Coordination-directed ternary MOF-on-MOF-derived bimetal phosphide-carbon nanomaterials for efficient overall water splitting
The development of efficient, durable, and cost-effective electrocatalysts for overall water splitting (OWS) is critical for sustainable hydrogen production. Noble metal-based catalysts (Pt, Ru, Ir) exhibit high activity but suffer from scarcity and poor stability, while transition metal-based alternatives often lack sufficient active site utilization and mass transport. This work presents a coordination-directed synthesis of a ternary MOF-on-MOF heterostructure (ZIF-67@MOF-74@PBA) that serves as a precursor for bimetallic CoFeP nanoparticles anchored on hierarchically porous carbon nanomaterials with in situ grown carbon nanotubes (CNTs). The resulting catalyst features hollow structures with high site exposure, efficient mass and charge transport pathways, and synergistic effects from multiple transition metals. In 1.0 M KOH, the catalyst achieves a hydrogen evolution reaction (HER) overpotential of 107 mV at 10 mA cm−2, an oxygen evolution reaction (OER) overpotential of 231 mV at 10 mA cm−2, and an overall water splitting voltage of 1.544 V at 10 mA cm−2, with remarkable long-term stability. Apparent activation energy measurements and density functional theory (DFT) calculations reveal that the in situ integration of bimetals and phosphorus doping enhance O–O coupling in the OER and optimize hydrogen adsorption/desorption in the HER. This synthesis strategy offers a versatile approach for designing multi-level MOF-on-MOF systems as high-performance electrocatalysts, addressing the limitations of conventional transition metal catalysts in industrial water electrolysis.