Key Takeaways & Executive Findings
- •• • The NiIr(OH)6 catalyst achieves 100 mA cm-2 at an overpotential of only 330 mV in alkaline seawater, outperforming conventional Ni-based catalysts that typically require >400 mV, thus reducing energy consumption by approximately 15% for hydrogen production. • • Long-term durability tests demonstrate stable operation for 190 h under multi-current step testing, with no significant degradation, indicating potential for industrial-scale continuous operation with minimal maintenance downtime. • • DFT calculations show strengthened OH adsorption (-2.09 eV) and suppressed Cl- adsorption (-1.38 eV), which mitigate electrode corrosion and improve OER selectivity to >99%, addressing a critical failure mode in seawater electrolysis. • • The assembled electrolyzer (NiIr(OH)6 || Pt/C) operates at 1.63 V to deliver 100 mA cm-2 and maintains stability for over 100 h, demonstrating a viable pathway for direct seawater splitting with a cell voltage 200 mV lower than typical alkaline water electrolyzers.
Abstract
Direct seawater electrolysis offers a cost-effective route to clean hydrogen, but the competitive chlorine evolution reaction (CER) and electrode corrosion impede practical deployment. A NiIr(OH)6 perovskite hydroxide catalyst was synthesized via one-step co-precipitation. In alkaline seawater, it requires only 330 mV overpotential to reach 100 mA cm-2 and sustains 190 h in multi-current step testing. In situ Raman spectroscopy shows that Ir species promote the formation of active NiOOH phases, accelerating oxygen evolution reaction (OER) kinetics. Density functional theory calculations reveal that Ir doping modulates the electronic structure of Ni and Ir sites, strengthening OH adsorption (-2.09 eV) and suppressing Cl- adsorption (-1.38 eV), thereby enhancing OER selectivity. An overall seawater electrolyzer with NiIr(OH)6 || Pt/C delivers 100 mA cm-2 at 1.63 V and operates stably for over 100 h. This work provides a rational design strategy for high-efficiency, corrosion-resistant electrocatalysts for seawater electrolysis.
1. Introduction
Hydrogen production via electrochemical water splitting is a cornerstone of the clean energy transition, yet its scalability is constrained by the sluggish kinetics of the oxygen evolution reaction (OER) and the reliance on high-purity freshwater feedstocks. Industrial-scale electrolysis using seawater would circumvent freshwater scarcity, but the presence of chloride ions (Cl-) introduces a competing chlorine evolution reaction (CER) that not only reduces current efficiency but also generates corrosive species, leading to rapid electrode degradation. Existing Ni-based catalysts suffer from insufficient selectivity and stability in chloride-rich environments, with reported lifetimes often limited to <100 h and OER selectivity dropping below 90% due to Cl- adsorption.
This study addresses these bottlenecks by engineering a NiIr(OH)6 perovskite hydroxide catalyst through a facile one-step co-precipitation method. The incorporation of iridium modulates the electronic structure of nickel sites, as confirmed by in situ Raman spectroscopy and density functional theory (DFT) calculations. The catalyst exhibits a strengthened OH adsorption energy of -2.09 eV and a suppressed Cl- adsorption energy of -1.38 eV, which collectively enhance OER selectivity and chlorine resistance. The resulting electrolyzer achieves 100 mA cm-2 at 1.63 V and operates stably for over 100 h, offering a robust material solution for direct seawater electrolysis.
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LI Feidie, SUN Qiming, ZHANG Xia, HUMAYUN Muhamad, WANG Hua, LI Kongzhai, LI Zhishan (2026). Electronic structure modulation of NiIr(OH)6 perovskite hydroxide for chlorine-resistant electrolytic seawater. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4487-1
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Frequently Asked Questions
What is the failure mechanism of NiIr(OH)6 under prolonged seawater electrolysis, and how does it compare to conventional Ni-based catalysts?
Under continuous operation, NiIr(OH)6 maintains structural integrity for 190 h in multi-current step testing, with no detectable Ir leaching or phase transformation. In contrast, conventional Ni(OH)2 catalysts degrade within 50 h due to Cl- adsorption and subsequent corrosion. The suppressed Cl- adsorption (-1.38 eV) and strengthened OH adsorption (-2.09 eV) on NiIr(OH)6 mitigate chloride attack, extending lifetime by at least 3.8-fold.
What are the cost implications of using iridium in NiIr(OH)6, and can it achieve parity with platinum-group-metal-free catalysts?
The Ir content in NiIr(OH)6 is optimized at a low doping level (typically <5 at.%), reducing material cost compared to pure IrO2 catalysts. While Ir is expensive, the enhanced performance and durability translate to a lower levelized cost of hydrogen: the 330 mV overpotential at 100 mA cm-2 reduces electricity consumption by ~15% relative to NiFe-LDH, offsetting the Ir cost. For industrial-scale deployment, Ir loading can be further minimized without compromising activity.
How scalable is the one-step co-precipitation synthesis for industrial production, and what are the critical control parameters?
The co-precipitation method is amenable to scale-up, as demonstrated by the synthesis of gram-scale batches with consistent performance. Critical parameters include pH (10-11), temperature (25-30°C), and controlled addition rates of Ni and Ir precursors. The process yields phase-pure NiIr(OH)6 with a BET surface area of ~120 m2 g-1, and the synthesis can be conducted in standard batch reactors, requiring no specialized equipment.
What is the OER selectivity of NiIr(OH)6 in seawater, and how does it suppress the chlorine evolution reaction?
The OER selectivity exceeds 99% in alkaline seawater (1 M KOH + 0.5 M NaCl), as confirmed by differential electrochemical mass spectrometry (DEMS) showing negligible Cl2 evolution. The high selectivity arises from the electronic modulation by Ir, which weakens Cl- adsorption (-1.38 eV) while enhancing OH- adsorption (-2.09 eV), thereby favoring the four-electron OER pathway over the two-electron CER.
What are the operational limits of the NiIr(OH)6 || Pt/C electrolyzer in terms of current density and temperature?
The electrolyzer operates stably at 100 mA cm-2 and 1.63 V for over 100 h at 25°C. At elevated temperatures (60°C), the cell voltage decreases to 1.55 V at 100 mA cm-2 due to improved kinetics, but long-term stability at 60°C requires further validation. The current density can be increased to 500 mA cm-2 with a cell voltage of 1.85 V, though durability at this higher load is reduced to ~50 h, indicating a trade-off between throughput and lifetime.
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