A ruthenium trick keeps seawater electrolysis anodes running for over 2,000 hours

Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences

The ocean covers 71% of Earth's surface and holds 97% of its water. If we could efficiently split seawater into hydrogen and oxygen, we would have an almost limitless source of clean fuel. The problem is chloride. Seawater is roughly 3.5% salt, and those chloride ions are viciously corrosive to the anodes used in water electrolysis. Most nickel-iron anodes - the workhorse materials for the oxygen evolution reaction in alkaline electrolyzers - corrode and fail within hours in salty conditions.

A team at the Ningbo Institute of Materials Technology and Engineering, part of the Chinese Academy of Sciences, has found a way to make those anodes last. Their solution involves adding small amounts of ruthenium - a platinum-group metal already used in industrial chlor-alkali processes - to create a dual protection mechanism that keeps chloride ions from destroying the electrode. The result is an anode that has operated for over 2,000 hours in highly corrosive conditions where conventional anodes fail in under 15.

Two defenses from one element

The research, led by Professors Yichao Lin, Yayun Zhao, and Liang Chen, introduces a material designated RuSA-NiFeOOH/Ni. The name describes its architecture: atomically dispersed ruthenium (RuSA) embedded within a nickel-iron oxyhydroxide (NiFeOOH) catalyst layer, all supported on nickel foam.

Ruthenium serves two distinct protective functions in this design. First, during the electrode's formation, ruthenium ions migrate toward the interface between the catalyst layer and the nickel foam substrate, forming a dense, ruthenium-enriched barrier layer. This physical barrier blocks chloride ions from reaching the vulnerable nickel substrate beneath.

Second, ruthenium atoms dispersed throughout the NiFeOOH catalyst create localized chloride-enriched regions around themselves. This sounds counterintuitive - why would attracting chloride ions be protective? The answer lies in electrostatics. By concentrating chloride ions near ruthenium sites, the dispersed atoms create a local negative charge that repels additional chloride ions away from the adjacent nickel and iron catalytic sites where the oxygen evolution reaction actually occurs.

The effect is something like a molecular decoy system. Ruthenium atoms attract and hold chloride ions, keeping them away from the sites that would be damaged by their presence.

From 15 hours to 2,000 - and counting

The performance gap is dramatic. In testing at 0.5 A/cm2 in a solution of 1 M potassium hydroxide plus 2 M sodium chloride - conditions far more corrosive than natural seawater - conventional NiFeOOH/Ni and NiFe-LDH/Ni anodes failed within 15 hours. The RuSA-NiFeOOH/Ni anode ran for over 2,000 hours with stable performance.

The catalytic performance is also strong. The optimized anode achieved an overpotential of just 220 millivolts at 100 mA/cm2 in simulated saline water, with a Tafel slope of 37.12 mV per decade - indicating fast reaction kinetics. These numbers are competitive with the best reported values for oxygen evolution in chloride-containing electrolytes.

In situ spectroscopy revealed the mechanism behind the stability. Ruthenium promotes the irreversible oxidation of Ni2+ to Ni3+, which transforms the catalyst layer into a more compact, crack-free structure. Conventional NiFeOOH forms a rod-like morphology with cracks that allow chloride penetration. The ruthenium-stabilized version forms dense nanosheets with no visible cracks, physically blocking the diffusion pathways that chloride ions would otherwise exploit.

Real seawater, industrial conditions, scalable fabrication

Lab conditions with pure salt solutions are one thing. The researchers also tested their anode in realistic scenarios. Paired with a commercial platinum-on-nickel cathode in a custom alkaline electrolyzer, the RuSA-NiFeOOH/Ni anode ran for over 500 hours in concentrated alkaline saline solution (6 M KOH plus saturated NaCl) at 55 degrees Celsius - conditions approaching industrial operating parameters.

They also tested the system with actual seawater collected from the Ningbo Beilun coast, made alkaline with 6 M KOH. The anode maintained stable operation for at least 500 hours with minimal degradation. Natural seawater contains not just sodium chloride but a complex mix of ions, organic matter, and microorganisms that can foul or corrode electrodes. The fact that the anode survived this environment adds practical credibility to the approach.

On the manufacturing side, the team successfully fabricated a uniform electrode measuring 35 by 35 centimeters - large enough to suggest the synthesis process can scale to industrial dimensions.

Ruthenium cost and the search for cheaper alternatives

The approach has clear limitations. Ruthenium is a platinum-group metal with limited global supply and volatile pricing. While the amounts used are small - the ruthenium is atomically dispersed, not applied as a bulk coating - any technology that depends on scarce noble metals faces questions about long-term scalability and cost.

The researchers acknowledge this directly. They note that future work should explore whether non-precious metal dopants can achieve similar dual stabilization effects. If the protective mechanism can be replicated with earth-abundant elements - cobalt, manganese, or cerium, for example - the approach becomes far more attractive for large-scale deployment.

The 2,000-hour durability figure, while impressive, also falls short of the tens of thousands of hours that commercial electrolyzers need to achieve for economic viability. Industrial alkaline electrolyzers typically target lifetimes of 60,000 to 90,000 hours. Whether the RuSA-NiFeOOH/Ni anode can approach those numbers remains to be demonstrated.

The testing conditions, while more realistic than much of the literature, still used alkaline saline solutions rather than direct seawater electrolysis without added base. True direct seawater splitting - without the cost and complexity of adding large quantities of potassium hydroxide - remains an unsolved challenge.

Fitting into the green hydrogen puzzle

The broader context for this work is the growing global push for green hydrogen - hydrogen produced from water using renewable electricity rather than from natural gas. Most current water electrolysis technology uses purified freshwater, which is itself a limited resource in many regions where solar and wind energy are abundant (deserts, coastal zones, islands).

If electrolyzers can be made to work with seawater or brackish water, hydrogen production facilities could be co-located with offshore wind farms or coastal solar installations without competing for drinking water. The anode is the bottleneck. Cathode materials handle salty conditions reasonably well; it is the oxygen-producing anode that corrodes.

This study demonstrates one credible path to solving that corrosion problem. Whether ruthenium-based or eventually adapted to cheaper materials, the dual stabilization strategy - combining a physical barrier layer with electrostatic chloride repulsion - offers a design principle that could shape the next generation of seawater electrolysis anodes.