The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the β-Mo₂C phase was formed in all metal-doped samples. X-ray photoelectron spectroscopy analysis indicated that the binding energy of Mo²⁺ species (Mo₂C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure β-Mo₂C, the electrocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-Mo₂C). The 2% Pt-Mo₂C required a η₁₀ of 79 mV, and outperformed that of pure β-Mo₂C (η₁₀ = 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpotential (32 mV) in 0.5 M H₂SO₄. Also, the 2% Pt-Mo₂C catalyst demonstrated a high stability for the HER in 0.5 M H₂SO₄. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure.

Seven 3′,8′′-linked bioflavonoids, including one new compound, (2′′S)-2′′, 3′′-dihydroamentoflavone-4′-methyl ether (1) and six known compounds: (2S)-2,3- dihydroamentoflavone-4′-methyl ether (2), (2S,2′′S)-2,3,2′′,3′′-tetrahydroamento- flavone-4′-methyl ether (3), (2S,2′′S)-tetrahydroamentoflavone (4), (2S)-2,3-dihydro- amentoflavone (5) and (2′′S)-2′′,3′′-dihydroamentoflavone (6) and amentoflavone (7), were isolated from the 60% ethanolic extract of Selaginella uncinata (Desv.) Spring. The structures of these compounds were elucidated mainly by analysis of their 1D and 2D NMR spectroscopic data, and their absolute configurations were determined by circular-dichroism (CD) spectroscopy. All the seven compounds showed protective effect against anoxia in the anoxic PC12 cells assay, in which compound 6 displayed particularly potent activity.