Atomic Pd dispersion in triangular Cu nanosheets with dominant (111) plane as a tandem catalyst for highly efficient and selective electrodehalogenation

Single-atom alloys (SAA) in which active metal atoms are atomically dispersed in an inert host possess unique geometric and electronic structures, and generally own higher catalytic performance than their monometallic counterparts. Whereas it is still challenging to facilely synthesize well-defined single atoms embedded in single crystals dominated with a specific active plane. Herein, we synthesized Pd single atoms anchored in triangular Cu nanosheets (Pd1Cu SAA) with dominant active (111) plane via wet chemical synthesis and galvanic replacement as a high-performance catalyst for the electrocatalytic hydrodehalogenation (ECHD) of the refractory tribromophenol. Based on intensive theoretical calculations and experimental work, a hydrogen spillover mechanism was firstly proposed and verified for the highly efficient and selective ECHD. Hydrogen spillover occurs from the hydrogen-rich Pd to the hydrogen-deficient Cu host with a marginal kinetic energy barrier due to the short reaction distance and the negligible interfacial resistance. Meanwhile, the strong metal-support interaction between Pd and peripheral Cu optimizes the adsorption of hydrogenated products to allow for the further catalytic reaction. Consequently, by decoupling the ECHD process into hydrogen adsorption, hydrogen spillover and hydrodebromination, Pd1Cu SAA as a tandem catalyst completely reduced tribromophenol with high phenol selectivity. The intrinsic catalytic activity of Pd and Cu in Pd1Cu SAA substantially outperforms their monometallic counterparts by 14.4 and 3.2 times, respectively. This work showcases that the atomic dispersion of noble metals in SAA offers a promising catalyst design strategy to attain unprecedented catalytic properties via isolating activation and desorption steps.