Controlled Reduction of a Ni-Based Metal–Organic Framework Regulates the Electron Penetration to Pd as a Bifunctional Catalyst for a Thermal/Electrochemical Hydrogenation Reaction

Precise modulation of interfacial electronic structures is crucial for enhancing the catalytic activity and selectivity in heterogeneous catalysis. The electron penetration effect (EPE), involving electron transfer from a metal core through a protective shell to surface active sites, has emerged as an effective strategy for tuning surface electronic properties and promoting catalytic performance. However, controlled manipulation of EPE remains challenging, particularly in regulating the phase structure of the metal core and the characteristics of the encapsulating shell. In this work, nitrogen-doped graphene-coated Ni nanoparticles were synthesized from a Ni-based metal-organic framework (Ni-MOF-<i>T</i>/<i>t</i>) by systematically adjusting the reduction temperature (<i>T</i>) and time (<i>t</i>). Subsequent deposition of Pd species yielded Pd/Ni-MOF-<i>T</i>/<i>t</i> catalysts. Among them, the optimized Pd/Ni-MOF-400 °C/2 h catalyst, featuring a hexagonal Ni core, exhibited enhanced electron penetration across the graphitic shell to the Pd sites, effectively modulating the surface electronic structure and boosting catalytic activity. The catalyst demonstrated excellent performance in both thermocatalytic hydrogenation of benzonitrile (90% conversion, 99.0% selectivity) and electrochemical hydrogenation of 4-nitrophenol (96.5% conversion, 90.5% Faradaic efficiency). These findings highlight that phase-controlled electron penetration provides a versatile and generalizable approach for constructing multifunctional catalysts with superior activity under mild conditions. This work establishes phase engineering of MOF-derived metal-carbon interfaces as an effective strategy to manipulate electron penetration effects and optimize catalytic performance.