The global energy system needs to undergo a profound transformation, from a
system based on fossil fuels, to an efficient and renewable low-carbon system. Given the
importance of this transition towards more sustainable models, hydrogen presents itself as
a renewable energy source with high capacity to enable this green future. Therefore, the
importance of developing studies that contribute to the analysis and optimization of
production processes and ways of using this source of energy is evident. Thus, this work
consists of an exploratory bibliographic review about the fundamental points related to the
production and use of hydrogen and its position in the current energy market. This study
focused on the evaluation of gray, brown, blue and green hydrogen. During the literature
review, emissions data in kgCO2eq were collected from life cycle assessments with similar
and comparable assessment perimeters. At the end of the study, simulations of the relative
reduction of greenhouse gases emissions are carried out in the scenarios of electricity
production and road transport, when hydrogen from different routes is used as a substitute
for fossil fuels. For the national electricity generation scenario, where 15% of the matrix is
still produced from natural gas and coal, the simulation results indicated reductions of up
to 40% in the carbon footprint of the Sistema Interligado Nacional, replacing both with
blue hydrogen. For the scenario of road transport, greater potential gains were found to be
made possible through green hydrogen. Internal combustion engine (ICE) with mix of
natural gas + green hydrogen and diesel + green hydrogen, up to approximately 34% and
31% were found, respectively, and proton exchange membrane fuel cell (PEMFC) with
green hydrogen, reductions of up to 70% were found in comparison with natural gas. But
due to the green hydrogen economic competitiveness difficulties, the blue hydrogen
reduction results of both scenarios generate optimism for its use as a means of boosting the
hydrogen economy and already acting now in the decarbonization of these sectors. Cases
using ICE with mix of diesel + blue hydrogen and ICE with mix of natural gas and blue
hydrogen from natural gas showed emission reductions of up to 18% and 23% respectively.
With PEMFC cars with blue hydrogen from natural gas, reductions reached up to 48%
when replacing diesel.
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