Key Takeaways & Executive Findings
- •• • The FNS/HEOXY(In) heterostructure electrocatalyst achieves overpotentials of 180 mV for OER and 230 mV for HER at 100 mA cm−2 in alkaline solution, outperforming conventional Ni3S2-based catalysts and approaching noble metal benchmarks. • • The catalyst sustains stable operation for 2000 hours at industrial current densities of 0.5, 1, and 2 A cm−2, demonstrating exceptional durability critical for commercial electrolysis. • • An AEMWE assembled with FNS/HEOXY(In) electrodes requires only 1.86 V to deliver 1 A cm−2 at 80 °C, with continuous operation for 400 hours, meeting industrial voltage and stability targets. • • The built-in electric field, induced by a large work function difference between crystalline FNS and amorphous HEOXY, optimizes adsorption energies of reaction intermediates, as confirmed by experimental and theoretical analyses.
Abstract
Exploring efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions is key to water electrolysis. However, the inherently slow reaction kinetics of electrocatalysis are constrained by mass transfer limitations and unsuitable adsorption/desorption dynamics. Herein, a Fe-doped-Ni3S2/NiFeCoCeIn oxide hydroxide (FNS/HEOXY) crystalline–amorphous heterostructure electrocatalyst with a large work function difference (ΔΦ) and strong built-in electric field (BEF) is successfully designed and synthesized. Benefiting from the electron transfer behavior from FNS to HEOXY, the FNS/HEOXY shows outstanding catalytic activity for both hydrogen and oxygen evolution, along with ultra-high stability in an alkaline medium at an industrial-level current density. Moreover, the anion exchange membrane water electrolyzer (AEMWE) assembled by the FNS/HEOXY requires only a minimal cell voltage of 1.83 V to reach 1 A cm−2 at 80 °C. Both experimental and theoretical results confirm the interfacial charge redistribution induced by the strong BEF, thus finely optimizing the adsorption energy. This work proposes a new design principle toward efficient electrocatalysts for energy conversion.
1. Introduction
Industrial water electrolysis for green hydrogen production is hindered by the sluggish kinetics of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), necessitating efficient and durable electrocatalysts. Noble metal-based catalysts (Pt, RuO2, IrO2) offer high activity but suffer from prohibitive cost and scarcity, limiting large-scale deployment. Transition metal-based catalysts, particularly nickel sulfides, have emerged as promising alternatives, yet their performance at industrially relevant current densities (>200 mA cm−2) is often compromised by poor stability and mass transport limitations. Conventional powder catalysts bound to electrodes with polymer binders exacerbate these issues, leading to active site blockage, high electrical resistance, and delamination under vigorous gas evolution.
This work addresses these bottlenecks by engineering a self-supported crystalline–amorphous heterostructure, FNS/HEOXY, directly grown on nickel foam. The strategic integration of Fe-doped Ni3S2 (crystalline) with a high-entropy oxide hydroxide (amorphous) creates a strong built-in electric field (BEF) due to a large work function difference, driving interfacial charge redistribution. This BEF optimizes the adsorption free energies of hydrogen and oxygen intermediates, dramatically enhancing intrinsic activity. The self-supported architecture eliminates the need for binders, ensuring robust mechanical integrity and rapid mass transport, enabling stable operation at current densities up to 2 A cm−2 for 2000 hours. This design principle offers a scalable pathway to high-performance, low-cost bifunctional electrocatalysts for anion exchange membrane water electrolyzers.
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Derun Li, Guo Wei, Tao Jiang, Hengyi Wu, Shixin Wu, Zhuo Xing, Liqiu Huang, Shuangshuang Huang, Feng Ren (2026). Constructing built-in electric field in crystalline-amorphous heterostructure bifunctional electrocatalysts for highly efficient overall water splitting at high current density. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3802-0
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Frequently Asked Questions
What is the fundamental mechanism by which the built-in electric field (BEF) enhances the electrocatalytic activity of the FNS/HEOXY heterostructure?
The BEF arises from the large work function difference between crystalline FNS and amorphous HEOXY, driving electron transfer from FNS to HEOXY. This interfacial charge redistribution optimizes the adsorption energies of hydrogen and oxygen intermediates, as confirmed by experimental and theoretical analyses, thereby lowering the activation barriers for HER and OER.
How does the FNS/HEOXY catalyst achieve stable operation at high current densities (up to 2 A cm−2) for 2000 hours without significant degradation?
The self-supported, binder-free architecture ensures strong adhesion to the nickel foam substrate, preventing delamination under vigorous gas evolution. The crystalline–amorphous heterostructure provides abundant active sites and facilitates rapid charge transfer, while the BEF maintains optimized adsorption dynamics, collectively contributing to exceptional long-term stability.
What are the specific overpotentials for OER and HER at 100 mA cm−2, and how do they compare to state-of-the-art non-noble metal catalysts?
The FNS/HEOXY(In) catalyst exhibits overpotentials of 180 mV for OER and 230 mV for HER at 100 mA cm−2 in alkaline solution. These values are competitive with or superior to many recently reported non-noble metal bifunctional catalysts, approaching the performance of noble metal benchmarks.
What is the practical cell voltage required for overall water splitting in an AEMWE at industrial current density, and what is the operational stability?
The AEMWE assembled with FNS/HEOXY(In) electrodes requires only 1.86 V to achieve 1 A cm−2 at 80 °C, with continuous operation for 400 hours. This performance meets the technical targets set by the U.S. Department of Energy and the European Commission (1.0 A cm−2 at <1.8 V), demonstrating industrial viability.
How does the high-entropy oxide hydroxide (HEOXY) component contribute to the catalytic performance beyond the BEF effect?
The high-entropy nature of HEOXY introduces multiple metal cations (Ni, Fe, Co, Ce, In) in a single amorphous phase, providing a diverse range of active sites and synergistic effects. This compositional complexity enhances the intrinsic activity and stability, while the amorphous structure offers a high density of unsaturated coordination sites, further promoting catalytic reactions.
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