The emergence and establishment of new techniques for material fabrication are of fundamental importance in the development of materials science. Thus, we herein report a general synthetic strategy for the preparation of monolayer graphene. This novel synthetic method is based on the direct solid-state pyrolytic conversion of a sodium carboxylate, such as sodium gluconate or sodium citrate, into monolayer graphene in the presence of Na₂CO₃. In addition, gram-scale quantities of the graphene product can be readily prepared in several minutes. Analysis using Raman spectroscopy and atomic force microscopy clearly demonstrates that the pyrolytic graphene is composed of a monolayer with an average thickness of ~0.50 nm. Thus, the present pyrolytic conversion can overcome the issue of the low monolayer contents (i.e., 1 wt.%–12 wt.%) obtained using exfoliation methods in addition to the low yields of chemical vapor deposition methods. We expect that this novel technique may be suitable for application in the preparation of monolayer graphene materials for batteries, supercapacitors, catalysts, and sensors.

Hierarchical yolk–shell structured cathodes with controllable composition are potentially attractive materials for the fabrication of lithium-ion batteries, but they are difficult to synthesize. In this work, we present a simple, scalable, and general morphology-inheritance strategy to synthesize spinel manganese cathodes with a hierarchical yolk–shell structure. Starting from uniform Mn carbonate spheres prepared by an ultrafast and scalable microwave-assisted method, we show that the subsequent sintering results in the formation of Mn₂O₃ precursors with a yolk–shell structure, which can be effectively transferred to spinel manganese cathodes via simple impregnation and solid-state reaction. Owing to the simple and scalable nature of the present strategy, materials prepared through this approach have great potential as cathodes of lithium-ion batteries, where they can lead to high specific capacity, outstanding cyclability, and superior rate capability. In particular, both LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ with hierarchical yolk–shell structure achieved nearly theoretical capacity, without any apparent decay after 100 cycles at 1 C. Moreover, 80% of the initial discharge capacities of both samples can be maintained for up to 500 cycles at a high rate of 10 C.

Catalysts for oxygen and hydrogen evolution reactions (OER/HER) are at the heart of renewable green energy sources such as water splitting. Although incredible efforts have been made to develop efficient catalysts for OER and HER, great challenges still remain in the development of bifunctional catalysts. Here, we report a novel hybrid of Co₃O₄ embedded in tubular nanostructures of graphitic carbon nitride (GCN) and synthesized through a facile, large-scale chemical method at low temperature. Strong synergistic effects between Co₃O₄ and GCN resulted in excellent performance as a bifunctional catalyst for OER and HER. The high surface area, unique tubular nanostructure, and composition of the hybrid made all redox sites easily available for catalysis and provided faster ionic and electronic conduction. The Co₃O₄@GCN tubular nanostructured (TNS) hybrid exhibited the lowest overpotential (0.12 V) and excellent current density (147 mA/cm²) in OER, better than benchmarks IrO₂ and RuO₂, and with superior durability in alkaline media. Furthermore, the Co₃O₄@GCN TNS hybrid demonstrated excellent performance in HER, with a much lower onset and overpotential, and a stable current density. It is expected that the Co₃O₄@GCN TNS hybrid developed in this study will be an attractive alternative to noble metals catalysts in large scale water splitting and fuel cells.