Electrocatalytic Perchlorate Reduction Using an Oxorhenium Complex Supported on a TiO Reactive Electrochemical Membrane.

An organometallic rhenium catalyst was deposited on a TiO reactive electrochemical membrane (Re/REM) for the electrocatalytic reduction of aqueous ClO to Cl. Results showed increasing ClO reduction upon increasing cathodic potential (i.e., -0.4 to-1.7 V/SHE). A 5 mM ClO solution was reduced by ∼21% in a single pass (residence time ∼0.2 s) through the Re/REM at a pH of 7, with >99% Cl selectivity and a current efficiency of ∼100%. Kinetic analysis indicated that the reaction rate constant increased from 3953 to 7128 L h g at pH values of 9 to 3, respectively, and was mass transport-limited at pH < 5. The rate constants were 2 orders of magnitude greater than reported values for an analogous catalytic system using hydrogen as an electron donor. A continuous flow Re/REM system reduced 1 ppm ClO in a groundwater sample by >99.9% for the first 93.5 h, and concentrations were lower than the EPA ClO guideline (56 ppb) for 374 h of treatment. The fast ClO reduction kinetics and high chloride selectivity without the need for acidic conditions and a continual hydrogen electron donor supply for catalyst regeneration indicate the promising ability of the Re/REM for aqueous electrocatalytic ClO treatment.