Brazil

Sao Paulo State Environmental Protection Agency CETESB Brazil adopts a so called Reference Distance (RD) from hazardous substances storage facilities to populated places as a decision making tool for the application of a simplified or a full Risk Analysis (RA). As for hydrogen RD was set up based on instantaneous release scenarios where consequences reaching off-site population were estimated for delayed ignition ending up in vapor cloud explosion (VCE) with a 0.1 bar blast wave overpressure as a chosen endpoint corresponding to a 1%2of death probability range. Procedures for RD evaluation and further adoption by CETESB are presented in this paper.

During the early phase of the transient process following a hydrogen leak into the atmosphere a contact surface appears separating air heated by the leading shock from hydrogen cooled by expansion. Locally the interface is approximately planar. Diffusion leads to a temperature decrease on the air side and an increase in the hydrogen-filled region and mass diffusion of hydrogen into air and of air into hydrogen potentially resulting in ignition. This process was analyzed by Li ˜nan and Crespo [1] for unity Lewis number and Li ˜nan and Williams [2] for Lewis number less than unity. We included in the analysis the effect of a slow expansion [3 4] leading to a slow drop in temperature which occurs in transient jets. Chemistry being very temperature-sensitive the reaction rate peaks close to the hot side of the interface where only a small fuel concentration present close to the warm air-rich side which depends crucially upon the fuel Lewis number. For Lewis number unity the fuel concentration due to diffusion is comparable to the rate of consumption by chemistry. If the Lewis number is less than unity diffusion brings in more fuel than temperature-controlled chemistry consumes. For a Lewis number greater than unity diffusion is not strong enough to bring in as much fuel as chemistry would burn; combustion is controlled by fuel diffusion. If the temperature drop due to expansion associated with the multidimensional jet does not lower significantly the reaction rate up to that point analysis shows that ignition in the jet takes place. For fuel Lewis number greater than unity chemistry does not lead to a defined explosion so that eventually expansion will affect the process; ignition does not take place [3 4]. In the current paper these results are extended to consider multistep chemical kinetics but for otherwise similar assumptions. High activation energy is no longer applicable. Instead results are obtained in the short time limit still as a perturbation superimposed to the self-similar solution to the chemically frozen diffusion solution. In that approximation the initiation step which consumes fuel and oxidant is taken to be slow compared with steps that consume one of the reactants and an intermediate species. The formulation leads to a two point boundary value problem for set of coupled rate equations plus an energy equation for perturbations. These equations are linear with variable co-effcients. The coupled problem is solved numerically using a split algorithm in which chemical reaction is solved for frozen diffusion while diffusion is solved for frozen chemistry. At each time step the still coupled linear problem is solved exactly by projecting onto the eigenmodes of the stiff matrix so that the solution is unaffected by stiffness. Since in the short time limit temperature is only affected at the perturbation level the matrix depends only on the similarity variable x t but it is otherwise time-independent. As a result determination of the eigenvalues and eigenvectors is only done once (using Maple) for the entire range of discretized values of the similarity variable. The diffusion problem consists of a set of independent equations for each species. Each of these is solved using orthogonal decomposition onto Hermite polynomials for the homogeneous part plus a particular solution proportional to time for the non-homogeneous (source) terms. That approach can be implemented for different kinetic schemes.

The Brazilian Fuel Cell Bus Project is being developed by a consortium comprising 14 national and international partners. The project was initially supported by the GEF/UNDP and MME/FINEP Brazil. The national coordination is under responsibility of MME and EMTU/SP the São Paulo Metropolitan Urban Transport Company that also controls the bus operation and bus routes. This work reports the efforts done in order to obtain the necessary licenses to operate the first fuel cell buses for regular service in Brazil as well as the first commercial hydrogen fueling station to attend the vehicles.

This work reports a numerical investigation of microcombustion in an undulate microchannel using premixed hydrogen and air to understand the effect of the burner design on the flame in order to obtain stability of the flame. The simulations were performed for a fixed equivalence ratio and a hyperbolic temperature profile imposed at the microchannel walls in order to mimic the heat external losses occurred in experimental setups. Due to the complexity of the flow dynamics combined with the combustion behavior the present study focuses on understanding the effect of the fuel inlet rate on the flame characteristics keeping other parameters constant. The results presented stable flame structure regardless of the inlet velocity for this type of design meaning that a significant reduction in the heat flux losses through the walls occurred allowing the design of new simpler systems. The increase in inlet velocity increased the flame extension with the flame being stretched along the microchannel. For higher velocities flame separation was observed with two detected different combustion zones and the temperature profiles along the burner centerline presented a non-monotonic decrease due to the dynamics of the vortices observed in the convex regions of the undulated geometry walls. The geometry effects on the flame structure flow field thermal evolution and species distribution for different inlet velocities are reported and discussed.

