The electrocatalytic dechlorination of chloroacetic acids at electrodeposited Pd/Fe-modified carbon paper electrode
Pd/Fe-modified carbon paper (Pd/Fe-C) electrode was prepared from PdCl2 and FeSO4 via electrodeposition onto carbon paper. It was observed that the diameters of electrodeposited Pd/Fe particles were around 20 nm with a uniform distribution on carbon paper, which is smaller than Pd/Fe particles of impregnated and calcined electrode. The electrodeposited Pd/Fe-C electrode exhibited higher activity in dechlorination of chloroacetic acids than impregnated and calcined electrode. Under optimal experiment conditions of Pd:Fe molar ratio of 2:1 at −1.5 V (vs SCE), 95% of trichloroacetic acid (TCAA) with the initial concentration of 500 μg/L was removed within 20 min at pH 3. The dechlorination of chloroacetic acids followed the order of TCAA > dichloroacetic acid (DCAA) > monochloroacetic acid (MCAA). MCAA cannot be dechlorinated at C and Fe-C electrodes via direct reduction. However, a part of chloroacetic acids was directly dechlorinated to acetic acid at Pd-C and Pd/Fe-C electrodes via indirect reduction. The Pd(0) and Pd(II) species were detected by X-ray photoelectron spectroscopy. Compared with the individual Pd-C electrode, in situ formation of Fe(0) decreased the interface impedance as observed by electrochemical impedance spectroscopy analysis. In conclusion, the presence of Pd(0) nanoparticles played a significant role in forming atomic H* to realize indirect reduction process which could achieve the complete dechlorination of chloroacetic acids.
Graphical abstract. The dechlorination of chloroacetic acids at Pd/Fe-modified carbon paper electrode proceeded by direct and indirect reduction. Indirect reduction by atomic H* was the primary process to realize the complete dechlorination of chloroacetic acids by Pd/Fe-modified carbon paper cathode.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Electrodeposited Pd/Fe-C cathode exhibited high dechlorination ability. ► Stepwise dechlorination of TCAA and DCAA to MCAA was achieved by direct reduction. ► Chloroacetic acids were reduced to acetic acid via indirect reduction by H*. ► Pd(0) nanoparticles of Pd/Fe-C cathode played a significant role in forming H*. ► Fe(0) nanoparticles of Pd/Fe-C cathode could enhance the transport of electrons.
Journal: Applied Catalysis B: Environmental - Volumes 111–112, 12 January 2012, Pages 628–635