Key technologies and development status of hydrogen energy utilization in the context of carbon neutrality

1. The role of hydrogen energy in the future green energy structure

At present, the world's energy production and consumption structure is forming a new future energy system under the joint action of two trends: the global carbon emissions are still intensifying, the proportion of renewable energy is increasing, and a variety of new energy sources coexist. However, the new system still faces many challenges, including the volatility brought about by the increase in renewable energy installations and the long distance between energy supply and demand.

The value of hydrogen energy is that it can provide solutions to various key energy challenges, that is, to provide solutions for the conversion of matter and energy between multiple energy sources. The role of hydrogen energy in the future energy mix is shown in Figure 1. The value of hydrogen energy in the European Hydrogen Roadmap is described as follows: First, hydrogen is the most realistic option for large-scale decarbonization of major carbon emitters such as transport, industry and buildings; Second, hydrogen plays an important role in the systematic regulation of renewable energy production, transportation and consumption, and can provide a flexible cross-field, cross-time and cross-place energy circulation system. Finally, hydrogen is used in a way that is more in line with the preferences and habits of current users. In the future energy system, hydrogen has the potential to replace traditional fossil fuels such as coal, oil and natural gas.

2. Main key technologies of hydrogen energy

Hydrogen as a raw material is widely used in industrial raw materials, direct combustion energy supply, household fuel cells and fuel cell vehicles and other fields is the main use and development direction of hydrogen energy, and related technologies have made great progress in recent years. However, the core of the development of new energy is to achieve cheap and efficient raw material sources and storage and transportation, and hydrogen energy development is also facing the same problem. Therefore, hydrogen production and hydrogen storage technology is the key to the efficient use of hydrogen, is an important bottleneck limiting the development of large-scale industrialization of hydrogen energy, and has become one of the key and difficult points in the current development of hydrogen energy industrialization.

2.1.1 Hydrogen source supply methods Hydrogen sources are very wide, the main hydrogen source supply methods include coal, natural gas and other fossil energy reforming hydrogen production, industrial by-product hydrogen production and electrolytic water hydrogen production, the future or large-scale hydrogen source supply potential of other ways include biomass hydrogen production, photothermal hydrogen production, photoelectric hydrogen production and nuclear hydrogen production. At present, more than 95% of hydrogen comes from fossil energy reforming hydrogen production and industrial by-production hydrogen, hydrogen from other sources is still very limited, however, the use of renewable energy electrolytic water hydrogen production, so that renewable energy through the "electricity - hydrogen - electricity (or chemical raw materials)" way to power, transportation, heat and chemical industry coupled together, to achieve the "green hydrogen" real efficient use. To realize the true role of hydrogen as an energy source. The key core technology of hydrogen production from renewable energy sources is the efficient hydrogen production technology from electrolytic water. Hydrogen production by electrolytic water is to dissociate water molecules into hydrogen and oxygen through an electrochemical process under the action of direct current, and precipitate them at the Yin and Yang poles respectively. Anode: H₂O→1/2O₂+2H++2e-1 Cathode: 2H++2e-→H₂ Total reaction: H₂O→H₂+1/2O₂ According to the difference in the electrolyte system, hydrogen production from electrolytic water can be divided into alkaline electrolytic water, proton exchange membrane (PEM) electrolytic water and solid oxide electrolytic water 3 kinds. The basic principle of the three is the same, that is, in the process of REDOX reaction, prevent the free exchange of electrons, and decompose the charge transfer process into the electron transfer of the external circuit and the ion transfer of the internal circuit, so as to achieve the generation and utilization of hydrogen.

2.1.2 Alkaline water electrolysis to produce hydrogen

Alkaline liquid electrolysis water technology is based on KOH, NaOH aqueous solution as electrolyte, using asbestos cloth as diaphragm, under the action of direct current water electrolysis, hydrogen and oxygen are generated, the reaction temperature is low (60~80℃). The produced hydrogen is about 99% pure and needs to be dealkali mist treatment. The main structural features of alkaline electrolyzer are liquid electrolyte and porous separator, as shown in Figure 2. The maximum operating current density of alkaline electrolyzers is less than 400mA/cm², and the efficiency is usually about 60%.