One of the core challenges in photocatalytic CO₂ reduction lies in the simultaneous optimization of both charge separation and proton transfer dynamics. These processes govern the efficiency of the half-reactions: the reduction of CO₂ to carbon monoxide (CO) and the oxidation of water to oxygen (O₂). Addressing this complexity requires engineering catalysts with multiple active sites that can facilitate these dual pathways concurrently and synergistically. To this end, the research team, led by Professor Benxia Li at Zhejiang Sci-Tech University, has designed a catalyst integrating both Pd single atoms (Pd₁) and Pd clusters (Pd_c) anchored within a 3DOM In₂O₃ framework. This architecture aims to harness the distinct catalytic properties of isolated atoms and nanoscale clusters within a highly porous and accessible support.

The 3DOM structure of In₂O₃ offers a large surface area and interconnected pore network, crucial for mass transport and substrate accessibility. This ordered macroporosity greatly enhances the exposure of active sites and facilitates the diffusion of reactants and intermediates, thereby optimizing reaction kinetics. Pd single atoms embedded in this matrix serve as highly selective active centers for the CO₂ reduction reaction, catalyzing the selective formation of CO with high efficiency. Meanwhile, Pd clusters exhibit localized surface plasmon resonance (LSPR), a phenomenon that amplifies their light absorption capabilities and induces a photothermal effect.

This photothermal effect, unleashed through the plasmonic excitation of Pd clusters under simulated sunlight, causes a rapid temperature increase on the catalyst surface, reaching temperatures around 230 °C. Such localized heating accelerates reaction kinetics by lowering activation energy barriers and improving charge carrier mobility, effectively coupling light absorption with thermal catalysis. Thus, this dual photocatalytic-photothermal mechanism introduces a new dimension to solar-driven catalysis, bridging photonic and thermal effects in a single catalyst system.

In terms of synthesis, the Pd₁+c/3DOM-In₂O₃ catalyst was fabricated via a template-assisted in situ pyrolysis method, followed by a controlled thermal treatment in a reducing atmosphere of mixed hydrogen and argon gases. This process ensures the stable coexistence of Pd single atoms and clusters, preserving the integrity of the 3DOM In₂O₃ scaffold. By carefully tuning synthesis parameters, the researchers achieved a balanced distribution of Pd species that facilitated the vital synergy between distinct catalytic sites.

Performance tests under simulated sunlight irradiation demonstrated that this catalyst attained an impressive CO evolution rate of approximately 192.52 μmol per gram of catalyst per hour. Importantly, selectivity towards CO production reached 88.51%, underscoring the catalyst’s ability to steer reaction pathways efficiently while suppressing competing side reactions such as hydrogen evolution. This level of activity and selectivity places the Pd-based 3DOM catalyst at the forefront of emerging photocatalysts in the field of solar fuel generation.

To unravel the catalytic mechanisms at the atomic level, the study employed density functional theory (DFT) calculations. These computational insights revealed that Pd clusters significantly reduce the thermodynamic barriers associated with H₂O dissociation, thereby facilitating proton-coupled electron transfer processes essential for CO₂ reduction. Concurrently, isolated Pd single atoms act as prime catalytic sites for the activation and selective reduction of CO₂ to CO. The enhanced CO₂ adsorption on neighboring Pd clusters further augments the overall catalytic activity through a cooperative interaction between atomically dispersed species and clustered ensembles.

This dual-site synergy also optimizes charge carrier dynamics by improving the separation and migration of photogenerated electrons and holes within the photocatalyst. The improved charge dynamics reduce recombination losses, boosting the overall quantum efficiency of the system. Such an integrated catalytic platform exemplifies the design principles necessary to overcome traditional limitations in photocatalytic CO₂ conversion technologies.

Beyond providing a potent catalyst for solar fuel production, this research offers broader implications for the design of multicomponent catalysts in heterogeneous photocatalysis. The architecture demonstrated here could inspire analogous strategies utilizing other metal single atoms and clusters embedded in tailored porous semiconductor supports. By rationally combining the unique attributes of single atoms’ selectivity with clusters’ plasmonic properties, future catalysts could target a wide range of complex chemical transformations under solar irradiation.

Moreover, the use of 3DOM In₂O₃ as a scaffold underscores the importance of hierarchical porosity and structural design in catalysis. Macroporous frameworks not only improve substrate diffusion and active site exposure but also enable better thermal management, which is critical when harnessing photothermal effects. Such design considerations are likely to influence next-generation photocatalyst development for energy conversion and environmental remediation applications.

The implications of this work extend to addressing critical energy and climate challenges through innovative materials chemistry. By converting abundant and inert CO₂ molecules into carbon-based fuels using sunlight and water, this catalytic system contributes towards sustainable carbon recycling. This approach could significantly reduce greenhouse gas emissions while generating renewable chemical feedstocks, thus supporting circular carbon economy goals.

