Tech Insights

Research: Iridium Gives Hydrogen Production Superior Boost of Efficiency, Stability

July 11, 2023 by Shannon Cuthrell

Australian researchers have demonstrated how a lattice-water-assisted oxygen exchange technique offers superior efficiency and stability as a catalyst in hydrogen production. 

A research team from the University of Adelaide in Australia has developed a modified oxygen exchange mechanism to boost the efficiency and stability of iridium-based electrocatalysts used for hydrogen energy production. 

 

Iridium

Iridium. Image used courtesy of Adobe Stock

 

The mechanism arranges water molecules in a pattern that improves the iridium oxide catalyst’s efficiency by 5% to 10%, consuming less energy to yield a higher output. 

The findings come as hydrogen is gaining global momentum as a resource aiding the ongoing transition to renewable energy. Green (low-carbon) hydrogen is produced with electrolysis and renewables such as solar and wind. Iridium, a platinum group metal, is an effective catalyst in proton exchange membrane (PEM) water electrolysis (WE) reactions because its characteristic corrosion resistance allows it to withstand harsh acidic conditions. 

Iridium is among Earth’s rarest elements, comprising a tiny portion of the crust. Though South Africa is the leading producer, iridium-containing ores can be found in the United States, Brazil, Australia, and other countries. 

A Wood Mackenzie analyst estimated that world iridium production would total 255,000 ounces (15,937 pounds) in 2022, far short of the forecasted demand growth amid the boom in green hydrogen development. However, hydrogen producers shifting to alternative PEM systems, such as alkaline and solid oxide electrolyzers, would help manage that demand. 

With current commercial methods, it’s difficult for iridium oxide catalysts to reach high activity and stability simultaneously. But the University of Adelaide researchers discovered that a lattice-water-assisted mechanism could help change that status quo. Their technique achieved superior efficiency and stability in a PEM water electrolyzer while reducing the amount of iridium used, thus driving down green hydrogen production costs. 

The university said that future studies could focus on how to scale up the synthesis. 

 

Here’s How It Works

The research, funded by grants from the Australian Research Council, was recently published in Science Advances. The team wanted to combine the advantages of oxygen evolution reaction (OER) catalysts in PEMWE: While crystalline iridium oxide offers good stability but poor activity, amorphous iridium oxide shows high activity but with low stability. 

In the study, the authors demonstrated how a short-range ordered lattice water-incorporated iridium oxide (or IrOx·nH2O) shows improved activity and ultra-high stability. Unlike conventional adsorbate evolution and lattice oxygen techniques, the lattice water-assisted modified OER achieves this without any apparent structural degradation. 

A high-performance PEMWE with IrOx·nH2O as the anode electrocatalyst can deliver a cell voltage of 1.77 volts at 1 A cm-2 for 600 hours at 140 degrees Fahrenheit. These results were also produced with less iridium-loading than commercial membrane electrode assembly—outperformed by 60 mV—and with an energy consumption of 4.27 kilowatt-hours (kWh) m-3 H2 at 1 A cm-2, less than commercial PEM electrolyzers. 

With an estimated cost of $0.95 per kilogram (kg) of hydrogen gas, this PEMWE mechanism nears the United States 2030 research and development target of reducing hydrogen production costs by 80% to $1 per kg. 

 

PEM performance graphs

PEM performance graphs: “a” shows steady-state polarization curves of the researchers’ PEM electrolyzer and commercial iridium oxide anodic catalysts; “b” displays the chronopotentiometric curve of the PEM electrolyzer, featuring photos of the device and parameters; “c” shows MEA and iridium signals near the anode catalyst/membrane interface. Image used courtesy of the authors (Creative Commons BY license)
 

In short, since IrOx·nH2O accommodates abundant lattice water, the modified oxygen exchange can uphold the stability of crystalline iridium oxide while meeting the strong activity of amorphous iridium oxide.