High energy density aqueous asymmetric supercapacitors based on MnO2@C branch dendrite nanoarchitectures

Iodine Adsorption in Nanoporous Carbon to Fabricate Assimilated Battery Electrodes for Durable Hybrid Supercapacitors

A hybrid supercapacitor is designed by coupling a battery electrode with a capacitive electrode in a single device/cell to enhance energy density. In iodine-based hybrid supercapacitors, the nanoporous carbon serves as the electrode material; however, the cathode or positive electrode is charged with iodine via electrodeposition from a redox aqueous electrolyte, while a negative electrode stores charges at the electric double-layer. In this work, iodine is loaded via physical adsorption into the porosity of a carbon electrode, keeping the aqueous electrolyte free from iodide redox moieties. By this way, the risk of polyiodide (I3- and I5-) generation at the positive electrode leading to a shuttling-related performance loss of the hybrid supercapacitor is prevented. Chemical interactions of iodine with the carbon surface and within the pores have been investigated with Raman spectroscopy, thermogravimetry and electron microscopy. Electrochemical methods have been used to test individual electrodes and hybrid supercapacitors in aqueous NaNO3 and aqueous LiTFSI at 5 mol/L concentration for performance parameters such as energy efficiency, capacitance, self-discharge and cyclability. The hybrid supercapacitor in aqueous LiTFSI exhibits stable capacitance and energy efficiency during long-term aging tests at 1.5 V. Carbon nanoarchitecturing with iodine as shown in the present work offers an economical approach to enhance the performance of hybrid supercapacitors.

Core-shell NiS2@C encased by thin carbon layer as high-rate and durable electrode for aqueous rechargeable battery

Nickel sulfides, as promising candidate for aqueous rechargeable battery, have aroused broad attention on account of abundant natural resources, rich phases, moderate price and high theoretical capacity. Nevertheless, tremendous volume expansion during repeated charging-discharging procedure leads to the poor rate capability and cycling stability of nickel sulfide electrodes. Therefore, in this work, core-shell NiS₂@C encapsulated by thin hydrothermal carbon (HC) layer (NiS₂@C/HC) has been designed and prepared without any surfactants or templates assistance, which avoid tedious process and shorten preparation cycle greatly. When matched with the treated iron powder (TIP) electrode to form NiS₂@C/HC//TIP aqueous rechargeable battery, the NiS₂@C/HC//TIP battery exhibits a high discharge capacity of 205.1 mAh g^-1 at 1 A g^-1, remarkable rate ability (176.4 mAh g^-1 at 5 A g^-1, about 86% capacity conversation) and superiorly durable stability (80.8 % capacity retention after 10,000 cycles at ultra-high current density of 15 A g^-1). The outstanding high-rate capability and cycling stability for aqueous rechargeable battery can be ascribed to the distinct cowpea-like architecture and intrinsic properties of NiS₂@C/HC. Specifically, the interior porous carbon provides a space to tolerate the volume expansion of the NiS₂ nanoparticles and prevent NiS₂ nanoparticles from aggregation, guaranteeing its high-rate capability. Meanwhile, the exterior HC layer is conducive to improve the electric conductivity to facilitate the electrons transfer and promote the mechanical strength of the whole active materials, ensuring its robust cycling stability.

Non-precious transition metal single-atom catalysts for the oxygen reduction reaction: progress and prospects

The massive exploitation and use of fossil resources have created many negative issues, such as energy shortage and environmental pollution. It prompts us to turn our attention to the development of new energy technologies. This review summarizes the recent research progress of non-precious transition metal single-atom catalysts (NPT-SACs) for the oxygen reduction reaction (ORR) in Zn-air batteries and fuel cells. Some commonly used preparation methods and their advantages/disadvantages have been summarized. The factors affecting the ORR performances of NPT-SACs have been focused upon, such as the substrate type, coordination environment and nanocluster effects. The loading mass of a metal atom has a direct effect on the ORR performances. Some general strategies for stabilizing metal atoms are included. This review points out some existing challenges of NPT-SACs, and also provides ideas for designing and synthesizing NPT-SACs with excellent ORR performances. The large-scale preparation and commercialization of NPT-SACs with excellent ORR properties are prospected.

Electrocatalyst Design for Conversion of Energy Molecules: Electronic State Modulation and Mass Transport Regulation

Electrocatalytic conversions of energy molecules are involved in many energy conversion processes. Improving the activity of electrocatalyst is critical for increasing the efficiency of these energy conversion processes. However, the...

Design and Regulation of Novel MnFe2O4@C Nanowires as High Performance Electrode for Supercapacitor

Bimetallic oxides have been considered as potential candidates for supercapacitors due to their relatively high electric conductivity, abundant redox reactions and cheapness. However, nanoparticle aggregation and huge volume variation during charging-discharging procedures make it hard for them to be applied widely. In this work, one-dimensional (1D) MnFe₂O₄@C nanowires were in-situ synthesized via a simply modified micro-emulsion technique, followed by thermal treatment. The novel 1D and core-shell architecture, and in-situ carbon coating promote its electric conductivity and porous feature. Due to these advantages, the MnFe₂O₄@C electrode exhibits a high specific capacitance of 824 F·g⁻¹ at 0.1 A·g⁻¹ and remains 476 F·g⁻¹ at 5 A·g⁻¹. After 10,000 cycles, the capacitance retention of the MnFe₂O₄@C electrode is up to 93.9%, suggesting its excellent long-term cycling stability. After assembling with activated carbon (AC) to form a MnFe₂O₄@C//AC device, the energy density of this MnFe₂O₄@C//AC device is 27 W·h·kg⁻¹ at a power density of 290 W·kg⁻¹, and remains at a 10 W·h·kg⁻¹ energy density at a high power density of 9300 W·kg⁻¹.