Unlike traditional ceramics used to make tableware, handicrafts, and other daily necessities, advanced ceramics have gained widespread application in high-tech fields such as aerospace, electronic information, biomedicine, and new energy due to their excellent performance.

One typical example related to everyone's daily life is the artificial material used in dental implants—zirconia ceramic.

This white crystalline powder is processed into shape and sintered to a dense state, minimizing residual pores and defects, so that the zirconia ceramic can achieve a semi-transparent state in optics, thus having luster like natural teeth.

It should be noted that most of the properties of ceramics are strongly related to their residual pores and defects, so whether the material is dense is very critical to its use.

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Tsinghua University Assistant Professor Dong Yanhao has been engaged in the research of inorganic non-metallic materials including zirconia ceramics since his undergraduate days, mainly focusing on the direction of ceramic sintering and microstructure, and has solved several problems in the fields of ceramic microstructure, thermodynamics, and kinetics.During his postdoctoral period, he chose interdisciplinary research in ceramic materials, focusing mainly on energy ceramics, and achieved breakthroughs in the fields of ceramic proton membrane fuel cells and high-energy lithium-ion battery cathode materials.

Specifically, in the field of ceramic proton membrane fuel cells, he and his collaborators proposed the concept of interfacial reaction sintering, designed and developed controllable surface acid treatment and co-firing technology, setting a new world record for peak power density under operating conditions.

In the field of lithium battery cathodes, he and his collaborators proposed several innovative technologies such as lanthanum-doping uniform coating and planetary centrifugal de-agglomeration of ceramic powders, elucidated the degradation mechanism dominated by stress corrosion cracking, and corrected the understanding of brittle mechanical fracture within the traditional theoretical framework.

By committing to the development of advanced ceramic materials with high reliability and multifunctionality through innovative ceramic preparation theories and technologies, enhancing the structural and functional properties of advanced ceramics and their adaptability to extreme conditions, Dong Yanhao became one of the Chinese inductees for the "35 Innovators Under 35" by MIT Technology Review in 2023.Introduce the concept of interfacial reaction sintering to improve the electrochemical performance and stability of ceramic proton membrane fuel cells.

Ceramic proton membrane fuel cells/electrolyzers are a core component in hydrogen energy technology that is related to ceramics.

It can provide a mid-temperature range application of 400 to 600 degrees Celsius for reversible conversion between chemical energy and electrical energy, with the advantages of high efficiency, zero emissions, and flexible catalyst selection.

That is to say, as a fuel cell, it can generate electricity from chemical substances; as an electrolyzer, it can use electricity for chemical synthesis and material transformation.

Although the ceramic proton membrane itself has good proton conductivity, its intrinsic performance is often not fully utilized when it is integrated into fuel cell or electrolyzer devices. Moreover, under the working conditions of high current density electrolysis, the performance of the device will rapidly decline."Therefore, in the research and application of materials and devices, we need to pay attention to two aspects of issues. One is the initial performance, and the other is the long-term stability," said Dong Yanhao.

In the research, he and his collaborators found that the reason for the above-mentioned problems is the difficulty in sintering at the interface between the oxygen electrode layer and the electrolyte layer in the device, resulting in poor contact and binding at the interface.

To address this, they proposed the concept of interfacial reaction sintering and innovated a series of technologies including ceramic preparation and sintering, enabling active bonding between the oxygen electrode layer and the electrolyte layer to improve the electrochemical performance and stability of ceramic proton membrane fuel cells/electrolyzers [1].

In terms of performance, the device still has excellent performance at as low as 350 degrees Celsius, and can achieve peak power densities of 1.6 watts per square centimeter, 650 milliwatts per square centimeter, and 300 milliwatts per square centimeter at conditions of 600 degrees Celsius, 450 degrees Celsius, and 350 degrees Celsius, respectively.

In addition, during electrolysis operation at 600 degrees Celsius and 1.4 volts, it can maintain a high current density of over 3.9 amperes per square centimeter and is in a stable operating state.The achievement has a significant role in promoting the industrialization of ceramic proton membrane fuel cells/electrolysis cell devices in the future.

Looking back on the memorable past in this research, Dong Yanhao said that he is not an expert in the field of ceramic proton membrane fuel cells/electrolysis cells, and much of the knowledge was learned in the process of joint development with collaborators.

During the writing of the paper, Dong Yanhao proposed a new data analysis strategy. Initially, he was uncertain whether the proposed analysis method would be accepted by reviewers in this field.

"It was not until the paper was submitted to Nature, and the reviewers highly praised our research work and data analysis in terms of originality and importance, that I further confirmed that this perspective, which is different from the mainstream in this field, is precisely one of the core factors for the publication of the article," he said.

He proposed several innovative technologies to overcome the challenge of oxygen loss in the oxide cathode of lithium-ion batteries.Due to their extremely high energy density, lithium-ion batteries are now used in various industry fields such as mobile electronic products, electric vehicles, and energy storage.