Published in the esteemed Chinese Journal of Catalysis, the findings underscore the growing global interest in advanced catalysis research underpinned by atomic-scale engineering and photothermal coupling. The collaboration of experimental synthesis, characterization, and theoretical modeling demonstrates a comprehensive path forward in photocatalyst design, combining mechanistic understanding with practical application.

This research not only marks a notable advance in photocatalytic CO₂ reduction but also exemplifies how interdisciplinary integration of materials science, surface chemistry, and photophysics can drive innovation in renewable energy technologies. As solar-driven CO₂ conversion moves closer to practical implementation, the lessons herein will help navigate the challenges of efficiency, selectivity, and stability in real-world conditions.

In summary, the pioneering Pd₁+c/3DOM-In₂O₃ catalyst system represents a new paradigm in solar fuel catalysis. By exploiting synergistic single atoms and clusters with 3DOM architecture and plasmonic photothermal effects, it achieves exceptional catalytic activity and selectivity for CO₂ reduction to CO. This approach offers a compelling blueprint for future sustainable catalysis systems that integrate multifunctional active sites and hierarchical material design to harness sunlight effectively for carbon resource utilization.

Subject of Research:
Photocatalytic reduction of carbon dioxide (CO₂) using water (H₂O) on Pd single atoms and clusters embedded in ordered macroporous indium oxide (In₂O₃) for solar fuel generation.

Article Title:
Synergistic Pd species anchored in ordered macroporous In2O3 boosting solar-driven CO2 and H2O conversion

News Publication Date:
11-Feb-2026

Web References:
DOI: 10.1016/S1872-2067(25)64919-9
Journal: Chinese Journal of Catalysis

Image Credits:
Chinese Journal of Catalysis

Keywords

Photocatalysis, CO2 Reduction, Palladium Single Atoms, Palladium Clusters, Indium Oxide, 3DOM Structure, Photothermal Effect, Localized Surface Plasmon Resonance, Solar Fuels, Density Functional Theory, Catalytic Synergy, Renewable Energy

Photocatalysts typically rely on the generation of electron-hole pairs upon light illumination to drive redox reactions, essential for processes like methane activation. However, these systems routinely grapple with significant limitations—chiefly charge carrier recombination and suboptimal minority-carrier diffusion lengths—that hinder reaction efficiencies. Prior strategies have sought to mitigate these drawbacks through complex heterojunctions and nanostructure engineering, yet inherent constraints persist. This study introduces an alternative avenue, harnessing the insulator-to-metal transition (IMT) in VO₂, which spontaneously creates mixed-phase domains that serve as efficient charge-separating interfaces.

At the heart of the discovery lies the VO₂ material’s remarkable phase transition, occurring near a critical temperature (approximately 68 °C). Below this threshold, VO₂ behaves as an insulator, while above it, it adopts metallic conductivity. Researchers exploited this temperature-dependent duality to create a material with coexisting insulating and metallic domains, which intriguingly feature non-integer dimensional boundaries. These boundaries, smaller than the minority-carrier diffusion length, function as internal junctions that effectively separate photogenerated electrons and holes, minimizing recombination losses and enhancing catalytic turnover.

The ability to spontaneously generate these nanojunctions during phase coexistence dramatically simplifies experimental fabrication, sidestepping the need for intricate structural designs. This intrinsic property enhances photocatalytic charge carrier dynamics, a major bottleneck in conventional semiconductors used for methane photoconversion. Extended by systematic thickness variation of the VO₂ films, the study demonstrates a clear correlation where thinning the film increases the length of charge-separating interfaces, leading to a pronounced boost in catalytic activity.

Strikingly, as the film thickness decreases, photocatalytic methane conversion is not only enhanced but also accompanied by a significant shift in product selectivity. The researchers observed a remarkable 100% selectivity toward propane formation via C–C coupling of surface-bound alkoxy intermediates—a highly sought-after outcome in methane valorization given the typically low selectivity of alternatives. This unprecedented selectivity arises because the augmented interface density facilitates efficient charge carrier separation and surface reaction kinetics that favor C–C coupling over undesired pathways such as CO₂ evolution.

In addition to thermal activation of the IMT via temperature, the team innovatively harnessed an electrical trigger to induce the phase transition at lower operating temperatures. This electric field application not only lowered the energy barrier for the IMT but also activated charge carriers through field-assisted mechanisms, further amplifying methane conversion rates. This electrically driven phase modulation injects new versatility into photocatalysis, offering real-time control of catalytic activity and making the process more adaptable for practical applications.

