What are the ways to produce hydrogen?
At present, there are mainly the following methods of hydrogen production:
Hydrogen production from fossil fuels: mainly including hydrogen production from natural gas and hydrogen production from coal. Hydrogen production from natural gas is currently the most important method of hydrogen production, mainly using the methane steam reforming method. Although the cost of producing hydrogen from coal is low, it is not environmentally friendly.
Industrial by-product hydrogen production: Using by-products produced in the industrial production process to produce hydrogen, the cost is low. It mainly includes hydrogen production from coke oven gas and hydrogen produced by chlor-alkali industry.
Hydrogen production by electrolysis of water: Hydrogen is produced through electrolysis of water. The product has high purity and no pollution. It is a key direction for future development. However, the current cost is relatively high and needs to be further reduced.
Low energy consumption and improved efficiency.
Biomass hydrogen production: Using biomass materials to produce hydrogen through biological or thermochemical processes, the technology is not yet fully mature.
Photolysis of water to produce hydrogen: Using solar energy to directly split water to produce hydrogen, the technology is still in the research and development stage.
From the perspective of economics and technological maturity, hydrogen production from natural gas and industrial by-product hydrogen currently dominate. But in the long run, hydrogen production by electrolysis of water is considered to be a key direction for future development due to its clean and environmentally friendly characteristics. With technological advancement and cost reduction, hydrogen production from water electrolysis is expected to usher in important development opportunities in the next 3-5 years.
What is green hydrogen, blue hydrogen, gray hydrogen?
Depending on the hydrogen production method and the degree of carbon emissions, hydrogen can be divided into three types: gray hydrogen, blue hydrogen and green hydrogen:
Gray hydrogen:
Gray hydrogen is hydrogen produced from fossil fuels (such as natural gas, coal, petroleum, etc.). This is currently the most important method of hydrogen production, accounting for approximately 95% of global hydrogen production. Gray hydrogen production costs are lower, but carbon emissions are large and have a greater impact on the environment.
Blue hydrogen:
Blue hydrogen is also produced from fossil fuels (mainly natural gas), but uses carbon capture and storage (CCS) technology in the production process. This method can significantly reduce carbon emissions, but the capture cost is high. Blue hydrogen is considered an intermediate product in the transition from gray hydrogen to green hydrogen.
Green hydrogen:
Green hydrogen is hydrogen produced by electrolyzing water using renewable energy sources (such as solar energy, wind energy, etc.). This method produces almost no carbon emissions during the entire production process and is the cleanest way to produce hydrogen. At present, the cost of green hydrogen is relatively high, but as the cost of renewable energy decreases and electrolysis technology advances, its economics is expected to continue to improve.
At present, there are mainly the following ways to produce hydrogen by electrolyzing water:
ALK is alkaline water electrolysis
ALK is alkaline water electrolysis, also often called AWE (Alkaline Water Electrolysis). This is a traditional and mature technology for electrolyzing water to produce hydrogen. The following are the main features of ALK/AWE:
working principle:
In an alkaline electrolyte (usually 20%-30% KOH or NaOH solution), hydrogen is generated by reducing water at the cathode through direct current, and oxygen is generated by oxidizing water at the anode.
01
Core components:
Electrode: Usually metal alloys such as nickel and molybdenum are used
Diaphragm: Made of porous materials such as asbestos, ceramics, nylon, etc.
Electrolyte: KOH or NaOH alkaline solution
02
Working conditions:
Electrolysis temperature: 70-90℃
Electrolysis pressure: 1-3 MPa
03
advantage:
Mature technology, earliest to achieve industrial application
The system structure is simple and easy to operate
Low requirements on raw material water quality
Long equipment life, up to 10-20 years or more
Lower cost and good economy
04
shortcoming:
Current density is relatively low
Poor dynamic response
There is a diaphragm cross-gas problem
Lye is corrosive
05
Proton exchange membrane electrolysis (PEM):
Using a solid polymer electrolyte membrane, no liquid electrolyte is required. At the cathode, protons (H+) combine with electrons to form hydrogen gas; at the anode, water decomposes to form oxygen and protons. PEM has the advantages of high current density and fast startup.
working principle:
Using a solid polymer electrolyte membrane, no liquid electrolyte is required. At the cathode, protons (H+) combine with electrons to form hydrogen gas; at the anode, water decomposes to form oxygen and protons. Protons are transported through the membrane to the cathode.
