Hierarchical Porous Co₉S₈/Nitrogen-Doped Carbon@MoS₂ Polyhedrons as pH Universal Electrocatalysts for Highly Efficient Hydrogen Evolution Reaction

Abstract

The development of highly active and stable earth-abundant electrocatalysts to reduce or eliminate the reliance on noble-metal based ones for hydrogen evolution reaction (HER) over a broad pH range remains a great challenge. Herein, hierarchical porous Co₉S₈/N-doped carbon@MoS₂ (Co₉S₈/NC@MoS₂) polyhedrons have been synthesized by a facile hydrothermal approach using highly conductive Co/NC polyhedrons composed of cobalt nanoparticles embedded in N-doped carbon matrices as both the structural support and cobalt source. The Co/NC polyhedrons were prepared by direct carbonization of Co-based zeolitic imidazolate framework (ZIF-67) in Ar atmosphere. Benefiting from the prominent synergistic effect of N-doped carbon enhancing the conductivity of the hybrid, MoS₂ and Co₉S₈ providing abundant catalytically active sites as well as the well-defined polyhedral structure promoting mechanical stability, the as-synthesized Co₉S₈/NC@MoS₂ shows excellent HER activity and good stability over a broad pH range, with onset overpotentials of 4, 38, and 45 mV, Tafel slopes of 60.3, 68.8, and 126.1 mV dec^-1, and overpotentials of 67, 117, and 261 mV at 10 mA cm^-2 in 1.0 M KOH, 0.5 M H₂SO₄, and 1.0 M phosphate buffer solution (PBS), respectively. This work provides a general and promising approach for the design and synthesis of inexpensive and efficient pH-universal HER electrocatalysts.