Engineering news
Electrolysis based on polymer electrolyte membranes (PEM) has potential for large-scale hydrogen production powered by renewable energy. The technique has been held back by the high cost of precious metal catalysts like platinum and iridium, however, said researchers from the Suncat partnership in the US.
Most hydrogen production is also based on fossil fuels, said lead researcher Thomas Jaramillo, adding to the level of carbon dioxide in the atmosphere. “We need a cost-effective way to produce it with clean energy,” he said.
Electrolysis uses electrical current to split water into hydrogen and oxygen. The reactions that generate hydrogen and oxygen gas take place on different electrodes using different precious metal catalysts. Manufacturer Nel Hydrogen in Connecticut replaced the platinum catalyst on the hydrogen-generating side with a catalyst consisting of cobalt phosphide nanoparticles deposited on carbon to form a fine black powder.
The cobalt phosphide catalyst reportedly operated “extremely well” for the duration of the test, more than 1,700 hours – an indication that it may be hardy enough 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. Jaramillo said that, to his knowledge, it was the first PEM to demonstrate high performance in a commercial electrolyser.
One of the most important elements of the study was scaling up the production of the cobalt phosphide catalyst while keeping it uniform. The process involved synthesising the starting material at the lab bench, grinding with a pestle and mortar, baking in a furnace and finally turning the fine black powder into an ink that could be sprayed onto sheets of porous carbon paper.
“The performance of the cobalt phosphide catalyst needs to get a little bit better, and its synthesis would need to be scaled up, but I was quite surprised at how stable these materials were,” said co-author Katherine Ayers from Nel Hydrogen. “Even though their efficiency in generating hydrogen was lower than platinum's, it was constant. A lot of things would degrade in that environment.”
The platinum market is so volatile that it could hold back development of electrolysis, said Ayers. Reducing and stabilising that cost will become increasingly important as other aspects of PEM electrolysis are improved to meet the increasing demand for hydrogen in fuel cells and other applications, she added.
An IMechE report last year, Energy from Gas: Taking a Whole System Approach, called on the government and industry to introduce several pro-hydrogen policies, including updating pipes and materials in the gas distribution network to handle concentrations of up to 20% by 2023.
“By widening our use of gas in the energy system, the UK will not be restricted to an electricity and battery future and will be able to adapt to a changing climate, emerging technologies, population and political demands,” said the report, led by IMechE head of engineering Dr Jenifer Baxter.
The new research from Suncat, a collaboration between the US Department of Energy's SLAC National Accelerator Laboratory and Stanford University, was published in
Nature Nanotechnology.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.