Topics in Current Chemistry (2019) 377:27
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of the use of such fuels due to the generation of greenhouse gases [1]. Among greenhouse gases, carbon dioxide (CO 2 ) is the largest contributor to climate change [2].
As a proof of the impact of anthropogenic activities in the emission of CO 2 , its concentration in the atmosphere has increased greatly since the Industrial Revolution
(270–275 ppm in 1750; 310 ppm in 1950; 408 ppm in 2018), with a total emission
of 36 Gt CO 2 per year, 91% of it being generated by anthropogenic activities [3].
The worldwide concern regarding climate change has resulted in global agreements to combat its tragic consequences. For example, the Kyoto Protocol and the
more recent Paris Agreement (United Nations Framework Convention on Climate
Change; UNFCCC) [4], aim to keep global warming below 2 °C. In such an energy
context, the role of renewable and clean energy is gaining more and more importance. Among renewable resources, the use of solar and wind energy as well as
hydropower are green energy power sources of interest in the quest to satisfy global
energy demand. Such renewable sources have several advantages compared to fossil
fuels and nuclear-based energy: (1) low variable cost of production; (2) no production of waste linked to the generation of power; and (3) suitable for decentralized
power generation [5].
However, their obvious advantages come with important drawbacks related to
their intrinsical dependence on day–night intervals, seasons, and fluctuating environmental conditions, which result in periods of deficit and surplus of energy output [6, 7]. In such a complicated energy scenario, hydrogen, as a never-ending and
renewable source of energy, emerges as an outstanding energy vector for mobile and
stationary applications. Hydrogen was recently defined by the International Energy
Agency (IEA) as a flexible energy carrier, which can be produced from any energy
source, and which can be converted into various energy forms [8].
The widespread implementation of the so-called “hydrogen economy” faces not
only technical barriers, but also headwinds related to the political and economic
interests of using fossil fuels. However, the scientific community has a moral obligation to search for possible solutions to issues related to the production, storage, and
transportation of hydrogen. The production of hydrogen can be carried out through
both renewable and non-renewable means; currently, steam methane reforming of
natural gas is the main process used, accounting for approximately 48% of total
production [9]. However, this process is linked to the generation of CO 2 emissions,
which tarnishes the concept of “green hydrogen production” [10]. Aside from that,
safety issues related to the physical storage of hydrogen by compression and cooling are also a focus of discussion because of the very high pressure levels (up to
700–800 bar) or very low temperatures (−252 °C) required [11–15].
The generation of molecular hydrogen (H 2 ) from hydrogen carrier molecules
that contain it in their structure has recently been claimed as an auspicious option.
Such molecules provide a unique way to deliver molecular hydrogen in a reversible
way by means of chemical reactions, and, although hydrogen production by these
means is not as mature as the classical alternatives, there are already a number of
potential candidates that show interesting characteristics [16–25]. Among them, liquid organic hydrogen carriers (LOHC) are recognized as an ideal option in terms
of cost, safety and manageability [26, 27]. Included within LOHC are all hydrogen storage systems that are liquid in their hydrogen-rich form [11]. Such molecules
194
Reprinted from the journal
1 3
of the use of such fuels due to the generation of greenhouse gases [1]. Among greenhouse gases, carbon dioxide (CO 2 ) is the largest contributor to climate change [2].
As a proof of the impact of anthropogenic activities in the emission of CO 2 , its concentration in the atmosphere has increased greatly since the Industrial Revolution
(270–275 ppm in 1750; 310 ppm in 1950; 408 ppm in 2018), with a total emission
of 36 Gt CO 2 per year, 91% of it being generated by anthropogenic activities [3].
The worldwide concern regarding climate change has resulted in global agreements to combat its tragic consequences. For example, the Kyoto Protocol and the
more recent Paris Agreement (United Nations Framework Convention on Climate
Change; UNFCCC) [4], aim to keep global warming below 2 °C. In such an energy
context, the role of renewable and clean energy is gaining more and more importance. Among renewable resources, the use of solar and wind energy as well as
hydropower are green energy power sources of interest in the quest to satisfy global
energy demand. Such renewable sources have several advantages compared to fossil
fuels and nuclear-based energy: (1) low variable cost of production; (2) no production of waste linked to the generation of power; and (3) suitable for decentralized
power generation [5].
However, their obvious advantages come with important drawbacks related to
their intrinsical dependence on day–night intervals, seasons, and fluctuating environmental conditions, which result in periods of deficit and surplus of energy output [6, 7]. In such a complicated energy scenario, hydrogen, as a never-ending and
renewable source of energy, emerges as an outstanding energy vector for mobile and
stationary applications. Hydrogen was recently defined by the International Energy
Agency (IEA) as a flexible energy carrier, which can be produced from any energy
source, and which can be converted into various energy forms [8].
The widespread implementation of the so-called “hydrogen economy” faces not
only technical barriers, but also headwinds related to the political and economic
interests of using fossil fuels. However, the scientific community has a moral obligation to search for possible solutions to issues related to the production, storage, and
transportation of hydrogen. The production of hydrogen can be carried out through
both renewable and non-renewable means; currently, steam methane reforming of
natural gas is the main process used, accounting for approximately 48% of total
production [9]. However, this process is linked to the generation of CO 2 emissions,
which tarnishes the concept of “green hydrogen production” [10]. Aside from that,
safety issues related to the physical storage of hydrogen by compression and cooling are also a focus of discussion because of the very high pressure levels (up to
700–800 bar) or very low temperatures (−252 °C) required [11–15].
The generation of molecular hydrogen (H 2 ) from hydrogen carrier molecules
that contain it in their structure has recently been claimed as an auspicious option.
Such molecules provide a unique way to deliver molecular hydrogen in a reversible
way by means of chemical reactions, and, although hydrogen production by these
means is not as mature as the classical alternatives, there are already a number of
potential candidates that show interesting characteristics [16–25]. Among them, liquid organic hydrogen carriers (LOHC) are recognized as an ideal option in terms
of cost, safety and manageability [26, 27]. Included within LOHC are all hydrogen storage systems that are liquid in their hydrogen-rich form [11]. Such molecules
194
Reprinted from the journal