A Novel Layered WO3 Derived from An Ion Etching Engineering for Ultrafast Proton Storage in Frozen Electrolyte

Aqueous proton batteries/pseudocapacitors are promising candidates for next-generation electrochemical energy storage. However, their development is impeded by the lack of suitable electrode materials that facilitate rapid transport and storage of protons. Herein, an open-layered hydrous tungsten oxide (WO₃·nH₂O) with larger layer spacing from Aurivillius Bi₂WO₆ via ion etching is proposed. Particularly, the WO₃·nH₂O electrode possesses a unique multi-level nanostructure and presents superior rate performance (254 F g⁻¹ at 1000 mV s⁻¹, surpassing most carbon-based electrode materials known). In situ X-ray Diffraction combined with crystallography study demonstrate that the open layered structure with negligible structural strain enables fast and reversible (de)intercalation of protons during electrochemical reaction. Furthermore, a full proton pseudocapacitor (Prussian blue analogues//WO₃·nH₂O) operating in a wide temperature range from −40 to 25 °C is fabricated. This device can deliver 70% of the room-temperature capacitance and stably cycle with negligible capacitance fading over 5000 cycles even in the solid-phase electrolyte at −20 °C. This study provides a valuable strategy to design electrode materials with layered structures for the development of high-performance aqueous proton batteries/pseudocapacitors at low temperatures.     

Hierarchical NiCo@NiOOH@CoMoO4 Core–Shell Heterostructure on Carbon Cloth for High-Performance Asymmetric Supercapacitors

The fabrication of low-cost, effective, and highly integrated nanostructured materials through simple and reproducible methods for high-energy-density supercapacitors is highly desirable. Herein, an activated carbon cloth (ACC) is designed as the functional scaffold for supercapacitors and treated hydrothermally to deposit NiCo nanoneedles working as internal core, followed by a dip-dry coating of NiOOH nanoflakes core–shell and uniform hydrothermal deposition of CoMoO₄ nanosheets serving as an external shell. The structured core–shell heterostructure ACC@NiCo@NiOOH@CoMoO₄ electrode resulted in exceptional specific areal capacitance of 2920 mF cm⁻² and exceptional cycling stability for 10 000 cycles. Moreover, the fabricated electrode is developed into an asymmetric supercapacitor which demonstrates excellent areal capacitance, energy density, and power density within the broad potential window of 1.7 V with a cycling life of 92.4% after 10 000 charge–discharge cycles, which reflects excellent cycle life. The distinctive core–shell structure, highly conductive substrate, and synergetic effect of coated material results in more electrochemical active sites and flanges for effective electrons and ion transportation. This unique technique provides a new perspective for cost-efficient supercapacitor applications.     

Aqueous Ammonium-Ion Supercapacitors with Unprecedented Energy Density and Stability Enabled by Oxygen Vacancy-Enriched MoO3@C

The use of non-metal charge carriers such as ammonium (NH₄⁺) in electrochemical energy storage devices offers advantages in terms of weight, element abundance, and compatibility with aqueous electrolytes. However, the development of suitable electrodes for such carriers lags behind other technologies. Herein, we present a high-performance anode material for ammonium-ion supercapacitors based on a MoO₃/carbon (MoO₃@C) composite. The NH₄⁺ storage performance of such composites and their practical application prospects are evaluated both in a three-electrode configuration and as symmetric supercapacitors. The optimized material reaches an unprecedented specific capacitance of 473 F·g⁻¹ (158 mAh·g⁻¹; 1592 mF·cm⁻²) at a current density of 1 A·g⁻¹, and 92.7% capacitance retention after 5000 cycles in a three-electrode set-up. This outstanding performance is related to the presence of oxygen vacancies that enhance the composites’ ionic/electronic transportation and electrochemical reaction site, while at the same time facilitating the formation of hydrogen bonds between NH₄⁺ and the host material. Using the optimized composite, symmetric supercapacitors based on an (NH₄)₂SO₄ gel electrolyte are fabricated and demonstrated to provide unmatched energy densities above 78 Wh·kg⁻¹ at a power density of 929 W·kg⁻¹. Besides, such devices are characterized by extraordinary capacitance retention of 97.6% after 10,000 cycles.     

Capillary Evaporation on High-Dense Conductive Ramie Carbon for Assisting Highly Volumetric-Performance Supercapacitors

Conductive biomass carbon possesses unique properties of excellent conductivity and outstanding thermal stability, which can be widely used as conductive additive. However, building the high-dense conductive biomass carbon with highly graphitized microcrystals at a lower carbonization temperature is still a major challenge because of structural disorder and low crystallinity of source material. Herein, a simple capillary evaporation method to efficiently build the high-dense conductive ramie carbon (hd-CRC) with the higher tap density of 0.47 cm³ g⁻¹ than commercialized Super-C45 (0.16 cm³ g⁻¹) is reported. Such highly graphitized microcrystals of hd-CRC can achieve the high electrical conductivity of 94.55 S cm⁻¹ at the yield strength of 92.04 MPa , which is higher than commercialized Super-C45 (83.92 S cm⁻¹ at 92.04 MPa). As a demonstration, hd-CRC based symmetrical supercapacitors possess a highly volumetric energy density of 9.01 Wh L⁻¹ at 25.87 kW L⁻¹, much more than those of commercialized Super-C45 (5.06 Wh L⁻¹ and 19.30 kW L⁻¹). Remarkably, the flexible package supercapacitor remarkably presents a low leakage current of 10.27 mA and low equivalent series resistance of 3.93 mΩ. Evidently, this work is a meaningful step toward high-dense conductive biomass carbon from traditional biomass graphite carbon, greatly promoting the highly-volumetric–performance supercapacitors.     

Rare Earth Doping Engineering Tailoring Advanced Oxygen-Vacancy Co3O4 with Tunable Structures for High-Efficiency Energy Storage

Co₃O₄ 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 Co₃O₄ lead to unsatisfactory charge storage capacity. For boosting its energy storage capability, rare earth (RE)-doped Co₃O₄ 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 Co₃O₄ 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 Co₃O₄ 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 Co₃O₄ 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 Co₃O₄ in the development of high-efficiency energy storage.