The research, led by Dr. Zhongqiu Lin together with Associate Professor Toshiki Sugimoto and colleagues, focused on anatase titanium dioxide, one of the most widely studied photocatalytic materials for hydrogen evolution. Although it has been recognized that interactions at the water-catalyst interface are key determinants of photocatalytic performance, systematic experimental studies that explicitly target the structure and reactivity of this interface have remained scarce. The central difficulty is a practical one: probing the molecular structure of interfacial water is challenging under normal circumstances, and it becomes even harder under the conditions where hydrogen is actually being evolved. Compounding the problem, the apparent hydrogen evolution activity measured in an experiment is highly sensitive not only to the surface area of the photocatalyst but also to the amount of water present at the interface, making it difficult to separate genuine differences in reactivity from simple differences in how much water is available to react.

To overcome these obstacles, the team designed a series of experiments using anatase TiO2 photocatalysts with different surface characteristics, allowing them to compare interfaces that interact with water in distinct ways. They combined infrared spectroscopy, which reveals the adsorption states and hydrogen-bonding arrangements of water molecules, with real-time mass spectrometry, which tracks the production of hydrogen gas as it happens. Crucially, the measurements were carried out under precisely controlled hydration conditions ranging from sub-monolayer coverages, where isolated water molecules dot the surface, to several molecular layers of adsorbed water. This control allowed the researchers to examine how water behaves in different interfacial environments while keeping the amount of water explicitly accounted for.

A key methodological advance came from the way the team analyzed their data. By normalizing the measured hydrogen formation rates with respect to both the specific surface area of the photocatalyst and the number of adsorbed water layers, they were able to quantitatively distinguish the intrinsic reactivity of interfacial water from effects that arise simply because different samples hold different amounts of water at their surfaces. This normalization framework meant that when two interfaces showed different hydrogen evolution rates, the difference could be attributed to the molecular structure of the water at those interfaces rather than to trivial differences in surface area or water loading. It is this careful separation of variables that gave the study its power to draw firm conclusions about structure-reactivity relationships.

With this framework in place, the researchers systematically investigated the adsorption state of interfacial water, examining both the strength with which water molecules bind to the TiO2 surface and the mode of adsorption, whether the molecules remain intact or dissociate into hydroxyl groups and protons upon adsorption. The conventional view in photocatalysis has held that strong water-TiO2 interactions should generally be favorable, because strong binding is thought to enhance the trapping of photogenerated charge carriers at the surface, suppress the recombination of electrons and holes, and thereby prolong the lifetimes of the charge carriers that are needed to drive the chemical reactions. Intuitively, longer-lived carriers should mean more opportunities for water molecules to be reduced or oxidized, and hence better catalytic performance.

The experimental results told a different story. Contrary to the conventional expectation, the team found that relatively weaker water-TiO2 interactions were associated with higher reactivity of the interfacial water toward hydrogen evolution. In other words, water molecules that were held less tightly to the surface were, on average, more reactive participants in the photocatalytic reaction than those bound strongly. This observation challenges the intuition that maximizing water-surface binding strength is a reliable design strategy, and it suggests that the factors governing interfacial reactivity are more subtle than charge-carrier dynamics alone.

The explanation, the researchers realized, lies in the fact that interfacial water does not exist as isolated molecules interacting only with the solid surface. Instead, water molecules at the interface also form hydrogen-bond networks with one another, and these networks possess collective structural and dynamical properties of their own. The team therefore turned their attention to how the hydrogen-bonding environment of the interfacial water influences its reactivity. Their analysis revealed that weaker and more flexible hydrogen-bond networks were associated with higher reactivity of the interfacial water. Water held in a rigid, strongly connected network was less reactive, while water embedded in a looser, more pliable network reacted more readily to produce hydrogen.

This finding provides molecular-level insight into what is believed to be the rate-determining step of photocatalytic hydrogen evolution: the initial oxidation of water, which proceeds through proton-coupled charge transfer at the water-TiO2 interface. In such a process, the transfer of a proton is coupled to the movement of electrical charge, and the reaction requires the surrounding molecular environment to reorganize as the reactants transform into products. From the perspective of Marcus theory, the foundational framework for describing electron transfer reactions, the rate of a reaction depends in part on the reorganization energy, that is, the energetic cost of rearranging the molecular environment to accommodate the charge transfer. Greater flexibility and larger fluctuations of the hydrogen-bond network reduce the barriers associated with this molecular reorganization, making it easier for the reaction to proceed. The experimentally observed higher reactivity of more flexible interfacial water is thus consistent with theoretical expectations, and it ties the macroscopic catalytic performance directly to the dynamics of the hydrogen-bond network at the interface.

