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Overcoming hydrogen fuel's chicken-and-egg conundrum is a question of purity
Dr Arul Murugan, senior research scientist at NPL in The Gas and Particle Metrology Group, explains how the industry can overcome the chicken-and-egg conundrum that currently faces hydrogen fuel
The hydrogen economy is at a tipping point. For decades the technology has been explored and developed, especially within the automotive market where many leading manufacturers have developed concept cars and technology showcasing hydrogen's potential as a future fuel. It has now reached a point where hydrogen vehicles can be seen on the roads, with hydrogen-fuelled buses being deployed in cities around the world.
However, the car industry has yet to fully embrace the technology thanks to a chicken-and-egg conundrum. People are not buying hydrogen cars because the re-fuelling infrastructure to support them is not in place, and the infrastructure is not being built because there is not enough public demand for the cars. Given hydrogen's potential to offer a zero emission fuel source, if the fuel is generated via renewables, there needs to be a concerted effort to break this cycle. There are projects working on this, such as the European-organised HyFive project to validate performance and capability with BMW, Daimler, Honda, Hyundai and Toyota. However, there is a more fundamental, industry wide issue that needs to be confronted if hydrogen re-fuelling infrastructure is to be successfully implemented.
Impurities in fuel can degrade the engines that use it. This is no different for hydrogen cars. Hydrogen fuel cells can be damaged significantly by impurities. This results in these cars failing after a relatively short time, far sooner than a normal, fossil-fuelled car. To counter this, guidelines for acceptable hydrogen purity have been laid out in International Standard ISO 14687, which outlines the maximum allowable impurity levels. EU directive 2014/94/EU also states that all refuelling stations must comply with these thresholds.
One could therefore think that the job is done. We know the limits by which fuel impurities should be kept at, so manufacturers and consumers can now have confidence that the fuel going into cars will be of sufficient quality. Unfortunately, this is only half the job. Knowing the levels to stick to is one thing, but how do you prove that the hydrogen purity complies with the standard? What measurements do you need to carry out and how? And how can we be sure that all hydrogen purity laboratories are providing results that are truly stable, comparable and accurate? This is where the hydrogen industry is currently faltering and is an area that the National Physical Laboratory (NPL), the UK's National Metrology Institute, is working to bring clarity to by providing measurements that are traceable to the internationally accepted SI system of units.
What is required is an accredited method of impurity measurement at the hydrogen fuel pumps that is traceable back to the SI system of units. In particular the challenge is to accurately measure the low level of impurities specified in the ISO standard. The oil and gas industry has this already, with the ISO 3170 and 3171 methods outlining sampling method for petroleum products . NPL is developing a suite of analytical methods for testing the purity of hydrogen fuel, using an enrichment device to concentrate the impurities to enable analysis to be performed using commercial gas chromatographs. All developed methods will be validated using primary reference gas mixtures that are directly traceable to the SI system of units, providing confidence in the measurements. Once this standard protocol is in place, NPL will be able to perform accredited hydrogen purity testing for refuelling stations and also provide traceability for all hydrogen purity laboratories to ensure that impurity measurements taken from refuelling stations will be of an approved standard, laying the foundations for a trusted fuel supply chain.
Overcoming this issue will give manufacturers and consumers the necessary trust that ISO 14687 is being followed and that their cars will perform as intended. It will also allow the hydrogen infrastructure to expand as developers of these technologies will know the standards and processes they will have to meet.
Hydrogen offers great advances in low-carbon transport, but it is only by solving the fundamental barriers, like standardizing fuel purity, that we can ensure that it lives up to its potential.
April 1, 2016