Heterojunction‐Assisted Co3S4@Co3O4 Core–Shell Octahedrons for Supercapacitors and Both Oxygen and Carbon Dioxide Reduction Reactions

Expedition of electron transfer efficiency and optimization of surface reactant adsorption products desorption processes are two main challenges for developing non‐noble catalysts in the oxygen reduction reaction (ORR) and CO₂ reduction reaction (CRR). A heterojunction prototype on Co₃S₄@Co₃O₄ core–shell octahedron structure is established via hydrothermal lattice anion exchange protocol to implement the electroreduction of oxygen and carbon dioxide with high performance. The synergistic bifunctional catalyst consists of p‐type Co₃O₄ core and n‐type Co₃S₄ shell, which afford high surface electron density along with high capacitance without sacrificing mechanical robustness. A four electron ORR process, identical to the Pt catalyzed ORR, is validated using the core–shell octahedron catalyst. The synergistic interaction between cobalt sulfide and cobalt oxide bicatalyst reduces the activation energy to convert CO₂ into adsorbed intermediates and hereby enables CRR to run at a low overpotential, with formate as the highly selective main product at a high faraday efficiency of 85.3%. The remarkable performance can be ascribed to the synergistic coupling effect of the structured co‐catalysts; heterojunction structure expedites the electron transfer efficiency and optimizes surface reactant adsorption product desorption processes, which also provide theoretical and pragmatic guideline for catalyst development and mechanism explorations.     

Robust Electrodes Based on Coaxial TiC/C–MnO2 Core/Shell Nanofiber Arrays with Excellent Cycling Stability for High‐Performance Supercapacitors

A coaxial electrode structure composed of manganese oxide‐decorated TiC/C core/shell nanofiber arrays is produced hydrothermally in a KMnO₄ solution. The pristine TiC/C core/shell structure prepared on the Ti alloy substrate provides the self‐sacrificing carbon shell and highly conductive TiC core, thus greatly simplifying the fabrication process without requiring an additional reduction source and conductive additive. The as‐prepared electrode exhibits a high specific capacitance of 645 F g^?1 at a discharging current density of 1 A g^?1 attributable to the highly conductive TiC/C and amorphous MnO₂ shell with fast ion diffusion. In the charging/discharging cycling test, the as‐prepared electrode shows high stability and 99% capacity retention after 5000 cycles. Although the thermal treatment conducted on the as‐prepared electrode decreases the initial capacitance, the electrode undergoes capacitance recovery through structural transformation from the crystalline cluster to layered birnessite type MnO₂ nanosheets as a result of dissolution and further electrodeposition in the cycling. 96.5% of the initial capacitance is retained after 1000 cycles at high charging/discharging current density of 25 A g^?1. This study demonstrates a novel scaffold to construct MnO₂ based SCs with high specific capacitance as well as excellent mechanical and cycling stability boding well for future design of high‐performance MnO₂‐based SCs.     

(Ni,Co)Se2/NiCo‐LDH Core/Shell Structural Electrode with the Cactus‐Like (Ni,Co)Se2 Core for Asymmetric Supercapacitors

Supercapacitors (SCs) have been widely studied as a class of promising energy‐storage systems for powering next‐generation E‐vehicles and wearable electronics. Fabricating hybrid‐types of electrode materials and designing smart nanoarchitectures are effective approaches to developing high‐performance SCs. Herein, first, a Ni‐Co selenide material (Ni,Co)Se₂ with special cactus‐like structure as the core, to scaffold the NiCo‐layered double hydroxides (LDHs) shell, is designed and fabricated. The cactus‐like structural (Ni,Co)Se₂ core, as a highly conductive and robust support, promotes the electron transport as well as hinders the agglomeration of LDHs. The synergistic contributions from the two types of active materials together with the superior properties of the cactus‐like nanostructure enable the (Ni,Co)Se₂/NiCo‐LDH hybrid electrode to exhibit a high capacity of ≈170 mA h g^?1 (≈1224 F g^?1), good rate performance, and long durability. The as‐assembled (Ni,Co)Se₂/NiCo‐LDH//PC (porous carbon) asymmetric supercapacitor (ASC) with an operating voltage of 1.65 V delivers a high energy density of 39 W h kg^?1 at a power density of 1650 W kg^?1. Therefore, the cactus‐like core/shell structure offers an effective pathway to engineer advanced electrodes. The assembled flexible ASC is demonstrated to effectively power electronic devices.     

α‐Ni(OH)2 Originated from Electro‐Oxidation of NiSe2 Supported by Carbon Nanoarray on Carbon Cloth for Efficient Water Oxidation

Development of effective oxygen evolution reaction (OER) electrocatalysts has been intensively studied to improve water splitting efficiency and cost effectiveness in the last ten years. However, it is a big challenge to obtain highly efficient and durable OER electrocatalysts with overpotentials below 200 mV at 10 mA cm^?2 despite the efforts made to date. In this work, the successful synthesis of supersmall α‐Ni(OH)₂ is reported through electro‐oxidation of NiSe₂ loaded onto carbon nanoarrays. The obtained α‐Ni(OH)₂ shows excellent activity and long‐term stability for OER, with an overpotential of only 190 mV at the current density of 10 mA cm^?2, which represents a highly efficient OER electrocatalyst. The excellent activity could be ascribed to the large electrochemical surface area provided by the carbon nanoarray, as well as the supersmall size (≈10 nm) of α‐Ni(OH)₂ which possess a large number of active sites for the reaction. In addition, the phase evolution of α‐Ni(OH)₂ from NiSe₂ during the electro‐oxidation process was monitored with in situ X‐ray absorption fine structure (XAFS) analysis.     

A Highly Conductive MOF of Graphene Analogue Ni3(HITP)2 as a Sulfur Host for High‐Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have been considered as one of the most promising energy storage systems owing to their high theoretical capacity and energy density. However, their commercial applications are obstructed by sluggish reaction kinetics and rapid capacity degradation mainly caused by polysulfide shuttling. Herein, the first attempt to utilize a highly conductive metal–organic framework (MOF) of Ni₃(HITP)₂ graphene analogue as the sulfur host material to trap and transform polysulfides for high‐performance Li–S batteries is made. Besides, the traditional conductive additive acetylene black is replaced by carbon nanotubes to construct matrix conduction networks for triggering the rate and cycling performance of the active cathode. As a result, the S@Ni₃(HITP)₂ with sulfur content of 65.5 wt% shows excellent sulfur utilization, rate performance, and cyclic durability. It delivers a high initial capacity of 1302.9 mAh g^?1 and good capacity retention of 848.9 mAh g^?1 after 100 cycles at 0.2 C. Highly reversible discharge capacities of 807.4 and 629.6 mAh g^?1 are obtained at 0.5 and 1 C for 150 and 300 cycles, respectively. Such kinds of pristine MOFs with high conductivity and abundant polar sites reveal broad promising prospect for application in the field of high‐performance Li–S batteries.