Transition metal phosphides (TMPs) are promising candidates for sodium ion battery anode materials because of their high theoretical capacity and earth abundance. Similar to many other P-based conversion type electrodes, TMPs suffer from large volumetric expansion upon cycling and thus quick performance fading. Moreover, TMPs are easily oxidized in air, resulting in a surface phosphate layer that not only decreases the electric conductivity but also hinders the Na ion transport. In this work, we present a general electrode design that overcomes these two major challenges facing TMPs. Using metal hydroxide and glucose as precursors, we show that the metal hydroxide can be converted into phosphide whereas the glucose simultaneously decomposes and forms carbon shell on the phosphide particles under a plasma ambient. Ni₂P@C core shell structures as a proof-of-concept are designed and synthesized. The in situ formed carbon shell protects the Ni₂P from oxidation. Moreover, the high-energy plasma introduces porosity and vacancies to the Ni₂P and more importantly produces phosphorus-rich nickel phosphides (NiP_x). As a result, the Ni₂P@C electrodes achieve high sodium capacity (693 mAh·g⁻¹ after 50 cycles at 100 mA·g⁻¹) and excellent cyclability (steady capacity maintained for at least 1, 500 cycles). Our work provides a general strategy for enhancing the sodium storage performance of TMPs, and in general many other conversion type electrode materials that are unstable in air and suffer from large volumetric changes upon cycling.

Creating pores in suprastructures of two-dimensional (2D) materials while controlling the orientation of the 2D building blocks is important in achieving large specific surface areas and tuning the anisotropic properties of the obtained functional hierarchical structures. In this contribution, we report that arranging graphitic carbon nitride (g-C₃N₄) nanosheets into one-dimensional (1D) architectures with controlled orientation has been achieved by using 1D oriented melem hydrate fibers as the synthetic precursor via a polycondensation process, during which the removal of water molecules and release of ammonia gas led to the creation of pores without destroying the 1D morphology of the oriented structures. The resulting porous g-C₃N₄ fibers with both meso- and micro-sized pores and largely exposed edges exhibited good sensing sensitivity and selectivity towards NO₂. The sensing performance was further improved by hybridization of the porous fibers with Au nanoparticles (Au NPs), leading to a detection limit of 60 ppb under ambient conditions. Our results suggest that the highly porous g-C₃N₄ fibers and the related hybrid structures with largely exposed graphitic layer edges are excellent sensing platforms and may also show promise in other electronic and electrochemical applications.