Enhanced indirect atomic H* reduction at a hybrid Pd/graphene cathode for electrochemical dechlorination under low negative potentials

A Pd/reduced graphene oxide (rGO) hybrid catalyst was fabricated on carbon fiber paper (CFP) via chemical reduction and a subsequent electrodeposition process. The catalytic properties of Pd/rGO/CFP were assessed in electroreductive dechlorination of trichloroacetic acid (TCAA), one of the most common disinfection by-products. In comparative tests of CFP, rGO/CFP, Pd/CFP, and Pd/rGO/CFP, atomic H* could be generated at all four electrodes by an appropriate choice of the applied potential, while Pd/rGO/CFP exhibited superior properties, with the lowest overpotential of -0.5 V. As evidenced by scavenger experiments, TCAA dechlorination mainly proceeded via indirect H* reduction at the Pd-containing catalytic electrodes. DFT calculations indicated easier adsorption of H* on the rGO supported Pd as compared to the bare Pd (E-ads: -3.63 eV vs. -2.93 eV), thereby resulting in an enhanced ability for Pd/rGO/CFP to retain a high surface concentration of atomic H*. Due to the enhanced production of H* stemming from electronic coupling between Pd and rGO sheets, combined with the unique ability of rGO-supported Pd particles to adsorb atomic H*, the hybrid Pd/rGO/CFP cathode possessed superior catalytic properties for TCAA dechlorination.