The implications for photocatalyst design are significant. Because strong water-catalyst interactions have beneficial effects on photogenerated charge carriers, photocatalyst development has traditionally favored hydrophilic interfaces, where water binds strongly to the catalyst surface. The new study reveals, however, that relatively weaker water-TiO2 interactions, which are associated with more flexible hydrogen-bond networks, favor higher reactivity of the interfacial water toward hydrogen evolution. This suggests that the optimal interface is not the one that binds water most tightly, but the one that allows the interfacial water to retain enough structural freedom to undergo the molecular reorganization demanded by the reaction. Surface chemistries, coatings, or morphologies that moderate the strength of water binding while preserving charge-carrier performance could therefore offer a path to more active photocatalysts.

More broadly, the work demonstrates the value of directly characterizing both the adsorption state and the hydrogen-bonding structure of interfacial water and correlating these properties with hydrogen evolution activity under well-controlled conditions. By establishing a quantitative link between the molecular structure of the interface and its catalytic reactivity, the study provides a molecular basis for engineering water-catalyst interfaces to enhance photocatalytic performance. As the field continues to pursue efficient solar-to-chemical energy conversion, the message from the Institute for Molecular Science team is clear: to design better photocatalysts, researchers should look not only at the solid surface itself but also at the delicate, dynamic architecture of the water molecules that sit upon it, and consider giving those molecules a little more room to move.

Subject of Research: Structure and reactivity of interfacial water in photocatalytic hydrogen evolution on anatase TiO2

Article Title: Bridging interfacial water structure and reactivity in photocatalytic hydrogen evolution at TiO₂ interfaces

Article References: Bridging interfacial water structure and reactivity in photocatalytic hydrogen evolution at TiO₂ interfaces. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: photocatalysis, hydrogen evolution, titanium dioxide, interfacial water, hydrogen-bond network, infrared spectroscopy, mass spectrometry, anatase TiO2, solar fuels, water splitting, Marcus theory, charge transfer

The chemical at the heart of the study, ammonia borane, is a white crystalline solid that packs roughly 19.6 percent hydrogen by weight, making it one of the most attractive chemical hydrogen carriers known. When mixed with methanol in the presence of a suitable catalyst, ammonia borane quantitatively releases three equivalents of hydrogen gas, a process called methanolysis. Compared with hydrolysis, which consumes water, methanolysis proceeds readily at ambient temperature, avoids freezing problems in cold climates, and yields a boron-containing product that can in principle be recycled back to ammonia borane. The catch has always been the catalyst. Precious metals such as ruthenium, platinum and gold perform superbly but are prohibitively expensive for scaled deployment, pushing researchers toward earth-abundant alternatives such as cobalt and nickel.

Cobalt-based catalysts are among the most promising non-noble options, but they suffer from sluggish kinetics, susceptibility to oxidation and aggregation, and the perennial problem of nanoparticle leaching during repeated use. The Jazan team tackled these weaknesses on two fronts simultaneously. First, they alloyed cobalt with molybdenum, a well-known electronic promoter in borohydride chemistry. Second, they locked the resulting bimetallic domains inside a piezoelectric polymer scaffold whose internal electric fields respond to mechanical agitation. The catalyst and its support, in other words, were designed as a single coupled system rather than as separate components bolted together after the fact.

The fabrication route is deceptively simple and potentially scalable. A solution containing PVDF-HFP, cobalt nitrate and controlled amounts of ammonium molybdate was electrospun into a nonwoven mat of polymer nanofibers. Electrospinning, which draws a charged polymer jet from a needle toward a grounded collector, produces fibers with diameters in the sub-micrometer range and enormous surface-area-to-volume ratios. The mats were then treated with an in situ sodium borohydride reduction, converting the metal salts directly into ultrafine cobalt–molybdenum domains dispersed throughout the fiber matrix. By varying the molybdenum loading from zero to 0.5 relative to cobalt, the researchers prepared a family of membranes designated by their Mo content and screened them for methanolysis activity in methanol at 298 kelvin.

