At present, the whole world including human civilization is suffering from the problem of global climate change. As such, the whole world is trying to minimize this problem at various scientific platforms including the ‘Net Zero’ target. The main reason for taking it into effect is the rise in global average temperature as a consequence of the increasing global atmospheric CO2 concentrations. This global warming phenomenon is responsible for frequent climatic hazards e.g. flooding, extreme climate, bushfires, poor air quality, and extinction of animal and plant species. These climate change phenomena are going to increase in future if critical measurements for the mitigation of global warming are not taken in present. Therefore, it is crucial to implement the net-zero plan as soon as possible to restrict the increase in world temperature to 1.5 °C. Reducing our energy usage from fossil-fuel-based sources to alternate sources of energy which are emission-free, can help in mitigation of direct carbon emission to a great extent. Solar and wind energy in particular are attracting attention on a global scale but due to their intermittent nature, renewable energy sources like wind and solar need to be stored on a massive scale. Hydrogen as a fuel for energy production is one of the most promising options for the deep decarbonization of the industrial, transport, and power sectors. But utilizing hydrogen in our energy mix is still a worldwide challenge for researchers regarding its bulk storage and a lower carbon footprint.
Hydrogen: The future fuel
Hydrogen is the most abundant element in the universe. It has a high specific capacity (120 MJ/kg) and its clean combustion products make hydrogen an attractive and green energy carrier. Due to the low density (0.09 kg/m3 at standard conditions) of hydrogen, only large-scale (GWhr to TWhr) storage can be economic. Hydrogen as an energy source can be utilized in many sectors, e.g. industries, mobility, building (and industry) heat, and power applications etc. Hydrogen is used extensively in industry for processes like metal forming, e.g. reducing iron into steel, and ammonia synthesis, which produces fertilizer. The direct use of hydrogen shows promise in several important mobility sectors, including aviation, heavy-duty vehicles, and ships. It has also shown potential in the integration of baseload power plants, backup generators, and seasonal energy (demand-supply) balancing. Due to the low density of hydrogen surface-based facilities for its storage is not very feasible due to low capacity. To utilize hydrogen economically and at a large scale in our energy mix storing it at high pressures and high energy densities in underground geological formations (aquifers, depleted hydrocarbon reserves, and salt caverns etc.) has more potential. If bulk hydrogen storage could be made economically feasible, hydrogen has been anticipated to be the greatest solution for our energy demand. The adaptability of hydrogen enables it to retain energy for lengthy periods of time and contributes to the energy system's resilience by enabling system balancing. Hydrogen can be systematically used in various sectors for rapid decarbonization of the economy. Even though being the most abundant and lightest element hydrogen bears a high energy density than gasoline of ~120 MJ/kg and 45.8 MJ/kg respectively. Because of its high energy density and environment-friendly combustion, industries and research organisation are actively engaged in research and development for a more competitive price for hydrogen production. The potential of hydrogen to efficiently power the fuel cells in zero-emission (on-road emissions) vehicles in a shorter amount of time (rapid filling) has increased interest in hydrogen as an alternative fuel, particularly in the transportation industry. When used as fuel in fuel cell-based vehicles water is the only byproduct as an emission. In order to address a variety of pressing energy concerns, hydrogen can be employed as a versatile energy carrier which can be used to store, transport, and deliver energy generated from other sources. As a result, it might be a desirable fuel choice for uses such as transportation and energy generation.
Hydrogen types and their production methods
Hydrogen is the most dominant element in the universe, but it mainly exists in the form of molecules by bonding with other elements and among them water is most abundant on planet Earth where hydrogen bonds with oxygen. By splitting water molecules, which is an energy-intensive operation pure hydrogen can be produced, turning it into a fuel that may help rescue the planet in terms of global greenhouse gas emissions. Almost all energy sources, including hydrocarbons, natural gas, biomass, and other organic matter, including a variety of household resources, can also be used to produce hydrogen, rather than using water electrolysis only. Today, there are various ways to make hydrogen fuel, including solar-powered processes, electrolysis, biological processes, and natural gas reforming (a thermal process). Nuclear energy can also be used to produce hydrogen (through electrolysis) and is a carbon-free method and can be considered as the best utilization of nuclear power plants. The hydrogen produced by biomass is termed brown hydrogen and upon capturing and storing the consequent CO2 it is termed blue hydrogen.
