UNSW researchers use precise 3D imaging to reveal how trapped bubbles affect the efficacy of electrolysers in the production of green hydrogen.
Hydrogen could be the key to a clean energy future, but a tiny problem has been holding it back: bubbles.
In a paper published in Energy & Environmental Science, a multidisciplinary team of UNSW researchers, in collaboration with researchers from TotalEnergies and EPFL, has found a new way to boost the efficiency of green hydrogen production.
Their solution focuses on optimising the design of electrolysers – the systems used to split water into hydrogen and oxygen using electricity – which, when powered by renewable energy, produce “green hydrogen”.
To date, industrial-scale electrolysers have faced a critical bottleneck: hydrogen bubbles generated during operation accumulate within the porous electrodes, blocking active sites and severely limiting mass transport at high current densities.
“Green hydrogen production through water electrolysis is essential for decarbonising hard-to-abate sectors such as steelmaking and heavy-duty transport,” says Prof. Peyman Mostaghimi , the lead researcher on the team from UNSW’s School of Civil & Environmental Engineering .
These hydrogen bubbles are generated in the electrolyser during the operation and accumulate on the porous electrode, blocking reaction sites.
“We found that the shape and structure of the porous electrode are just as important as the electrochemistry. If the structure is designed properly, you can stop bubbles from clogging the system and make it much more efficient.”
X-ray vision
The team combined X-ray imaging with simulations to look inside the porous structures. This provided them unprecedented access to observe gas bubble behaviour over time, without taking the cell apart.
“If you want to generate green hydrogen at a mass scale, you need to make sure it’s first economically viable. One of the challenges the industry is facing is limitations in mass transport,” says Prof. Mostaghimi.
“When water is split, we found tiny hydrogen and oxygen bubbles get trapped inside the electrode, blocking the reaction sites and slowing the movement of water and ions, effectively starving the catalyst of fresh water.
“We looked at the architecture of these porous materials and found that a highly ordered, uniform pore structure resulted in minimal gas trapping.
“This tells us that the pore structure is directly linked to gas trapping, which gives manufacturers a pathway to designing more efficient systems.”
It was also the first time operando synchrotron imaging, coupled with state-of-the-art pore-scale numerical methods, had been used to visualise hydrogen bubble formation, growth, and accumulation during electrolysis.
“Before this, scientists couldn’t really see what was happening inside the electrode the way we could using our advanced technologies,” says Professor Ryan Armstrong, a co-investigator from UNSW School of Civil & Environmental Engineering .
“This work shows that mass transport limitations are fundamentally linked to electrode architecture, not just catalytic activity,” says Dr Ying Da Wang, who led the flow simulation and analysis from UNSW School of Minerals & Energy Resources Engineering .
“By combining real-time imaging, advanced two-phase flow simulations, and performance measurements, we now understand how the accumulation of hydrogen bubbles influences performance during water electrolysis,” says Dr Quentin Meyer, who, with Professor Chuan Zhao, contributed the electrochemistry expertise from the UNSW School of Chemistry .
Next steps
The researchers are now extending their focus to the techno-economic assessment of coupling green hydrogen production with transport and large-scale storage in underground porous reservoirs.
“A clean hydrogen economy depends on getting every link in the chain right,” says Prof. Mostaghimi.
“By looking at production, transport, and underground storage together, we can show policymakers and industry what is actually feasible, and at what cost.”
