RESEARCHERS have shown for the first time that a cheap catalyst can be used to split water for hydrogen generation, in a commercial device. The developed catalyst operated for more than 1,700 hours in the device’s harsh environmental conditions.
Hydrogen can be used to produce fuel, fertiliser, and to store “clean” energy. It is primarily generated by steam reforming methane which contributes to CO2 emissions. It can also be generated by electrolysis of water, a process which uses electricity to split water into oxygen and hydrogen gas. The process can be carried out in devices known as electrolysers.
Electrolyser technology, which is based on a polymer electrolyte membrane (PEM), has the potential to produce hydrogen at a large scale, using renewable energy. However, the technology is limited as it requires costly precious metal catalysts, such as platinum and iridium.
Researchers at the US Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, US developed a low-cost, non-precious metal cobalt phosphide (CoP) catalyst which was used at the hydrogen generating electrode within an electrolyser. The catalyst performed well within the electrolyser compared to a commercial platinum catalyst.
The CoP catalyst’s performance was compared to the Pt catalyst under the same operating conditions, ie 50°C and hydrogen pressure of 400 psi (2.76 mPa). Under these conditions the operating efficiencies of the CoP- and platinum-based electrolysers were 55% and 61%, respectively.
In durability tests, the CoP catalyst was able to operate stably for more than 1,700 hours of continuous hydrogen production at a current density of 1.86 A cm−2, at 55°C, and 400 psi. It showed negligible degradation.
According to study co-author McKenzie Hubert, as the catalyst was able to operate well for the duration of the test it may be suitable for “everyday use in reactions that can take place at elevated temperatures, pressures and current densities and in extremely acidic conditions over extended lengths of time”. Hubert is a graduate student in the Jaramillo Research Group at Stanford University.
In this work, the researchers showed a successful translation of the CoP catalyst from lab-scale (1 cm2 experiments) to commercial scale (86 cm2 PEM electrolyser).
According to Thomas Jaramillo, as far as he knows this is the first work investigating an alternative precious metal catalyst for a PEM system to demonstrate high performance in a commercial electrolyser. Jaramillo is Director of the SUNCAT Center for Interface Science and Catalysis and led the research team. SUNCAT is a partnership between SLAC and the Stanford School of Engineering.
Katherine Ayers, co-author and Vice President of Research and Development at Nel Hydrogen which supplied the electrolyser used in the research, said she was surprised by the stability of the CoP catalyst. Additionally, Ayers noted that though it had lower operating efficiency than platinum it was constant in an environment that a lot of things would degrade in. However, she also acknowledged that the performance of the CoP catalyst needs to be improved and the synthesis needs to be scaled up.
Ayers said that though the platinum catalyst only accounts for 8% of PEM electrolyser manufacturing costs, the platinum market is volatile, and prices swing up and down. This could hold back the development of technology. Reducing and stabilising catalyst cost will become increasingly important as other aspects of PEM electrolysis technology improve to meet increasing hydrogen demand.
Though this work highlights a significant step towards non-precious metal catalysts for commercial electrolysers the difference in performance between CoP and platinum is still too substantial for widescale commercial deployment. Further research and development is required.
McKenzie Hubert said the researchers are currently not doing any further projects to develop CoP catalysts, but the group did recently show that the hydrophilicity of carbon can impact catalyst dispersion. In the present study, carbon sheets were used as a support for the CoP catalyst.
The development of the PEM electrolyer was funded by the US Department of Defense, which is interested in oxygen-generation for submarines. According to Jaramillo, the work also aligns with the Department of Energy’s H2@Scale initiative, which brings stakeholders together to advance affordable hydrogen production, transport, storage, and use in a number of applications.
SUNCAT’s fundamental catalyst research was funded by the Department of Energy’s Office of Science.
Nature Nanotechnology: http://doi.org/ddgk
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