Abstract
Surface wettability is of importance for electrochemical reactions. Herein, its role in electrochemical hydrogen evolution reactions is investigated using light-sensitive nanotubular TiO2 supported Pt as hydrogen evolution electrodes (HEEs). The HEEs are fabricated by photocatalytic deposition of Pt particles on TiO2 nanotubes followed by hydrophobization with vaporized octadecyltrimethoxysilane (OTS) molecules. The surface wettability of HEEs is subsequently regulated in situ from hydrophobicity to hydrophilicity by photocatalytic decomposition of OTS molecules using ultraviolet light. It is found that hydrophilic HEEs demonstrate a larger electrochemical active area of Pt and a lower adhesion force to a gas bubble when compared with hydrophobic ones. The former allows more protons to react on the electrode surface at small overpotential so that a larger current is produced. The latter leads to a quick release of hydrogen gas bubbles from the electrode surface at large overpotential, which ensures the contact between catalysts and electrolyte. These two characteristics make hydrophilic HEEs generate a much high current density for HERs. Our results imply that the optimization of surface wettability is of significance for improving the electrocatalytic activity of HEEs.
Highlights
Surface wettability, as one of fundamental surface properties of an electrode, shows a significant influence on electrolyte-wetting, redox electron transfer and gas release in electrochemical reactions[8,9,10,11]
The magnified SEM image of TiO2-NTs without covering of Pt aggregates (Inset of Fig. 2b) show that Pt nanoparticles with a size of ~10 nm distribute on the perimeter of nozzles of TiO2-NTs, which indicates that Pt catalysts distributes throughout the whole surface of TiO2-NTs
Our results are consistent with the findings of Herrmann et al that some Pt particles are present as large aggregates after a long-time photocatalytic reaction besides the small Pt nanoparticles[30]
Summary
Hydrogen Evolution Reactions received: 09 August 2016 accepted: 30 December 2016 Published: 06 February 2017. It is found that hydrophilic HEEs demonstrate a larger electrochemical active area of Pt and a lower adhesion force to a gas bubble when compared with hydrophobic ones The former allows more protons to react on the electrode surface at small overpotential so that a larger current is produced. It is found that hydrophilic HEEs generate a much higher current density for HERs when compared with hydrophobic ones We conclude that this high electrocatalytic activity is associated with their large electrochemical active area of Pt and low adhesion force to a gas bubble
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