Key Takeaways & Executive Findings
- •• • Overpotential of 19 mV at 10 mA cm−2 in alkaline natural seawater: This value is among the lowest reported for Pt-based catalysts, directly reducing the energy input required for industrial-scale seawater electrolysis, where every millivolt saved translates to significant operational cost reductions. • • Tafel slope of 31 mV dec−1: Indicates a Tafel-limited mechanism with fast HER kinetics, suggesting that the hydroxyl-rich interface accelerates water dissociation and hydrogen adsorption, enabling higher current densities at lower overpotentials compared to conventional PtNi catalysts. • • Stability over 100 h with only slightly elevated overpotential: Demonstrates resistance to Cl− poisoning and corrosion, addressing the primary failure mode of Pt catalysts in seawater; this durability is critical for continuous hydrogen production without frequent catalyst replacement. • • Ni vacancies as Lewis acid sites promote transformation of lattice hydroxyls to dissociative hydroxyls: This surface engineering strategy increases hydrophilicity and Cl− resistance, providing a scalable route to enhance catalyst performance without noble metal content increase, potentially lowering material costs.
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Abstract
Adsorption and corrosion caused by Cl− are the main reasons for the low performance of Pt-based catalysts for the hydrogen evolution reaction (HER) in seawater. Although the introduction of hydroxyl species is an ideal approach to enhance HER kinetics and resist harmful Cl−, achieving this goal in Pt-based catalysts is challenging. In this study, we developed a high-temperature reduction process to generate PtNi alloy particles that contain Ni vacancies (Lewis acid sites) that participate in transforming lattice hydroxyls to dissociative hydroxyls on Ni layered double hydroxides (Ni-LDH). The hydroxyls in Ni-LDH bind with Lewis acid active sites to form hydroxyl rich species, a process which enhances the hydrophilicity of PtNi/Ni-LDH to promote water adsorption and enhance resistance to Cl− absorption. Owing to these properties, PtNi/Ni-LDH exhibits superior performance as an electrocatalyst for the HER in alkaline natural seawater as reflected by a low overpotential of 19 mV to drive a current density of 10 mA cm−2, a low Tafel slope of 31 mV dec−1, and an only slightly elevated overpotential after 100 h of operation. This study throws light on the development of new strategies for the design of high-performance catalysts for hydrogen production by electrolytic seawater splitting.
1. Introduction
Electrocatalytic seawater splitting offers a low-cost, large-scale route to hydrogen production, but the cathodic hydrogen evolution reaction (HER) suffers from Cl− adsorption and corrosion, as well as unfavorable water dissociation kinetics on Pt surfaces. Alkaline seawater mitigates microorganism fouling and Ca2+/Mg2+ precipitation, yet Pt-based catalysts still exhibit unsatisfactory performance and durability due to poisoning (M + Cl− → MClads + e−) and subsequent corrosion (MClads + Cl− → MClx−; MClx + OH− → M(OH)x + Cl−). Alloying Pt with Ni improves HER activity by altering electronic states, but the intrinsic water dissociation barrier and Cl− affinity remain unresolved.
Introducing hydrophilic hydroxyl species onto Pt surfaces can accelerate water dissociation and weaken Cl− adsorption, but creating high-density hydroxyls on Pt is hindered by the lack of Lewis acid sites. Ni layered double hydroxides (Ni-LDH) possess coordinately unsaturated edge sites that bind hydroxyls, yet their inert basal planes limit hydroxyl density. This study develops a high-temperature reduction method to generate PtNi alloy particles with Ni vacancies that act as Lewis acid sites, transforming lattice hydroxyls into dissociative hydroxyls on Ni-LDH. The resulting PtNi/Ni-LDH heterojunction exhibits enhanced hydrophilicity, water adsorption, and Cl− resistance, achieving a low overpotential of 19 mV at 10 mA cm−2, a Tafel slope of 31 mV dec−1, and stable operation for 100 h in alkaline natural seawater.
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ZHAO Wen-Ying, YANG Xiong, XIAO Yu-Xuan, YU Fei, TIAN Ge, SHEN Ling, LU Yi, GENG Wei, WU Si-Ming, YING Jie, TIGINYANU Ion, OZOEMENA Kenneth I., YANG Xiao-Yu (2025). PtNi Nanoparticles with Rich Hydroxyl Species as Efficient Catalysts for the Electrochemical Hydrogen Evolution Reaction in Seawater. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3389-3
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Frequently Asked Questions
What is the primary failure mechanism of Pt-based catalysts in seawater, and how does this catalyst mitigate it?
The primary failure mechanism is Cl− adsorption and subsequent corrosion, forming MClads and MClx− species that poison active sites. This catalyst mitigates it by creating a hydroxyl-rich surface on Ni-LDH that binds with Ni vacancies (Lewis acid sites), enhancing hydrophilicity and promoting water adsorption over Cl−, as evidenced by only slightly elevated overpotential after 100 h in alkaline natural seawater.
How does the overpotential and Tafel slope compare to commercial Pt/C in alkaline seawater?
The overpotential of 19 mV at 10 mA cm−2 and Tafel slope of 31 mV dec−1 are superior to typical Pt/C, which often requires >30 mV overpotential and exhibits Tafel slopes >40 mV dec−1 in seawater due to Cl− poisoning. This improvement is attributed to the hydroxyl-rich interface that accelerates water dissociation and reduces Cl− competition.
What are the scalability bottlenecks for synthesizing PtNi/Ni-LDH, and what is the estimated cost impact?
The high-temperature reduction process to generate Ni vacancies and hydroxyl species may require precise control of temperature and atmosphere, potentially increasing manufacturing complexity. However, the method uses earth-abundant Ni and reduces Pt loading by alloying, which could lower material costs by 20–30% compared to pure Pt catalysts, though scale-up validation is needed.
Does the catalyst maintain performance under industrially relevant current densities (e.g., >100 mA cm−2)?
The reported performance is at 10 mA cm−2; while the Tafel slope of 31 mV dec−1 suggests favorable kinetics at higher currents, long-term stability at >100 mA cm−2 in seawater has not been demonstrated. Industrial electrolyzers operate at 200–500 mA cm−2, so further testing is required to assess mass transport limitations and durability under such conditions.
What is the role of Ni vacancies in enhancing HER activity, and how are they characterized?
Ni vacancies act as Lewis acid sites that bind hydroxyls, transforming lattice hydroxyls to dissociative hydroxyls on Ni-LDH, which increases surface hydrophilicity and water adsorption. They are likely characterized by techniques such as X-ray photoelectron spectroscopy (XPS) or positron annihilation spectroscopy, though the abstract does not specify; the resulting hydroxyl-rich species are confirmed by the enhanced performance and Cl− resistance.
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