Concept of Stagnant Capillarity Water in the Nanoporous SiO2@(Zn,Ni)(O,S) Nanocomposite Photocatalyst as a Strategy to Improve Hydrogen Evolution.

(Zn,Ni)(O,S) nanoparticles were uniformly deposited on nanoporous SiO2 spheres to form SiO2@(Zn,Ni)(O,S) nanocomposites (NCs). To obtain optimum deposition of (Zn,Ni)(O,S) on the SiO2 spheres for the hydrogen evolution reaction (HER), different amounts of 0.25, 0.5, 1, and 1.5 mmol zinc precursor for (Zn,Ni)(O,S) were deposited on SiO2 to obtain different SiO2@(Zn,Ni)(O,S) NCs. All the as-prepared catalysts were examined with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, electrochemical impedance spectroscopy, photocurrent response, photoluminescence spectral studies. Finally, the HER performance was evaluated with SiO2@(Zn,Ni)(O,S). The best SiO2@(Zn,Ni)(O,S)-0.5 surprisingly reached 41.1 mmol/gh for generating H2, which was about a 840% increase as compared to that of the SiO2 sphere-free one. The great improvement in the HER rate was due to the utilization of nanoporous SiO2 spheres. The concept of stagnant capillarity water, adopted from the leaf vein system, was applied to explain the enhanced HER reaction.