01
Core components:
Electrode: Usually noble metal catalysts are used, such as platinum and iridium
Electrolyte membrane: commonly used perfluorosulfonic acid membrane (such as Nafion membrane)
Bipolar plates: used to separate unit cells and conduct current
02
Working conditions:
Temperature:50-80℃
Pressure: up to dozens of atmospheres
03
advantage:
High current density, up to 2 A/cm² or more
Starts quickly and responds quickly
The system is compact and occupies a small area
The purity of hydrogen produced is high, up to 99.999%
Can operate under high pressure to reduce subsequent compression costs
04
shortcoming:
Higher costs, especially precious metal catalysts and proton exchange membranes
High water quality requirements require the use of ultrapure water
Lifespan is relatively short, usually 20,000-50,000 hours
05
development trend:
Research focuses include developing low-cost catalysts, improving membrane performance and durability, and optimizing system design to reduce costs.
PEM technology is particularly suitable for use with renewable energy sources with high volatility due to its high efficiency and rapid response. With technological advancement and cost reduction, PEM is expected to be more widely used in the next 5-10 years, especially in the fields of distributed hydrogen production and renewable energy hydrogen production.
Anion exchange membrane electrolysis (AEM):
The structure is similar to PEM, but uses an anion exchange membrane. The advantage is that non-noble metal catalysts can be used, which is expected to reduce costs. The technology is still in the research and development stage.
working principle:
Using an anion exchange membrane as the electrolyte, OH- ions are transported from the cathode through the membrane to the anode. At the cathode, water decomposes to produce hydrogen and OH-; at the anode, OH- is oxidized to produce oxygen and water.
01
Core components:
Electrode: non-noble metal catalysts can be used, such as nickel-based and cobalt-based materials
Electrolyte membrane: anion exchange membrane, usually composed of a polymer backbone and positively charged functional groups
Electrolyte: pure water or weak alkaline solution
02
Working conditions:
Temperature: Typically in the range 50-70°C
Pressure: Can operate at normal pressure or slightly pressurized
03
advantage:
Non-precious metal catalysts can be used to reduce costs
The current density is higher, between AWE and PEM
Simple system, no complex water treatment system required
Environmentally friendly, use pure water or weakly alkaline solution
04
shortcoming:
The technology is relatively new and has not yet been commercialized on a large scale
The stability and durability of anion exchange membranes need to be further improved
Ionic conductivity is relatively low
05
development trend:
Research focuses include the development of high-performance, high-stability anion exchange membranes and matching efficient catalysts.
High Temperature Solid Oxide Electrolysis (SOE):
Performing electrolysis at high temperatures (700-900°C) can reduce the electrical energy required for electrolysis. However, this technology is still in the demonstration stage and has not yet achieved large-scale commercialization.
working principle:
At high temperatures (700-900°C), water vapor is reduced at the cathode to generate hydrogen and oxygen ions. Oxygen ions are transported through the solid oxide electrolyte to the anode, where they are oxidized to generate oxygen.
01
Core components:
Electrodes: usually use nickel-based materials as the cathode and cobalt-based or lanthanum strontium manganese oxide as the anode
Electrolyte: Solid oxide ceramic material, such as yttrium-doped zirconia (YSZ)
Interconnect board: usually using high temperature resistant alloy materials
02
Working conditions:
Temperature:700-900°C
Pressure: Can operate under normal pressure or pressurized conditions
03
advantage:
High electrolysis efficiency, the theoretical efficiency can reach 100%
High-temperature heat sources such as industrial waste heat or nuclear energy can be used to reduce electricity consumption
Reversible operation, can produce hydrogen and generate electricity (solid oxide fuel cell mode)
No precious metal catalysts required, reducing costs
04
shortcoming:
High-temperature operation places high demands on materials, and there are problems with thermal cycling and thermal stress.
Long startup time, not suitable for frequent starts and stops
The technology is not yet fully mature and is still in the demonstration stage
05
development trend:
Research focuses include developing high-temperature-resistant, long-life electrode and electrolyte materials, and optimizing system design to improve efficiency and reduce costs.
