THE INFLUENCE OF ELECTRODE POROSITY AND TEMPERATURE ON ELECTROCHEMICAL GAS EVOLUTION AT PLATINUM AND RHODIUM

The influence of electrode porosity and temperature on the rate of electrochemical gas evolving processes (H2, Cl2, O2) was investigated. The experiments were carried out at electrodes with small pores (≤3 nm) and at smooth electrodes. To understand the results the hydrogen evolution process was used for detailed investigations. It was shown that the pores are only effective if the gas evolving process is an irreversible one (as with oxygen). The pores do not operate in the case of hydrogen and chlorine evolution. An explanation of this different behaviour is given. The temperature dependencies of the overvoltages of the chlorine and hydrogen processes are in contrast. An increase of hydrogen overvoltage with rising temperature is not yet fully understood. It can be stated, however, that the effectiveness of the hydrogen transport from the electrode surface into the bulk of solution decreases with increasing temperature. © 1990 Chapman and Hall Ltd.