ELECTROCHEMICAL STUDY OF DIAMOND THIN-FILMS IN NEUTRAL AND BASIC SOLUTIONS OF NITRATE

The electrochemical behavior of boron-doped diamond films has been inv estigated in a number of neutral and alkaline solutions with and witho ut nitrate ions. Two kinds of diamond electrode were studied: self-sup ported film (100 mu m) (sample A) and diamond film (10 mu m) supported on a Si substrate (sample B). It was found that water oxidation and r eduction appear at much larger polarizations for diamond electrodes, a s compared with platinum and platinized platinum electrodes. In partic ular, the higher (cathodic) overpotential for hydrogen reduction permi ts efficient nitrate reduction to ammonia. The underlying Si substrate is shown to take part in the electrochemistry of the diamond electrod es. In the case of the Si-supported electrode (sample B) the reaction with the Si substrate was imminent. For the free-standing diamond elec trode (sample A) various impurities in the grain boundaries and at the back of the electrode, including the back metallic contact, intervene d with the electrochemistry of the diamond electrode, but to a much le sser extent than with sample B. Meticulous cleaning and careful workin g practices permitted this interference to be excluded altogether in s ample A.