Single Iridium Atoms on a Layered Support Drive Both Water-Splitting Reactions at Once

Producing green hydrogen through water electrolysis requires two simultaneous electrochemical reactions: splitting water into hydrogen at the cathode and releasing oxygen at the anode. For decades, these reactions have been treated as separate problems requiring separate catalysts - expensive platinum-group metals for each side. A team at the Korea Institute of Science and Technology has designed a single catalyst that handles both reactions at once, with the precious metal content reduced to a small fraction of conventional requirements.

The work, from researchers led by Dr. Na Jongbeom and Dr. Kim Jong Min at KIST's Center for Extreme Materials Research, centers on precise atomic-scale control: iridium atoms individually dispersed across the surface of a manganese-nickel layered double hydroxide (LDH) support that incorporates phytic acid into its structure. Rather than deploying iridium as bulk metal or nanoparticles - where most of the atoms are buried inside and unavailable for catalysis - this approach maximizes the fraction of iridium that sits at the surface, exposed to reactants.

How the Catalyst Works

The iridium single atoms serve a dual role through their interaction with the layered support. At the hydrogen evolution reaction (HER) site, the iridium atom itself acts as the direct active site - the location where protons are reduced to hydrogen gas. At the oxygen evolution reaction (OER) site, the mechanism is different: the iridium single atom does not perform the oxygen reaction directly but enhances the catalytic performance of the nickel-based active sites within the LDH, which are responsible for oxidizing water to oxygen. A single class of atoms thus participates in both reactions through two distinct chemical mechanisms.

The analogy offered by the research team captures the efficiency logic: instead of relying on a single large rock (bulk metal), the approach spreads fine grains evenly across a large surface. With iridium dispersed as isolated atoms, virtually all of the precious metal is accessible for catalysis rather than buried inside a particle. This is what allows the total iridium loading to drop to 1.5% of the amount used in conventional precious metal catalysts - not by compromising active site density, but by making far more of the existing iridium do actual work.

The Binder-Free Electrode

A second technical contribution addresses a different part of the electrolysis system. Standard electrodes use a polymer binder to fix the catalyst to the electrode surface. Binders are functional but imperfect: they reduce electrical conductivity by introducing resistive material between the catalyst and the current collector, and they can degrade or allow catalyst detachment during long-term operation, causing performance to drop over time.

The KIST team bypassed this limitation by growing the catalyst directly on the electrode surface rather than applying it as a powder held in place by binder. The directly grown electrode structure achieves better electrical contact between the catalyst and the current collector, reducing resistance losses, and maintains structural integrity more effectively during extended operation. Performance degradation was minimal after more than 300 hours of continuous operation in an anion exchange membrane (AEM) water electrolysis system - a practical duration that begins to approach commercially relevant lifetimes.

Why AEM Electrolysis Matters

The demonstration in an AEM system is significant context for the work. Anion exchange membrane electrolysis occupies a middle ground between the two dominant competing technologies. Alkaline electrolysis, the oldest approach, is cheap and scalable but slow and limited in current density. Proton exchange membrane (PEM) electrolysis handles higher current densities and responds more dynamically to fluctuating renewable energy inputs, but requires large amounts of platinum-group metals and expensive fluoropolymer membranes. AEM systems aim to combine the higher performance of PEM with the cheaper, more abundant materials of alkaline systems - but catalyst development for AEM has lagged behind both competing technologies.

A bifunctional catalyst that performs both HER and OER on a single electrode simplifies AEM system design further, reducing the number of distinct catalyst materials that must be sourced, characterized, and integrated. Simplification of the electrode stack is one of the practical routes to lower system costs alongside reduced precious metal content.

Green Hydrogen Context

Green hydrogen - produced by water electrolysis powered by renewable electricity - is central to decarbonization strategies for sectors that cannot be directly electrified, including steel production, ammonia synthesis, and long-haul heavy transport. The economic viability of green hydrogen at scale depends critically on two factors: the cost and efficiency of the electrolyzer stack, and the cost of the renewable electricity input. This research directly addresses the first factor.

Current commercial electrolyzers using platinum and iridium at conventional loadings contribute significantly to system capital costs. Reducing precious metal use by roughly 98.5% while maintaining or improving performance and durability would, if the approach scales, substantially change the economics of hydrogen production hardware. The 300-hour stability demonstrated here is a necessary proof of concept but is still far from the tens of thousands of hours required for commercially deployed electrolyzers. The pathway from laboratory demonstration to commercial production-grade equipment requires significant further engineering - materials consistency at scale, stack integration, and long-term degradation testing under variable operating conditions.

Dr. Na Jongbeom characterized the result as resolving the two essential reactions for hydrogen production using a single catalyst while reducing precious metal consumption, and pointed to commercialization of water electrolysis devices as the ultimate target. The published results establish that the atomic-level design strategy works in principle; translating it to production-scale systems is the next challenge for the field.

Scale-Up and Long-Term Stability Challenges

The KIST results demonstrate a strong proof of concept, but several engineering challenges stand between this laboratory demonstration and commercial electrolyzer deployment. Single-atom catalyst synthesis requires precise control of deposition conditions to ensure that iridium atoms remain isolated rather than clustering into nanoparticles during fabrication or extended operation. At scale, maintaining that atomic-level uniformity across large electrode areas is substantially harder than in a laboratory setting.

The 300-hour stability demonstrated in the AEM system is encouraging but represents a fraction of the thousands of hours expected of commercial electrolyzers in industrial operation. Long-term testing under variable operating conditions - reflecting the fluctuating power supply from renewable energy sources like wind and solar - is a necessary step before performance claims can be translated into product specifications. The growth of the catalyst directly on the electrode surface, while advantageous for conductivity and adhesion, may also introduce challenges for electrode replacement and recycling at end of life, which are important considerations for the commercial economics of any electrolyzer technology.