(2bv) Harnessing Hydrogen Transfer in Energy Science to Boost Sustainability

Our world is currently confronted with a variety of global energy and environmental challenges. Solutions that hold promise lie in the development of effective catalysis and energy conversion. However, there exists a gap between desired catalytic and electrochemical pathways and material redox properties. To bridge this gap, control over the transfer of the hydrogen atom (H) offers intriguing opportunities. Catalyzing the H transfer is critical for the activation of chemical bonds in many essential molecules. Manipulating the H transfer between solids, liquids and gases can transform our mechanistic understandings and enrich the functionalities in redox-active materials. The exploration of H and its activity has revolutionized our scientific knowledge of the world. My research vision is that this journey can continue in catalysis and energy conversion through a better understanding and manipulation of the H transfer pathway.

Past and current research: My doctoral work elucidated design principles in single-site heterogeneous catalysts for electrosynthesis, and the non-equilibrium science in the amorphization and phase transition of functional oxides in reactions. My postdoctoral research revealed the molecular-level H transfer pathways that determine the energy density of batteries and developed effective chemical transformation strategies for methane conversion.

Future research plan: Among the many exciting research opportunities in this field, I highlight three areas of particular interest in Fig. 1 (attached), where I can leverage my experience in heterogenous catalysis, electrochemistry, material physics, solid state chemistry, and in-situ studies of dynamic material transformations to make significant contributions.

1) Transforming Magic Clusters for Low Temperature CH₄ Activation

Although methane (CH₄) is an abundant natural resource with energy content, it is a greenhouse gas. The reduction of methane emissions is known to be critical for addressing the energy crisis and global warming. Current H transfer strategies rely on high temperatures (~1000 °C) with a high energy cost, resulting in severe sintering and catalyst degradation as well as undesired by-products such as NO_x. Extension of H transfer to the low-temperature regime is therefore immensely important and relevant to emissions control, methane removal, and light alkane conversion. One promising opportunity lies in the use of multinuclear, magic-sized clusters that contain a specific number of metal and oxygen atoms in optimum, stable configurations. Binuclear clusters, like the di-iron center in methane monooxygenase, can promote low-temperature H transfer for methane activation. However, a cluster-catalyzed H transfer mechanism has yet to be discovered, and multinuclear clusters are easily subject to many degradation pathways in reactive environments, often limiting their applications.

My lab will investigate the rational design of robust interfacial clusters for low-temperature methane activation. Instead of the traditional size-selective approach, interfacial clusters can be created from isolated metal sites on supports (Fig. 1a). As a proof of concept, my research demonstrated the creation of dimer clusters that significantly boost the performance for low-temperature methane oxidation. Instead of cluster aggregation, a modest increase in temperature causes them to thermally decompose, regenerating single sites that are ready for the next activation. Control over the reductive gas and the treatment time allows for the creation of interfacial trimers and larger clusters.

An important short-term goal of this research is to understand and develop a reaction-mediated transformation pathway that creates more active magic clusters for effective methane activation at temperatures below 250 °C. This has the potential to develop innovative catalysis science where dynamic charge transfer between clusters and oxides can be better understood and tailored for oxidation reaction at low temperature. When integrated with combustion, these pathways can be used to reduce methane leaks and emissions from natural gas engines and shale gas production using the low-grade heat which is abundantly available and often wasted as a source of energy.

My long-term goals for this research lie in understanding and manipulating the characteristics that differentiate oxide-supported magic clusters from molecules and bulk matter and comparing the properties of different clusters in H transfer-initiated reactions. The kinetic improvement in H transfer and the extension of methane activation to the low-temperature regime using magic clusters would bypass the rate-limiting step in methane conversion and facilitate chemical transformations such as the direct functionalization of natural gas through the selective oxidation of methane.