Hydrogen is a promising commodity a renewable secondary energy source and feedstock alike to meet greenhouse gas emissions targets and promote economic decarbonization. A common goal pursued by many countries the hydrogen economy receives a blending of public and private capital. After European Green Deal state members created national policies focused on green hydrogen. This paper presents a study of energy transition considering green hydrogen production to identify Portugal’s current state and prospects. The analysis uses energy generation data hydrogen production aspects CO2 emissions indicators and based costs. A comprehensive simulation estimates the total production of green hydrogen related to the ratio of renewable generation in two different scenarios. Then a comparison between EGP goals and Portugal’s transport and energy generation prospects is made. Portugal has an essential renewable energy matrix that supports green hydrogen production and allows for meeting European green hydrogen 2030–2050 goals. Results suggest that promoting the conversion of buses and trucks into H2-based fuel is better for CO2 reduction. On the other hand given energy security thermoelectric plants fueled by H2 are the best option. The aggressive scenario implies at least 5% more costs than the moderate scenario considering economic aspects.

The maritime shipping sector is a major contributor to CO₂ emissions and this figure is expected to rise in coming decades. With the intent of reducing emissions from this sector this research proposes the utilization of the jet stream to transport a combination of cargo and hydrogen using airships or balloons at altitudes of 10–20 km. The jet streams flow in the mid-latitudes predominantly in a west–east direction reaching an average wind speed of 165 km/h. Using this combination of high wind speeds and reliable direction hydrogen-filled airships or balloons could carry hydrogen with a lower fuel requirement and shorter travel time compared to conventional shipping. Jet streams at different altitudes in the atmosphere were used to identify the most appropriate circular routes for global airship travel. Round-the-world trips would take 16 days in the Northern Hemisphere and 14 in the Southern Hemisphere. Hydrogen transport via the jet stream due to its lower energy consumption and shorter cargo delivery time access to cities far from the coast could be a competitive alternative to maritime shipping and liquefied hydrogen tankers in the development of a sustainable future hydrogen economy.

The world is undergoing a substantial energy transition with an increasing share of intermittent sources of energy on the grid which is increasing the challenges to operate the power grid reliably. An option that has been receiving much focus after the COVID pandemic is the development of a hydrogen economy. Challenges for a hydrogen economy are the high investment costs involved in compression storage and long-distance transportation. This paper analyses an innovative proposal for the creation of hydrogen ocean links. It intends to fill existing gaps in the creation of a hydrogen economy with the increase in flexibility and viability for hydrogen production consumption compression storage and transportation. The main concept behind the proposals presented in this paper consists of using the fact that the pressure in the deep sea is very high which allows a thin and cheap HDPE tank to store and transport large amounts of pressurized hydrogen in the deep sea. This is performed by replacing seawater with pressurized hydrogen and maintaining the pressure in the pipes similar to the outside pressure. Hydrogen Deep Ocean Link has the potential of increasing the interconnectivity of different regional energy grids into a global sustainable interconnected energy system.

This paper describes the development of a general-purpose geospatial model for assessing the economic viability of hydrogen production from offshore wind power. A key feature of the model is that it uses the offshore project's location characteristics (distance to port water depth distance to gas grid injection point). Learning rates are used to predict the cost of the wind farm's components and electrolyser stack replacement. The notional wind farm used in the paper has a capacity of 510 MW. The model is implemented in a geographic information system which is used to create maps of levelised cost of hydrogen from offshore wind in Irish waters. LCOH values in 2030 spatially vary by over 50% depending on location. The geographically distributed LCOH results are summarised in a multivariate production function which is a simple and rapid tool for generating preliminary LCOH estimates based on simple site input variables.

