Strategic route for impending green hydrogen energy in Oman

. Since energy and its sustainability are key global issues, extensive research is currently underway to advance the emerging energy sector. Hydrogen is anticipated to assume a substantial role as a worldwide energy carrier in forthcoming energy frameworks. Oman has set an ambitious target to annually produce one million tons of green hydrogen by 2040, aspiring to become one of the leading global producers and exporters of green hydrogen. These hydrogen scenarios are integral components of the broader global energy scenarios, primarily focused on achieving de-carbonization. Green hydrogen serves as a pivotal element in Oman's pursuit of de-carbonization, as well as its economic and energy security objectives. This paper aims to accentuate the challenges associated with hydrogen development, particularly in the context of green hydrogen production, by examining both present and future advancements. It provides a comprehensive overview of the consumption, applications, and economic considerations of green hydrogen based on expert organizations' projections. Additionally, the paper addresses key considerations pertaining to the utilization and transportation of hydrogen as compared to electricity.


Introduction
Human influence on climate has been a dominant cause of global warming.Energy production, transformation, storage, and usage in all of its forms are undergoing a significant transition on a global scale.People are becoming more and more aware of the need to transition to a civilization in which renewable energy sources, rather than fossil fuels, replace those that cause local pollution and climate change.In 2015, several pivotal agreements were established by nations worldwide, signifying important strides toward climate action [1].Among these are the 1992 United Nations Framework Convention on Climate Change (UNFCCC), the Sustainable Development Goals (SDGs), the Sendai and the Addis Ababa United Nations agreements focusing on disaster risk reduction.____________________________________ Moreover, as outlined in the Paris Agreement, the primary objectives are "to limit the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature rise to 1.5°C above pre-industrial levels." In the year 2020, the global average surface temperature had already ascended by approximately 1°C above pre-industrial levels.As articulated in the sixth Assessment Report (AR6) released by the Intergovernmental Panel on Climate Change (IPCC), the emissions of greenhouse gases over the past decade have attained their pinnacle, marking the highest levels ever recorded in human history.This unequivocally underscores the pressing exigency for swift and resolute action.The realization of the objective to confine global warming within the confines of 1.5°C hinges precariously upon immediate and substantial reductions in emissions spanning across all sectors.However, despite the disclosure of the Nationally Determined Contributions (NDC) prior to COP26, there persists a disconcerting projection: an anticipated surge in Global Greenhouse Gas (GHG) emissions.This trajectory accentuates the probability of surpassing the critical 1.5°C threshold, amplifying the formidable challenge of remaining beneath the 2°C target [2].
Stopping global warming necessitates achieving net zero carbon dioxide (CO2) emissions worldwide and curbing other greenhouse gas (GHG) emissions.Net zero is reached when human activities neither add to nor subtract from the atmospheric CO2 levels, balancing the emissions with removals.By attaining and sustaining zero CO2 emissions, it becomes plausible to stabilize global warming.Advancing towards net negative CO2 emissions would trigger a peak followed by a decline in CO2-induced warming, reducing overall cumulative net CO2 emissions upon reaching net zero.
The Intergovernmental Panel on Climate Change (IPCC) was established collaboratively by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988.Since its inception, the IPCC has diligently provided policymakers with the most credible and impartial scientific and technical evaluations, tailored to inform policy decisions without advocating for specific policy directives.
The transition toward a global community characterized by reduced carbon emissions, enhanced climate resilience, and sustainability demands purposeful and increasingly coordinated planning and decision-making across various governance levels, spanning from local to global tiers.This assertion is supported by robust evidence and high agreement among experts.
The insights unveiled within the IPCC's AR6 have profoundly augmented our understanding of the potential pathways available for mitigating emissions, with the ultimate aim of achieving a state of net-zero CO2 emissions.Although the prospect of completely halting CO2 emissions across multifarious industries poses a formidable challenge, it remains within the realm of attainability.The adoption of pioneering production methodologies, harnessing the potential of low and almost zero GHG energy sources, the integration of hydrogen and alternative fuels, as well as the deployment of sophisticated carbon capture and utilization techniques, represents a beacon of hope for industries to make significant strides towards the ambitious goal of attaining net-zero GHG emissions [3].
The utilization of electricity generated with minimal GHG emissions is anticipated to be pivotal in shaping low-carbon energy systems for various end-use applications.This strategy involves substituting fossil fuels with electricity across sectors such as building and industrial heating, transportation, and other pertinent activities.The future significance of hydrogen and its derivatives hinges upon the pace and scope of technological advancements in production methodologies.These approaches encompass electrolysis, recognized as "green" hydrogen production, as well as biogasification and fossil fuel reforming with carbon capture and storage, referred to as "blue" hydrogen production [4].
Hydrogen emerges as one of the most promising alternatives to oil, playing a pivotal role in fulfilling governments' commitments to achieve net-zero greenhouse gas emissions.
Considerable investments in the sector are being channeled towards initiatives that employ Carbon Capture, Utilization, and Storage (CCUS) technologies, enabling hydrogen production via methodologies such as water electrolysis or the utilization of fossil fuels coupled with carbon capture mechanisms.Amidst the swiftly escalating global energy crisis, triggered by the Russian Federation's invasion of Ukraine, there has been a notable surge in these investments.Many nations are actively exploring low-emission hydrogen as a viable means to lessen their dependence on fossil fuels.This avenue not only presents opportunities to bolster energy security but also aligns with the imperative goal of advancing decarbonization initiatives [5].

