1 3
need to be developed. Electrochemical reduction of nitrogen to ammonia is thermodynamically predicted to be more efficient than the HBP by about 20%. Besides, an
electrochemical process could provide the advantage of eliminating fossil fuels as
the precursor of H 2 and energy by the use of water molecules for hydrogen production [78]. In this manner, electrochemical systems offer additional benefits, including scalability and on-demand ammonia generation. The electrochemical catalysis
community has progressed somewhat towards the fabrication of efficient electrochemical nitrogen reduction materials, but most efforts are plagued by low Faradaic
efficiencies due to the competing hydrogen production reaction, which dominates
all metal-based catalyst surfaces [19, 79–81]. Therefore, natural biocatalytic systems
that are able to efficiently catalyze NRR reactions are highly desirable alternatives.
Recently, several works on biological catalysts based on protein compounds have
been published. These state that the conversion of N 2 into ammonia occurs naturally
in diazotrophic microorganisms through the enzyme nitrogenase, as shown in Fig. 6.
[77] Also, they reported that nitrogenase operates at mild conditions of around
150 bar. The synthesis of NH 3 from dinitrogen by nitrogenase follows this reaction
under optimal conditions.
(where ATP is adenosine tri-phosphate, ADP is adenosine diphosphate and Pi is
inorganic phosphate). The reaction includes the obligatory hydrolysis of ATP to
release stored chemical energy and kinetic limitations of nitrogen reduction. According to the results of this work, for the molecule of nitrogen that is reduced, two molecules of ammonia are produced, and protons are also reduced to form one molecule
of hydrogen. Following these ideas, theoretical scientists are starting to work on
the design of nature-inspired NRR nanostructured materials. In this regard, a giant
advance was recently achieved by He and coworkers in this innovative research line
[82]. They reported the first theoretically designed asymmetrical dual-metal dimer
catalytic centers embedded on N-doped carbon nanostructures toward the electrochemical reduction of N 2 –NH 3 inspired by the function of FeMo cofactors in the
nitrogenase molecules. The simulated Mo–Ru, Mo–Co, Mo–W, Mo–Fe and Fe–Ru
dimers exhibited ultra-low onset potentials of only 0.17, 0.27, 0.28, 0.36 and 0.39 V
vs reversible hydrogen electrode (RHE), opening the way for the development of
promising nature-inspired NRR electrocatalysts (Fig. 7) [82].
6 Conclusions
The development of protein-based nanomaterials for water-splitting reactions has
becoming cutting-edge research in recent years. Their unique properties to competently catalyze several electrocatalytic reactions at the nanometric scale make
them excellent candidates for the fabrication of promising enzymatic biofuel
cells. Undoubtedly, the role of proteins as effective nanomachines in the overall
catalytic process is crucial. In this direction, it is well-established that conformational and/or structural changes in protein structures significantly enhance their
N 2 + 8H
+ + 16MgATP + 8e
− → 2NH 3 + H 2 + 16MgADP + 16Pi
250
Reprinted from the journal
Topics in Current Chemistry (2020) 378:43
need to be developed. Electrochemical reduction of nitrogen to ammonia is thermodynamically predicted to be more efficient than the HBP by about 20%. Besides, an
electrochemical process could provide the advantage of eliminating fossil fuels as
the precursor of H 2 and energy by the use of water molecules for hydrogen production [78]. In this manner, electrochemical systems offer additional benefits, including scalability and on-demand ammonia generation. The electrochemical catalysis
community has progressed somewhat towards the fabrication of efficient electrochemical nitrogen reduction materials, but most efforts are plagued by low Faradaic
efficiencies due to the competing hydrogen production reaction, which dominates
all metal-based catalyst surfaces [19, 79–81]. Therefore, natural biocatalytic systems
that are able to efficiently catalyze NRR reactions are highly desirable alternatives.
Recently, several works on biological catalysts based on protein compounds have
been published. These state that the conversion of N 2 into ammonia occurs naturally
in diazotrophic microorganisms through the enzyme nitrogenase, as shown in Fig. 6.
[77] Also, they reported that nitrogenase operates at mild conditions of around
150 bar. The synthesis of NH 3 from dinitrogen by nitrogenase follows this reaction
under optimal conditions.
(where ATP is adenosine tri-phosphate, ADP is adenosine diphosphate and Pi is
inorganic phosphate). The reaction includes the obligatory hydrolysis of ATP to
release stored chemical energy and kinetic limitations of nitrogen reduction. According to the results of this work, for the molecule of nitrogen that is reduced, two molecules of ammonia are produced, and protons are also reduced to form one molecule
of hydrogen. Following these ideas, theoretical scientists are starting to work on
the design of nature-inspired NRR nanostructured materials. In this regard, a giant
advance was recently achieved by He and coworkers in this innovative research line
[82]. They reported the first theoretically designed asymmetrical dual-metal dimer
catalytic centers embedded on N-doped carbon nanostructures toward the electrochemical reduction of N 2 –NH 3 inspired by the function of FeMo cofactors in the
nitrogenase molecules. The simulated Mo–Ru, Mo–Co, Mo–W, Mo–Fe and Fe–Ru
dimers exhibited ultra-low onset potentials of only 0.17, 0.27, 0.28, 0.36 and 0.39 V
vs reversible hydrogen electrode (RHE), opening the way for the development of
promising nature-inspired NRR electrocatalysts (Fig. 7) [82].
6 Conclusions
The development of protein-based nanomaterials for water-splitting reactions has
becoming cutting-edge research in recent years. Their unique properties to competently catalyze several electrocatalytic reactions at the nanometric scale make
them excellent candidates for the fabrication of promising enzymatic biofuel
cells. Undoubtedly, the role of proteins as effective nanomachines in the overall
catalytic process is crucial. In this direction, it is well-established that conformational and/or structural changes in protein structures significantly enhance their
N 2 + 8H
+ + 16MgATP + 8e
− → 2NH 3 + H 2 + 16MgADP + 16Pi
250
Reprinted from the journal
Topics in Current Chemistry (2020) 378:43