As the global market develops for green hydrogen and ammonia derived from renewable electricity the bulk transmission of hydrogen and ammonia from production areas to demand-intensive consumption areas will increase. Repurposing existing infrastructure may be economically and technically feasible but increases in supply and demand will necessitate new developments. Bulk transmission of hydrogen and ammonia may be effected by dedicated pipelines or liquefied fuel tankers. Transmission of electricity using HVDC lines to directly power electrolysers producing hydrogen near the demand markets is another option. This paper presents and validates detailed cost models for newly-built dedicated offshore transmission methods for green hydrogen and ammonia and carries out a techno-economic comparison over a range of transmission distances and production volumes. New pipelines are economical for short distances while new HVDC interconnectors are suited to medium-large transmission capacities over a wide range of distances and liquefied gas tankers are best for long distances.

Hydrogen fuel cell technology is securing a place in the future of advanced mobility and the energy revolution as engineers explore multiple paths in the quest for decarbonization. The feasibility of hydrogen-based fuel cell vehicles particularly relies on the development of safe lightweight and cost-competitive solutions for hydrogen storage. After the demonstration of hundreds of prototype vehicles today commercial hydrogen tanks are in the first stages of market introduction adopting configurations that use composite materials. However production rates remain low and costs high. This paper intends to provide an insight into the evolving scenario of solutions for hydrogen storage in the transportation sector. Current applications in different sectors of transport are covered focusing on their individual requirements. Furthermore this work addresses the efforts to produce economically attractive composite tanks discussing the challenges surrounding material choices and manufacturing practices as well as cutting-edge trends pursued by research and development teams. Key issues in the design and analysis of hydrogen tanks are also discussed. Finally testing and certification requirements are debated once they play a vital role in industry acceptance.

This article presents the development integration and experimental validation of a modular microgrid for sustainable hydrogen production addressing global electricity demand and environmental challenges. The system was designed for initial validation in a thermoelectric power plant environment with scalability to other applications. Centered on a six-compartment skid it integrates photovoltaic generation battery storage and a liquefied petroleum gas generator to emulate typical cogeneration conditions together with a high-purity proton exchange membrane electrolyzer. A supervisory control module ensures real-time monitoring and energy flow management following international safety standards. The study also explores the incorporation of blockchain technology to certify the renewable origin of hydrogen enhancing traceability and transparency in the green hydrogen market. The experimental results confirm the system’s technical feasibility demonstrating stable hydrogen production efficient energy management and islanded-mode operation with preserved grid stability. These findings highlight the strategic role of hydrogen as an energy vector in the transition to a cleaner energy matrix and support the proposed architecture as a replicable model for industrial facilities seeking to combine hydrogen production with advanced microgrid technologies. Future work will address large-scale validation and performance optimization including advanced energy management algorithms to ensure economic viability and sustainability in diverse industrial contexts.

The main objective of this paper is to select the optimal configuration of a ship’s power system considering the use of fuel cells and batteries that would achieve the lowest CO2 emissions also taking into consideration the number of battery cycles. The ship analyzed in this work is a Platform Supply Vessel (PSV) used to support oil and gas offshore platforms transporting goods equipment and personnel. The proposed scheme considers the ship’s retrofitting. The ship’s original main generators are maintained and the fuel cell and batteries are installed as complementary sources. Moreover a sensitivity analysis is pursued on the ship’s demand curve. The simulations used to calculate the CO2 emissions for each of the new hybrid configurations were developed using HOMER software. The proposed solutions are auxiliary generators three types of batteries and a protonexchange membrane fuel cell (PEMFC) with different sizes of hydrogen tanks. The PEMFC and batteries were sized as containerized solutions and the sizing of the auxiliary engines was based on previous works. Each configuration consists of a combination of these solutions. The selection of the best configuration is one contribution of this paper. The new configurations are classified according to the reduction of CO2 emitted in comparison to the original system. For different demand levels the results indicate that the configuration classification may vary. Another valuable contribution of this work is the sizing of the battery and hydrogen storage systems. They were installed in 20 ft containers since the installation of batteries fuel cells and hydrogen tanks in containers is widely used for ship retrofit. As a result the most significant reduction of CO2 emissions is 10.69%. This is achieved when the configuration includes main generators auxiliary generators a 3119 kW lithium nickel manganese cobalt (LNMC) battery a 250 kW PEMFC and 581 kg of stored hydrogen.