Hydrogen Demand Worldwide
In the year 2021, the global demand for hydrogen in emerging sectors such as heavy industry, transportation, power generation, construction, and the production of hydrogenderived fuels remained relatively modest.This demand accounted for approximately 40 kilotonnes (kt) of H2, representing only a small fraction, about 0.04%, of the total global demand for hydrogen.Notably, this increase in demand was influenced by the growing use of Fuel Cell Electric Vehicles (FCEVs), particularly in China, specifically in the heavy-duty truck segment for transportation purposes.While this sector experienced significant growth of around 60%, it began from a considerably low starting point.China held the position of the largest consumer of hydrogen globally in 2021, with a demand of approximately 28 million tonnes (Mt) of H2, marking a 5% increase from the previous year.Following China, the Middle East and the United States were the second and third largest consumers, each utilizing over 12 Mt of H2.Their demand was projected to rise by 8% and 11% in 2021 compared to the previous year, respectively [6].The global demand for hydrogen witnessed a 5% upsurge compared to the previous year, surpassing 94 Mt in 2021, marking a notable increase from the pre-pandemic level of 91 Mt recorded in 2019.The primary driver behind this escalation was attributed to conventional applications, notably within the chemical sector, which observed a rise of approximately 3 Mt, and in refining, experiencing an increase of around 2 Mt compared to 2020.The subsectors, especially refining, were notably affected by the Covid-19 pandemic, resulting in a discernible impact on hydrogen usage.However, as lockdown measures eased and the global economy began recovering in 2021, there was a conspicuous resurgence in hydrogen consumption.It's important to highlight that a significant portion of the provided hydrogen was generated through processes reliant on fossil fuels, thereby offering limited advantages concerning climate change mitigation [6].
According to the International Energy Agency (IEA) in their Stated Policies Scenario (STEPS), it is forecasted that hydrogen consumption could potentially climb to 115 Mt by the year 2030.However, this growth is expected to be primarily driven by traditional applications, with minimal demand, less than 2 Mt, allocated for new uses or the substitution of unabated fossil-based hydrogen in existing uses.Consequently, established applications are anticipated to account for the majority of this projected growth in hydrogen consumption.
Oman anticipates a significant rise in renewable energy capacity, projecting an increase of 4.8 gigawatts (GW) between 2022 and 2027, with a strong emphasis on solar photovoltaic (PV) projects driving the majority of this growth.Among the new renewable capacity additions, more than half, specifically 2.8 GW, will be dedicated to renewable hydrogen generation.The favorable conditions in Oman, including ample solar and wind resources, a well-developed hydrogen sector, and its strategic location near major shipping routes, position the country favorably for renewable hydrogen production and ammonia export.As a result, several proposed projects are in progress, particularly at port locations.A notable initiative in Oman aiming to produce ammonia from renewable sources received the pioneering clean hydrogen accreditation issued by the German certifying authority TÜV Rhineland [7].
However, despite the increasing demand for hydrogen, a considerable portion is still sourced from fossil fuels.In 2021, the global hydrogen production reached 94 Mt of H2, contributing to over 900 Mt of CO2 emissions.The predominant method of production, accounting for 62% of hydrogen output that year, involved natural gas extraction without implementing CCUS.Additionally, refineries contributed 18% of hydrogen production through the byproduct of naphtha reforming, utilized for various refinery processes like hydrocracking and de-sulphurization.
3 Current hydrogen production status