Beyond the immediate scope of methane conversion, this research opens avenues for broader photocatalytic and photoelectrochemical applications centered on energy conversion and chemical synthesis. The fundamental concept of utilizing dynamic phase transitions with coexisting electronic domains introduces a powerful tool to regulate charge carrier behavior intrinsically. This could inspire the design of future catalysts with tunable efficiencies that eschew intricate nanoscale architectures in favor of self-organized phase phenomena.

The study’s implications resonate beyond materials science, with potential transformative effects on catalysis-driven efforts to mitigate climate change. Methane is a potent greenhouse gas, and its efficient conversion into value-added chemicals like propane offers a way to curb emissions while generating useful fuels and feedstocks. By leveraging VO₂’s IMT, this approach melds advanced solid-state physics with green chemistry, marrying fundamental science with urgent environmental challenges.

Methodologically, the researchers deployed a suite of advanced characterization techniques to elucidate the phase morphology and interface properties of VO₂ films. High-resolution microscopy and spectroscopy revealed the nanoscale coexistence of metallic and insulating domains with complex fractal-like boundaries, which were pivotal in charge separation. Complementary photocatalytic assays validated that the peak activity aligned precisely with the temperature regime of phase coexistence, underscoring the intrinsic role of these mixed-phase structures.

Moreover, carrier dynamics were probed using ultrafast spectroscopic techniques, highlighting reduced recombination rates correlated with increased interface density. These findings confirm that the emergent phase boundaries act as efficient sinks or pathways for minority carriers, thus enhancing their utilization for surface chemical transformations. Such insights are vital for developing theoretical models that can predict and optimize photocatalyst performance based on phase transition physics.

The research team also explored the durability and repeatability of the photocatalytic response, demonstrating stable methane conversion and propane selectivity over multiple transition cycles. This stability is critical for real-world applicability, where catalysts must withstand operational stresses without losing efficacy. The robust nature of VO₂’s phase transition under cyclic conditions solidifies its candidacy for scalable photocatalytic applications.

From a mechanistic perspective, the enhanced C–C coupling is thought to stem from prolonged lifetimes and higher surface concentrations of reactive alkoxy intermediates, favored by spatial charge separation at phase boundaries. These interfaces provide localized electronic environments that modulate adsorbate binding and reactivity. Detailed kinetic studies corroborate this hypothesis, revealing that enhanced charge separation suppresses competing pathways, thereby steering selectivity toward more complex hydrocarbon products.

Looking forward, this paradigm may extend beyond VO₂ to other correlated electron materials exhibiting phase transitions with tunable domain morphologies. The principle of harnessing phase coexistence to promote efficient charge manipulation could be generalized to design multifunctional photocatalysts and photoelectrodes, furthering sustainable energy conversion technologies. Additionally, integrating such materials into hybrid or heterostructure devices provides a rich landscape for optimizing performance through external stimuli.

In summary, this pioneering work transforms the landscape of photocatalytic methane conversion by exploiting the insulator–metal phase transition in VO₂. The formation of mixed-phase nanodomains with non-integer dimensional boundaries offers a naturally occurring platform for exceptional charge separation and enhanced catalytic function. The merger of thermal and electrical control over phase states allows fine-tuning of activity and selectivity, crowned by perfect propane yield under optimized conditions. This research reinvigorates the role of phase transitions in catalysis, opening innovative routes toward efficient solar-to-chemical energy transformations.

Subject of Research: Photocatalytic methane conversion via insulator–metal transition in VO₂.

Article Title: Exploiting the insulator–metal transition of VO₂ in photocatalytic methane conversion.

Article References:
Tran, M.N., Nguyen, D.M., Ahounou, M.K. et al. Exploiting the insulator–metal transition of VO₂ in photocatalytic methane conversion. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02013-w

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41560-026-02013-w

Hydrogen peroxide is an essential oxidant in numerous industrial domains, ranging from bleaching in papermaking to sterilization in medical fields. Traditional production routes, predominantly the anthraquinone process, are energy-intensive and environmentally problematic, motivating the scientific community to seek greener, more sustainable synthetic methods. Photocatalytic synthesis utilizing sunlight, water, and oxygen promises a transformative path but is hindered by intrinsic material limitations that compromise efficiency. Achieving a harmonious balance among light absorption, charge separation, migration, and surface catalytic reactions has remained a herculean challenge due to conflicting mechanistic requirements within a single photocatalyst.