SOE technology is considered a promising hydrogen production technology due to its high efficiency and utilization of high-temperature heat sources. It is especially suitable for use in combination with high-temperature heat sources such as nuclear energy and solar thermal power generation. With the advancement of materials science and system integration technology, SOE is expected to achieve commercial application in the next 10-15 years, providing new possibilities for large-scale, high-efficiency green hydrogen production.
Among these methods, AWE and PEM are currently the two most widely used technologies. AWE occupies a dominant position due to its low cost and mature technology, and is particularly suitable for large-scale hydrogen production. PEM is more suitable for use with renewable energy sources with greater volatility due to its high efficiency and rapid response. With technological advancement, PEM is expected to be more widely used in the next 5-10 years.
The cost of different hydrogen production methods
The different preparation methods of green hydrogen mainly refer to the use of renewable energy to electrolyze water to produce hydrogen. The cost is as follows:
Alkaline electrolyzer hydrogen production:
The cost is about US$3-6/kg. This is currently the most mature and widely used water electrolysis hydrogen production technology.
Proton exchange membrane (PEM) electrolyzer hydrogen production:
The cost is about US$4-8/kg. Compared with alkaline electrolyzers, PEM electrolyzers are more efficient, but the cost is also slightly higher.
Solid oxide electrolyzer (SOEC) hydrogen production:
The cost is about US$5-9/kg. SOEC technology is still in the development stage and currently costs relatively high.
With technological advancement and scale expansion, the cost of green hydrogen preparation is expected to be further reduced. It is expected that the cost of hydrogen production from renewable energy water electrolysis is expected to drop to about US$2-3/kg in the future, making it cost-competitive with fossil fuel hydrogen production.
It should be noted that the specific cost of green hydrogen is also affected by factors such as renewable energy power costs and equipment utilization, and may differ in different regions and application scenarios.
|
Hydrogen preparation process |
raw materials |
Technology maturity |
Energy conversion efficiency (%) |
Cost (yuan/kg) |
Co2 emissions (per kilogram of hydrogen) |
|
|
Hydrogen production from fossil energy |
Coal gasification to produce hydrogen |
coal |
Mature |
47 |
6-10 |
11-25 |
|
Coal gasification+CCS |
coal |
Completed pilot scale testing |
- |
12-16 |
2-7 |
|
|
Coal supercritical water gasification |
coal, water |
Completed pilot scale testing |
60 |
8 |
0 |
|
|
CH4 steam reforming (SMR) |
Methane |
Mature |
- |
9-18 |
8-16 |
|
|
Industrial by-product hydrogen production |
industrial by-products |
Mature |
- |
10-16 |
- |
|
|
Electrolysis of water to produce hydrogen |
Traditional energy power electrolysis water AEL |
water |
Mature |
about 25 |
30-40 |
45 |
|
Renewable energy electrolyzed water AEL |
water |
Mature |
about 25 |
18-23 |
1-3 |
|
|
Renewable energy electrolyzed water PEMEL |
water |
Relatively mature and close to industrialization |
about 35 |
<62 |
1-3 |
|
|
Renewable energy electrolyzed water SOEL |
water |
Demonstration project |
52-59 |
- |
1-3 |
|
|
Renewable energy waste electricity electrolysis water |
water |
Demonstration project |
- |
10 |
1-3 |
|
|
Other new technologies |
Solar photolysis hydrogen production |
water |
laboratory stage |
<10 |
- |
0 |
|
Biomass fermentation to produce hydrogen |
biomass |
Demonstration project |
10-40 |
- |
0 |
|
|
Thermochemical conversion of biomass to hydrogen |
biomass |
Mature |
35-50 |
16 |
0.4-5.6 |
|
|
Thermochemical cycle hydrogen production |
water |
laboratory stage |
About38 |
18 |
0.3-0.86 |
|
Hydrogen energy will play a key role in the future energy structure. With the development of electrolytic water hydrogen production technology and the reduction of costs, hydrogen energy will be combined with renewable energy to improve the stability and reliability of the energy system, promote energy transformation in transportation, industry, power generation and other fields, and achieve sustainable development. For ordinary people, the popularization of hydrogen energy can not only reduce pollution and improve air quality, but also provide stable and clean household energy, and bring new job opportunities and economic growth points, thus improving the overall welfare of society and creating a better world. s future.