Coal-based hydrogen production
In 2021, the production of hydrogen derived from coal constituted around 19% of the global total, predominantly concentrated in China.Moreover, a minuscule proportion, less than 1%, of oil was employed in the hydrogen production process worldwide during that period.

Low-emission hydrogen production
In 2021, the production of low-emission hydrogen amounted to less than 1 Mt or 0.7% of the total.The majority of this production was derived from fossil fuels utilizing CCUS methods, accounting for the bulk of low-emission hydrogen.Specifically, only 35 kt of hydrogen were produced using water electrolysis.Despite its limited scale, the output from water electrolysis witnessed an approximate 20% increase from 2020, indicating a growing trend toward the adoption of water electrolyzers [8].

Outlook for low-emission hydrogen production to 2030
The IEA's hydrogen production project pipeline reveals a swift surge in the number of announced initiatives focused on generating low-emission hydrogen.Should all the ongoing projects dedicated to hydrogen production through water electrolysis or fossil fuels with CCUS come to fruition, the annual production of low-emission hydrogen could potentially exceed 24 Mt by the year 2030.
Water electrolysis produces hydrogen by splitting it into hydrogen and oxygen using electricity.Water electrolysis produced only around 0.1% of the world's hydrogen in 2021.Alkaline electrolysis accounted for roughly 70% of the installed capacity in 2021, with proton exchange membrane (PEM) electrolyzers making up the remaining 25%.Solid oxide electrolysis cells and anion exchange membrane electrolysis are other new technologies, but they are less developed than alkaline and PEM electrolyzers and only make up a small portion of the installed capacity at the moment [5,8].In many cases, especially for projects going online after 2025, according to the project pipeline, the electrolyzer type has not yet been disclosed by the developers.Alkaline electrolysis continues to make up roughly 60% of the total installed capacity (for which technological data is known) for the next five years, but then starts to decline.By 2030, the total installed capacity may be split equally between alkaline and PEM electrolyzers.In comparison to 2021, when the total capacity of projects in the pipeline intending to be operational by 2030 was 54-90 GW, this represents a huge rise.However, the project pipeline needs to grow up considerably more quickly in order to keep up with the Net Zero Scenario, which calls for installing more than 700 GW of electrolyzers worldwide by 2030.Fig. 2. IEA, Global hydrogen production, 2019-2030 [8] Currently, the overall cost of a fully installed electrolyzer, which covers equipment, gas treatment, plant balancing, as well as engineering, procurement, and construction expenses, ranges between USD 1,400 to USD 1,770 per kilowatt (kW).Alkaline electrolyzers tend to fall towards the lower end of this cost range, while PEM electrolyzers are positioned at the higher end.Notably, the costs for solid oxide electrolyzers are notably higher and thus are not included in this range.In particular, alkaline electrolyzers manufactured in China can be as inexpensive as USD 300/kW, considerably lower compared to those produced in Europe or North America, which can range from USD 750 to USD 1300/kW.The following table presents a summary of various technologies utilized in green hydrogen production [9].The steam reforming process involves catalytically converting hydrocarbons and steam at high temperatures ranging between 1000C to 1100C.This process results in the generation of hydrogen, carbon oxides, and a mixture of steam.To address the issue of CO2 emissions, supplementary measures like carbon dioxide capture and storage (CCS) can be incorporated into the process.Typically, common raw materials or feedstocks utilized for this process include natural gas and various liquid fuels such as nickel, copper, zinc, and other elements.

