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High electroactive areas, high electrochemical activity and low charge transfer resistance are crucial for high electrochemical performance, but their simultaneous realization is still a great challenge. In this work, porous M 3 S 4 (M = Ni, Co) samples with different Ni to Co ratios have been synthesized by anion-exchange-based precursor conversion method. Wherein, the anions exchange causes outer motion and recombination of transition metal ions with S 2− , giving rise to a porous microstructure enriched with electroactive edge sites. The synergy between Ni and Co results in superior electrochemical activity for high specific capacity performance. The M 3 S 4 phase contributes to low charge transfer resistance for better rate performance. As a result, the Ni 2 CoS 4 exhibits the best specific capacity of 768 C g −1 at 1 A g −1 and retains 59% of capacity value at 50 A g −1 . In addition, the Ni 2 CoS 4 is also used as the cathode materials to assemble hybrid supercapacitor (HSC) with reduced graphene oxide (RGO), and the resulting HSC device demonstrates both high energy and power densities of 34.3 Wh kg −1 at 0.66 kW kg −1 or 19.8 Wh kg −1 at 18.5 kW kg −1 . Our work demonstrates that the electrochemical performance can be maximized by the microstructure designing in terms of edge sites of microstructure and crystal structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Heterogeneous Ni–Co phosphide/phosphate with a specific hollow sea-urchin-like structure has been constructed. • The heterogeneous sample exhibits improved electrolyte interfacial property from the specific hollow sea-urchin-like structure. • The heterogeneous sample combines the merits from bimetal phosphide and phosphate. • The heterogeneous sample exhibits promising potential for both HSC and AZB applications. Constructing well-defined nanostructures consisting of the multiple components with distinctive features are a promising but challenging strategy to develop advanced electroactive materials for energy storage applications. Herein, heterogeneous Ni–Co phosphide/phosphate with a specific hollow sea-urchin-like structure has been synthesized as advanced electroactive materials for both hybrid supercapacitor (HSC) and alkaline zinc-metal battery (AZB) applications. The heterogeneous Ni–Co phosphide/phosphate combines the merits of improved electrolyte interfacial property from the specific hollow sea-urchin-like structure, high electron-conductivity of phosphide, and better ion adsorption and solid diffusion property of phosphate. As a result, the Ni–Co phosphide/phosphate achieves a high capacity to 180.7 mA h g−1 at 1 A g−1, excellent rate capability of 51% capacity retention when the specific current increases by 50 times, and stable cycling stability of 85% capacity retention when cycled for 1000 cycles. Ex situ test was conducted to investigate the formation mechanism for the hollow and sea-urchin-like structure, which can be ascribed to the anion exchange reaction between pre-formed hydroxide and CO 3 2– ions. When used to assemble HSCs with reduced graphene oxide (RGO), the HSCs exhibit a high specific energy of 49.4 W h kg−1, an ultrahigh specific power to 11.7 kW kg−1, and an eminent cycling stability over 10,000 cycles. Meanwhile, Ni 2 Co–P/PO x -based AZB also achieves both high-energy and high-power performance with the specific energy of 308.0 W h kg−1 at 828.4 W kg−1 and 117.4 W h kg−1 at 30.8 kW kg−1. These results above suggest that heterogeneous Ni–Co phosphide/phosphate has great potential to be used as a candidate for both HSC and AZB applications. [ABSTRACT FROM AUTHOR]

Transition metal selenides are very ideal as electroactive battery material for hybrid supercapacitors owing to their high electrochemical activity and metallic electrical conductivity, but their environmental friendly fabrication and complex structure construction is still a big challenge. Here, a simple low-temperature selenization method has been developed to green synthesize a series of Ni–Co selenide samples with a hierarchical nanoparticle/nanosheet structure. The hierarchical structure has been constructed by the recrystallization of sample during the selenization process, which can be greatly influenced by the Co composition. The specific hierarchical structure provides more electroactive sites for charge storage, and the optimized synergy between the Ni and Co compositions further greatly tunes the charge storage performance, as a result, the Ni 0.67 Co 0.33 Se 2 shows the best performance with a specific capacity of 447 C g−1 at 1 A g−1, which is much higher than the Ni–Co selenides with the other Ni to Co ratios and the Ni–Co oxides. The Ni 0.67 Co 0.33 Se 2 retains 97% of the specific capacity after 2000 cycles, demonstrating its excellent cycling stability. A hybrid supercapacitor has been assembled using Ni 0.67 Co 0.33 Se 2 as the positive electrode, which shows both high specific energy and specific power performances. [ABSTRACT FROM AUTHOR]

