Enhanced atomic hydrogen utilization on ordered Pd1Cu intermetallic single-atom alloy for electrochemical hydrodechlorination.
Electrochemical hydrodehalogenation (ECHD) offers a green route to remove refractory haloacetic acids (HAAs), yet conventional catalysts often fail to achieve effective dehalogenation, producing more toxic partially dehalogenated intermediates. Here, we report a synergistic ECHD process of Cu-O capture, Pd-X activation, and H* utilization on uniform bipolar sites Pdδ--Cuδ+ that enable efficient ECHD of HAAs. These bipolar sites, with a defined coordination environment and a precise 1:1 Pd:Cu atomic ratio, are periodically embedded within a three-layer ordered intermetallic single-atom alloy shell grown on a cubic Cu core. The well-defined motif provides an ideal platform for elucidating the structure-function relationship. Theory and experimental data reveal that the bipolar sites downshift the Pd d-band center, enhance Pd binding energy, and reduce the water-dissociation barrier relative to Cu and Pd nanocubes, thereby optimally balancing the kinetics and thermodynamics of dehalogenation and hydrogenation while mitigating Pd deactivation. The facilitated H* generation over these bipolar sites increases the availability of reactive H* species and markedly promotes effective ECHD. Consequently, Cu/B2 Pd1Cu exhibits the highest trichloroacetic acid (TCAA) degradation rate, acetic acid formation, and overall dechlorination ratio compared with Cu and Pd nanocubes. The TCAA degradation rate constant on Cu/B2 Pd1Cu is nearly twice that of Cu and Pd nanocubes, and the acetic acid yield (0.78 mg L-1) is 1.55 and 3.71 times higher, respectively. This study establishes ordered Pd1Cu intermetallic single-atom alloy layers with uniform bipolar sites as an effective platform for efficient ECHD of HAAs and provides a general design strategy for multifunctional electrocatalysts that couple substrate activation with efficient H* utilization.