Partial Oxidation (POX)
POX is a chemical process that involves the conversion of a mixture of steam, oxygen, and hydrocarbons into hydrogen and carbon oxides.This catalytic conversion takes place at lower temperatures, typically around 950°C, and is compatible with various types of feedstocks.In addition to the catalytic approach, there is also a noncatalytic version of the process which occurs at higher temperatures, ranging from 1150C to 1315°C, and uses hydrocarbons like methane and coal.After sulfur removal, pure oxygen is introduced to facilitate the oxidation of the hydrocarbons, resulting in the production of syngas, which is then treated similarly to the SR process.POX technology is particularly well-suited for the production of hydrogen from heavier feedstocks like heavy oil residues and coal.These heavier hydrocarbon sources contain complex molecules that might not be easily processed through other conventional methods like steam reforming.POX technology enables the controlled oxidation of these heavier hydrocarbons in the presence of oxygen and steam, allowing for the efficient extraction of hydrogen along with carbon oxides.Therefore, POX stands as a suitable method for converting these heavier and less-refined feedstocks into hydrogen gas.

Auto Thermal Reforming (ATR)
In contrast to POX reforming, the Autothermal Reforming (ATR) process operates at lower pressure.This technique involves injecting steam along with either oxygen or air into the reformer, resulting in concurrent reforming and oxidation reactions.The ATR process merges partial oxidation to produce heat along with steam reforming to enhance the production of hydrogen.Typically, methane serves as the main feedstock utilized in this process.

Gasification
In the solid fuel gasification process, coal and steam undergo gasification to form "water gas."However, this synthesis gas has notable downsides, notably elevated levels of contaminants and carbon oxides compared to the SR process used with methane.The thermochemical process of gasification takes place at high temperatures between the organic components (e.g., coal) and the gasifying agents like oxygen, steam, air, and carbon dioxide.Hydrogen extraction occurs through the water gas shift method, followed by the conversion of carbon monoxide into carbon dioxide.

5.
Pyrolysis This process encompasses the thermal decomposition of organic materials, primarily fossils, where the hydrocarbon serves as the exclusive hydrogen source.The reactions occur within the range of 350°C to 400°C, influenced by the coal's characteristics.Transition metal catalysts like Ni and Fe can reduce the temperature required for the pyrolysis process.Unlike other procedures, water and air are not involved in this specific method.

Plasma Reforming
This novel technique for generating hydrogen integrates electricity as an additional energy source.Its primary goal is to produce hydrogen with the utmost energy efficiency.This method can be categorized into thermal and nonthermal variations based on temperature and energy levels employed.Due to the frequent degradation of electrodes, it primarily relies on solid fuels and occasionally incorporates liquid fuels.Moreover, the non-thermal plasma aspect of this process has the potential to benefit from the utilization of a catalyst to further enhance its effectiveness.

Biomass Pyrolysis
In this thermochemical process, biomass undergoes heating at temperatures ranging between 350-550°C under pressures of 0.1-0.5 MPa, resulting in the production of liquid oils and gaseous chemicals.Notably, this process occurs in the absence of oxygen.The quantity of hydrogen derived from biomass pyrolysis is influenced by factors such as the type of feedstock, the catalyst employed, temperature variations, and the duration of residence.While most pyrolysis operations aim for biofuels production, hydrogen can be generated directly through rapid pyrolysis, provided high temperatures and additional gas purification measures are allowed.8.

