian soil

The ultimate goal of Mars exploration is to construct a Mars base. In particular, it is necessary to prepare fibres by using Martian soil as a raw material. High-strength "Martian glass fibres" can be used to reinforce composite materials to meet the requirements of high-strength functional materials in base construction. Owing to the wide variation in MgO content in Martian soil, in this study, the effects of MgO on the structure, strength and acid resistance of "Martian glass and glass fibres" were investigated. The preparation conditions and mechanical properties of simulated Martian soil fibre (SMSF) were studied via DSC, XRD, Raman, NMR, FT-IR and high-temperature rotational viscometry. The corrosion behaviour of MgO-SMSF in H2SO4 solution was subsequently studied via SEM/EDS. The results showed that MgO reduces the spinnability window and prevents the fibres from stretching continuously, and a threshold appears to exist at 10.89 % MgO. The viscosity of the melt decreased significantly, and the crystallization trend increased with MgO above the threshold. The fibre tensile strength showed a nonlinear relationship with a 22.85 % increase in the fibre tensile strength at 9.24 % MgO. SEM/EDS revealed that the surface of the SMSF formed a gel layer, and the mass retention of the MgO-SMSF in the H2SO4 solution reached 90.17 %. The corrosion of SMSF under acidic conditions was controlled by ion diffusion, with Mg+ and Ca+ diffusing to the fibre surface, resulting in nonuniform corrosion. Raman-based statistical structureproperty modelling further explains the impact of MgO-induced structural changes on the tensile strength and elastic modulus, with good agreement between the model predictions and measured values.

Leveraging Ion Pairing and Transport in Localized High-Concentration Electrolytes for Reversible Lithium Metal Anodes at Low Temperatures.

Coulombic efficiency of over 99% is rarely achieved for Li metal anode below -40°C, hindering the practical application of high-energy-density Li metal batteries under extreme conditions. Herein, limiting factors for Li metal reversibility are investigated utilizing ether-based localized high-concentration electrolytes of different solvent-diluent combinations. We find that along with the desolvation barrier, bulk ion transport properties including ionic conductivity, transference number, and diffusivity are also crucial factors for low-temperature Li deposition behavior. Superior Li metal reversibility was observed within the combination of the solvent with moderately weak solvating power and the diluent with minimal viscosity, highlighting the role of ion transport and the necessity for a trade-off with desolvation. The optimized electrolyte composed of lithium bis(fluorosulfonyl)imide, methyl n-propyl ether, and 1,1,2,2-tetrafluoroethyl methyl ether delivers exceptional Coulombic efficiency of 99.34% at -40°C and 98.96% at -60°C under a current density of 0.5 mA cm-2. Furthermore, Li||LiCoO2 (2.7 mAh cm-2) cells demonstrate impressive reversible capacity and cycling stability at these temperatures. This work sheds light on the less-recognized relevance of bulk ion transport to low-temperature performance and provides guidelines for the electrolyte design of Li metal batteries operating in cold environments.

Carbon-Based 3D Architectures as Anodes for Lithium-Ion Battery Systems.

Graphite, with its exceptional cyclic performance, continues to dominate as the preferred anode material for lithium-ion batteries. However as high-energy application gains momentum, there is growing demand for higher capacities that alloying/de alloying and conversion type anode materials can offer. Despite their potential, these materials are plagued by challenges such as volumetric fluctuations, low conductivities, and poor cyclic stability. Carbon nanostructures, on the other hand, show tremendous promise with their low volume expansion, high ion diffusion rates, and excellent conductivity. Nevertheless, their limited areal and volumetric densities restrict their widespread utilization. To address these limitations, various strategies such as doping, composite formation, and structural modification have been proposed. This article provides a succinct overview of carbon nanomaterials and their electrochemical performance as 3D carbon-based anodes, along with a comprehensive analysis of the strategies employed to overcome associated challenges while evaluating their potential prospects in the field.

Covalent triazine framework nanosheets for photo-enhanced uranium extraction

Uranium extraction is the cornerstone of the sustainable development of the nuclear industry. Although a variety of porous framework materials for uranium extraction have been explored over the past few decades, almost all of them have been limited to bulk powder materials. In particular, due to the strong interlayer π-π interaction, the specific recognition sites and photocatalytic active centers of bulk two-dimensional framework materials are severely buried, resulting in the inability to exploit the optimal performance of the materials. In this study, a novel hydroquinone modified covalent triazine frame nanosheets (H-CTF-NSs) is reported for the first time, which is designed for specific extraction and photocatalytic reduction of uranium. The densely distributed hydroquinone and triazine units in the H-CTF-NSs synergistically form high-affinity binding sites, and the ultrathin nanosheets facilitate the exposure of binding sites and catalytically active centers, and accelerate the diffusion of uranyl ions, it is ideally suited as an advanced platform for the selective extraction and efficient reduction of U(VI). Remarkably, H-CTF-NSs demonstrated an unprecedented uranium extraction capacity of 3230.3 mg/g, which is almost 1.71 times that of its bulk counterpart H-CTF, making it one of the best uranium-trapping photocatalysts known to date.

