Disrupted Spin Degeneracy Promoted C≡C Triple Bond Activation for Efficient Electrochemical Acetylene Semihydrogenation

Disrupting the spin degeneracy of the electrocatalyst and further manipulating the related orbital electron arrangement are highly desirable for activating acetylene molecules. Herein, a squarate cobalt-based metal-organic framework (Co-MOF) ([Co₃(C₄O₄)₂(OH)₂]·3H₂O) is post-treated to accelerate the evolution from CoO₆ octahedron to CoO₅ pentahedron and further utilized for the electrochemical acetylene semihydrogenation reaction. Comprehensive analyses corroborate that the disrupted spin degeneracy of active sites originated from the breakage of the Co-O bond, which promotes the cleavage of the orbital energy level and the rearrangement of the d-orbital electron. The newly emerged half-occupied d_x²_-y² orbitals and empty d_z² orbitals in CoO₅ pentahedron concerted interplay with the bonding and antibonding orbitals of acetylene, which reduces the adsorption energy of acetylene and facilitates the activation of the inert C≡C triple bond. Thus, the defective Co-MOF exhibits the superior ethylene Faradaic efficiency of 96% and partial current density of 128 mA cm^-2 at −1.0 V vs RHE compared to that of pristine Co-MOF (FE_C2H4: 60%; J_C2H4: 66 mA cm^-2). This work delivers inspiration for spin-state regulation of active sites and sparks renewed interest in designing highly efficient electrocatalysts.