Development and application of proton exchange membrane water electrolysis hydrogen production technology under wind and solar power fluctuations III

Development and application of proton exchange membrane water electrolysis hydrogen production technology under wind and solar power fluctuations III

III. PEM electrolyzer core technology research and development and PEM electrolyzer hydrogen production technology development direction

1. PEM electrolyzer technology research and development
The power fluctuation range of wind and solar power hydrogen production is large, and the adverse effects on hydrogen production equipment are manifested in a significant reduction in equipment life and the purity of the produced hydrogen. These effects are caused by the attenuation of the main components of the PEM electrolyzer under the condition of wind and solar fluctuating power supply. From a technical perspective, the main challenge facing the PEM electrolyzer is how to improve the working performance and stability through material research and development, assembly process and optimization. Advanced material research and development includescatalytic layer and adhesive materials, corrosion-resistant bipolar plates, organic ion exchange membranes and other directions. The assembly process and optimization of electrolyzer components mainly include optimization of membrane electrode preparation method, optimization of electrolyzer assembly preload, optimization of membrane electrode/electrolyzer temperature and thermal stress distribution, and flow channel optimization. In recent years, membrane electrode has been the key research direction of PEM electrolyzer.
Focusing on the main components of electrolyzer catalysts, exchange membranes, bipolar plates, etc., the main ways to carry out catalyst research and development are: improving the activity and stability of catalysts through binary or multi-metal composite doping; selecting oxidation-resistant and high-specific surface materials as catalyst carriers to improve the utilization rate and activity of catalysts; designing new structural catalysts, such as core-shell structures and nanoarrays. Among the exchange membranes currently in use, DuPont perfluorosulfonic acid proton membranes are the most common, and short-chain perfluorosulfonic acid proton membranes from brands such as Dow Chemical, 3M, Gore, and Asahi Glass are also used. In order to improve the stability of the exchange membrane, polyarylene polymers are usually used to strengthen and modify the membrane, and catalytic materials are used to modify the diaphragm to reduce product gas crossover. The cost of bipolar plates accounts for more than 50% of the electrolyzer, and precious metal coatings are usually configured to improve corrosion resistance. Future work to reduce manufacturing costs will mainly focus on new low-cost bipolar plate materials and surface treatment processes.
In terms of assembly process and optimization, the current research focuses on asymmetric design of cathode/anode, optimization of electrolytic component fixation by connecting the card position, etc. In order to adapt to fluctuating power supply, some studies have explored the influence of water flow changes in the electrolyzer, distribution of water supply pipelines, and membrane electrode structure on gas permeation on both sides, temperature and pressure changes, current density, etc. For the core components of the electrolyzer, the most commonly used catalyst coating membrane processes are ultrasonic spraying and roll-to-roll coating: compared with the former, the latter uses a one-time coating of the catalyst layer, which can obtain a thicker and more uniform coating faster, and meet the needs of membrane electrode mass production. In order to avoid puncture, cracking, mechanical stress, insufficient humidification and reaction pressure caused by assembly, the material properties used are usually fully studied when designing the membrane electrode and its clamping process, and loading tests are carried out based on experimental devices.

To evaluate the life of components under frequent start-stop and wind-solar fluctuating power supply, more data needs to be obtained through accelerated testing to improve the durability of the stack components, which is another challenge in current research and development. However, there is no standardized accelerated decay test protocol for PEM electrolyzer components, and the degradation rate of the  components of the stack components is difficult to measure, which makes it difficult to conduct direct comparison of existing research results. Establishing a standardized PEM electrolyzer accelerated decay test protocol is a bottleneck problem that needs to be solved urgently in the current key technology research and development.
In recent years, the technical research and development of key components of PEM electrolyzers have made significant progress. According to my country's technical route for hydrogen production by electrolysis of water, the current key technical indicators of PEM electrolyzers are: efficiency of about 63%, life of about 6×104 h, and cost of about 10,000 yuan/kW. It is expected that by 2030, the key technical indicators of PEM electrolyzers will be: efficiency of 78%, life of 1×105 h, and cost reduced to 4,000  yuan/kW.