Harnessing Holey MXene/Graphene Oxide Heterostructure to Maximize Ion Channels in Lamellar Film for High-Performance Capacitive Deionization.

2D Ti3C2Tx MXene-based film electrodes with metallic conductivity and high pseudo-capacitance are of considerable interest in cutting-edge research of capacitive deionization (CDI). Further advancement in practical use is however impeded by their intrinsic limitations, e.g., tortuous ion diffusion pathway of layered stacking, vulnerable chemical stability, and swelling-prone nature of hydrophilic MXene nanosheet in aqueous environment. Herein, a nanoporous 2D/2D heterostructure strategy is established to leverage both merits of holey MXene (HMX) and holey graphene oxide (HGO) nanosheets, which optimize ion transport shortcuts, alleviate common restacking issues, and improve film's mechanical and chemical stability. In this design, the nanosized in-plane holes in both handpicked building blocks build up ion diffusion shortcuts in the composite laminates to accelerate the transport and storage of ions. As a direct outcome, the HMX/rHGO films exhibit remarkable desalination capacity of 57.91mg g-1 and long-term stability in 500mgL-1 NaCl solution at 1.2V. Moreover, molecular dynamics simulations and ex situ wide angle X-ray scattering jointly demonstrate that the conductive 2D/2D networks and ultra-short ion diffusion channels play critical roles in the ion intercalation/deintercalation process of HMX/rHGO films. The study paves an alternative design concept of freestanding CDI electrodes with superior ion transport efficiency.

Acid-modified biomass-based N-doped O-rich hierarchical porous carbon as a high-performance electrode for supercapacitors.

In contemporary society, the conversion and efficient utilization of waste biomass and its derivatives are of great significance. Carbonized wood (CW) is an easily accessible and cost-effective green resource, but it has limitations as an electrode material due to its low specific surface area, limited active sites and poor conductivity. Therefore, it is crucial to improve the performance of biomass-based materials by using activation, heteroatom doping and modification methods to enhance the specific surface area and active sites. In this study, we developed acid-modified urea-doped activated carbonized wood (AUACW) with a three-dimensional (3D) porous structure and porosity, achieving a high specific surface area of 1321.3 m2 g-1. In addition, the degree of graphitization (ID/IG = 1.0) provides good conductivity and a large number of active sites, which are conducive to charge transfer and ion diffusion. The increase of nitrogen and oxygen elements enhances the surface wettability of the material and provides additional pseudocapacitance. The specific capacitance of AUACW reaches 435.84 F g-1 at 0.8 A g-1 with a 93.6% capacitance retention after 10 000 cycles in a 1 M KOH electrolyte. More attractively, a symmetrical supercapacitor (SSC) based on AUACW delivers an energy density of 22.61 W h kg-1 at a power density of 533.26 W kg-1. This work demonstrates the promising potential of utilizing waste biomass to develop green and valuable carbon materials for supercapacitors.

Adjusting Ion Diffusion Kinetics of Li Deposition Enabled by an Elastic Porous Melamine Sponge Host for Stable Lithium Metal Anodes.

Lithium (Li) dendritic growth and huge volume expansion seriously hamper Li-metal anode development. Herein, we design a lightweight 3D Li-ion-affinity host enabled by silver (Ag) nanoparticles fully decorating a porous melamine sponge (Ag@PMS) for dendrite-free and high-areal-capacity Li anodes. The compact Ag nanoparticles provide abundant preferred nucleation sites and give the host strong conductivity. Moreover, the high specific surface area and polar groups of the elastic, porous melamine sponge enhance the Li-ion diffusion kinetics, prompting homogeneity of Li deposition and stripping. As expected, the integrated 3D Ag@PMS-Li anode delivered a remarkable electrochemical performance, with a Coulombic efficiency (CE) of 97.14% after 450 cycles at 1 mA cm-2. The symmetric cell showed an ultralong lifespan of 3400 h at 1 mA cm-2 for 1 mAh cm-2. This study provides a facile and cost-effective strategy to design an advanced 3D framework for the preparation of a stable dendrite-free Li metal anode.

Al-Based MOF-Derived Amorphous/Crystalline Heterophase Cobalt Sulfides as High-Performance Supercapacitor Materials.