Microscopy and diffraction told a consistent story about what the reduction produced. Scanning electron microscopy with energy-dispersive X-ray mapping confirmed that cobalt and molybdenum were uniformly co-localized along the fiber lengths, with no evidence of segregated metal clusters. Notably, X-ray diffraction revealed no crystalline metal phases at all, indicating that the Co–Mo domains are either amorphous or so small that they escape detection. That absence of crystallinity is not a defect; amorphous alloy catalysts are widely prized in hydrogen-release chemistry because their disordered atomic arrangements expose a high density of low-coordination active sites and short diffusion paths for reactants, often outperforming their crystalline counterparts of the same composition.

The performance data identified a clear optimum. Increasing molybdenum content boosted activity up to the 0.3 loading, which delivered the headline hydrogen generation rate of 70.22 mol H₂ min⁻¹ g⁻¹Co, but further Mo addition diminished performance, likely because excess molybdenum dilutes the cobalt active sites or partially blocks access to them. Kinetic analysis showed a near-first-order dependence on both catalyst loading and ammonia borane concentration, consistent with surface-mediated reaction control rather than mass-transfer limitations. Temperature-dependence measurements yielded an apparent activation energy of just 19.21 kJ mol⁻¹, a remarkably low barrier that reflects how readily the bimetallic interfaces drive the O–H bond cleavage and B–H protolysis steps of methanolysis.

Durability, often the Achilles heel of supported metal catalysts, proved respectable. After six consecutive methanolysis cycles, the 0.3 Mo@PVDF-HFP membrane retained approximately 80 percent of its initial activity, a level of stability the authors attribute primarily to the polymer confinement preventing nanoparticle migration and agglomeration. In conventional powder catalysts, the mechanical stress of stirring and the heat of reaction gradually sinter nanoparticles into larger, less active aggregates. Here, the fibers act as nanoscale cages: metal domains nucleated and grew within the polymer network, and the surrounding matrix physically anchors them against dissolution, leaching and coalescence across successive uses.

The most conceptually interesting aspect of the work is the role of piezoelectricity. PVDF-HFP is a ferroelectric polymer in which the polar crystalline phases carry a spontaneous dipole moment. When the catalyst membrane is stirred in methanol, the resulting mechanical deformation and vibration strain the fibers and induce piezoelectric polarization, generating local electric fields and interfacial charge at the polymer–metal boundary. According to the authors, this stirring-induced polarization enriches interfacial charge, accelerates electron transfer between the catalyst surface and the reacting ammonia borane–methanol complex, and thereby complements the intrinsic electronic synergy between cobalt and molybdenum. In essence, ordinary mechanical agitation, which any practical reactor supplies anyway, is harvested as a free auxiliary energy input that lowers the effective kinetic barrier.

The mechanistic picture of why the molybdenum addition matters parallels established understanding of transition-metal promotion in borohydride and ammonia borane chemistry. Cobalt provides the primary sites for adsorbing and activating boron–hydrogen bonds, while molybdenum, which is more oxophilic, preferentially binds the hydroxyl hydrogen of methanol and the protic hydrogens of the reaction intermediates. The juxtaposition of electron-rich and electron-poor sites across the Co–Mo interface creates dual active centers that accept hydride and proton on adjacent positions, accelerating their recombination into molecular hydrogen. X-ray photoelectron measurements in related systems consistently show charge transfer between the two metals, and the authors invoke this electronic synergy, together with the amorphous bimetallic active sites and the piezoelectric polarization of the support, as the three factors underpinning the observed 2.6-fold rate enhancement.

The broader significance lies in the design template rather than any single number. The study demonstrates a scalable, electrospinning-based route to flexible, polymer-confined bimetallic catalysts in which the support is an active electrochemical participant, coupling ambient mechanical energy into catalytic charge dynamics. Because ammonia borane methanolysis proceeds quantitatively at room temperature with an inexpensive, earth-abundant metal pair, and because the catalyst is a flexible membrane rather than a loose powder, the approach lends itself to cartridge-like hydrogen generators for fuel cells in portable, automotive and backup-power applications. The authors frame the work as enabling efficient, on-demand hydrogen production, and the combination of low activation energy, cycling stability and piezo-assisted kinetics suggests a credible path toward chemical hydrogen storage systems that respond, quite literally, to the shake of a reactor. Future work will need to probe the long-term mechanical fatigue of the piezoelectric polymer, refine catalyst regeneration strategies for the spent boron product, and translate the laboratory stirring protocol into engineered flow reactors, but the central demonstration, that a vibrating plastic fiber can make a non-precious catalyst work substantially harder, offers an unusually elegant answer to one of the hydrogen economy’s most persistent engineering problems.

