Abstract
The anodic oxidation of various reactants dissolved in water was studied on a zinc oxide single‐crystal electrode by electrical techniques. It was found that only a few substances inject electrons into the conduction band. However, many reactants are oxidized by holes, which are created in the crystal by illumination: A class of two‐or multi‐equivalent reducing agents, called current‐doubling agents, undergoes oxidation by a two‐step mechanism in which reaction with a hole leads to the formation of a radical‐type intermediate, which then injects an electron in the conduction band. Relative hole reactivities for different reagents were determined by making current measurements during competitive oxidation of current‐doubling and noncurrent‐doubling reactants. The reactivity of different radical‐type intermediates toward oxidizing agents was investigated. Experimental support is given for the idea that a common intermediate, the hydrogen atom, is formed during the oxidation of many organic current‐doubling species. Differences in behavior depending on the crystal face are discussed.