CC BY
6TECHNICAL SCIENCE
UDC: 621.35
Krasulevska K.A.,
Student at the Department of Technical Electrochemistry, National Technical University "Kharkiv Polytechnic Institute "
Maizelis A.O.
Doctor of Science, Senior Researcher, Associate Professor at the Department of Technical Electrochemistry, National Technical University "Kharkiv Polytechnic Institute " DOI: 10.24412/2520-6990-2023-14173-53-56 COMPARISON OF METHODS OF GREEN HYDROGEN PRODUCTION
Abstract.
Modern methods of hydrogen production are considered and place of electrochemical technologies in the green hydrogen system is shown. A comparison of electrolyzers for hydrogen production is carried out according to the principle of operation, technological parameters, advantages and disadvantages. The elements of electro-lyzers that limit the development of technologies are determined and the ways of their further development are shown.
Keywords: hydrogen; electrolysis; electrode; catalyst; membrane.
Introduction
Nowadays, with the constant increase in energy consumption and rapid climate change, the provision of a sustainable and environmentally friendly source of energy is becoming critical for our society. In this context, hydrogen plays a key role as one of the most promising energy sources. Particular attention is drawn to
Green hydrogen is produced using processes that use only renewable energy and generate no CO2 emissions, making a significant contribution to the fight against climate change. Electrolysis is the most mature and consolidated process on the market. It consists in splitting water molecules into oxygen and hydrogen in electrolyzer, which is powered by electrical energy from renewable sources (e.g., wind, sun, etc.). There are other ways to produce hydrogen (including biomass gasification, pyrolysis, thermochemical water splitting, photocatalysis), but they have not yet reached commercial scale.
An unprecedented global energy transition based on the use of renewable energy sources is currently taking place. Hydrogen energy, in particular green hydrogen, plays a key role in this process. Some countries are
green hydrogen - hydrogen produced using renewable energy sources with a minimal carbon footprint [1].
Generally, according to the data of Global Energy Infrastructure, there are 8 ways to produce hydrogen (Table 1).
Table 1
actively involved in hydrogen diplomacy, seeing access to hydrogen as a strategic element of their energy security. Negotiations on hydrogen have become the norm in international forums. A race for technological leadership in hydrogen energy is predicted, where green hydrogen will compete with traditional sources. The impact of developing a hydrogen economy could change the global energy market by reducing dependence on oil and gas. However, the success of this industry will depend on solving challenges such as increasing production efficiency, reducing costs and developing the necessary infrastructure, which requires the support of governments.
Role of electrochemical processes in hydrogen energy system
Methods of hydrogen production
"Colour" of hydrogen Technology Feedstock / Electricity source Greenhouse gas (GHG) footprint
Green Production via electricity Electrolysis Wind / Solar / Hydro / Geothermal / Tidal Low
Purple/Pink Nuclear Minimal
Yellow Mixes-origin grid energy Medium
Blue Production via fossil fuels Natural gas + CCUS + Gasification + CCUS Natural gas / coal Low
Turquoise Pyrolysis Natural gas Solid-carbon (by product)
Grey Natural gas reforming medium
Brown Gasification Brown coal (lignite) High
Black Black coal
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First, let us consider the path of green hydrogen from production to customer. Hydrogen can be produced in electrolyzes using different sources of energy, and in the case of green hydrogen they are renewable sources of energy. Produced hydrogen can be stored
and/or transported anywhere to customers, e.g., hydrogen fueling or industry (ammonia production). Also, hydrogen can be used to produce energy in fuel cells anywhere where it is transported. On the other side, hydrogen can be produced for hydrogen fueling in elec-trolyzes using electricity from electric grid.
Figure 1 - Production, transportation, storage and utilization of green hydrogen
The path of green hydrogen from its production to transportation and storage can be as follows:
1. Production of green hydrogen. Green hydrogen is produced by splitting water into hydrogen and oxygen using water electrolysis, which utilizes renewable energy. Wind energy installations, solar panels or other sources of renewable energy can be used for water electrolysis.
2. Cleaning and storage. Green hydrogen needs to be cleaned of any residual gases or other impurities. After that, it can be stored in special containers designed for high pressure and low temperature. A promising method of storage the hydrogen is storage in the solid phase (bounded, e.g., in the form of hydrides).
3. Transportation. Green hydrogen can be transported through pipelines that are specially designed to
transport hydrogen. Other methods of transportation include the transportation of hydrogen in containers that are able to reserve large volumes of hydrogen under high pressure, or the transportation of hydrogen in the form of liquid gas or solid state in hydrides.
The central element in the production of green, as well as pink and yellow hydrogen is the electrolyzer. Table 2 shows a comparison of the main types of elec-trolyzers. The oldest and most common is alkaline water electrolyzer [2]. The most promising is the electrolyzer with alkaline anion exchange membrane [3]. Main advantages and disadvantages of electrolyzers of different types are listed in Table 2 (based on information from International Energy Agency and [1,4,5]).