Source: Figure shows different types of hydrogen and its production techniques, (Ahmed I Osman et al., Environmental Chemistry Letters, (2022) 20: 153-188)
The hydrogen produced by the electrolysis of water using renewable energy is called green hydrogen and it is considered the most environmentally friendly because its production also emits zero carbon. Hydrogen has a colour spectrum that ranges from black to green, and it depends upon the carbon emission/intensity associated with the hydrogen production method utilized. Nowadays, the most widely used approach for creating "grey hydrogen" is steam methane reforming (natural gas to electricity, a thermal process). Blue hydrogen, referred to that hydrogen when the CO2 produced during hydrogen production is captured and stored and it's thought to be a better source of low-carbon energy. As an alternative, 'green hydrogen' produced by water electrolysis using renewable energy, is a carbon-free energy source. The carbon produced by coal gasification is known as ‘brown hydrogen’ and when the liberated CO2 during hydrogen’s production is captured and stored the the hydrogen turns into blue hydrogen. The ‘turquoise hydrogen" can be produced through the pyrolysis of methane, a by-product of which is solid carbon. Fracking is used to create ‘white hydrogen’, a form of hydrogen that naturally exists in subsurface deposits. At the moment, no plans exist to utilize this hydrogen. However, a more recent word for hydrogen created through electrolysis using solar electricity is yellow hydrogen.
What is Net zero? How hydrogen can help achieve net zero?
The term "Net Zero" describes a situation in which the balance between greenhouse gas emissions and removal from the atmosphere has been reached. The increase in the Earth’s average global temperature—which is currently roughly 1°C higher than it was in the pre-industrial era is predicted to grow to 3–5°C by 2100. To stop the rise in global average temperature net zero emission is needed to be implemented. This rise in global average temperature is a result of the rising levels of atmospheric CO2, which peaked at 413 ppm in May 2020, or 149% over pre-industrial levels, and has since been rising at a rate of 2.3±0.4 ppm per year. Along with carbon removal technology, clean energy and low-carbon solutions are currently a critical requirement for the future. All nations must achieve net-zero emissions (though not simultaneously), but high polluters should start making progress as soon as practicable. However, limiting deforestation and concurrent plantation on a global scale merits top priority. Nearly all nations (137) agreed to participate in the race to net-zero aim, a global drive to meet carbon reduction targets as quickly as possible, with a commitment to the Paris Agreement. According to the Climate Action Tracker, net-zero targets currently account for 73% of all worldwide emissions. Only Bhutan and Suriname, the first two nations to achieve net zero emissions, represent carbon neutrality and are practically carbon negative (releasing less carbon than they remove). Uruguay has established 2030 as its goal to achieve net zero at the earliest possible time compared to other nations. Finland, Germany, Austria, Sweden, and Iceland are among the European nations aiming for 2045 or earlier. 124 (or around 90%) of the 137 countries studied have set a deadline of 2050 for achieving full carbon neutrality.
Source: Graph shows the global emissions which can be abated by hydrogen and global hydrogen demand until 2050 (Sunil Kumar et al., 2023, Fuel, 350 (128849); modified after Hydrogen for the net-zero report, Hydrogen council (2021), Mckinsey & Company)
A small number of (just five) nations, including Canada, South Korea, and the European Union member states, have previously proposed laws to achieve this goal. In the meantime, 24 nations, including the United States, Brazil, Germany, and China, have established their climate targets as official policies. India has also given itself until 2030 to lower its GDP-related emissions by one billion tonnes (or 45%), which equates to 2.44 billion tons in 2020 (or 2.55 in the previous three years). Out of the remaining 137 nations, 99 (72%), are still simply in the discussion phase and have not taken a formal position in support of future action. But soon, pressure on nations will increase, forcing them to follow through on their commitments to become carbon-neutral. By switching to a low-carbon energy mix and working toward a net-zero goal, the globe is battling climate change. To help with this shift, hydrogen is a promising fuel for the future, but there are several challenges still associated with it e.g. cost-effective production, bulk storage, safety etc. Since hydrogen permits energy storage, offers resilience, and makes bulk transit over large distances (through pipelines and ships) easier, so integrating it with renewable energy sources can build an eco-system of clean energy and help in offsetting global carbon emissions to a considerable scale. Renewable energy sources due to their intermittent nature still face a big problem of energy storage because making gigawatt battery storage parks is neither economic nor environment friendly. The Norway-based risk management expert in the hydrogen forecast 2050 claimed that hydrogen would need to reach 13% in order to satisfy the Paris Agreement's goal of limiting global warming to 1.5 degrees by 2050. But at the present speed, it is predicted that hydrogen will only cover 5 % of the total energy mix by 2050. So a high investment in the production and research and development to raise the proportion of hydrogen at a cost-effective level in our energy mix is needed.
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