One day, people may use hydrogen and oxygen from water electrolysis as fuel, becoming an infinite energy source for heating and lighting...
This excerpt from a sci-fi novel over a century ago envisioned "future fuel," now within reach, shaping our reality today.
Development of Efficient and Stable Catalysts for Water Electrolysis
Hydrogen-powered vehicles, hydrogen fuel cells... More and more high-tech hydrogen energy products are entering the public eye. How to obtain this efficient and environmentally friendly energy has always been a question that many researchers are exploring.
Recently, Professor Xu Xiaoyong's team from the School of Physical Science and Technology at Yangzhou University proposed a groundbreaking new method to maintain the lasting stability of hydrogen production catalyst activity through the reconstruction mediated by two-dimensional transition metal carbides.
Building upon this, the team successfully developed a high-performance nickel-iron hydroxide catalyst, achieving "cost-effective and efficient" green hydrogen production processes. This provides a potential solution for sustainable development of the environment and energy, with the research results published in the Proceedings of the National Academy of Sciences (PNAS).
The Rise of Hydrogen: Cost Reduction and Efficiency Enhancement are Key
With the continuous progress of society and rapid technological development, the overconsumption of fossil fuels that humanity relies on has led to increasingly prominent energy crises and environmental pollution issues. Therefore, developing clean energy and increasing the "green" content of energy has become a top priority.
Hydrogen energy is a clean, low-carbon, flexible, and efficient energy source that plays an indispensable role in promoting global economic decarbonization, especially in the industrial and transportation sectors. It is considered one of the most promising secondary clean energy sources of the 21st century.
Based on the carbon emission intensity of the hydrogen production process, hydrogen is classified into three categories: "grey hydrogen," "blue hydrogen," and "green hydrogen." Xu Xiaoyong explained to the Science Times, "Currently, over 98% of the hydrogen on the market comes from fossil fuels, known as grey hydrogen. Although grey hydrogen is relatively low in price, with a cost of about 9 to 14 yuan per kilogram, its production process often involves significant carbon dioxide emissions, contradicting our pursuit of the 'dual carbon' strategic goals."
Meanwhile, using renewable energy for electrolytic water splitting to produce hydrogen (green hydrogen) does not pose carbon emission concerns. However, it still faces challenges of high energy consumption and low efficiency in current industrial production, severely limiting its prospects for large-scale applications.
Xu Xiaoyong further analyzed the root cause of this dilemma: water molecules are known for their excellent stability and require abundant electrical energy input and efficient catalysts to work together to break bonds and separate hydrogen molecules. He pointed out, "If we only focus on increasing current density and neglect improving catalyst activity, it may not only increase energy consumption but also reduce efficiency."
Currently, widely used catalysts in the market are mainly precious metals (such as platinum), which exhibit excellent stability. However, their high cost and relatively low level of commercialization limit their widespread application. According to data, the cost of producing one kilogram of hydrogen through electrolysis is approximately between 32 to 35 yuan, significantly exceeding the cost of hydrogen production from fossil fuels.
In this context, for green hydrogen energy economy to achieve industrialization, popularization, and commercialization, overcoming the major challenge of reducing the cost and increasing the efficiency of catalysts is crucial.
Reconstructing CP: Reconstruction of Low-Cost Catalysts
For a long time, Professor Xu Xiaoyong's team has been dedicated to researching "cost-effective and efficient" catalysts for electrolytic hydrogen production.
The team's research found that nickel-iron hydroxide catalysts demonstrate outstanding "leading" capabilities during the electrolysis process. Its advantages lie in significantly reducing energy losses during electrolysis, improving electrolysis efficiency, and possessing low cost and abundant resource reserves, making it an ideal alternative to precious metal catalysts.
"However, during continuous electrolysis, this catalyst experiences leakage of iron elements, leading to a decrease in its activity," Xu Xiaoyong pointed out, which is also a bottleneck hindering its widespread application in hydrogen production through electrolysis.
To overcome this challenge, the research team ingeniously designed a solution: a method of reconstructing through the mediation of two-dimensional transition metal carbides, precisely controlling the coordination state of iron sites in the catalyst structure to ensure lasting stability of catalytic activity.
"During the reconstruction process, the original 'iron-carbon-nitrogen-nickel' coordination in the catalyst, in the process of electrolysis, the iron elements flow into the electrolyte, and the two-dimensional transition metal carbides rebind the iron elements that flow into the electrolyte, forming a new 'iron-oxygen' coordination," said Yu Qian, the first author of the paper and a master's student at the School of Physical Science and Technology at Yangzhou University, vividly likening it to "restructuring 'cp' with a new dance partner at a dance party."
"In addition, using two-dimensional transition metal carbides as mediators is also a key factor in ensuring the success of the reconstruction experiment," said Li Cheng, one of the team members and a doctoral student at the School of Physical Science and Technology at Yangzhou University.
It is reported that the team invested a considerable amount of time and effort in the preliminary stage, conducting in-depth research on various materials. They were pleasantly surprised to find that the surface of two-dimensional transition metal carbides carries electronegative groups, providing extremely favorable conditions for anchoring iron sites in the catalyst. Additionally, this material has excellent conductivity and hydrophilicity, undoubtedly making it the preferred experimental material.
"After the coordination is reconstructed, the catalyst accelerates the reaction rate during the electrolytic hydrogen production process, while also building a solid protective barrier for its iron sites, resisting oxidation and thereby improving the efficiency and stability of the entire electrolysis process," Li Cheng stated.
Continuous Exploration: Boosting New Productivity in the "Fuel" Era
"In actual industrial environments, to achieve efficient production, the water electrolysis process usually needs to be carried out under conditions of high current density (>500 milliamps per square centimeter)," emphasized Xu Xiaoyong, noting that this requirement makes traditional operating methods unable to meet the needs of industrial development in water electrolysis hydrogen production. It is reported that traditional nickel-iron hydroxide catalysts experience a gradual decrease in activity as the current increases during electrolysis for hydrogen production. This phenomenon is particularly pronounced under high current density conditions.
However, in the team's latest experiment, nickel-iron-based catalysts obtained through restructuring mediated by two-dimensional transition metal carbides have shown outstanding catalytic performance even with a significant increase in current density up to 1000 milliamperes per square centimeter.
"To our knowledge, there are few reports on the durability of nickel-iron hydroxide catalysts at industrial-level current densities exceeding 500 milliamperes per square centimeter," said Xu Xiaoyong. "This means that our research results provide a basis and potential for the large-scale development of hydrogen production through water electrolysis."
As a key development direction in China's strategic emerging industries and future industries, hydrogen energy new quality productivity is accelerating. "In the future, the team will align with industrial demands, increase efforts in the independent research and development of PEM electrolyzers and other hydrogen production equipment, continue to carry out key technology breakthroughs and advancements in renewable energy hydrogen production, and strive to contribute more to leading the 'zero-carbon era,'" Xu Xiaoyong stated.
Related paper information: https://doi.org/10.1073/pnas.2319894121