Subject of Research: Piezoelectric polymer-confined cobalt–molybdenum bimetallic nanocatalysts for hydrogen generation from ammonia borane methanolysis.

Article Title: Piezoelectric-Assisted Co–Mo Bimetallic Nanocatalysts Confined in PVDF-HFP Nanofibers for Efficient H2 Generation from Ammonia Borane Methanolysis

Article References: Kuku, M., Arishi, M., Abutaleb, A., Yousef, A., & El-Halwany, M. M. (2026). Piezoelectric-Assisted Co–Mo Bimetallic Nanocatalysts Confined in PVDF-HFP Nanofibers for Efficient H2 Generation from Ammonia Borane Methanolysis. Catalysis Letters, 156(10), Article 273. https://doi.org/10.1007/s10562-026-05433-1

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05433-1

Keywords: hydrogen production, ammonia borane, methanolysis, piezoelectric catalysis, PVDF-HFP, nanofibers, electrospinning, cobalt molybdenum catalyst, bimetallic nanocatalysts, chemical hydrogen storage, hydrogen energy, non-precious metal catalysts

Through the innovative application of a cutting-edge technique called phase-resolved second harmonic generation (PR-SHG), Northwestern chemists have for the first time directly observed water molecules "flipping" their orientation at the interface with a metallic electrode during the OER. This molecular acrobatics occurs in the fleeting moment before oxygen atoms are released, demanding a significant input of extra energy beyond theoretical calculations. The discovery elucidates a key barrier in water splitting’s energy requirements, highlighting the pivotal role that water molecule orientation plays in the overall reaction efficiency.

The crux of this phenomenon lies in the electrostatic environment of the electrode surface. Initially, water molecules tend to position themselves with their positively charged hydrogen atoms facing the negatively charged electrode. In this orientation, electron transfer is impeded because oxygen atoms—the actual sites for electron donation—are turned away from the electrode surface. It is only when the applied electric field reaches a critical strength that water molecules flip, reorienting so that oxygen atoms face the electrode, facilitating efficient electron transfer. This flipping, however, is energetically expensive, contributing to the departure from the ideal 1.23 volts theorized for water splitting, with actual operational voltages registering closer to 1.5 or 1.6 volts.

Remarkably, the PR-SHG technique enabled precise measurement of not just the occurrence of flipping but also the energy associated with this reorientation. These measurements revealed a striking correlation between the energy barrier for flipping and the inherent molecular forces that maintain the cohesion of liquid water. This insight suggests that the fundamental properties of water itself impose a baseline energetic hurdle for efficient OER, a factor previously unaccounted for in catalyst design.

Another significant finding from the team shows that this energy barrier is sensitive to the pH level of the water solution. At lower pH values, flipping water molecules require substantially more energy, effectively stalling the electrochemical reaction. Conversely, when the pH exceeds nine, the energy demand decreases, and the flipping process supports robust electrochemical activity. This pH dependency offers a tangible parameter for optimizing water splitting conditions, signaling that managing solution acidity could be a straightforward way to enhance efficiency.

The implications of these findings are profound in the context of developing practical and economically viable water splitting technologies. The traditional reliance on precious metals like iridium, which offers excellent catalytic performance but is scarce and costly, is unsustainable for large-scale deployment. Northwestern’s research pivots toward more abundant and affordable materials such as hematite, an iron oxide mineral known for its earth-abundance and favorable semiconductor properties. Despite its promise, hematite faces challenges related to surface chemistry and catalytic inefficiency, issues now better understood through the lens of water molecule flipping.

By deploying PR-SHG on hematite electrodes immersed in water, the research team could monitor water molecule behavior in real-time, an achievement likened by lead scientist Franz Geiger to an "optical equivalent of noise-canceling headphones." This metaphor captures how the technique isolates signals at half the laser wavelength, allowing precise quantification of molecular orientations without interference. The dynamic insights gained provide a powerful new tool for probing electrochemical interfaces with unprecedented clarity.

