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

The first hydride‐containing 2‐electron palladium/copper alloys, [PdHCu11{S2P(OiPr)2}6(C≡CPh)4] (PdHCu11) and [PdHCu12{S2P(OiPr)2}5{S2PO(OiPr)} (C≡CPh)4] (PdHCu12), are synthesized from the reaction of [PdH2Cu14{S2P(OiPr)2}6(C≡CPh)6] (PdH2Cu14) with trifluoroacetic acid (TFA). X‐ray diffraction reveals that the PdHCu11 and PdHCu12 kernels consist of a central PdH unit encapsulated within a vertex‐missing Cu11 cuboctahedron and complete Cu12 cuboctahedron, respectively. DFT calculations indicate that both PdHCu11 and PdHCu12 can be considered as axially‐distorted 2‐electron superatoms. PdHCu11 shows excellent HER activity, unprecedented within metal nanoclusters, with an onset potential of −0.05 V (at 10 mA cm−2), a Tafel slope of 40 mV dec−1, and consistent HER activity during 1000 cycles in 0.5 M H2SO4. 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. The acid treatment of PdH2Cu14 leads to the transformation of a bicapped icosahedral Cu14 core into an uncomplete Cu11 (in PdHCu11) and a Cu12 (in PdHCu12) cuboctahedron, both of which are 2e superatoms. Electrochemical HER experiments indicate while PdHCu11, PdHCu12, and PdH2Cu14 are active catalysts, the stability and efficiency of PdHCu11 is much higher than those of PdHCu12 and PdH2Cu14.