Heterostructures are enriched with interfacial effects from the separated materials with different chemical properties and crystal phases, which can be used to design advanced materials with novel properties. Besides, high-performance electroactive materials are still urgently needed for both hybrid supercapacitors (HSCs) and alkaline zinc batteries (AZBs), while single phase materials cannot meet comprehensive performance requirements of high-capacity, high-rate performance, and long-term cycling stability. Here, NiCoP-NiCoO 2 /NiCo−PO x heterostructure is designed to achieve enriched interfacial effect between crystallized phosphides and amorphous phosphates. Our heterostructure is transformed from Ni 1.5 Co 1.5 O 4 which is phosphatized using NaH 2 PO 2 ·H 2 O, while this conversion method creates a great amounts of high-crystallized NiCoP nanoparticles which distributed in an amorphous NiCo−PO x matrix. The heterostructure exhibits a high capacity of 177.0 mA h g–1 at 1 A g–1 and a high capacity retention of 125.0 mA h g–1 at 50 A g–1, combined with 78.7 % of capacity retention after 10,000 cycles. More significantly, NiCoP-NiCoO 2 /NiCo−PO x heterostructure can be used as the cathode material for both HSCs and AZBs, and its excellent performance results in both high-energy and high-power performances in above two-type devices. Our investigations demonstrate excellent performance from the interfacial effect of our heterostructure, and give some insights to design advanced materials for energy storage applications. • NiCoP-NiCoO/NiCo-PO x heterostructure is constructed by controllable phosphating effect. • The heterostructure is enriched with interfacial effects. • The heterostructure exhibits high capacity, high capacity and long-term cycling stability. • The heterostructure can be used as the cathode material for both hybrid supercapacitor and alkaline zinc battery. [ABSTRACT FROM AUTHOR]

• Ni-Co-Mn sulfide with a mesoporous structure has been synthesized. • The transition metals show strong synergy for energy storage. • Mn activate the 3 d electrons of Co and enhance affinity for electrolyte. • The synergy between transition metals contributed to improved performance. Nickel-cobalt-manganese sulfide (NiCoMn-S) with a mesoporous structure was synthesized as the electroactive battery materials for hybrid supercapacitors. The synergy between transition metals of NiCoMn-S was investigated theoretically by performing density functional theory calculations and experimentally by comparing the charge storage properties of sulfides with different transition metals. It is found that the Mn composition can activate the 3 d electrons of Co and enhance affinity of NiCo–S with electrolyte ions, leading to synergy between transition metals for enhanced electrochemical activity and rate performance. The Mn composition also increases the specific area for more electroactive sites and reduces the charge transfer resistance of sulfides. In addition, it is found that the Mn and Ni compositions can greatly enhance the charge storage activity of sulfide, and the Co composition greatly improves the rate performance. The strong synergy between Ni, Co and Mn results in enhanced specific capacity, high rate performance and excellent cycling stability. The NiCoMn-S exhibits a specific capacity of 661 C g−1 at 1 A g−1, which retains 440 C g−1 at 50 A g−1. More significantly, the NiCoMn-S demonstrates well matched performance with the capacitive RGO electrode, and the resulting hybrid supercapacitor (HSC) demonstrates both high power and high energy performances. The HSC exhibits a specific energy of 42.1 Wh kg−1 at a specific power of 750 W kg−1, and showing a specific energy of 13.2 Wh kg−1 at a specific power of 22.5 kW kg−1. [ABSTRACT FROM AUTHOR]