Super Critical Water (SCW)-GasTransformation
Under specific conditions, SCW demonstrates the capability to dissolve organic molecules.This intricate process encompasses multiple stages, including carbohydrate steam reforming, CO methanation, and water-gas shift.Utilizing catalysts has the potential to amplify the yields of hydrogen produced.However, despite its perceived efficacy, the expenses associated with this method are nearly twice as high as those incurred by alternative thermochemical approaches utilized for generating hydrogen from biomass.9.

Dark Fermentation
Fermentation, a biological process, involves microorganisms deriving energy from a carbon source.This phenomenon encompasses two forms: phototrophic fermentation, which utilizes light as an energy source (photo-fermentation), and non-phototrophic fermentation (dark-fermentation) occurring independently of light for energy conversion.10.
Aquas Phase Reforming (APhR) A catalytic process aimed at producing hydrogen involves oxygenated molecules, sugars, and chemicals extracted from biomass dissolved in water, reacting to generate H2.This method, termed APhR, operates at lower temperatures compared to steam reforming, thereby minimizing unfavorable decomposition reactions.Notably, its advantages encompass the ability to execute the entire process within a single reactor and eliminate the need for water evaporation.The primary focus of research revolves around discovering the optimal catalyst, notably leaning towards nickel-based options, to enhance the efficiency of this method.
PhF represents a process utilized for hydrogen production by harnessing light-induced fermentation.This method is reliant on three distinct groups of light-dependent microorganisms: aerobic green algae (eukaryotes), cyanobacteria (commonly known as blue-green algae), and anaerobic photosynthetic bacteria.Among these groups, photosynthetic purple bacteria have gained considerable attention for their effectiveness in generating hydrogen via photobiological mechanisms.Their noteworthy versatility in utilizing both light and industrial waste materials positions them as a promising and sustainable option for hydrogen production.12.
Biomass Gasification (BG) BG can be compared to a type of high-temperature decomposition similar to pyrolysis, resulting in a gas mixture enriched with hydrogen.This transformation can take place either with or without the aid of catalysts.Broadly, gasification entails the partial heating of substances in a low-oxygen environment, leading to the substantial creation of gaseous compounds such as CO2, water vapor, CO, hydrogen, and gaseous hydrocarbons like methane.Importantly, there is minimal formation of solid residues such as char and ashes, as well as condensed substances like tars and oils.The temperature within the system typically ranges between 500°C and 1400°C.13.
Bio-Photolysis (BPh) BPh, known as Biological Photolysis, utilizes principles akin to those found in plants but is tailored for the explicit purpose of generating hydrogen [10,11].Certain algae, equipped with hydrogen-producing enzymes, can produce hydrogen under specific conditions.Diverse forms of algae have the ability to decompose water molecules into hydrogen ions and oxygen through direct and indirect bio photolysis processes.14.
Biological Water-Gas Shift (WGS) The process of WGS denotes the oxidation of CO by water, leading to the generation of CO2 and subsequent production of H2.Certain photoheterotrophic bacteria possess the ability to subsist without light by relying solely on CO as their carbon source.These bacteria merge CO oxidation with the transformation of H + into H2 during this metabolic process.While the primary application of the biological water-gas shift reaction for hydrogen production primarily occurs within laboratory settings, researchers share the common objective of identifying suitable microorganisms capable of efficiently utilizing high amounts of CO as input for this process.15.

Microbial Electrolysis cells (MEC)
MEC employs electro-hydro-genesis to directly convert biodegradable material into hydrogen.Specialized microorganisms oxidize or decompose organic matter within the cell.Notably, in an operating MEC, there is an absence of oxygen at the cathode.Consequently, the process is not naturally spontaneous under typical conditions, requiring an external voltage to be supplied to the cell.The generation of hydrogen occurs at the cathode during this process.16.
Thermolysis (ThL) An efficiency rate of up to 50% is attainable when employing solely heat for the separation of water into hydrogen and oxygen.The ThL (Thermal-Lysis) process involves the direct thermal splitting of water at extremely elevated temperatures.Research indicates that at temperatures exceeding 2500°C, water begins to decompose without the necessity of additional chemical elements.However, numerous materials encounter challenges in enduring such extreme temperatures.17.

