Electrolytic reduction of trichloroethylene and chloroform at a Pt- or Pd-coated ceramic cathode

Trichloroethylene (TCE) and chloroform (CF) were electrolytically dechlorinated in a two-compartment cell in which the working electrode (cathode) consisted of an Ebonex ceramic sheet plated with platinum (Pt) or palladium (Pd). The halogenated targets were not reduced using a cathode of untreated Ebonex. Under typical experimental conditions (e.g., cathode potentials E_c = -0.3 V to -1.4 V vs SHE, pH 7.0), transformations were first order in TCE and CF. Reaction kinetics were mass transport limited at E_c < -1.4 V. Transport-limited rate constants were 0.45 cm min_-1 for TCE reduction and 0.42 cm min_-1 for CF. The primary products of CF reduction were methane and hydrochloric acid. For TCE reduction, major products were ethane, ethylene and hydrochloric acid. Carbon and chlorine mass balances were within 5-10%. Current efficiencies ranged from nearly 100% at E_c = -0.5 V (both reactants) to 24.4% for TCE and 16.6% for CF at E_c = -l.4 V. Rate constants for TCE and CF transformations were inversely related to pH in the range 2 < pH < 11. Pt-Ebonex resisted sulfate and chloride poisoning. The Pd-Ebonex electrode quickly lost activity (50% loss in 5-10 min) in 0.1 M K₂SO₄ electrolyte (cathode potential, E_c = -1.15to -1.4 V vs SHE).