Hydride-containing 2-Electron Pd/Cu Superatoms as Catalysts for Efficient Electrochemical Hydrogen Evolution.

The first hydride-containing 2-electron palladium/copper alloys, [PdHCu {S P(O Pr) } (C≡CPh) ] (PdHCu ) and [PdHCu {S P(O Pr) } {S PO(O Pr)} (C≡CPh) ] (PdHCu ), are synthesized from the reaction of [PdH Cu {S P(O Pr) } (C≡CPh) ] (PdH Cu ) with trifluoroacetic acid (TFA). X-ray diffraction reveals that the PdHCu and PdHCu kernels consist of a central PdH unit encapsulated within a vertex-missing Cu cuboctahedron and complete Cu cuboctahedron, respectively. DFT calculations indicate that both PdHCu and PdHCu can be considered as axially-distorted 2-electron superatoms. PdHCu shows excellent HER activity, unprecedented within metal nanoclusters, with an onset potential of -0.05 V (at 10 mA cm ), a Tafel slope of 40 mV dec , and consistent HER activity during 1000 cycles in 0.5 M H SO . Our study suggests that the accessible central Pd site is the key to HER activity and may provide guidelines for correlating catalyst structures and HER activity.