INVESTIGATION OF FIXATION MECHANISM OF CARBON-DIOXIDE ON OXIDE SEMICONDUCTORS BY CURRENT TRANSIENTS

The fixation mechanism of CO, on tin oxides which are likely to be deg raded during the reduction processes was investigated by a current tra nsient technique, which enables us to make a quick measurements for th e electrode before being degraded. A current transient observed when a step bias is applied was analyzed in terms of CO2 pressure, pH, and e lectrode potential. The total charge passed during the transient was f ound to depend on the square root of CO2 pressure and pH. Combining wi th the XPS data, it was concluded that the hydrocarbonization mechanis m of CO2 on SnO2 in acidic solutions is given by CO2 + H+ + 2e --> HCO O(ad)-It is pointed out that the electroreduction mechanism deduced fr om a long-term electrolysis which is performed under the steady-state condition can be much different from that estimated from the transient technique proposed here. A pulsed electroreduction technique will off er a useful tool in synthesizing desired products from CO2.