Table 2
Types of electrolyzers and their brief characteristics
Proton Exchange Membrane Elec-trolyzer (PEM) Alkaline Water Electro-lyzer (AWE) Alkaline Anion Exchange Membrane (AEM) Solid Oxide Electro-lyzer (SOEC)
Maturity Commercial Commercial Full scale prototype Early commercial
Charger carrier H+ OH- OH- O2-
Electrolyte Solid polymer Aqueous solution 10-40% KOH/NaOH Solid polymer Solid ceramic
Anode material Pt /Ir /Ru Ni, Ni-based alloy Ni-based alloy LSMYSZ; CaTiO3
Cathode material Pt; Pt=C Ni alloys Ni, Ni-Fe, NiFe2O Nicermets
Electrode area, cm2 ~1 500 10 000-30 000 < 300 200
Anode reaction H2O ^ ^ '/2 O2 + 2H+ + 2e 2OH- ^ / O2 + H2O + 2e O2- ^ / O2 + 2e
Cathode reaction 2H+ + 2e ^ H2 2H2O + 2e ^ H2 + 2OH- H2O + 2e ^ ^ H2 + O2-
Total reaction H2O ^ H2 + / O2
Temperature, °C 70 - 90 65 - 100 50 - 70 650 - 1 000
Operation pressure, bar 15 - 30 2 - 10 <35 >30
Efficenty, % 67 - 84 62 - 82 - ~90
Cell voltage, V 1.8 - 2.4 1.8 - 2.4 ~ 1.85 0.95 - 1.3
Current density, A/cm2 0.6 - 2 0.2 - 0.4 0.1 - 0.5 0.3 - 1
Launch time, min <15 15 - >60
Service term, h < 40 000 < 90 000 > 10 000 < 40 000
Energy consumption, kWh/Nm3 4.5 - 7.5 4.5 - 7 ~ 4.8 2.5 - 3.5
H2 purity, % 99.9-99.9999 99.5 - 99.9998 99.9 -99.9999 99.9%
Advantages • High purity of hydrogen • Short launch time • Low capital costs • Stable and well established • No noble material is used • The purity of hydrogen is high, but lower than PEM • Cheap components • Compact design • High purity of hydrogen • High efficiency
Disadvantages • Precious metals are used • High cost • Short service life • Low purity of hydrogen • Low current density • Corrosive electrolyte • Low service life • Safety issues and sealing issues • Bulky design • Use of fragile material • The technology is at the demonstration stage
The development of technologies for the use of renewable energy is a key element in achieving carbon neutrality. It is important to share hydrogen production technologies based on natural renewable energy
sources. Photovoltaic and wind energy sources generate energy unevenly, and their power fluctuations are carefully analyzed for efficient use. Reducing the range of power fluctuations can be achieved by combining
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electricity produced in different places. However, the relationship between operating conditions under power fluctuations, various methods of water electrolysis, and performance evaluation of electrolyzers requires further study. It is important to understand the effect of power fluctuations on the electrolysis of water and to ensure the stability of the system. Designing electrolyz-ers to take into account power fluctuations and equipment that is compatible with them is of great importance to improve the efficiency of renewable energy use.
Research in the field of PEM electrolyzers is aimed at reducing the cost of catalysts, both through the search for new compositions and nanostructuring of materials, and by reducing the load of catalyst. In addition, existing proton-conducting membranes still need to be made cheaper. Research in the field of SOEC elec-trolyzers is mainly aimed at increasing the stability of the process.
Further development of AWE technology aims to reduce severe catalyst degradation due to reverse current during start and stop. Even in large photovoltaic and wind power plants, where smoothing effects can be expected, start and stop operations are inevitable, so it is necessary to develop electrodes and catalysts that are highly resistant to these operations. The authors are developing such electrodes [6].
AEM is a new technology that combines the advantages and reduces the disadvantages of both PEM and AWE [7]. Research is aimed at improving the operation of anodes, as well as at increasing the catalytic activity and characteristics of polyfunctional catalysts. Such a process would require the use of bipolar membranes (a combination of anion and cation exchange membranes): in combination with bifunctional catalysts, they would allow the production of hydrogen on a large scale with minimal energy consumption. A possible increase in costs can be offset by an increase in the kinetics of the entire process.
Conclusions
Electrochemical technologies play an important role in achieving high efficiency and economic feasibility of obtaining and using green hydrogen. The most appropriate low-temperature electrolyzers. The oldest and proven technology of alkaline water electrolysis can be improved to increase the efficiency of electrolysis by creating electrode catalysts. Promising technologies for PEM and AEM electrolyzers require the development of both electrode materials and stable (in the case of AEM) and cheap (in the case of PEM) membranes.
References
1. Kumar, S. Shiva, and Hankwon Lim. "An overview of water electrolysis technologies for green hydrogen production." Energy Reports 8 (2022): 13793-13813.
2. David, Martín, Carlos Ocampo-Martínez, and Ricardo Sánchez-Peña. "Advances in alkaline water electrolyzers: A review." Journal of Energy Storage 23 (2019): 392-403.
3. Li, Changqing, and Jong-Beom Baek. "The promise of hydrogen production from alkaline anion exchange membrane electrolyzers." Nano Energy 87 (2021): 106162.
4. Nasser, Mohamed, et al. "A review of water electrolysis-based systems for hydrogen production using hybrid/solar/wind energy systems." Environmental Science and Pollution Research (2022): 1-25.
5. Benghanem, Mohamed, et al. "Hydrogen Production Methods Based on Solar and Wind Energy: A Review." Energies 16.2 (2023): 757.
6. Maizelis, Antonina, and Alexei Pilipenko. "Electrode Materials for Hydrogen Production by Alkaline-Water Electrolysis Powered by Renewable Energy Sources." 2021 IEEE 2nd KhPI Week on Advanced Technology (KhPIWeek). IEEE, 2021, 313316.
7. Palmas, Simonetta, et al. "Anion exchange membrane: a valuable perspective in emerging technologies of low temperature water electrolysis." Current Opinion in Electrochemistry (2022): 101178.