The core reason for their aforementioned advantages lies in their high voltage and good cycle stability, which mainly depends on the cathode materials of the lithium-ion batteries.

For example, by designing the redox potential, crystal structure, and chemical composition of the oxide cathode materials, lithium-ion batteries can always provide a sufficiently high energy density during hundreds or even thousands of charge and discharge cycles.

However, because the high voltage in electrochemistry corresponds to strong oxidative conditions in chemistry, as the working voltage of lithium-ion batteries increases, the oxygen ions in the lithium cathode oxides also become thermodynamically unstable and tend to escape in the form of gas.

"The release of oxygen induced by high voltage will bring a series of problems. For example, oxygen will react with the electrolyte of the battery. When the electrolyte is consumed, the battery can no longer be used; for pouch batteries, after oxygen oxidizes the organic electrolyte, a large amount of carbon dioxide will be produced, causing the battery to expand in volume, which is what we commonly call 'swelling'," explained Dong Yanhao.Based on this, in the process of continuously developing high-voltage, high-energy-density lithium-ion batteries, the problem of oxygen loss in oxide cathodes must be resolved.

In response, Yanhao Dong and his collaborators proposed a lanthanum doping process that can regulate the near-surface structure of energy materials, surpassing traditional surface doping methods[2].

Taking the commonly used cathode material lithium cobalt oxide in lithium-ion batteries as an example, they demonstrated effective surface passivation, suppression of surface degradation, and improved electrochemical performance, proving that high-voltage stable cycling can reach up to 4.8 volts.

The new surface phase they designed can prevent oxygen escape reactions under high voltage.

"In addition to this, we can also start from the microstructure of the cathode material of lithium-ion batteries to solve its oxygen loss problem," said Yanhao Dong.Single-crystal lithium-rich manganese-based cathode materials are an ideal high-performance electrode material, but scaling up the production of single-crystal lithium-rich manganese-based cathodes with high phase purity and excellent electrochemical performance still faces significant challenges.

To address this issue, Dong Yanhao and his collaborators have developed a new mechanochemical activation process, based on the mechanisms of interfacial reaction wetting and eutectic lithium salt grain boundary corrosion. By using a mild planetary centrifugal deagglomeration process, they have obtained transition metal oxide precursors uniformly dispersed in the lithium salt matrix.

This method can disperse polycrystalline precursors and improve the electrochemical performance and stability of single-crystal lithium-rich manganese-based cathode materials while promoting the well-developed single-crystal form [3].

Looking forward to the development of more energy solutions based on ceramic materials to help achieve the "dual carbon" goals.

In fact, from the perspective of material classification, the core ceramic materials used in ceramic proton membrane fuel cells are perovskite-structured oxide ceramics, and those used in the cathode of lithium-ion batteries are called layered structure oxide ceramics.These two materials share many commonalities in terms of material properties and the entire manufacturing process.

It is precisely because of the commonality of fundamental scientific issues, coupled with Dong Yanhao's understanding of the basic theory of materials, that has enabled him to make breakthrough achievements in these two seemingly different fields.

When talking about the original intention of researching the above fields, Dong Yanhao said: "They are all fields related to energy. In my view, the energy issue is a global challenge faced by the youth of our era. I hope to make my own efforts, while focusing on the research of ceramic materials, to propose energy solutions related to them, thereby helping to achieve the 'dual carbon' goal."

At present, Dong Yanhao is mainly committed to the research of new types of ceramic materials with high reliability and multifunctionality. He hopes to improve the reliability of advanced ceramic materials through microstructure design and plastic deformation response, and also looks forward to integrating mechanical, electrical, optical, and other functional characteristics into the same material to create more new application scenarios.

It is reported that Dong Yanhao was born in Shucheng County, Anhui Province. He graduated from the Department of Materials Science and Engineering at Tsinghua University in 2012, and then went to the University of Pennsylvania in the United States to pursue a doctoral degree in materials science.In 2017, he came to the Massachusetts Institute of Technology in the United States to conduct postdoctoral research, and since July 2022, he has joined the School of Materials Science and Engineering at Tsinghua University as an assistant professor.

Looking back on the most impressive scientific research experience, Dong Yanhao said it was during his doctoral studies when he read a paper. Initially, although he felt it was valuable, he could not truly understand it. After more than a year of repeated reading, he suddenly realized one day, which had a great impact on his future research.

In fact, every learner will inevitably encounter a similar bottleneck period in the learning process.

Based on his own experience, Dong Yanhao also gave the following suggestions.

Firstly, one should persist in what they have chosen with full confidence and should not retreat when encountering difficulties.Secondly, one should draw strength from basic education to help oneself to perform their current work more steadily and deeply.

For example, "Where there is a will, there is a way," is a phrase from ancient texts that everyone is familiar with from a young age.

In Dong Yanhao's view, the "will" in this phrase is actually a concept with rich connotations, not only including ambitions for the future but also including one's courage, perseverance, and the tangible efforts made to achieve goals.

"This is the sentence that resonates with me the most recently, and I also hope it can provide more insights to everyone," said Dong Yanhao.