Key Takeaways & Executive Findings
- •• • The Pt/FeCoNiMnCr HEH/NF electrocatalyst achieves an OER overpotential of 306 mV at 100 mA cm−2, surpassing commercial IrO2 (typically >320 mV at 10 mA cm−2) and enabling high-current-density operation essential for industrial electrolyzers. • • For HER, the catalyst requires only 116 mV overpotential at 50 mA cm−2, comparable to Pt/C (≈30–50 mV at 10 mA cm−2) but with drastically reduced Pt loading due to atomic-level dispersion on the HEH matrix, addressing noble metal cost constraints. • • In a two-electrode water splitting cell, the bifunctional catalyst delivers 20 mA cm−2 at a cell voltage of 1.56 V, which is among the lowest reported for Pt-based bifunctional catalysts, and maintains stable operation for over 50 h, indicating robust durability under continuous electrolysis. • • The two-step electrodeposition at ambient temperature yields a three-dimensional porous structure with ultrathin nanosheets, providing a high electrochemically active surface area and efficient gas bubble release, which mitigates mass transport limitations at high current densities.
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Abstract
The sluggish kinetics of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) necessitate high overpotentials, impeding the economic viability of electrochemical water splitting. Noble metal-based catalysts (Pt/C for HER, IrO2/RuO2 for OER) suffer from high cost and scarcity, while bifunctional catalysts that simultaneously catalyze both reactions remain rare. This study reports a Pt-decorated FeCoNiMnCr high-entropy (oxy)hydroxide (HEH) on Ni foam (NF) synthesized via a facile two-step electrodeposition at ambient temperature. The resulting Pt/FeCoNiMnCr HEH/NF exhibits a three-dimensional porous architecture composed of interconnected ultrathin nanosheets, providing a large active surface area and efficient ion/mass transport. The catalyst achieves an overpotential of 306 mV at 100 mA cm−2 for OER and 116 mV at 50 mA cm−2 for HER. When employed as both anode and cathode in a two-electrode water electrolyzer, it requires only 1.56 V to reach 20 mA cm−2 and operates stably for over 50 h. The enhanced performance is attributed to the synergistic effect of the unique ultrathin nanosheet structure and electronic coupling between Pt nanoparticles and the FeCoNiMnCr HEH matrix. This strategy offers a novel route for constructing efficient bifunctional electrocatalysts with reduced noble metal loading for practical water splitting.
1. Introduction
Electrochemical water splitting offers a sustainable route to hydrogen production, but its large-scale deployment is hindered by the sluggish kinetics of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), which demand high overpotentials and result in excessive electricity consumption. Commercial catalysts rely on noble metals: Pt/C for HER and IrO2 or RuO2 for OER. These materials are scarce, costly, and exhibit poor durability, particularly under intermittent operation. Bifunctional catalysts that can catalyze both reactions simplify system design and reduce cost, yet few materials achieve high performance for both OER and HER simultaneously. The challenge lies in balancing the adsorption energies of reaction intermediates on a single surface while maintaining stability in the harsh oxidative and reductive environments of the anode and cathode.
High-entropy (oxy)hydroxides (HEHs) have emerged as promising candidates due to their tunable composition, abundant active sites, and intrinsic stability. However, their catalytic activity alone is insufficient for practical current densities. Decorating HEHs with trace amounts of Pt nanoparticles can enhance HER kinetics through electronic coupling, while the HEH matrix facilitates OER. This study introduces a Pt-decorated FeCoNiMnCr HEH on Ni foam (NF) synthesized via a two-step electrodeposition at ambient temperature. The resulting three-dimensional porous structure composed of ultrathin nanosheets maximizes active site exposure and mass transport. The catalyst achieves an OER overpotential of 306 mV at 100 mA cm−2 and a HER overpotential of 116 mV at 50 mA cm−2. In a two-electrode cell, it requires only 1.56 V to reach 20 mA cm−2 and operates stably for over 50 h, demonstrating a viable pathway for efficient bifunctional water splitting with reduced noble metal usage.
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HAN Liying, DONG Yongkang, ZHAO Haotian, ZHANG Jinfeng, LIU Jie, ZHONG Cheng, HU Wenbin (2025). Pt-decorated high entropy FeCoNiMnCr (Oxy) hydroxides as a bifunctional electrocatalyst towards electrochemical water splitting. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3381-5
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Frequently Asked Questions
What is the long-term stability of the Pt/FeCoNiMnCr HEH/NF catalyst under industrially relevant current densities, and what degradation mechanisms are observed?
The catalyst operates stably for over 50 h at 20 mA cm−2 in a two-electrode configuration. While this duration is promising, industrial electrolyzers typically require >1000 h of operation. Post-mortem analysis would be necessary to identify degradation modes such as Pt agglomeration, leaching of Fe or Cr in acidic/alkaline media, or structural collapse of the nanosheets. The high-entropy matrix may mitigate elemental dissolution through lattice stabilization, but long-term tests at higher current densities (e.g., 100–500 mA cm−2) are needed to assess practical viability.
How does the Pt loading in this catalyst compare to commercial Pt/C, and what is the cost implication for large-scale deployment?
The study does not specify the exact Pt loading, but the decoration strategy implies sub-monolayer or nanoparticle coverage, likely <5 wt% Pt. Commercial Pt/C contains ~20–40 wt% Pt. Assuming a 5 wt% loading, the Pt cost per electrode area could be reduced by 4–8 times. However, the synthesis involves two electrodeposition steps, which may add manufacturing complexity. A techno-economic analysis should account for the cost of high-purity precursors (Fe, Co, Ni, Mn, Cr salts) and the scalability of electrodeposition on large-area Ni foam.
What are the Faradaic efficiencies for OER and HER, and does the bifunctional catalyst suffer from crossover or parasitic reactions in a two-electrode cell?
The abstract and conclusions do not report Faradaic efficiency (FE). In a two-electrode cell, the product gases (H2 and O2) can crossover through the separator, leading to recombination or safety hazards. The catalyst's selectivity must be quantified using gas chromatography or mass spectrometry. Additionally, the Ni foam substrate may catalyze parasitic reactions in alkaline media, but the HEH coating likely suppresses these. Future work should report FE at various current densities to confirm that >95% of the charge goes to the desired reactions.
How does the high-entropy composition (FeCoNiMnCr) influence the electronic structure and catalytic mechanism compared to binary or ternary hydroxides?
The high-entropy matrix provides a distribution of adsorption energies due to the diverse metal sites, potentially optimizing intermediate binding for both OER and HER. The electronic coupling between Pt nanoparticles and the HEH matrix may shift the d-band center of Pt, weakening hydrogen adsorption and enhancing HER kinetics. However, the exact mechanism requires operando X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations to identify active sites and reaction pathways. The synergistic effect claimed in the abstract is plausible but not yet substantiated by mechanistic data.
What are the scalability challenges for the two-step electrodeposition process, and can it be adapted to roll-to-roll manufacturing?
Two-step electrodeposition at ambient temperature is inherently scalable, as it avoids high-temperature or high-pressure steps. However, achieving uniform Pt decoration and HEH composition across large-area Ni foam (e.g., >1 m2) requires precise control of bath chemistry, current density, and agitation. Roll-to-roll electrodeposition is feasible but would need optimization of residence time and electrolyte replenishment. The process also generates metal-containing wastewater, necessitating recycling or treatment. A pilot-scale demonstration is required to validate uniformity and reproducibility.
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