Crystallization-induced thickness tuning of carbon nanosheets for fast potassium storage

Carbon nanosheets (CNS) have garnered significant interest as anode materials for potassium-ion batteries (PIBs) due to the excellent potassium storage kinetics and rate performance. Moreover, tuning the thickness of CNS can enhance the potassium storage performance by exposing abundant surface active sites and shortening the K+ migration path. Herein, crystallization-induced thickness tuning of carbon nanosheets in polyvinyl pyrrolidone-potassium chloride (PVP-KCl) solution is reported to enhance the fast potassium storage. PVP with varying molecular weights is employed to induce the crystallization behavior of KCl, leading to the formation of KCl grains with controllable sizes. Concurrently, these KCl grains act as hard templates for dispersing the PVP molecules to fabricate carbon nanosheets on the surface during annealing. PVP with high molecular weight is beneficial for hindering ion migration to reduce crystal sizes, which can decrease the thickness of carbon nanosheets. The ultrathin structure exposes abundant potassium storage sites, endowing CNS with high reversible capacity (359.0 mAh/g at 100 mA/g). The reduction in the migration path of K+ ions facilitate rapid ion and electron transport kinetics, resulting in rate performance with a capacity of 181.9 mAh/g at 1 A/g. Our work extends the application of the crystallization-induced strategy for controllable designing carbon nanosheets, and puts forward some conceptions on improving the potassium storage performance of carbon anode materials.

DES mediated synthesis of sewage sludge-derived B, N-doped carbons for electrochemical applications

In order to effectively utilize organic matter in sewage sludge (SS), a new porous carbon material was successfully prepared from SS with deep eutectic solvents (DES) (boric acid and urea), in which DES was firstly used to solvent to separate organic matter, also playing the role as a B and N donor as well as acid activator to form porous B, N-carbons. As-synthesized B, N-carbon electrode materials possessed a high specific capacitance of 251.4 F/g at a current density of 1 A/g. It retained 84.28% of the capacitance at an ultrahigh current density of 5 A/g. The energy density was 9.502 Wh/Kg at a power density of 245.4 W/kg in 6 M KOH in symmetric supercapacitor.

Recent advances in the template-confined synthesis of two-dimensional materials for aqueous energy storage devices

The template-confined synthesis strategy is a simple and effective methodology to prepare two-dimensional nanomaterials. It has multiple advantages including green process, controllable morphology and adjustable crystal structure, and therefore, it is promising in the energy storage realm to synthesize high-performance electrode materials. In this review, we summarize the recent advances in the template-confined synthesis of two-dimensional nanostructures for aqueous energy storage applications. The material design is discussed in detail to accommodate target usage in aqueous supercapacitors and zinc metal batteries. The remaining challenges and future prospective are also covered.