The Lanzhou University team, led by Professors Yu Tang and Fengjuan Chen, has introduced a cleverly orchestrated mixed ligand methodology to address these constraints. By fine-tuning the ratio between two complementing aldehyde monomers—terephthalaldehyde (TA) and 2,5-di(thiophen-2-yl)terephthalaldehyde (DTTA)—in conjunction with 2,4,6-trimethyl-1,3,5-triazine (TMT), their approach achieves a synergistic enhancement across all critical stages of photocatalysis. This rational design not only broadens the spectral absorption capabilities of the COFs but also fortifies charge carrier dynamics and hydrophilicity, all while maintaining robust crystallinity.

The inclusion of the DTTA unit notably extends the light-harvesting range of the photocatalyst, engaging a broader swath of the solar spectrum and effectively generating higher densities of excited charge carriers. Concurrently, the TA unit contributes significantly to the framework’s structural order and improves surface hydrophilicity—facilitating superior charge transport and active site accessibility. The interplay between these two structural motifs embodies a molecular “barrel effect,” wherein complementary functional components collectively produce performance enhancements unattainable by individual constituents.

Experimental characterization, including PXRD patterns and spectroscopy analyses, reveal that the hybrid COFs maintain exceptional crystallinity and porosity, essential features for efficient photocatalytic processes. Moreover, computational modeling substantiates the synergistic charge separation facilitated by the unique molecular architectures, showing suppressed recombination rates and enhanced charge mobility. This meticulous balance is critical for driving the surface redox reactions that convert water and oxygen into hydrogen peroxide with high selectivity and yield.

Among the synthesized variants, the sample denoted as TA/DTTA-2-TMT emerged as the optimized configuration, delivering a staggering H2O2 production rate of 3451 micromoles per gram per hour under visible light illumination of 100 milliwatts per square centimeter in pure water and open air conditions. This level of photocatalytic activity not only eclipses that of COFs constructed solely from either TA or DTTA monomers but also outperforms a vast majority of pervious COF-based photocatalysts reported to date.

The implications of this discovery extend far beyond mere numerical advancements. The work encapsulates a fundamental shift towards multi-parameter molecular engineering for photocatalyst design—where competing photocatalytic attributes are harmonized through precise compositional control. This paves the way for fabricating next-generation photocatalytic materials possessing tailor-made properties for energy conversion, environmental remediation, and chemical synthesis.

Furthermore, the research challenges conventional approaches that predominantly target singular aspects like band gap tuning or surface functionalization in isolation. Instead, it exemplifies a systems-level optimization, addressing the intricate trade-offs that typically impede photocatalytic performance. Such a holistic strategy is crucial in accelerating the transition from laboratory breakthroughs to practical, scalable solutions for green and economical hydrogen peroxide production.

In addition to the fundamental science, this advancement bears notable practical promise. Photocatalytic production of H2O2 directly from water and oxygen under mild conditions significantly reduces reliance on fossil fuel-derived raw materials and complex industrial setups. It opens avenues for decentralized, on-demand generation of this versatile chemical, potentially revolutionizing sectors that demand sustainable oxidants and disinfectants.

Looking ahead, the Lanzhou team’s methodology sets a precedent for future explorations into covalent organic frameworks and other molecularly engineered materials. The modularity inherent in COF chemistry combined with mixed linker strategies provides vast compositional freedom to finesse optoelectronic and catalytic properties. This work thus inspires further efforts to explore novel monomer combinations, doping elements, and framework topologies—all aimed at harnessing sunlight with maximal efficiency.

This research was published in CCS Chemistry, the flagship journal of the Chinese Chemical Society, highlighting the institution’s commitment to advancing frontier chemistry research. The corresponding authors Prof. Yu Tang and Prof. Fengjuan Chen, alongside their team, have showcased exemplary multidisciplinary collaboration, integrating synthetic chemistry, material characterization, theoretical computation, and photocatalytic evaluation to deliver this impactful discovery.

Funded by significant grants from the National Natural Science Foundation of China and provincial science initiatives, this work stands as a testament to the fruitful intersection of strategic funding and innovative scientific inquiry. It underscores the pivotal role of molecular precision in addressing sustainable energy and chemical production challenges, exemplifying how fundamental chemistry continues to lead the charge toward a greener future.

With this transformative advance, the field edges closer to realizing the full potential of photocatalytic H2O2 synthesis as an industrially viable and environmentally benign technology. The Lanzhou University research heralds a promising horizon where solar-driven chemical manufacturing could dramatically reduce humanity’s ecological footprint, achieving multiple societal benefits including cleaner water, safer disinfection, and greener industrial processes.

Subject of Research: Not applicable

Article Title: Thiophene-Doped Fully Conjugated Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Peroxide Generation

News Publication Date: 21-Oct-2025

Web References:
https://www.chinesechemsoc.org/journal/ccschem
http://dx.doi.org/10.31635/ccschem.025.202506161

Image Credits: CCS Chemistry

Keywords

Covalent organic frameworks