The Role of Fugitive Hydrogen Emissions in Selecting Hydrogen Carriers

G lobal energy demand has been increasing drastically due to rapid population growth and economic development, more than tripling from 4242 million tons of oil equivalent per year (Mtoes/yr) in 1971 to 14,314 Mtoes/yr in 2018. 1 More than 80% of the total global energy is derived from fossil fuels, in the forms of oil, coal, and natural gas (NG). 2 Hydrocarbons as an energy source is finite, and this constitutes one very obvious incentive in identifying alternatives.Another and perhaps more pressing reason is that the increase in anthropomorphic activities and the dependence on fossil fuels has led to an alarming increase in carbon dioxide (CO 2 ) concentration in the atmosphere (currently approximately 420 ppm), which could impact the global climate. 3To curtail CO 2 emissions, a range of lowcarbon resources, including geothermal, solar-, wind-, tidal-, hydropower, etc., have been proposed as viable alternatives.However, their large-scale implementation requires proper energy storage and carrying systems due to the inconsistent availability of local renewable resources and their intrinsic intermittency. 4 In this context, hydrogen (H 2 ) is often considered the most promising clean energy carrier to diversify and alleviate the dependence on fossil fuels, one of the key decarbonizing strategies to achieve the goals set by the Paris Agreement. 5Predicted projections by the International Energy Agency's (IEA) net zero emission and Intergovernmental Panel on Climate Change (IPCC) SR1.5 scenarios showed that by 2050, the consumption of H 2 -based fuels may reach 18-33 exajoules (EJ = 10 18 J), corresponding to a potential reduction of CO 2 emissions by 4 Gt. 6 The strong demand for H 2 growth and the adoption of cleaner technologies for its production is expected to mitigate up to 60 Gt of CO 2 emissions from 2021 to 2050, representing 6% of the total reduction in cumulative emissions. 7This prospect has spurred several nations to announce ambitious projects, numerous targets, and policy incentives to decarbonize their energy sectors with a keen focus on developing sustainable H 2 technologies. 1,8,9As H 2 has a quintessential role in helping to tackle climate change, significant efforts and resources have been devoted toward developing suitable hydrogen technologies with proper infrastructures and large-scale applications.In the fervent migration from a fossil fuel-based economy toward a low-carbon hydrogen future, a vital but often overlooked process is the fugitive emission (FE, representing unanticipated leaks) which will have a significant impact at the industrial scale.H 2 is a small molecule that readily escapes and disperses into the atmosphere.As H 2 is very flammable in air