Impurities in carbon dioxide can affect several aspects of the carbon capture and storage process, including storage capacity, rock erosion, accuracy of flow meters, and toxicity of potential leaks. There is an industry need for guidance on performing purity analysis before carbon dioxide is transported and stored. This paper reviews selected reports that specifically provide threshold amount fraction limits for impurities in carbon dioxide for the purpose of transport and storage, with rationales for these limits. A carbon dioxide purity specification is provided (including threshold amount fractions of impurities) on the basis of the findings, as well as recommendations on further work required to develop a suitable gas metrology infrastructure to support these measurements including primary reference materials, sampling methods, and instruments for performing purity analysis. These recommendations provide important guidance to operators and gas analysis laboratories for performing quality assurance.

Maritime transport is investigating several options to reduce its greenhouse gases and air pollutant emissions. An experimental ship, Energy Observer, is using excess renewable energy to generate onboard hydrogen by electrolysis of purified seawater. As a promising option for storing energy, it can provide on-demand energy to the ship through a hydrogen fuel cell (FC). As hydrogen FCs lifetime and performance are correlated to hydrogen quality, the hydrogen produced onboard needs to be monitored. This study assesses the probability of contaminants presence for this electrolyser, using purified seawater and supports the results with a hydrogen fuel quality analysis from the Energy Observer ship. It demonstrates that an electrolyser using onboard purified seawater can generate hydrogen of a quality compliant with ISO 14687:2019. Additional contaminants (i.e., ions, heavy metal) were also measured. The study highlights the potential contaminants to be monitored and future research on new contaminants from seawater to further develop hydrogen fuel for maritime applications.

The widescale distribution of hydrogen through gas networks is promoted as a viable and cost-efficient option for optimising its application in heat, industry, and transport. It is a key step towards achieving decarbonisation targets in the UK. A key consideration before the injection of hydrogen into the UK gas networks is an assessment of the difference in hydrogen contaminants presence from different production methods. This information is essential for gas regulation and for further purification requirements. This study investigates the level of ISO 14687 Grade D contaminants in hydrogen from steam methane reforming, proton exchange membrane water electrolysis, and alkaline electrolysis. Sampling and analysis of hydrogen were carried out by the National Physical Laboratory following ISO 21087 guidance. The results of analysis indicated the presence of nitrogen in hydrogen from electrolysis, and water, carbon dioxide, and particles in all samples analysed. The contaminants were at levels below or at the threshold limits set by ISO 14687 Grade D. This indicates that the investigated production methods are not a source of contaminants for the eventual utilisation of hydrogen in different applications including fuel cell electric vehicles (FCEV’s). The gas network infrastructure will require a similar analysis to determine the likelihood of contamination to hydrogen gas.

Fuel cell electric vehicles are expanding quickly from light-duty to heavy-duty applications such as buses or trucks. Hydrogen fuel quality needs to comply with ISO14687:2019 to avoid any improper performance of the vehicles. Total sulphur is one of the most impactful contaminants to a fuel cell system and has a threshold of 4 nmol/mol. Most analytical methods provide a limit of detection (LOD) of 1 nmol/mol for total sulphur in hydrogen. Total sulphur is often not quantified and reported as below LOD due to lack of sensitivity. A new analytical method using cryo-focussing gas chromatography with sulphur chemiluminescence detector (cryo-GC-SCD) was developed for picomol/mol analysis of total sulphur. The method achieved linearity between 150–16,000 picomol/mol, validated against NPL reference materials, and relative expanded uncertainty of 21% (k = 2). Samples from 11 hydrogen refuelling stations (HRS) were analysed using this method. The total sulphur amount fraction for all the HRSs was more than 10 times lower than the actual ISO14687:2019 threshold with highest value around 290 picomol/mol. The study demonstrated that the cryo-GC-SCD method can measure total sulphur at picomol/mol in hydrogen fuel. Additionally, it provided the first results on sulphur compound stability in an aluminium gas cylinder for which further study is needed.