Impact of this research: Success in this fundamental and comparative research will shed light on the working principles of magic clusters and create new opportunities for low-temperature chemical bond activation

2) Radical-assisted H Transfer toward Environment Methane Removal

Environmental methane removal is an emerging field likely to be critical in addressing our climate challenges; methane removal can lower the global temperature and decrease the rate of warming much faster than CO₂ capture andremoval. High-temperature combustion is used in existing artificial systems for converting methane to CO₂. However, owing to the extremely dilute methane (2-200 ppm) and catalyst degradation by water, this approach is insufficient for atmospheric methane removal. At ambient temperature, free radicals can initiate H transfer in CH₄: this is how tropospheric ozone cleans methane in nature. Photo-redox catalysis, using renewable solar energy, has emerged as a powerful strategy to generate hydroxyl radicals (·OH) from water that are otherwise difficult to access with traditional methods. My lab will investigate accelerating environmental methane removal by •OH radicals which would be new area of exploration (Fig. 1b), and a topic that remains unexplored.

My research demonstrated this concept using Au-TiO₂ and ultraviolet (UV) light, which can remove 100 ppm CH₄ within 1 hour in a fluidized-bed reactor. One important short-term goal is to evaluate the benefits and limitations of UV-generated ·OH on water-assisted dilute methane removal and compare that to traditional high-temperature combustion methods.

My long-term targets include: 1) Harvesting the visible-light spectrum of sunlight effectively using plasmonic photocatalysis to promote the generation of •OH radicals when and where needed; 2) Identifying the competing reactions in the environment, taking into account additional radical reactions and atmosphere molecules, and the trace levels of sulfur present in nature gas resources; 3) Demonstrating water-assisted photocatalytic systems to remove the dilute methane from shale oil and gas development leakage, as well as from livestock emissions.

Impact of this research: This research has the potential to result in large-scale negative emission technologies using renewable energy and promote the exploration of controlling radical reactions for environmental protection.

3) H-Transfer Tailored Non-Equilibrium States with Enriched Functionalities

Understanding non-equilibrium behavior is considered as basic challenge. Non-equilibrium states such as disordered solids and transient states have been widely observed and play key roles in various environmental and energy-related applications. However, existing knowledge has been largely limited to crystalline systems and static phenomena. Hydrogen-transfer represents a prospective knob to manipulate non-equilibrium states and enrich catalytic and electrochemical functionalities (Fig. 1c). In water oxidation, my research shows that the high reactivity in oxide electrocatalysts is often coupled with surface amorphization. In non-aqueous batteries, my research revealed H-transfer between solids and liquids in non-aqueous electrochemical devices.

Based on these discoveries and the lessons learned, my short-term goal is to comprehend the effects of H transfer between solids and liquids on the creation of heterogeneities and dynamic disorder in the context of room-temperature electrochemical reactions. In a typical electrochemical operation, when oxide solids in liquids are anodically polarized, redox-active cations are oxidized at high electrochemical potentials, downshifting the Fermi level (E_F) closer to the oxygen p band, triggering oxygen loss, metal dissolution, and chemo-mechanical degradation, all of which can lead to failure in electrochemical devices. Among other migration scenarios, facilitating H transfer from liquids to solids can mitigate these issues by reducing high valence cations in-situ in reactions with minimized detrimental effects. The H intercalation-induced chemical expansion, heterogeneity, boundary formation, and amorphization in oxides, and their new avenue toward enhancing catalysis and electrochemistry applications, will the subjects of my group.

The long-term goal of my lab will aim to apply H-transfer to create new non-equilibrium states and investigate the fundamental science behind improved performance. The interplay between H-transfer, disorder and tailoring heterogeneities is expected to help lead to materials and processes that are non-equilibrium.

Impact of this research: This research would enable the development of unified frameworks to guide the design of non-equilibrium materials and processes to harness the chemical and electrochemical redox reaction to promote sustainability

Teaching Interests

In my teaching and mentoring, my primary objective is to support students in their quest for success in life and academia. I help my students feel more comfortable with the unknown, think more critically about what they do know and ask bolder research questions. I accomplish this goal by challenging students with problem sets from brand-new research, by designing projects that turn a cultural mirror onto the students and their experiences, and by organically modelling the research process in front of and with the class.

Students leave my classes ready to explore new worlds in chemical engineering and think critically about their own experiences. Most importantly, they approach problems with more confidence. These are all essential tools to bring with them into their lives, whether in other classes, the workforce, or graduate school and reflects my values of creating global citizens through my teaching.