Pompon-like MnO2 and N/O doped nanoporous carbon composites with an ultrahigh capacity for energy storage

Investigating composite electrode materials of metal oxides for advanced energy storage applications

Electrochemical energy systems mark a pivotal advancement in the energy sector, delivering substantial improvements over conventional systems. Yet, a major challenge remains the deficiency in storage technology to effectively retain the energy produced. Amongst these are batteries and supercapacitors, renowned for their versatility and efficiency, which depend heavily on the quality of their electrode materials. Metal oxide composites, in particular, have emerged as highly promising due to the synergistic effects that significantly enhance their functionality and efficiency beyond individual components. This review explores the application of metal oxide composites in the electrodes of batteries and SCs, focusing on various material perspectives and synthesis methodologies, including exfoliation and hydrothermal/solvothermal processes. It also examines how these methods influence device performance. Furthermore, the review confronts the challenges and charts future directions for metal oxide composite-based energy storage systems, critically evaluating aspects such as scalability of synthesis, cost-effectiveness, environmental sustainability, and integration with advanced nanomaterials and electrolytes. These factors are crucial for advancing next-generation energy storage technologies, striving to enhance performance while upholding sustainability and economic viability.

Boosting activity on copper functionalized biomass graphene by coupling nanocrystalline Nb2O5 as impressive rate capability for supercapacitor and outstanding catalytic activity for oxygen reduction

A novel and hierarchical porous but cross-linked copper-doped biomass graphene (Cu@HPBG) combined with Nb2O5 (denoted as Nb2O5/Cu@HPBG) is successfully fabricated on a large-scale using fig peels as biomass carbon and copper as the graphitization catalyst. During the synthesis process, basic copper carbonate serves dual functions of pore-forming agent, as well as homogeneous copper provider, and NH3 is employed as a defect-forming agent and N dopant. Owing to the porous hierarchical structure increased availability of contact interface and pseudo capacitance active sites provided by copper and Nb2O5, the assembled asymmetrical supercapacitor (ASC) employing Nb2O5/Cu@HPBG as positive electrode and HPBG as negative electrode can not only widen the stability window range of 0～1.9 V, but also deliver a maximum gravimetric energy density of 82.8 W h kg-1 at the power density of 950.0 W kg-1 and maintain a remarkable cycling stability of 97.1% after 15,000 cycles. Impressively, due to the synergistic enhancement of Cu@HPBG and Nb2O5, the resulting Nb2O5/Cu@HPBG hybrid displays more positive half wave potential (∼0.85 V) and a long-life stability than Pt/C electrode toward oxygen reduction reaction (ORR). Our research provides a feasible strategy to fabricate renewable biomass graphene electroactive composites for large-scale supercapacitor electrodes and efficient ORR catalysts toward energy applications.

Different metal cation-doped MnO2/carbon cloth for wide voltage energy storage

Aqueous gel supercapacitors, as an important component of flexible energy storage devices, have received widespread attention for their fast charging/discharging rates, long cycle life and high electrochemical stability under mechanical deformation condition. However, the low energy density of aqueous gel supercapacitors has greatly hindered their further development due to the narrow electrochemical window and limited energy storage capacity. Therefore, different metal cation-doped MnO₂/carbon cloth-based flexible electrodes herein are prepared by constant voltage deposition and electrochemical oxidation in various saturated sulphate solutions. The influence of different metal cations as K⁺, Na⁺ and Li⁺ doping and deposition conditions on the apparent morphology, lattice structure and electrochemical properties are explored. Furthermore, the pseudo-capacitance ratio of the doped MnO₂ and the voltage expansion mechanism of the composite electrode are investigated. The specific capacitance and pseudo-capacitance ratio of the optimized δ-Na_0.31MnO₂/carbon cloth as MNC-2 electrode could be reached 327.55 F/g at 10 mV/s and 35.56% of the pseudo-capacitance, respectively. The flexible symmetric supercapacitors (NSCs) with desirable electrochemical performances in the operating range of 0-1.4 V are further assembled with MNC-2 as the electrodes. The energy density is 26.8 Wh/kg at the power density of 300 W/kg, while the energy density can still reach 19.1 Wh/kg when the power density is up to 1150 W/kg. The energy storage devices with high-performance developed in this work can provide new ideas and strategic support for the application in portable and wearable electronic devices.

Excellent performance supercapacitors with the compounding of Ni(OH)2 and ZIF-67 derived Co-C-N nanosheets as flexible electrode materials

Owing to the advantages of high theoretical capacity, low cost, and excellent chemical stability, Ni(OH)₂ is considered as a potential candidate for electrode materials of supercapacitors. However, its further applications are limited by its adverse surface chemical properties. In this paper, a composite material consisting of ZIF-67 derived Co-C-N nanosheets and Ni(OH)₂ was synthesized facilely on carbon cloth in situ, and based on the collective advantages of the various components, excellent electrochemical performance could be achieved when used as a flexible electrode material of supercapacitors. In detail, the as-obtained sample Ni(OH)₂/Co-C-N/CC exhibits an ultrahigh specific capacitance of 2100 F g^-1 at a current density of 1 A g^-1. Moreover, the further assembled asymmetric supercapacitor device exhibits a maximum energy density of 78.6 W h kg^-1 at a power density of 749.4 W kg^-1. Furthermore, the device also shows outstanding cycling stability with 90.2% capacitance retention after 5000 cycles of charge-discharge. Basically, the remarkable performance can be attributed to the well-developed structure, abundant active sites, complex beneficial components, and their intrinsic properties. Significantly, rational design can broaden the research directions of corresponding electrode materials.