The formation of a hollow structure and a synergistic effect between CoP and Ni₂P can obviously enhance the electrocatalytic performance of CoP/Ni₂P@HPNCP.

Rational design and construction of high-efficiency and low-cost non-noble metal-based electrocatalysts for the hydrogen evolution reaction (HER) is critical for future renewable energy systems. Herein, a multi-channel V-doped CoP (MC-V-CoP) hollow nanofiber is fabricated via electrospinning and a subsequent oxidation/phosphorization process. The formation of a multi-channel hollow structure and V doping can enlarge the exposure of active sites, facilitate the electron transfer and tune the electronic structure of the active sites, resulting in the enhancement of the HER performance. As a result, the MC-V-CoP hollow nanofiber exhibits excellent HER activity with a low overpotential of 65 and 189 mV at 10 and 300 mA cm⁻² in alkaline medium, respectively. This is superior to the commercial 20 wt% Pt/C catalyst at a high current density (212 mV at 300 mA cm⁻²), manifesting its outstanding performance toward the HER at a high current density. In addition, the MC-V-CoP hollow nanofiber also exhibits outstanding HER activity in neutral medium. The proposed strategy for fabricating multi-channel hollow nanofibers can also be used to prepare other transition metal phosphides for advanced electrochemical applications.

2H-NbSe2 single crystal flake (ca. 2 × 2 × 0.5 mm in size) by chemical vapor transport is employed as the precursor for a top-down preparation of NbSe2 micro/nanoparticles by two kinds of processes, i.e. (1) mechanical exfoliation; (2) ultrasonic-assisted exfoliation in ethanol without ageing and with ageing for 210 days. NbSe2 micro/nanoparticles are applied on top of a Cu disk by a drop-casting process and the tribological property in sliding against a Cu pin under sliding electrical contact is investigated at room temperature. Mechanical exfoliation produces NbSe2 microplatets with typical sizes of 1 μm to 30 μ m with a thickness less than 2 μm. Ultrasonic-assisted exfoliation without aging facilitates the formation of NbSe2 micro/nanoplatets with sizes of 0.1 μm to 25 μm and nano-whiskers with 100 nm in diameter and 1 ~ 3 μm in length, but Nb2O5 and Se are also found on the basis of XPS results. Prolonged aging of the suspensions modifies the morphology by converting platets and whiskers into corrugated floccules (hybrid material), which are composed of Nb2O5, Se, NbSe2, and graphene. Notably, NbSe2 micro/nanoparticles by ultrasonic-assisted exfoliation without ageing exhibit an excellent lubricating property with low friction coefficient (0.3), mild wear, and longer wear lifetime (120 min) than that of mechanical exfoliated NbSe2 microplatets (10 min). The wear lifetime for the aged NbSe2 micro/nanoparticles can be as long as 504 min and are 4.2 times of the sample without aging, which can be a good solid lubricant for sliding electrical contact.