Thermochemical Water Splitting
In this particular procedure, catalysts, known as chemical agents, are integral to the process alongside thermolysis.Their role is to lower the temperature required for the decomposition of water, typically around 900°C.Catalysts commonly employed include those derived from elements such as copper, zinc, nickel, and manganese.However, a significant obstacle encountered in this process is the need to optimize efficiency, especially regarding cost-effectiveness, particularly when transitioning to larger-scale applications.18.
Photo Electrolysis PhE stands as a promising renewable method for hydrogen production, showcasing advantageous cost and efficiency characteristics.However, its application primarily resides within the experimental phase.This approach harnesses both electrical and photonic energy during the hydrogen production process.A notable feature is the integration of a photocatalyst on one of the electrodes, enabling interaction with light.This marks a significant departure from the conventional method of water electrolysis.19.

Photocatalytic Water Splitting
This method directly utilizes solar energy to split water, eliminating the requirement to convert solar energy into either heat or electricity.Given that pure water is not particularly effective in absorbing solar radiation, the water splitting process necessitates a photosemiconductor capable of efficiently absorbing solar energy to initiate the molecule-splitting reaction.Titanium oxide (TiO2) is primarily utilized in these photolysis reactions for its proficiency in this role.20.
Electrolysis Electrolysis is a process that separates compounds or elements by passing an electric current through them in an electrolytic cell.This involves the use of electrodes-an anode and a cathode-submerged in an electrolyte.When the electric current flows, ions within the compound move towards oppositely charged electrodes.At the anode, oxidation occurs, causing the formation of new compounds or elements, while reduction occurs at the cathode, leading to the creation of different substances.This results in the decomposition or splitting of the initial compound into its constituent elements or simpler compounds.For instance, in water electrolysis, the application of electricity can split water molecules into hydrogen and oxygen gases.

Transportation of green hydrogen
Transporting hydrogen presents significant challenges, requiring a robust distribution infrastructure.Hydrogen can be transported either in liquid or gaseous forms, utilizing cryogenic tanks, pipelines, tube trailers, or cylinders [12].Despite its expansive energy capacity, hydrogen possesses a relatively low energy density.Techniques such as compression and liquefaction can enhance its energy density; however, these methods are costly.For example, liquefying hydrogen demands approximately one-third of its lower heating value.Thus, the selection between gaseous or liquid transport mediums necessitates consideration of factors like cost, safety, and storage technology for end use.Notably, the projected cost of distributing hydrogen is estimated to be 15 times higher than that of liquid hydrocarbon fuels [13].This cost disparity underscores the complexity and financial considerations associated with establishing an efficient hydrogen distribution network.

Storage of green hydrogen
As illustrated in Fig. 3, hydrogen storage technologies are categorized into three primary groups: (a) physical storage methods, (b) chemical storage methods (also known as materialsbased hydrogen storage), and (c) hybrid storage methods.These encompass various techniques such as compressed storage, liquefaction, and the utilization of materials for physisorption-based storage.Cryo-adsorption, identified as a hybrid technique, combines both physical and chemical aspects, utilizing cryogenic conditions for the adsorption process [14].6 Conclusions According to the research, the year 2040 will be a turning point for the widespread use of clean, economical hydrogen as an oil substitute.A smart strategy is needed to encourage the wider production of low-cost, environmentally friendly hydrogen while also creating new markets and meeting increased demand.This policy should rely on dependable industrial uses of hydrogen to establish a strong and trustworthy basis for its broader adoption.While hydrogen and hydrogen-based fuels may be among the sole remaining low-carbon choices in some industries, they may not ultimately be economically viable or necessitate further study in others.Overall, more people around the world are realizing how important hydrogen may be.By fully using these short-term opportunities, low-carbon hydrogen might be in a position to contribute significantly to the long-term global endeavour to create a safe, reliable, and affordable global energy system.

Table 1 .
Hydrogen production Technologies