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Developing bifunctional electrocatalysts with both high catalytic activity and high stability is crucial for efficient water splitting in alkaline media. Herein, a Fe-incorporated dual-metal selenide on nickel foam (Co0.9Fe0.1-Se/NF) is synthesized via a facile one-step electrodeposition method. As-synthesized materials could serve as self-supported bifunctional electrocatalysts with excellent catalytic activity towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. Experimental results show that delivering a 10 mA cm−2 water splitting current density only requires a cell voltage of 1.55 V. In addition, a very stable performance could be kept for about 36 hours, indicating their excellent working stability. Moreover, by means of phase analysis, we have identified that the evolution of the synthesized Co0.9Fe0.1-Se/NF experiences two entirely different processes in HER and OER, which hydroxide and oxyhydroxide are regarded as the real active sites, respectively. This work may pave the way to further understanding the relationships between the reactivity and stability of chalcogenide-based electrocatalysts and facilitating the rational design of efficient electrocatalysts for future renewable energy system applications.

Lithium-ion hybrid supercapacitors (Li-HSCs) and dual-ion batteries (DIBs) are two types of energy storage devices that have attracted extensive research interest in recent years. Li-HSCs and DIBs have similarities in device structure, tendency for ion migration, and energy storage mechanisms at the negative electrode. However, these devices have differences in energy storage mechanisms and working potentials at the positive electrode. Here, we first realize the integration of a Li-HSC and a DIB to form a dual-ion hybrid supercapacitor (DIHSC), by employing mesocarbon microbead (MCMB)-based porous graphitic carbon (PGC) with a partially graphitized structure and porous structure as a positive electrode material. The MCMB-PGC-based DIHSC exhibits a novel dual-ion battery-capacitor hybrid mechanism: it exhibits excellent electronic double-layer capacitor (EDLC) behavior like a Li-HSC in the low-middle wide potential range and anion intercalation/de-intercalation behavior like a DIB in the high-potential range. Two types of mechanisms are observed in the electrochemical characterization process, and the energy density of the new DIHSC is significantly increased.

Sodium ion batteries (SIBs) are very promising for large-scale energy storage in virtue of its high energy density, abundant sodium resources and low environmental impact, etc. However, it is still a big challenge to develop high-performance and durable cathode materials for SIBs. Among different candidate materials, Na3V2(PO4)3 has attracted great attentions due to its high theoretical capacity (117 mAh/g), stable framework structure and excellent ionic conductivity. However, Na3V2(PO4)3 delivers inferior rate capability and cycling stability due to its poor electronic conductivity. In this work, free-standing Na3V2(PO4)3/carbon nanofiber membranes are synthesized by an electrospinning-sintering route. The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250 cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C, which is superior to many state-of-the-art SIB cathode materials. This can be attributed to the hierarchically distributed Na3V2(PO4)3 crystals in carbon nanofiber network, which possesses outstanding electronic/ionic conductivity and thus leads to an ultrahigh rate capability.

Developing high-performance noble metal-free and free-standing catalytic electrodes are crucial for overall water splitting. Here, nickel sulfide (Ni3S2) and nickel selenide (NiSe) are synthesized on nickel foam (NF) with a one-pot solvothermal method and directly used as free-standing electrodes for efficiently catalyzing hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution. In virtue of abundant active sites, the Ni3S2/NF and the NiSe/NF electrodes can deliver a current density of 10 mA cm−2 at only 123 mV, 137 mV for HER and 222 mV, 271 mV for OER. Both of the hierarchical Ni3S2/NF and NiSe/NF electrodes can serve as anodes and cathodes in electrocatalytic overall water-splitting and can achieve a current density of 10 mA cm−2 with an applied voltage of ∼1.59 V and 1.69 V, respectively. The performance of as-obtained Ni3S2/NF||Ni3S2/NF is even close to that of the noble metal-based Pt/C/NF||IrO2/NF system.