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Topics in Current Chemistry (2019) 377:27
can be dehydrogenated and re-hydrogenated, and show great potential for use in stationary and transportation applications [5, 28]. Among LOHC investigated for this
application (e.g., N-ethylcarbazole, dibenzyltoluene, naphthalene, methanol, toluene, etc. [26, 27]), the suitability of formic acid (HCOOH, FA) has been highlighted
by a plethora of recent publications reporting the investigation of H 2 production
from FA via dehydrogenation reaction (HCOOH ↔ H 2 + CO 2 ) [29–35]. FA is the
simplest carboxylic acid and has attracted great attention due to its non-toxic character, stability, and high hydrogen content (4.4 wt% and 53 g L
−1
) [30, 31]. Furthermore, FA is readily available from sources such as oxidation of biomass, and it is an
intermediate, byproduct, and product of the chemical industry, as well as a product
of the hydrogenation of CO 2 [36].
The HCOOH/CO 2 system has been claimed to be an ideal environmentally
friendly system for hydrogen storage, with the CO 2 produced in the dehydrogenation reaction being re-hydrogenated to HCOOH in a carbon-free emission process
[37]. The use of catalysts is vital in the reactions involved in hydrogen storage and
release. Traditionally, homogeneous systems have been used to boost the dehydrogenation of FA, starting with the pioneering investigation reported by Coffey in
1967, in which Pt, Ru and Ir phosphine complexes were used [38]. Although FA
has attracted interest for the H 2 production for more than five decades, its use as a
LOHC was not claimed until 2008 by the independent investigations of Laurenczy
[39] and Beller [40, 41].
The more convenient use of heterogeneous catalysts has motivated the search for
new alternatives to achieve competitive and selective heterogeneous systems able
to catalyze the dehydrogenation of FA under mild or moderate conditions. Significant breakthroughs in the field have been achieved while exploring aspects such
as the features of the metallic active phase [42–46] or the properties of the support [44, 47–50]. Most investigations reported so far use relatively high temperatures to achieve acceptable conversion of FA into H 2 . However, CO can be also
produced from FA at high temperatures by following the dehydration reaction
(HCOOH → CO + H 2 O), which is a poison of the catalysts used in fuel cells [51].
Recently, the photocatalytic dehydrogenation of FA has also attracted great attention as a promising option for the generation of H 2 at room temperature. In most
cases, the catalysts used are Mott–Schottky photocatalysts, which use a semiconductor support and metal nanoparticles of diverse composition (i.e., Pd, Pt, Au, Ag,
etc.) [52].
The use of sunlight, as a green and abundant energy source, is of great interest
in the current energy scenario. In particular, the use of sunlight for the production
of H 2 unites two pillars of research aimed at the realization of a sustainable energy
future. Most solar-to-hydrogen production is based on the water splitting reaction
[53, 54], but photocatalytic processes have also been utilized for the production of
H 2 from other molecules, such as ethanol [55, 56], methanol [57, 58], glycerol [59,
60], hydrazine [61], ammonia [62, 63], ammonia borane [17, 20, 64, 65], etc.
Here, we review some of the most representative investigations dealing with the
production of H 2 from the photocatalytic decomposition of FA. The photodecomposition of FA has frequently been investigated from other points of view, such as
the degradation of pollutants, the use of FA in photoelectrochemical cells, or the
195
Reprinted from the journal
Topics in Current Chemistry (2019) 377:27
can be dehydrogenated and re-hydrogenated, and show great potential for use in stationary and transportation applications [5, 28]. Among LOHC investigated for this
application (e.g., N-ethylcarbazole, dibenzyltoluene, naphthalene, methanol, toluene, etc. [26, 27]), the suitability of formic acid (HCOOH, FA) has been highlighted
by a plethora of recent publications reporting the investigation of H 2 production
from FA via dehydrogenation reaction (HCOOH ↔ H 2 + CO 2 ) [29–35]. FA is the
simplest carboxylic acid and has attracted great attention due to its non-toxic character, stability, and high hydrogen content (4.4 wt% and 53 g L
−1
) [30, 31]. Furthermore, FA is readily available from sources such as oxidation of biomass, and it is an
intermediate, byproduct, and product of the chemical industry, as well as a product
of the hydrogenation of CO 2 [36].
The HCOOH/CO 2 system has been claimed to be an ideal environmentally
friendly system for hydrogen storage, with the CO 2 produced in the dehydrogenation reaction being re-hydrogenated to HCOOH in a carbon-free emission process
[37]. The use of catalysts is vital in the reactions involved in hydrogen storage and
release. Traditionally, homogeneous systems have been used to boost the dehydrogenation of FA, starting with the pioneering investigation reported by Coffey in
1967, in which Pt, Ru and Ir phosphine complexes were used [38]. Although FA
has attracted interest for the H 2 production for more than five decades, its use as a
LOHC was not claimed until 2008 by the independent investigations of Laurenczy
[39] and Beller [40, 41].
The more convenient use of heterogeneous catalysts has motivated the search for
new alternatives to achieve competitive and selective heterogeneous systems able
to catalyze the dehydrogenation of FA under mild or moderate conditions. Significant breakthroughs in the field have been achieved while exploring aspects such
as the features of the metallic active phase [42–46] or the properties of the support [44, 47–50]. Most investigations reported so far use relatively high temperatures to achieve acceptable conversion of FA into H 2 . However, CO can be also
produced from FA at high temperatures by following the dehydration reaction
(HCOOH → CO + H 2 O), which is a poison of the catalysts used in fuel cells [51].
Recently, the photocatalytic dehydrogenation of FA has also attracted great attention as a promising option for the generation of H 2 at room temperature. In most
cases, the catalysts used are Mott–Schottky photocatalysts, which use a semiconductor support and metal nanoparticles of diverse composition (i.e., Pd, Pt, Au, Ag,
etc.) [52].
The use of sunlight, as a green and abundant energy source, is of great interest
in the current energy scenario. In particular, the use of sunlight for the production
of H 2 unites two pillars of research aimed at the realization of a sustainable energy
future. Most solar-to-hydrogen production is based on the water splitting reaction
[53, 54], but photocatalytic processes have also been utilized for the production of
H 2 from other molecules, such as ethanol [55, 56], methanol [57, 58], glycerol [59,
60], hydrazine [61], ammonia [62, 63], ammonia borane [17, 20, 64, 65], etc.
Here, we review some of the most representative investigations dealing with the
production of H 2 from the photocatalytic decomposition of FA. The photodecomposition of FA has frequently been investigated from other points of view, such as
the degradation of pollutants, the use of FA in photoelectrochemical cells, or the
195
Reprinted from the journal