Researchers have developed a new design for hydrogen fuel cells that could significantly reduce charging times.
As countries around the world strive to reach their respective clean energy targets, people are increasingly turning to hydrogen as an alternative fuel solution. Hydrogen is often regarded as an efficient way to store ‘green energy’ from renewables such as wind and solar. Commonly, hydrogen is stored as a compressed gas, however, it is also possible for hydrogen storage to occur in a liquid or solid state.
Researchers from the University of Technology Sydney (UTS) and Queensland University of Technology (QUT) believe that solid hydrogen storage, in particular metal hydride, is attracting interest because it is safer, more compact, and lower cost compared to compressed gas or liquid. It can also reversibly absorb and release hydrogen.
Despite these advantages, there is a significant problem with using metal hydride for hydrogen energy storage. Metal hydride has low thermal conductivity, leading to slow charging and discharging times. Because of this, researchers have developed a new method to improve solid-state hydrogen fuel cell charging times.
The study was recently published in the journal Scientific Reports.
Metal hydride hydrogen storage technology
Dr Saidul Islam, from the University of Technology Sydney, outlined the advantages of using metal hydride for hydrogen storage: “Metal hydride hydrogen storage technology is ideal for onsite hydrogen production from renewable electrolysis. It can store the hydrogen for extended periods and once needed, it can be converted as gas or a form of thermal or electric energy when converted through a fuel cell.
“Applications include hydrogen compressors, rechargeable batteries, heat pumps and heat storage, isotope separation, and hydrogen purification. It can also be used to store hydrogen in space, to be used in satellites and other ‘green’ space technology.”
However, because its low thermal conductivity has resulted in slow charging and discharging times, researchers have worked to address this.
A new method to improve solid-state hydrogen charging and discharging times
First author of the study, Puchanee Larpruenrudee, a PhD candidate in the UTS School of Mechanical and Mechatronic Engineering, said faster heat removal from the solid hydrogen fuel cell results in faster charging times.
“Several internal heat exchangers have been designed for use with metal hydride hydrogen storage. These include straight tubes, helical coil or spiral tubes, U-shape tubes, and fins. Using a helical coil significantly improves heat and mass transfer inside the storage.
“This is due to the secondary circulation and having more surface area for heat removal from the metal hydride powder to the cooling fluid. Our study further developed a helical coil to increase heat transfer performance.”
The team used a semi-cylindrical coil as an internal heat exchanger, which substantially improved heat transfer performance. By using the new semi-cylindrical coil, the hydrogen charging time was reduced by 59%, compared to when using the traditional helical coil heat exchanger.
The next steps
They are now working on the numerical simulation of the hydrogen desorption process and continuing to improve absorption times. To assist with this effort, the semi-cylindrical coil heat exchanger will be further developed.
The researchers aim to develop a new design for hydrogen energy storage, which will combine other types of heat exchangers. In the future, they hope to work alongside industry partners to investigate real tank performance based on the new heat exchanger.