Potential-Driven Dynamic Spring-Effect of Pd─Cu Dual-Atoms Empowered Stability and Activity for Electrocatalytic Reduction.

Atomic-level catalysts are extensively applied in heterogeneous catalysis fields. However, it is a general but ineluctable issue that active metal atoms may migrate, aggregate, deactivate, or leach during reaction processes, suppressing their catalytic performances. Designing superior intrinsic-structural stability of atomic-level catalysts with high activity and revealing their dynamic structure evolution is vital for their wide applications in complex reactions or harsh conditions. Herein, high-stable Pd─Cu dual-atom catalysts with PdN─CuN coordination structure are engineered via strong chelation of Cu-ions with electron pairs from palladium-source, achieving the highest turnover frequency under the lowest overpotential for Cr(VI) electrocatalytic reduction detection in strong-acid electrolytes. In situ X-ray absorption fine structure spectra reveal dynamic "spring-effect" of Cu─Pd and Cu─N bonds that are reversibly stretched with potential changes and can be recovered at 0.6 V for regeneration. The modulated electron-orbit coupling effect of Pd─Cu pairs prevents Cu-atoms from aggregating as metallic nanoparticles. Pd─Cu dual-atoms interact with two O atoms of HCrO, forming stable bridge configurations and transferring electrons to promote Cr─O bond dissociation, which prominently decreases reaction energy barriers. This work provides a feasible route to boost the stability and robustness of metal single-atoms that are easily affected by reaction conditions for sustainable catalytic applications.