This study builds upon earlier work by the same group, which observed similar water flipping phenomena on nickel electrodes, demonstrating the universality of this mechanism across both metallic and semiconductor substrates. The generality of the behavior across electrode types underscores the fundamental nature of water flipping as a prerequisite for OER, emphasizing the necessity to factor this step into catalyst design and operation protocols for efficient water splitting.

The energy cost associated with water flipping represents a significant portion of the overall energy overhead in water splitting. Recognizing this opens avenues for designing next-generation catalysts equipped with surface structures tailored to lower the flipping energy barrier. Such catalysts could facilitate easier reorientation of water molecules, thus reducing the voltage gap between theoretical and practical water splitting and improving the economic viability of hydrogen production.

Beyond immediate applications on Earth, these insights carry potential ramifications for space exploration and extraterrestrial colonization. Efficient water splitting is critical not only for hydrogen fuel generation but also for producing breathable oxygen, an essential resource for human life in off-world environments such as Mars. By enhancing our understanding of the molecular steps in OER, this research aids the development of technologies that could support sustainable human presence beyond our planet.

Additionally, the findings align with broader efforts to transition from fossil fuels to a hydrogen economy. Integrating catalysts such as hematite into solar water oxidation systems could leverage sunlight to reduce the necessary applied voltage for splitting water. This synergy between solar energy and electrochemical catalysis promises to produce green hydrogen cost-effectively, a key step toward decarbonizing the global energy landscape.

Funded by the U.S. Department of Energy, National Science Foundation, and the Air Force Office of Scientific Research, this study represents a seminal advance in physical chemistry and energy research. The interdisciplinary collaboration, involving researchers from Northwestern University, Argonne National Laboratory, and Pacific Northwest National Laboratory, exemplifies the cooperative spirit driving innovation in clean energy technologies.

The demonstrated influence of water’s intrinsic molecular behavior on electrochemical processes challenges prior assumptions and sets a new paradigm for investigating and optimizing water splitting. Future research inspired by these results will likely delve deeper into molecular-scale engineering of electrode interfaces, aspiring to harness or manipulate water flipping to break efficiency barriers and enable viable hydrogen energy on a global scale.

Subject of Research: Not applicable
Article Title: Water flipping and the oxygen evolution reaction on Fe2O3 nanolayers
News Publication Date: 15-Apr-2025
Web References: http://dx.doi.org/10.1038/s41467-025-58842-y
References: Geiger et al., Nature Communications, 2025
Image Credits: Franz Geiger/Northwestern University

Keywords

Water splitting, Hydrogen energy, Water molecules, Solar water splitting, Water, Hydrogen fuel

Recent research published in the prestigious Journal of the American Chemical Society delves deeper into the intricacies of PEC water splitting. Conducted by Dr. Yohei Cho at the Japan Advanced Institute of Science and Technology (JAIST) alongside Prof. Fumiaki Amano from Tokyo Metropolitan University and a collaborative team from notable institutions such as Imperial College London and Swansea University, the study employs cutting-edge techniques to monitor electron behavior in real-time. This innovative approach brings forth new understanding and potential strategies to mitigate losses in the PEC process.

The research’s primary methodology hinges on the combination of intensity-modulated photocurrent spectroscopy (IMPS) with distribution of relaxation times (DRT), enabling researchers to distinguish charge transport behaviors that traditional methods have failed to separate. Unlike established techniques that depend on predefined circuit models, this interdisciplinary approach offers a clearer pathway for analysis. Dr. Cho, the lead researcher, emphasizes the significance of their methodology, stating that it provides unprecedented detail on electron movement, revealing processes that have remained elusive through conventional means.

Historically, energy losses in PEC water splitting were not differentiable in a quantitative manner. However, this groundbreaking study elucidates that recombination occurs via three distinct mechanisms. At elevated voltages, inefficiencies manifest from a phenomenon termed over-penetration induced recombination (OPR), where light penetrates excessively into the photoanode material. Conversely, at medium voltages, excessive photogenerated holes lead to what is known as excess hole induced recombination (EHR). In contrast, at lower voltages, the study identifies back electron-hole recombination (BER), wherein returning electrons combine with holes before they can effectively participate in the chemical reactions.

