Alloying promotion of Pd-based metallenes in electrocatalytic hydrogenation of functionalized nitroarenes

Electrocatalytic hydrogenation (ECH) provides a controllable and sustainable reduction of organic compounds via multi-electron-transfer processes under ambient conditions, which urgently demands high-performance electrocatalysts with satisfactory activity and selectivity. Here, two-dimensional Pd-based metallenes are for the first time introduced as efficient electrocatalysts for the ECH of nitroarenes, showing the intrinsic promotion of active sites by alloying effects. Thereinto, a Pd-Mo metallene with a highly exposed active surface and strong electronic interactions between Pd and Mo atoms affords the chemoselective hydrogenation of 4-nitrostyrene (4-NS) toward value-added 4-vinylaniline (4-VA). At -0.25 V vs. RHE, it reaches a high selectivity (>90.0%) and faradaic efficiency (78.3%) of 4-VA, outperforming the counterparts of a home-made Pd metallene and commercial Pd/C. The consistent alloying promotion is further verified on a series of Pd-M (M = Cr, Mo, and W) metallenes, with the specific activity sequence (Pd-Mo > Pd-W > Pd-Cr > Pd) that can be theoretically interpreted by the gradually strengthened chemisorption of 4-NS after alloying Pd with M. Moreover, the good efficiency within a broad substrate scope highlights the promise of Pd-based metallenes in electrochemical refinery.