A model for a fuel cell propelled 50 PAX hydrogen aircraft is developed. In terms of year 2045 Nordic air travel demand this aircraft is expected to cover 97% of travel distances and 58% of daily passenger volume. Using an ATR 42 as a baseline cryogenic tanks and fuel cell stacks are sized and propulsion system masses updated. Fuselage and wing resizing are required which increases mass and wetted area. Sizing methods for the multi-stack fuel cell and the cryogenic tanks are implemented. The dynamic aircraft model is updated with models for hydrogen consumption and tank pressure control. For the Multi-layer insulation (MLI) tank a trade study is performed. A ventilation pressure of 1.76 bar and 15 MLI layers are found to be optimal for the design mission. A return-without-refuel mission is explored where for a 10-hour ground hold 38.4% of the design range is retained out of the theoretically achievable 50%.

Background: This study applied levelized cost of hydrogen (LCOH) and environmental cost accounting techniques to evaluate the feasibility of producing green hydrogen (GH2) via alkaline electrolysis for use in a bus fleet in Fortaleza Brazil. Methods: A GH2 plant with a 3 MW wind tower was considered in this financial project. A sensitivity analysis was conducted to assess the economic viability of the project considering the influence of production volume the number of electrolysis kits financing time and other kay economic indices. Revenue was derived from the sale of by-products including green hospital oxygen (GHO2) and excess wind energy. A life cycle assessment (LCA) was performed to quantify material and emission flows throughout the H2 production chain. A zero-net hydrogen price scenario was tested to evaluate the feasibility of its use in urban transportation. Results: The production of GH2 in Brazil using alkaline electrolysis powered by wind energy proved to be economically viable for fueling a hydrogen-powered bus fleet. For production volumes ranging from 8.89 to 88.9 kg H2/h the sensitivity analysis revealed high economic performance achieving a net present value (NPV) between USD 19.4 million and USD 21.8 million a payback period of 1–4 years an internal rate of return (IRR) of 24–90% and a return on investment (ROI) of 300–1400%. The LCOH decreased with increased production ranging from 56 to 25 USD/MWh. Over the project timeline GH2 production and use in the bus fleet reduced CO2 emissions by 53000–287000 t CO2 eq. The fuel cell bus fleet project demonstrated viability through fuel cost savings and revenue from carbon credit sales highlighting the economic social and environmental sustainability of GH2 use in urban transportation in Brazil.

Hydrogen (H2) is presented as an important alternative for clean energy and raw material in the modern world. However the environmental benefits are linked to its process of production. Herein the chemical aspects advantages/disadvantages and challenges of the main processes of H2 production from petroleum to water are described. The fossil fuel (FF)-based methods and the state-of-art strategies are outlined to produce hydrogen from water (electrolysis) wastewater and seawater. In addition a discussion based on a color code to classify the cleanliness of hydrogen production is introduced. By the end a summary of the hydrogen value chain addresses topics related to the financial aspects and perspective for 2050: green hydrogen and zero-emission carbon.

This work addresses the energy efficiency of hydrogen refueling stations (HRS) using a first principles model and optimal control methods to find minimal entropy production operating paths. The HRS model shows good agreement with experimental data achieving maximum state of charge and temperature discrepancies of 1 and 7% respectively. Model solution and optimization is achieved at a relatively low computational time (40 s) when compared to models of the same degree of accuracy. The entropy production mapping indicates the flow control valve as the main source of irreversibility accounting for 85% of the total entropy production in the process. The minimal entropy production refueling path achieves energy savings from 20 to 27% with respect to the SAE J2601 protocol depending on the ambient temperature. Finally the proposed method under nearreversible refueling conditions shows a theoretical reduction of 43% in the energy demand with respect to the SAE J2601 protocol.

The most challenging aspect of developing a green hydrogen economy is long-distance oceanic transportation. Hydrogen liquefaction is a transportation alternative. However the cost and energy consumption for liquefaction is currently prohibitively high creating a major barrier to hydrogen supply chains. This paper proposes using solid nitrogen or oxygen as a medium for recycling cold energy across the hydrogen liquefaction supply chain. When a liquid hydrogen (LH2) carrier reaches its destination the regasification process of the hydrogen produces solid nitrogen or oxygen. The solid nitrogen or oxygen is then transported in the LH2 carrier back to the hydrogen liquefaction facility and used to reduce the energy consumption cooling gaseous hydrogen. As a result the energy required to liquefy hydrogen can be reduced by 25.4% using N2 and 27.3% using O2. Solid air hydrogen liquefaction (SAHL) can be the missing link for implementing a global hydrogen economy.