An especially notable finding of the study was the identification of a previously unknown slow reaction termed the “satellite peak.” This discovery is paramount; it provides insight into the rate-limiting steps of the water splitting process. As Dr. Cho elaborates, understanding and addressing this peak can significantly enhance the efficiency of PEC systems. Thus, the implications of this discovery extend beyond theoretical understanding – they could translate into practical solutions to overcome inefficiencies in hydrogen production.

The relevance of this breakthrough research extends far beyond hydrogen fuel generation. It could have transformative implications for various applications, including carbon dioxide reduction, advanced wastewater treatment, and the development of self-cleaning and antibacterial surfaces. Prof. Amano complements this perspective by stating that the developed methodology holds vast potential across diverse photocatalytic systems, allowing for optimization geared toward a multitude of clean energy and environmental applications.

Given the findings of this research, a promising future lies ahead for the field of PEC water splitting. The focus on precise tools for diagnosing and mitigating energy losses could accelerate the development of new materials that enhance hydrogen production efficiency. As researchers hone in on these methodologies and the nuances of electron behavior, solar-powered hydrogen production could evolve into a more viable and affordable energy source. This evolution would not only diminish reliance on fossil fuels but also mark a pivotal step toward a more sustainable and greener global energy landscape.

In light of ongoing research and the need for further validation of long-term impacts, Dr. Cho underscores that this work lays a firm groundwork for future advancements in semiconductor technology. The fusion of insights derived from this study with real-world applications could yield significant payoffs in the pursuit of efficient energy solutions, ultimately steering us closer to a cleaner future.

As the urgency intensifies to address climate change and energy independence, findings like those from Dr. Cho’s research represent critical progress. The evolution of hydrogen fuel as a major player in the energy market may not be a distant reality. With concerted efforts from the scientific community and increased focus on understanding complex processes within photocatalytic systems, a sustainable energy future seems within reach.

Continual innovation and interdisciplinary collaboration will be essential as we endeavor to explore all facets of PEC water splitting. This study serves as an exemplar of how cutting-edge technologies can be leveraged to confront pressing energy challenges. The pathway forward involves not only extending our knowledge of theoretical principles but also ensuring the practical application of these innovations leads to real-world solutions for a sustainable tomorrow.

The combination of advanced imaging techniques and critical analysis positions researchers to tackle complex energy challenges. In the wake of climate change, understanding the mechanisms of energy generation becomes increasingly vital. This research exemplifies the capacity of scientific inquiry to contribute towards meaningful environmental solutions. As we look ahead, the ramifications of this work could catalyze a broader movement towards harnessing clean energy technologies.

Through ongoing investigation and refinement of renewable energy technologies, we can anticipate a future where hydrogen plays a significant and efficient role in our energy systems. The discoveries made in this study not only enhance our foundational knowledge but also energize the possibilities for significant innovations that align with our environmental objectives. Given the pressing need to move toward sustainable solutions, the insights gained from understanding electron dynamics in PEC systems will be instrumental in realizing cleaner forms of energy.

In summary, this research represents a beacon of hope amid the challenges of energy production and environmental sustainability. The combination of advanced methodologies and profound insights into electron behavior may pave the way for transformative changes in how we approach energy generation. With such contributions, we inch closer to realizing a sustainable energy future that can power the world while preserving its resources.

The continuing evolution of hydrogen production technologies, guided by fundamental research like that of Dr. Cho’s team, is crucial to achieving the overarching goal of a greener, low-carbon future. The acceleration of clean energy technologies holds remarkable promise for addressing the global energy crisis and mitigating environmental degradation.

Subject of Research: Photoelectrochemical (PEC) water splitting and electron transport in TiO₂ photoanodes
Article Title: Analysis of TiO2 Photoanode Process Using Intensity Modulated Photocurrent Spectroscopy and Distribution of Relaxation Times
News Publication Date: 22-Feb-2025
Web References: https://doi.org/10.1021/jacs.4c17345
References: –
Image Credits: Credit: Dr. Yohei Cho from JAIST

Keywords
Physical sciences, Chemistry, Analytical chemistry, Chemical analysis, Chemical engineering, Hydrogen production, Photonics, Spectroscopy