Decarbonisation of the energy sector is becoming increasingly more important to the reduction in climate change. Renewable energy is an effective means of reducing CO₂ emissions, but the fluctuation in demand and production of energy is a limiting factor. Liquid hydrogen allows for long-term storage of energy. Hydrogen quality is important for the safety and efficiency of the end user. Furthermore, the quality of the hydrogen gas after liquefaction has not yet been reported. The purity of hydrogen after liquefaction was assessed against the specification of Hydrogen grade D in the ISO-14687:2019 by analysing samples taken at different locations throughout production. Sampling was carried out directly in gas cylinders, and purity was assessed using multiple analytical methods. The results indicate that the hydrogen gas produced from liquefaction is of a higher purity than the starting gas, with all impurities below the threshold values set in ISO-14687:2019. The amount fraction of water measured in the hydrogen sample increased with repeated sampling from the liquid hydrogen tank, suggesting that the sampling system used was affected by low temperatures (−253 °C). These data demonstrate for the first time the impact of liquefaction on hydrogen purity assessed against ISO-14687:2019, showing that liquified hydrogen is a viable option for long-term energy storage whilst also improving quality.

To explore the potential of combining non-contact profilometry (NCP) and confocal laser scanning microscopy (CLSM) data to measure the entire erosive process non-destructively and to validate findings using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), scanning electron microscopy (SEM) and surface microhardness (SMH) using the same samples throughout. Polished bovine enamel samples (n = 35) were divided into groups (7/group) with similar SMH values. Samples underwent individual erosive challenges (1 % citric acid, pH3.8) for 1, 5, 10, 15 or 30 min under stirring and aliquot extracts were analysed for Ca and P by ICP-AES. SMH was used to measure erosive softening. Profilometry was used to assess bulk volume loss (BVL). Images were captured by SEM. Samples were stained with rhodamine-B (0.1 mM, 24 h) and images captured by CLSM. Image processing was used to determine changes in fluorescent volume for the first 10 μm (ΔFV10) for each enamel sample which were combined with BVL to calculate total lesion volume (TLV). ANOVA, linear regression and Pearson correlation analysis were used where applicable. Surface softening, [Ca], [P], BVL and ΔFV10μm increased with acid erosion duration which were significant by 10 min (P < .01). The Ca:P ratio increased to 1.57 then decreased after 5 min erosion suggesting a sub/surface phase change, which was observed by SEM and CLSM showing significant changes to the enamel surface and subsurface morphology with time. Combination of BVL and ΔFV10 as TLV strengthened the significant correlations with [Ca], [P], and SMH (P < .01). This novel combination of CLSM and NCP allows for concurrent non-destructive quantification of the entire erosive process by mineral loss, and qualitatively characterise microstructural changes during dental erosion.

Formic acid is an intermediate of the steam methane reforming process for hydrogen production. According to International Standard ISO 14687, the amount fraction level of formic acid present in the hydrogen supplied to fuel cell electric vehicles must not exceed 200 nmol·mol⁻¹. The development of formic acid standards in hydrogen is crucial to validate the analytical results and ensure measurement reliability for the fuel cell electric vehicles industry. NPL demonstrated that these standards can be gravimetrically prepared and validated at 4 to 100 µmol·mol⁻¹, with a shelf-life of 1 year (stability uncertainty < 7%; k = 2). Stability was not affected over 1 year or by low temperature or pressure. At sub-µmol·mol⁻¹ level, formic acid amount fraction was found to decrease due to adsorption on the gas cylinder surface; however, it is possible to certify the formic acid amount fraction after a period of 20 days and ensure the certified value validity for 1 year with an uncertainty below 7% (k = 1) confirmed by thermodynamic investigation. This study demonstrated that formic acid in hydrogen gas reference materials can be prepared with reasonable uncertainty (>7%, k = 1) and shelf life (>1 year). Potential applications include the calibration of analysers and for studying the impact of formic acid on future application with relevant traceability and accuracy.

The deployment of hydrogen fuel cell electric vehicles (FCEVs) is critical to achieve zero emissions. A key parameter influencing FCEV performance and durability is hydrogen fuel quality. The real impact of contaminants on FCEV performance is not well understood and requires reliable measurements from real-life events (e.g., hydrogen fuel in poor-performing FCEVs) and controlled studies on the impact of synthetic hydrogen fuel on FCEV performance. This paper presents a novel methodology to flow traceable hydrogen synthetic fuel directly into the FCEV tank. Four different synthetic fuels containing N₂ (90–200 µmol/mol), CO (0.14–5 µmol/mol), and H₂S (4–11 nmol/mol) were supplied to an FCEV and subsequently sampled and analyzed. The synthetic fuels containing known contaminants powered the FCEV and provided real-life performance testing of the fuel cell system. The results showed, for the first time, that synthetic hydrogen fuel can be used in FCEVs without the requirement of a large infrastructure. In addition, this study carried out a traceable H₂ contamination impact study with an FCEV. The impact of CO and H₂S at ISO 14687:2019 threshold levels on FCEV performance showed that small exceedances of the threshold levels had a significant impact, even for short exposures. The methodology proposed can be deployed to evaluate the composition of any hydrogen fuel.