Brazil has emerged as one of the global leaders in adopting renewable energy standing out in the implementation of onshore wind energy and more recently in the development of future offshore wind energy projects. Onshore wind energy has experienced exponential growth in the last decade positioning Brazil as one of the countries with the largest installed capacity in the world by 2023 with 30 GW. Wind farms are mainly concentrated in the northeast region where winds are constant and powerful enabling efficient and cost-competitive generation. Although in its early stages offshore wind energy presents significant potential of 1228 GW due to Brazil’s extensive coastline which exceeds 7000 km. Offshore wind projects promise greater generating capacity and stability as offshore winds are more constant than onshore winds. However their development faces challenges such as high initial costs environmental impacts on marine ecosystems and the need for specialized infrastructure. From a sustainability perspective this article discusses that both types of wind energy are key to Brazil’s energy transition. They reduce dependence on fossil fuels generate green jobs and foster technological innovation. However it is crucial to implement policies that foster synergy with green hydrogen production and minimize socio-environmental impacts such as impacts on local communities and biodiversity. Finally the article concludes that by 2050 Brazil is expected to consolidate its leadership in renewable energy by integrating advanced technologies such as larger more efficient turbines energy storage systems and green hydrogen production. The combination of onshore and offshore wind energy and other renewable sources could position the country as a global model for a clean sustainable and resilient energy mix.

Conventional hydrogen production processes which often involve fossil raw materials emit significant amounts of carbon dioxide into the atmosphere. This study critically evaluates the feasibility of using sugarcane biomass as an energy source to produce green hydrogen. In the 2023/2024 harvest Brazil the world’s largest sugarcane producer processed approximately 713.2 million metric tons of sugarcane. This yielded 45.68 million metric tons of sugar and 29.69 billion liters of first-generation ethanol equivalent to approximately 0.0416 liters of ethanol per kilogram of sugarcane. A systematic literature review was conducted using Scopus and Clarivate Analytics Web of Science resulting in the assessment of 335 articles. The study has identified seven potential biohydrogen production methods including two direct approaches from second-generation ethanol and five from integrated bioenergy systems. Experimental data indicate that second-generation ethanol can yield 594 MJ per metric ton of biomass with additional energy recovery from lignin combustion (1705 MJ per metric ton). Moreover advances in electrocatalytic reforming and plasma-driven hydrogen production have demonstrated high conversion efficiencies addressing key technical barriers. The results highlight Brazil’s strategic potential to integrate biohydrogen production within its existing bioenergy infrastructure. By leveraging sugarcane biomass for green hydrogen the country can contribute significantly to the global transition to sustainable energy while enhancing its energy security.

The increasing demand for carbon-free energy in recent years has positioned hydrogen as a viable option. However its current production remains largely dependent on carbon-emitting sources. In this context natural hydrogen generated through geological processes in the Earth’s subsurface has emerged as a promising alternative. The present study provides the first national-scale assessment of natural dihydrogen (H2) potential in Uruguay by developing a catalog of potential H2-generating rocks identifying prospective exploration areas and proposing H2 systems there. The analysis includes a review of geological and geophysical data from basement rocks and onshore sedimentary basins. Uruguay stands out as a promising region for natural H2 exploration due to the significant presence of potential H2-generating rocks in its basement such as large iron formations (BIFs) radioactive rocks and basic and ultrabasic rocks. Additionally the Norte Basin exhibits potential efficient cap rocks including basalts and dolerites with geological analogies to the Mali field. Indirect evidence of H2 in a free gas phase has been observed in the western Norte Basin. This suggests the presence of a potential H2 system in this area linked to the Arapey Formation basalts (seal) and Mesozoic sandstones (reservoir). Furthermore the proposed H2 system could expand exploration opportunities in northeastern Argentina and southern Brazil given the potential presence of similar play/tramp.

This paper investigates technological pathways for the conversion of coal-fired power plants toward sustainable energy sources using an integrated multi-criteria decisionmaking approach that combines Proknow-C AHP and PROMETHEE. Eight alternatives were identified: full conversion to natural gas full conversion to biomass coal and natural gas hybridization coal and biomass hybridization electricity and hydrogen cogeneration coal and solar energy hybridization post-combustion carbon capture systems and decommissioning with subsequent reuse. The analysis combined bibliographic data (26 scientific articles and 13 patents) with surveys from 14 energy experts using Total Decision version 1.2.1041.0 and Visual PROMETHEE version 1.1.0.0 software tools. Based on six criteria (environmental structural technical technological economic and social) the most viable option was full conversion to natural gas (ϕ = +0.0368) followed by coal and natural gas hybridization (ϕ = +0.0257) and coal and solar hybridization (ϕ = +0.0124). These alternatives emerged as the most balanced in terms of emissions reduction infrastructure reuse and cost efficiency. In contrast decommissioning (ϕ = −0.0578) and carbon capture systems (ϕ = −0.0196) were less favorable. This study proposes a structured framework for strategic energy planning that supports a just energy transition and contributes to the United Nations Sustainable Development Goals (SDGs) 7 and 13 highlighting the need for public policies that enhance the competitiveness and scalability of sustainable alternatives.

