Hydrogen production from photolysis of steam adsorbed onto platinized SrTiO₃

Abstract

Photodissociation of high pressure (1–8 atm) water vapour adsorbed onto the partially platinized surface of single crystal SrTiO₃ has been observed. The reaction is catalytic; several thousands of monolayers of hydrogen have been produced. The reaction requires light of greater than bandgap (3.1 eV) energy, and proceeds vigorously only if elevated temperatures (375–450 K) and high pressures are used. Recombination of products and poisoning of the metal apparently diminishes the reaction rate after several hours. Previous work on this reaction has been done in the presence of an electrolyte, generally at room temperature. The present work is a significant departure from such an environment, and is important because the surface is not contaminated with an electrolyte. The surface is therefore accessible to ultra high vacuum surface analytical techniques such as electron spectroscopy, before and after the reaction. From these studies detailed information about the mechanism may be obtained. In addition, the existence of a surface hydrogen species at elevated temperatures allows us to combine water photolysis directly with other catalytic reactions, such as ammonia synthesis with N₂ and methane synthesis with CO or CO₂.