Structural design of FeCo alloy implanted into N,S co-doped carbon nanotubes via self-catalyzed growth for advanced liquid and flexible all-state-state Zn-air battery.

The introduction of transition bimetallic alloys can effectively improve oxygen reduction reaction (ORR) activity. However, the alloy particles are inclined to dissolve under harsher conditions, resulting in a serious decrease in catalytic activity and stability. Herein, an efficient ORR catalyst, FeCo alloy nanoparticles (NPs) encapsulated in N,S co-doped carbon nanotubes (FeCo10-NSCNTs), was developed through a self-catalyzed growth strategy. Due to the delicate structural design, the N,S co-doped structure can effectively improve the ORR performance by modulating the electronic properties and surface polarity of the carbon substrate, and the randomly connected carbon nanotube structure with large specific surface area can further enhance the adsorption and dissociation of gas molecules, accelerating the kinetics of gas participation in the reaction. Carbon-encapsulated FeCo alloys are beneficial for improving catalytic activity and durability. The FeCo10-NSCNTs displayed excellent ORR activity with a half-wave potential of E1/2 = 0.84 V and robust stability of 13 k cycles. More impressively, the assembled liquid-state Zn-air battery (ZAB) with FeCo10-NSCNTs as the air-electrode delivers an output power density of 146.68 mW cm-2 along with excellent operation durability. The assembled all-solid ZAB has good cyclic stability under 0-180° bending conditions. The synthesized N,S co-doping, carbon nanotubes and FeCo alloys provide important guidance for the construction of cheap non-noble metal-carbon hybrid nanomaterials.

Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2 O2 Production.

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn-N2 O2 moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn-N2 O2 -S). Systematic analyses demonstrate that the synergetic effects between the N2 O2 species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O2 reduction to H2 O2 . Remarkably, the Zn-N2 O2 moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H2 O2 generation. Consequently, the Zn-N2 O2 -S SAC exhibits impressive electrochemical H2 O2 production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm-2 in the flow cell, it shows a high H2 O2 production rate of 6.924 mol gcat -1 h-1 with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.

Prussian blue coupling with zinc oxide as a protective layer: an efficient cathode for high-rate sodium-ion batteries.

Prussian blue coupled with zinc oxide has been synthesized via a facial heat treatment process. As a cathode for sodium ion batteries, the PB coupled with ZnO delivers an excellent rate performance, retaining 86.2 mA h g-1 at 10 A g-1 and a high reversible capacity of 89.9 mA h g-1 at 0.2 A g-1 after 500 cycles.

Role of Acid in Tailoring Prussian Blue as Cathode for High-Performance Sodium-Ion Battery.

Prussian blue (PB) with concave centers is synthesized successfully through a hydrothermal method with the assistance of acid. In this study, the role of the acid is investigated systematically by adjusting the reaction temperature and time, using different kinds and amounts of acid, and changing the amount of PVP surfactant added. It is found that the acid can not only trigger the chemical reaction to form cubic PB, but also act as an etching reagent to tailor the morphology. The as-obtained cubic PB with concave centers demonstrates a superior cycle stability and rate performance, which can achieve a capacity of 107 mA h g-1 at 0.2 A g-1 . The corresponding capacity retention is 74 % after 500 cycles relative to the second cycle. Even at a current density of 5 A g-1 , the specific capacity remains at 82 mA h g-1 . Furthermore, the full cell, using PB as the cathode and hard carbon as the anode, exhibits a high capacity of 70 mA h g-1 at 0.1 A g-1 , and can power an LED light successfully. This work provides new insights into the role of acid in tailoring the morphology of PB, and opens a new avenue toward the design of unique structures to improve sodium storage.

Nanostructured potassium and sodium ion incorporated Prussian blue frameworks as cathode materials for sodium-ion batteries.

Nanostructured KxNayMnFe(CN)6 (x + y ≤ 2) has been synthesized via a facile co-precipitation method. As a cathode, KNMF-3 presents a highly reversible capacity of 133.3 mA h g-1 at 20 mA g-1 as well as an excellent rate capacity of 92.0 mA h g-1 at 600 mA g-1. This material could be a good candidate as a cathode for sodium-ion batteries.