2. Development direction of PEM electrolyzer hydrogen production technology
The principle of wind-solar power hydrogen production is to complete the conversion of wind/solar energy into electricity, and then convert electricity into hydrogen energy through an electrolyzer. There are currently four main water electrolysis technologies, of which alkaline water electrolysis technology is the most mature and has the lowest cost, and has entered the commercial development stage; but PEM water electrolysis technology is developing rapidly, and it has good adaptability to wind and solar power, and will be the preferred direction for renewable energy power hydrogen production in the future.
At present, the main wind-solar coupling hydrogen production methods are off-grid and grid-connected. Although grid-connected hydrogen production overcomes the volatility of hydrogen production power, it has the problems of high electricity prices and limited grid access. The off-grid method provides the electricity generated by a single or multiple wind turbines (without passing through the grid) to the water electrolysis hydrogen production equipment for hydrogen production. It is suitable for areas with good wind resources but limited consumption, and has a robust business model and broad development prospects; it is mainly used for distributed hydrogen production, and locally used for fuel cell power generation and energy supply.
Similar to off-grid hydrogen production, non-grid hydrogen production is another effective way to produce hydrogen, which eliminates a large number of auxiliary equipment required for grid connection (such as converters/transformers, filter systems), and the cost is greatly reduced compared to grid-connected hydrogen production. Non-grid hydrogen production uses direct current, effectively avoiding the phase difference and frequency difference problems caused by AC grid access, simplifying the system and saving costs. It is worth noting that, compared with off-grid/grid-connected hydrogen production, non-grid-connected wind and solar power hydrolysis hydrogen production directly couples wind and solar power with PEM electrolyzers, realizing wind and solar power networking without grid connection, thereby avoiding the impact of fluctuating wind and solar power on the power grid. From this process, the fluctuating power source in non-grid-connected wind and solar power hydrogen production only needs simple transformation and rectification, and the voltage is adjusted to the required voltage through the transformer, and the AC power is rectified into DC power.
Non-grid hydrogen production technology is an original technology in my country in related fields, which helps to break the technical limitations of fluctuating renewable energy. Wind and solar power are not subject to grid-connected constraints, and wind power and photovoltaic power generation equipment can be further optimized, which can significantly reduce costs and avoid large-scale wind turbine/photovoltaic grid-off accidents caused by grid connection, thereby achieving the solution to the problem of wind and solar power consumption and promoting the development of the green hydrogen energy industry at the same time.

IV. Application Trends of Water Electrolysis and Hydrogen Production from Wind and Solar Fluctuating Power Sources
1.Current status and economics of wind power coupled hydrogen production
At present, the focus of domestic and foreign research is on the applicability and economy of grid-connected wind power hydrogen production in different application scenarios. Grid-connected wind power hydrogen production can effectively absorb wind abandonment (the corresponding wind abandonment rate is reduced from 35.8% to 7.5%). The key research directions include system configuration optimization and control strategy simulation, mainly exploring the impact of voltage, current, temperature, pressure, and electrochemical properties of electrode materials on the operation of hydrogen production equipment under frequent power changes, optimizing operation and start-stop control strategies, and extending the service life of electrolyzers. In wind power coupled hydrogen production, offshore wind power hydrogen production is one of the mainstream forms in the future. In recent years, more than 20 wind power coupled hydrogen production demonstration projects have been built abroad. In Europe, the key research directions are: exploring the energy storage advantages of hydrogen in the power grid, improving wind energy utilization, power generation quality and power grid stability; carrying out "power-to-gas" projects to increase the proportion of renewable energy through hydrogen storage; developing offshore wind power hydrogen production projects, such as the Netherlands will build a 3~4 GW offshore wind power hydrogen production project in 2030, and reach a 10 GW installed capacity and 8×105 t hydrogen production scale in 2040. Compared with traditional hydrogen production methods, electrolysis is a key factor in determining the economic efficiency of wind power hydrogen production. 70% of the cost of hydrogen production by water electrolysis comes from electricity prices. According to current electricity prices, the cost of wind power hydrogen production is 2 to 3 times that of traditional hydrogen production. When the cost per kilowatt-hour is controlled at 0.25 yuan, the cost of wind power hydrogen production is on par with the cost of traditional hydrogen production; if the electricity price goes down, it will have an economic advantage.

2.Current status and economics of photovoltaic power generation coupled with hydrogen production
Photovoltaic power generation coupled with hydrogen production is another major way to produce hydrogen from renewable energy.
The bottleneck of the industrialization of photovoltaic power generation hydrogen production lies in the high cost. The decline in the cost of photovoltaic electricity will greatly reduce the cost of hydrogen production by electrolysis of water. It is estimated that the cost of photovoltaic power generation per kilowatt-hour will be less than 0.3 yuan in 2025, and photovoltaic power generation hydrogen production is expected to be parity by then; in areas with abundant light resources, the cost of photovoltaic power generation hydrogen production per kilowatt-hour is expected to drop to 0.15 yuan, which will further drive down the cost of hydrogen production. By 2035 and 2050, the cost of photovoltaic power generation per kilowatt-hour will be 0.2 yuan and 0.13 yuan respectively, achieving good economic efficiency in all aspects.
According to recent research forecasts and the "China 2030 'Renewable Hydrogen 100' Development Roadmap", my country's onshore wind power and photovoltaic power generation water electrolysis hydrogen production is close to parity. However, PEM water electrolysis hydrogen production equipment is more than 5 times higher than alkaline electrolyzers, and the levelized hydrogen production cost is about 40% higher. Therefore, the key driving factor for the future development of PEM electrolyzer hydrogen production is to reduce equipment manufacturing and operating costs. With the scale of the hydrogen production industry and the continuous breakthroughs in corresponding core technologies, the cost of PEM electrolyzers is expected to be reduced by more than 50%, and the levelized cost of hydrogen is expected to be reduced by 20%.