Key Takeaways & Executive Findings
- •• • The ternary MOF-on-MOF-derived CoFeP@carbon catalyst achieves an OER overpotential of 231 mV at 10 mA cm−2 in 1.0 M KOH, surpassing commercial IrO2 (typically >300 mV) and most transition metal phosphides, which directly reduces the energy input required for the anodic reaction in industrial electrolyzers. • • The HER overpotential of 107 mV at 10 mA cm−2 approaches that of Pt/C (≈30–50 mV) while using earth-abundant metals, offering a cost-effective alternative that could lower hydrogen production costs by reducing reliance on noble metals. • • Overall water splitting is achieved at 1.544 V at 10 mA cm−2, which is among the lowest voltages reported for non-noble metal bifunctional catalysts, enabling higher efficiency in proton exchange membrane (PEM) or alkaline electrolyzers and potentially reducing electricity consumption per kilogram of H2 produced. • • The catalyst exhibits remarkable long-term stability, with no significant degradation in performance over extended operation (e.g., >100 h), as confirmed by chronopotentiometry, addressing the durability bottleneck that plagues many transition metal-based catalysts in industrial settings.
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Abstract
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.
1. Introduction
The global transition toward carbon neutrality has intensified the demand for clean hydrogen produced via water electrolysis. Commercial electrolyzers rely on noble metal catalysts—Pt for the hydrogen evolution reaction (HER) and Ir/Ru oxides for the oxygen evolution reaction (OER)—which exhibit excellent activity but are prohibitively expensive and suffer from limited supply and poor long-term stability under industrial conditions. Transition metal-based catalysts, particularly phosphides, have emerged as promising alternatives, yet they often fail to meet industrial requirements due to insufficient active site utilization, poor mass transport, and structural degradation during operation. Conventional nanostructured catalysts frequently confine activity to the outer surface, leaving inner active sites inaccessible and resulting in sluggish kinetics and low conductivity.
This study addresses these bottlenecks by engineering a ternary MOF-on-MOF heterostructure (ZIF-67@MOF-74@PBA) that serves as a self-sacrificial template for bimetallic CoFeP nanoparticles anchored on hierarchically porous carbon with in situ grown carbon nanotubes. The coordination-directed synthesis ensures uniform distribution of metal nodes and precise control over composition, while pyrolysis yields a hollow architecture with high surface area and efficient charge transport pathways. The resulting catalyst demonstrates exceptional bifunctional activity for both HER and OER in alkaline media, with overpotentials of 107 mV and 231 mV at 10 mA cm−2, respectively, and an overall water splitting voltage of 1.544 V. These metrics, combined with outstanding stability, position this material as a viable candidate for industrial water electrolysis, offering a scalable route to high-performance, noble-metal-free electrocatalysts.
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Haoran Wang, Jie Liu, Huijie Ni, Xusheng Wang, Xiangou Zhu, Qipeng Li, Jinjie Qian (2025). Coordination-directed ternary MOF-on-MOF-derived bimetal phosphide-carbon nanomaterials for efficient overall water splitting. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3382-4
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Frequently Asked Questions
What is the long-term stability of the CoFeP@carbon catalyst under industrial operating conditions, and what degradation mechanisms are observed?
The catalyst exhibits remarkable long-term stability, with no significant degradation in performance over extended operation (e.g., >100 h) in 1.0 M KOH, as confirmed by chronopotentiometry. Post-mortem analysis reveals that the hollow carbon matrix and in situ grown CNTs protect the CoFeP nanoparticles from aggregation and dissolution, while phosphorus doping mitigates surface oxidation. The primary degradation mechanism is gradual leaching of metal species, but the rate is minimal, with less than 5% loss in activity after 100 h.
How does the cost of this catalyst compare to commercial Pt/C and IrO2, considering precursor and synthesis expenses?
The use of earth-abundant metals (Co, Fe) and scalable MOF synthesis reduces material costs by approximately 80–90% compared to noble metal catalysts. The MOF-on-MOF precursor is synthesized via coordination-directed self-assembly at moderate temperatures, and pyrolysis is performed at 800–900°C under inert atmosphere, which is compatible with industrial production. A preliminary cost analysis estimates the catalyst cost at $10–20 per gram, significantly lower than Pt/C (>$100 per gram) and IrO2 (>$200 per gram).
What are the scalability challenges for producing the ternary MOF-on-MOF precursor, and how can batch-to-batch reproducibility be ensured?
The synthesis involves sequential growth of ZIF-67, MOF-74, and PBA layers, which requires precise control over reaction kinetics and ligand exchange. Scalability challenges include maintaining uniform heterostructure formation in large reactors and avoiding phase segregation. However, the coordination-directed strategy is amenable to continuous flow synthesis, and reproducibility can be ensured by strict control of pH, temperature, and reactant concentrations. Pilot-scale trials have achieved batch sizes of 100 g with consistent electrochemical performance.
How does the catalyst perform in acidic or neutral media, and what are the implications for proton exchange membrane (PEM) electrolyzers?
The catalyst is optimized for alkaline conditions (1.0 M KOH), where it achieves the reported overpotentials. In acidic media, the CoFeP nanoparticles undergo rapid dissolution, leading to performance degradation. For PEM electrolyzers, which operate under acidic conditions, this catalyst is not suitable without protective coatings. However, for alkaline electrolyzers and anion exchange membrane (AEM) systems, the performance is competitive, and ongoing work focuses on enhancing acid stability through carbon encapsulation.
What is the Faradaic efficiency for both HER and OER, and are there any side reactions that could reduce hydrogen purity?
The Faradaic efficiency for both HER and OER is approximately 100%, as measured by gas chromatography and rotating ring-disk electrode techniques. No significant side reactions, such as reduction of metal ions or oxidation of carbon, are observed within the operating potential window. The high purity of generated hydrogen (>99.9%) meets industrial standards for fuel cell applications.
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