Rare Earth-Based Nanomaterials for Supercapacitors: Preparation, Structure Engineering and Application

Coupling of Nd doping and oxygen-rich vacancy in CoMoO4@NiMoO4 nanoflowers toward advanced supercapacitors and photocatalytic degradation

In this paper, we successfully prepared rare earth element-doped 0.8% Nd-CoMoO4@NiMoO4 nanoflowers with a large specific surface area using the sol-gel method for the first time. In the experiment, we added a structure-directing agent to successfully assemble the nanosheets into a three-dimensional ordered micro-flower shape. By using the strategy of forming a flower-shaped morphology with a structure-directing agent and doping Nd elements to generate oxygen vacancies, the problems of the collapse of the active material structure and slow reaction kinetics were solved. Through relevant electrochemical performance tests, it was found that when the rare earth element Nd was doped at a concentration of 0.8%, the material exhibited exceptional specific capacitance (2387 F g-1 at 1 A g-1) and cycling stability (99.3% after 10 000 cycles at 5 A g-1). These performance characteristics far surpassed those of the other synthesized products. We assembled 0.8% Nd-CoMoO4@NiMoO4 with hydrophilic CNTs into an asymmetric device, 0.8% Nd-CoMoO4@NiMoO4//CNTs. This device exhibited high specific capacitance (262 F g-1 at 1 A g-1) and cycling stability (99.2% after 3000 cycles), with a good energy storage effect. In addition, 0.8% Nd-CoMoO4@NiMoO4 has a low band gap, which broadens the absorption range of the product and improves the utilization rate of visible light. The photocatalyst showed good degradation efficiency (all exceeding 96%) and cycling stability (96%) for all four dyes. This paper provides a new strategy and method for preparing doped polymetallic mixtures, which has potential application value.

Combining Structural Modification and Electrolyte Regulation to Enable Long-Term Cyclic Stability of MoO3-x @TiO2 as Cathode for Aqueous Zn-Ion Batteries

Orthorhombic MoO3 (α-MoO3 ) with multivalent redox couple of Mo6+ /Mo4+ and layered structure is a promising cathode for rechargeable aqueous Zn-ion batteries (AZIBs). However, pure α-MoO3 suffers rapid capacity decay due to the serious dissolution and structural collapse. Meanwhile, the growth of byproduct and dendrite on the anode also lead to the deterioration of cyclic stability. This article establishes the mechanism of proton intercalation into MoO3 and proposes a joint strategy combining structural modification with electrolyte regulation to enhance the cyclic stability of MoO3 without sacrificing the capacity. In ZnSO4 electrolyte with Al2 (SO4 )3 additive, TiO2 coated oxygen-deficient α-MoO3 (MoO3-x @TiO2 ) delivers a reversible capacity of 93.2 mA h g-1 at 30 A g-1 after 5000 cycles. The TiO2 coating together with the oxygen deficiency avoids structural damage while facilitating proton diffusion. Besides, the additive of Al2 (SO4 )3 , acting as a pump, continuously supplements protons through dynamic hydrolysis, avoiding the formation of Zn4 SO4 (OH)6 ·xH2 O byproducts at both MoO3-x @TiO2 and Zn anode. In addition, Al2 (SO4 )3 additive facilitates uniform deposition of Zn owing to the tip-blocking effect of Al3+ ion. The study demonstrates that the joint strategy is beneficial for both cathode and anode, which may shed some light on the development of AZIBs.

Rare Earth Doping Engineering Tailoring Advanced Oxygen-Vacancy Co3 O4 with Tunable Structures for High-Efficiency Energy Storage

Co₃ O₄  with high theoretical capacitance is a promising electrode material for high-end energy applications, yet the unexcited bulk electrochemical activity, low conductivity, and poor kinetics of Co₃ O₄  lead to unsatisfactory charge storage capacity. For boosting its energy storage capability, rare earth (RE)-doped Co₃ O₄  nanostructures with abundant oxygen vacancies are constructed by simple, economical, and universal chemical precipitation. By changing different types of RE (RE = La, Yb, Y, Ce, Er, Ho, Nd, Eu) as dopants, the RE-doped Co₃ O₄  nanostructures can be well transformed from large nanosheets to coiled tiny nanosheets and finally to ultrafine nanoparticles, meanwhile, their specific surface area, pore distribution, the ratio of Co²⁺ /Co³⁺ , oxygen vacancy content, crystalline phase, microstrain parameter, and the capacitance performance are regularly affected. Notably, Eu-doped Co₃ O₄  nanoparticles with good cycle stability show a maximum specific capacitance of 1021.3 F g^-1 (90.78 mAh g^-1 ) at 2 A g^-1 , higher than 388 F g^-1 (34.49 mAh g^-1 ) of pristine Co₃ O₄  nanosheets. The assembling asymmetric supercapacitor delivers a high energy density of 48.23 Wh kg^-1  at high power density of 1.2 kW kg^-1 . These findings denote the significance and great potential of RE-doped Co₃ O₄  in the development of high-efficiency energy storage.

Rational Design of Porous Nanowall Arrays of Ultrafine Co4N Nanoparticles Confined in a La2O2CN2 Matrix on Carbon Cloth for a High-Performing Supercapacitor Electrode

Transition metal nitrides (TMNs) have received special concern as important energy storage materials, owing to their high conductibility, good mechanical strength, and superior corrosion resistance. However, their insufficient capacitance and poor cycling stability limit their practical applications for supercapacitors. Here, a novel three-dimensional (3D) self-supported integrated electrode consisted of porous nanowall arrays of ultrafine cobalt nitride (Co₄N) nanoparticles encapsulated in a lanthanum oxycyanamide (LOC) matrix on carbon cloth (Co₄N@LOC/CC) for outstanding electrochemical energy storage is rationally designed and fabricated. The 3D monolithic configuration of porous nanowall arrays facilitates the mass/charge transfer, the exposure of electroactive sites, and the enhancement of electrical conductivity. Meanwhile, the unique core-shell structure of Co₄N@LOC can prevent ultrafine Co₄N nanoparticles from sintering, agglomeration, and oxidation and promotes electron transfer dynamics during the redox reaction, meanwhile enhancing the stability of the electrode. Additionally, the synergy of Co₄N and LOC can result in an efficient electron/ion transport in the process of the charge-discharge. Because of these features, the Co₄N@LOC/CC electrode displays superior specific capacitance (895.6 mF cm^-2 or 613.4 F g^-1 at 1 mA cm^-2) and admirable cycling durability (87.9% capacitance reservation after 10 000 cycles), surpassing the majority of nitride-based electrodes reported thus far. Furthermore, after being assembled into an asymmetric supercapacitor using active carbon (AC) as an anode, the obtained Co₄N@LOC/CC//AC/CC device displays a high energy density of 41.7 Wh kg^-1 at the power density of 875.8 W kg^-1 with a high capacitance reservation of 87.6% after 5000 cycles at 2 mA cm^-2. This work offers an efficient approach of combining TMNs with rare earth compounds to enhance the capacitance and stability of TMNs for supercapacitor electrodes.