Nanoscale Double‐Heterojunctional Electrocatalyst for Hydrogen Evolution

The active sites and charge/mass transfer properties in electrocatalysts play vital roles in kinetics and thermodynamics of electrocatalysis, and impose direct impacts on electrocatalytic performance, which cannot be achieved by a simplex structure. As a prototype, the authors propose a double‐heterojunctional nanostructure of NiS(2)/Ni(3)C@C containing NiS(2)/Ni(3)C and Ni(3)C/C heterojunctions as a general model to optimize the above issues and boost electrocatalytic performance. During the thermal reorganization, the in situ reaction between NiS(2) nanoparticles and carbon induces the formation of Ni(3)C between them and constructs tightly contacted two kinds of interfaces among the three components. The TEM and XPS reveal the intimately contacted three components and the as‐constructed interacted dual interfaces, further confirming the formation of a porous double‐heterojunctional nanostructure. Theoretical calculations uncover that the electron density redistribution occurs at Ni(3)C/C interface by spontaneous electron transfer from defected carbon to Ni(3)C and lower ΔG(H*) achieves at NiS(2)/Ni(3)C interface by the concentrated interfacial charge density, which favors the simultaneous realization of high catalytic activity and rapid charge/mass transfer. When applied for hydrogen evolution reaction (HER), the porous double‐heterojunctional NiS(2)/Ni(3)C@C exhibits excellent HER activity and durability among all pH values. Profoundly, this special double‐heterojunctional structure can provide a new model for high‐performance electrocatalysts and beyond.