Transition metal sulfides (TMSs) are promising electrode materials due to their high theoretical specific capacitance, but sluggish charge transfer kinetics and an insufficient number of active sites hamper their applications in supercapacitors. In this work, a self-sacrificial template strategy was employed to construct Al-based MOF-derived metal sulfides with an amorphous/crystalline (a/c) heterophase, in which aluminum, nitrogen, and carbon species were evenly coordinated in the amorphous phase. The metal sulfides a/c-Co(Al)S-1 and a/c-Co(Al)S-2, originating from the CAU-1 and CoAl-MOF on NF as self-sacrificial templates, were investigated as electrode materials, respectively, in which the a/c-Co(Al)S-1 showed a more excellent electrochemical performance. Through acid etching CAU-1 using Co(NO3)2 followed by sulfuration, the a/c-Co(Al)S-1 with a unique 3D network structure was constructed, whose unique architecture expanded the interfacial contact with the electrolyte and provided vast active sites, accelerating the charge transportation and ion diffusion. Notably, the a/c-Co(Al)S-1 displayed a high specific charge of 1791.8 C g-1 at 1 A g-1, satisfactory cycle stability, and good rate capability. The corresponding assembled a/c-Co(Al)S-1//AC device delivered a high energy density of 77.1 Wh kg-1 at 800 W kg-1 and good durability (87.4% capacitance retention over 10 000 cycles).

High-performance flexible asymmetric supercapacitor utilizing hierarchical NiCo2O4 nanosheets supported on porous carbonized Verbena leaves

This study employed three-dimensional porous carbon with high surface area as the conductive substrate for composite electrode materials, aiming to facilitate rapid charge transfer and ion diffusion to increase the specific capacitance of pseudo-capacitive materials. We employed an in-situ hydrothermal method to anchor NiCo2O4 onto the porous carbonized verbena leaves, yielding nanostructured VC@NiCo2O4-8 composite electrode materials. At a current density of 1.0 A g-1, VC@NiCo2O4-8 exhibited a high specific capacitance of up to 2061.8 F g−1 and remarkable cycling stability (with only 7.8 % capacitance loss after 10000 cycles). Additionally, we assembled VC@NiCo2O4-8//VC asymmetric all-solid-state flexible supercapacitors, attaining a significant energy density of 54.0 Wh kg−1 at a power density of 695 W kg−1, while maintaining good flexibility and stability. This study provides a simple and effective method for the design and construction of high-performance electrode materials for flexible energy storage devices.

Tailoring Alkalized and Oxidized V2CTx as Anode Materials for High-Performance Lithium Ion Batteries

V2CTx MXenes have gained considerable attention in lithium ion batteries (LIBs) owing to their special two-dimensional (2D) construction with large lithium storage capability. However, engineering high-capacity V2CTx MXenes is still a great challenge due to the limited interlayer space and poor surface terminations. In view of this, alkalized and oxidized V2CTx MXenes (OA-V2C) are envisaged. SEM characterization confirms the accordion-like layered morphology of OA-V2C. The XPS technique illustrates that undergoing alkalized and oxidized treatment, V2CTX MXene replaces -F and -OH with -O groups, which are more conducive to pseudocapacitive properties as well as Na ion diffusion, providing more active sites for ion storage in OA-V2C. Accordingly, the electrochemical performance of OA-V2C as anode materials for LIBs is evaluated in this work, showing excellent performance with high reversible capacity (601 mAh g−1 at 0.2 A g−1 over 500 cycles), competitive rate performance (222.2 mAh g−1 and 152.8 mAh g−1 at 2 A g−1 and 5 A g−1), as well as durable long-term cycling property (252 mAh g−1 at 5 A g−1 undergoing 5000 cycles). It is noted that the intercalation of Na+ ions and oxidation co-modification greatly reduces F surface termination and concurrently increases interlayer spacing in OA-V2C, significantly expediting ion/electron transportation and providing an efficient way to maximize the performance of MXenes in LIBs. This innovative refinement methodology paves the way for building high-performance V2CTx MXenes anode materials in LIBs.

Influence of Oxygen Vacancies Introduced via Acceptor (Gadolinium) Doping to the Pseudocapacitive Properties of Nano-Sized Cerium Oxide.

The voluntary introduction of defects can be considered an effective strategy for enhancing the electrochemical properties of metal oxide electrodes. In this study, the enhanced pseudocapacitive properties of an acceptor (Gd) doped cerium oxide nanoparticle-a sustainable metal oxide with low environmental and human toxicity-are investigated in depth using ex situ X-ray photoemission spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Interestingly, with 15at% Gd doping (15GDC), the specific capacitance of the nanoparticles measured at 1Ag-1 enhanced to 547.8Fg-1, which is fivefold higher than undoped CeO2 (98.7Fg-1 at 1Ag-1). The rate-dependent capacitance is also improved for 15GDC, which showed a 31.0% decrease in the specific capacitance upon a tenfold increase in the current density, while CeO2 showed a 49.9% decrease. The enhanced electrochemical properties are studied in depth via ex situ XPS and EIS analysis, which revealed that the oxygen vacancies at the surface of the nanoparticles played important roles in enhancing both the specific capacitance and the high-rate performance of 15GDC by acting as the active site for pseudocapacitive redox reaction and allowing fast diffusion of oxygen ions at the surface of 15GDC nanoparticles.