This work describes a thermodynamic comparison of the thermal efficiency of gas turbine engines featuring a conventional combustion chamber and a detonation combustion chamber using methane ethanol and mixtures of both ethanol and hydrogen and methane and hydrogen as fuels. The composition of gases was determined by the minimization of the Gibbs free energy whereas temperature pressure and velocity of detonation waves were determined by the Chapman-Jouguet theory. The results obtained here show that the DCC gas turbine cycle has a higher net work output and thermal efficiency than the CCC gas turbine cycle for all fuels studied in this work. The maximum thermal efficiency obtained with the DCC gas turbine cycle is indeed 57.22% which represents a 53.75% improvement over the maximum thermal efficiency obtained with the CCC gas turbine cycle (which has a peak thermal efficiency of 37.22%) under the same pressure ratio and turbine inlet temperature.

The chances of a global hydrogen economy becoming a reality have increased significantly since the COVID pandemic and the war in Ukraine and for net zero carbon emissions. However intercontinental hydrogen transport is still a major issue. This study suggests transporting hydrogen as a gas at atmospheric pressure in balloons using the natural flow of wind to carry the balloon to its destination. We investigate the average wind speeds atmospheric pressure and temperature at different altitudes for this purpose. The ideal altitudes to transport hydrogen with balloons are 10 km or lower and hydrogen pressures in the balloon vary from 0.25 to 1 bar. Transporting hydrogen from North America to Europe at a maximum 4 km altitude would take around 4.8 days on average. Hydrogen balloon transportation cost is estimated at 0.08 USD/kg of hydrogen which is around 12 times smaller than the cost of transporting liquified hydrogen from the USA to Europe. Due to its reduced energy consumption and capital cost in some locations hydrogen balloon transportation might be a viable option for shipping hydrogen compared to liquefied hydrogen and other transport technologies.

The biological production of hydrogen offers a renewable and potentially sustainable alternative for clean energy generation. In Northeast Brazil depleted oil reservoirs (DORs) present a unique opportunity to integrate biotechnology with existing fossil fuel infrastructure. These subsurface formations rich in residual hydrocarbons (RH) and native H2 producing microbiota can be repurposed as bioreactors for hydrogen production. This process often referred to as “Gold Hydrogen” involves the in situ microbial conversion of RH into H2 typically via dark fermentation and is distinct from green blue or grey hydrogen due to its reliance on indigenous subsurface biota and RH. Strategies include nutrient modulation and chemical additives to stimulate native hydrogenogenic genera (Clostridium Petrotoga Thermotoga) or the injection of improved inocula. While this approach has potential environmental benefits such as integrated CO2 sequestration and minimized surface disturbance it also presents risks namely the production of CO2 and H2S and fracturing which require strict monitoring and mitigation. Although infrastructure reuse reduces capital expenditures achieving economic viability depends on overcoming significant technical operational and biotechnological challenges. If widely applied this model could help decarbonize the energy sector repurpose legacy infrastructure and support the global transition toward low-carbon technologies.

This paper aims to perform a systematic review with a bibliometric approach of the technoeconomic evaluation studies of hydrogen production. To achieve this objective a comprehensive outline of hydrogen production processes from fossil and renewable sources is presented. The results reveal that electrolysis classified as water splitting is the most investigated process in the literature since it contributes to a reduction in greenhouse gas emissions and presents other advantages such as maturity and applicability energy efficiency flexibility and energy storage potential. In addition the processes of gasification classified as thermochemical and steam reforming classified as catalytic reforming are worth mentioning. Regarding the biological category there is a balance between research on photo fermentation and dark fermentation. The literature on the techno-economic evaluation of hydrogen production highlights significant gaps including a scarcity of comprehensive studies a lack of emphasis on commercial viability an absence of sensitivity analysis and the need for comparative analyses between production technologies.