A crystalline–amorphous Co₉S₈/CoOOH heterostructure enables efficient and stable SOR-coupled hydrogen evolution

The development of efficient and durable electrocatalysts for SOR-coupled HER systems is critical for advancing sustainable hydrogen production. Herein, we present a crystalline-amorphous Co₉S₈/CoOOH heterostructure anchored on nickel foam (NF) synthesized <i>via</i> a hydrogen peroxide-assisted hydrothermal method, where lattice-ordered Co₉S₈ is partially oxidized and reconstructed into amorphous CoOOH. This crystalline-amorphous heterostructure catalytic system enhances charge transfer efficiency, reducing the SOR onset potential from 1.42 V to 0.417 V. Moreover, the resultant Co₉S₈/CoOOH@NF nanocomposite exhibits exceptional bifunctional performance in a 1.0 M NaOH + 1.0 M Na₂S electrolyte, achieving a current density of 100 mA cm^-2 at an ultralow potential of 0.373 V and sustaining stable operation for 40 h with negligible degradation. The enhanced activity arises from synergistic interfacial interactions, where the Co₉S₈/CoOOH@NF nanocomposite optimizes charge transfer pathways, increases active site density, and dynamically manages sulfur intermediates to prevent electrode passivation. Furthermore, the amorphous CoOOH layer acts as a self-adaptive shield, alleviating structural stress during prolonged electrolysis and resisting sulfur-induced corrosion. This work provides a novel structural regulation paradigm for designing multifunctional electrocatalysts for SOR-coupled hydrogen evolution.