Electrochemical reduction of dichlorodifluoromethane at a Nafion® solid polymer electrolyte cell

The electrochemical reduction of dichlorodifluoromethane (CFC-12) at Ag, Pd, Cu and Au electrodes (which were deposited on Nafion(R) 117 (H+ form) membranes, by reduction with NaBH4 (10% w/v) solution) was studied. The products of the reduction were CHCIF2, CH2F2, CH3F and CH4, as well as small amounts of dimers, CF2=CF2 and CHF2CHF2. The silver electrode gave the highest current efficiency (CE) and reduction rate. The rate of reduction at the silver electrode was almost 10-160 times higher than that measured for the other electrodes, under the same conditions. Selectivity of CH4 production increased for all metals with increasing negative potential, except for CHCIF2 where it decreased. For the other products, a maximum in the selectivity-potential curve appeared. This fact led us to the conclusion that the reduction proceeds by the following mechanism: CCl2F2--> CHClF2 --> CH2F2 --> CH3F --> CH4. The rate of reduction of CFC-12 and the product distribution also depend on the pi-I of the solution, which is in contact with the membrane. The rate of reduction at the silver electrode was about 4000 times higher at pH 14 than at pH 1. The cation of the supporting electrolyte was also important: the rate of reduction was lowered in the order K+ > Na+ > Li+, and this was attributed to the size of the cations, which influenced the structure of the double layer. (C) 2000 Elsevier Science S.A. All rights reserved.