RESUMO
As the most promising anodic candidate for alkali ion batteries, red phosphorus (P) still faces big challenges, such as the poor rate and cycling performance, which are caused by the insulative nature and the large volume change throughout the alloy/dealloy process. To ameliorate above issues, the traditional way is confining P into the carbon host. However, investigations on maximizing P utilization are inadequate; in other words, how to achieve entire confinement with a high loading amount is still a problem. Additionally, the application of P in potassium-ion batteries (PIBs) is in its infant stage, and the corresponding potassiation product is controversial. Herein, a nitrogen-doped stripped-graphene CNT (N-SGCNT) as carbon framework is prepared to exclusively confine ultrafine P to construct P@N-SGCNT composites. Benefitting from the in situ cross-linked structure, N-SGCNT loaded with 41.2 wt % P (P2@N-SGCNT) shows outstanding Na+/K+ storage performance. For instance, P2@N-SGCNT exhibits high reversible capacities of 2480 mAh g-1 for sodium-ion batteries (SIBs) and 762 mAh g-1 for PIBs, excellent rate capabilities of 1770 mAh g-1 for SIBs and 354 mAh g-1 for PIBs at 2.0 A g-1, and long cycling stability (a capacity of 1936 mAh g-1 after 2000 cycles for SIBs and 319 mAh g-1 after 1000 cycles for PIBs). Furthermore, due to this exclusively confined P structure, the K+ storage mechanism with the end product of K4P3 has been identified by experimental and theoretical results.
RESUMO
Developing sodium ion battery (SIB) anode materials of a low-cost and high-capacity nature for future large-scale applications still involves challenges. Herein, we have reported gallium sulfide (Ga2S3) as a novel SIB anode material for the first time. Ga2S3 nanorods have been synthesized via the facile hydrothermal preparation of a GaOOH precursor with subsequent H2S annealing. Mixed with graphene upon electrode preparation, this Ga2S3 electrode maintains a reversible specific capacity of 476 mA h g-1 after 100 cycles at a current density of 0.4 A g-1, with a coulombic efficiency of over 99%. Ex situ XRD analysis and theoretical calculations are employed to comprehensively elucidate the detailed sodium ion storage mechanism of Ga2S3, which is composed of initial Na+ intercalation, a subsequent multi-step conversion reaction between S and Na+, and an eventual alloying reaction between Ga and Na+ with the end product of Na7Ga13. Further kinetics analysis has demonstrated that the conversion reaction is the rate-limiting step due to a multi-step reaction with the intermediate phase of GaS. Moreover, the appearance of liquid metal Ga, as confirmed via TEM observations and theoretical calculations, can serve as a self-healing agent that repairs cracks in the electrode. Our findings shed light on the further design of Ga-based materials, and they also can be extended to solid-state-battery systems.
RESUMO
Developing cheap and efficient transition metal-based catalysts for the oxygen evolution reaction (OER) plays the key role in large-scale implementation of hydrogen production. However, there is still a lack of effective ways to tune the catalysts performance for the OER reaction from the aspect of structure design and element modulation simultaneously. Herein, a novel Cu0.33Co0.67S2 hexagonal nanosheet has been synthesized through the coprecipitation reaction followed by subsequent vapor sulfidation. Simply mixed with carbon nanotubes (CNTs) during electrode preparation, this Cu0.33Co0.67S2 exhibits an overpotential of 284 mV vs. RHE at a current density of 10 mA cm-2 in 1.0 M KOH. The improved OER performance of the Cu0.33Co0.67S2 electrode can be attributed to the electrocatalytically active sites involved in octahedral coordination structures and further activated by Cu substitution. The encouraging results provide insight into further rational design of transition metal-based electrochemical catalysts towards OER applications.