With ruthenium, hydrogen will soon become cheaper

It is not easy to establish a hydrogen economy, but Rice University engineers have found a technique that may make oxygen evolution catalysis in acids, one of the trickiest areas of water electrolysis for creating clean hydrogen fuels, more feasible and affordable.

The rare and expensive precious metal iridium has been replaced by the much more common precious metal ruthenium in the lab of chemical and biomolecular engineer Haotian Wang at Rice’s George R. Brown School of Engineering as the positive-electrode catalyst in a reactor that splits water into hydrogen and oxygen.

When nickel was successfully added to ruthenium dioxide (RuO2) in the lab, a strong anode catalyst was created that could produce hydrogen from water electrolysis for a long time in ambient settings.

Clean hydrogen is very popular in the sector, according to Wang. It serves as a substantial energy transporter and is necessary for the synthesis of many chemicals, but the worldwide chemical manufacturing industry’s current production contributes significantly to carbon emissions. Water-splitting with clean power is generally regarded as the most promising solution for producing it more sustainably.

According to him, iridium is around eight times more expensive than ruthenium and might add 20% to 40% to the cost of making commercial devices, especially for large-scale deployments in the future.

In Nature Materials, Wang, Rice postdoctoral associate Zhen-Yu Wu, graduate student Feng-Yang Chen, and associates from the Universities of Virginia and Pittsburgh describe the procedure they created.

By rearrangement of the water molecules by polarized catalysts, oxygen and hydrogen are released during the process of water splitting. The cathode, which is a negative electrode, produces hydrogen, according to Wu. By oxidizing water to produce oxygen on the anode side, it must also balance the charge at the same time.

The anode is more susceptible to corrosion when employing an acidic electrolyte, but the cathode is quite stable and not a huge problem, according to Chen. Transition metals that are frequently utilized, such as manganese, iron, nickel, and cobalt, oxidize and dissolve in the electrolyte.

Because of this, he explained, iridium is the only material that can be utilized in commercial proton exchange membrane water electrolyzers. Although pricey, it is stable for tens of thousands of hours.

Wang’s group set out to find a replacement, and after trying a number of different metals, opted for ruthenium dioxide for its recognized action.

The researchers showed that water-splitting was facilitated for more than 1,000 hours at a current density of 200 milliamps per square centimeter with little degradation when ultrasmall and highly crystalline RuO2 nanoparticles with nickel dopants were utilized at the anode.

They put their anodes up against pure ruthenium dioxide counterparts, which could catalyze water electrolysis for a few hundred hours before degrading.

In order to integrate its ruthenium catalyst into current commercial processes, the lab is striving to improve it. “Our challenge is to increase the current density by at least five to ten times while still keeping this level of stability,” Wang said. “Now that we’ve attained this stability milestone.” Although difficult, it is nevertheless feasible.

The requirement is urgent in his eyes. The amount of hydrogen we currently require cannot be produced with the annual iridium output, according to Wang. “Even using all the iridium produced globally, we simply won’t be able to manufacture the necessary amount of hydrogen if we wish to produce it via water electrolysis.

That implies that we can’t entirely rely on iridium, he added. “We must create new catalysts to either cut down on its use or completely eliminate it from the process.”