Dr Yiyang Li

Abstract:

Two-dimensional layered perovskite oxides have emerged as promising photocatalysts for solar-driven hydrogen evolution. Although doping has been widely employed to enhance photocatalytic performance, its role in modulating the electronic structure and the local chemical environment of these materials remains poorly understood. Here in this study, we investigate the codoping of Rh and La into exfoliated nanosheets of the Dion–Jacobson perovskite KCa2Nb3O10 to enhance photocatalytic hydrogen evolution reaction (HER) activity. A substantial increase in H2 evolution rate, from 12.3 to 69.0 μmol h–1, was achieved at an optimal doping level of 0.2 wt % Rh and 1.3 wt % La. Comprehensive structural and spectroscopic analyses, including synchrotron techniques and high-resolution microscopy, revealed that Rh3+ substitutes Nb5+ to introduce shallow 4d acceptor states that mediate charge separation, while La3+ substitutes Ca2+, compensates for aliovalent charge imbalance, and modulates local lattice distortions and oxygen vacancy formation. This codoping strategy enhances charge carrier lifetime and separation efficiency through a trap-mediated mechanism. The observed volcano-shaped activity trend highlights a narrow compositional window, where electronic and structural factors are optimally balanced. These findings establish a mechanistic foundation for defect engineering in layered perovskites and offer a pathway for the rational design of photocatalysts.

Abstract:

Photocatalytic ammonia decomposition offers a sustainable route for hydrogen production, but its development is limited by low catalytic efficiency and poorly understood mechanisms. Here, a protonated layered perovskite, HPrNb2O7 (HPNO), is reported as an efficient catalyst for ammonia decomposition under mild photo‐thermal conditions. Upon exposure to NH3 at elevated temperatures, HPNO promotes the in situ formation and intercalation of hydrazine intermediates within its interlayer galleries, enabled by thermally generated oxygen vacancies and hydrogen bonding. Advanced characterization techniques have been applied to confirm the formation and stabilization of hydrazine. It is also shown that thermal energy prolongs charge carrier lifetimes and enhances oxygen vacancy formation, contributing to a strong photo‐thermal synergy. The stabilization of hydrazine intermediate promotes the associative mechanism, lowering the activation barrier, thus leading to an enhanced hydrogen evolution rate of 1311.2 µmol·g−1·h−1 at 200 °C under simulated solar irradiation without any noble metal co‐catalyst. This work reveals a distinct, hydrazine‐mediated reaction pathway and positions layered protonated perovskites as promising materials for efficient, solar‐driven ammonia decomposition and sustainable hydrogen generation.

Abstract:

Despite operational mildness, hydroconversion’s reliance on fossil hydrogen raises sustainability concernsare hydrogen-free alternatives a more viable long-term strategy?

Abstract:

External magnetic fields emerge as a promising method for enhancing the electrocatalytic oxygen evolution reaction (OER), yet the underlying magneto‐electric (ME) mechanisms are not well understood. The slow kinetics of OER make it a key challenge in electrocatalytic water‐splitting, a promising technique for sustainable H2 fuel production. Herein, a systematic approach is presented to analyzing the ME mechanisms governing OER, using metallic‐plate (Ni foam, Ni sheet, and Pt sheet) and powder‐based (Co3O4/BaFe12O19 on carbon paper) electrodes. Through controlled experiments using varying magnetic field strengths and orientations, Lorentz force and spin‐polarization mechanisms are separated. For metallic electrodes, the effects are orientation‐dependent, indicating domination by Lorentz force. Magnetic flux density about the electrode surface is shown to govern the Lorentz force behavior. Interestingly, a “pseudo” effect is discovered which results from the relative position of the reference electrode, highlighting the importance of experimental design. The Co3O4 systems display minimal orientation dependence, indicating spin‐polarization domination. Introducing BaFe12O19 as a magnetic co‐catalyst further amplifies the ME effect, marking the first demonstration of magnetic co‐catalyst enhancement in magneto‐electrocatalysis. This work provides key insights into ME mechanisms, linking electrode composition, magnetism, and geometry to performance, offering new pathways for optimizing future magneto‐electrocatalytic systems.

Abstract:

Green ammonia evolution by photocatalytic means has gained significant attention over recent decades, however, the energy conversion efficiency remains unsatisfactory, and deep mechanistic insights are absent. Here in this work, this challenge is addressed by developing a photothermal system that synthesizes ammonia from nitrogen and natural seawater under simulated solar irradiation, employing ruthenium‐doped barium tantalum oxynitride semiconductors. This method significantly enhances solar‐to‐ammonia conversion efficiency, providing a viable alternative to the energy‐intensive Haber–Bosch process. Optimized at 240 °C, the system achieves an ammonia evolution rate of 5869 µmol g−1 h−1 in natural seawater. Moreover, detailed characterizations have shown that the use of seawater not only leverages an abundant natural resource but also improves the reaction kinetics and overall system stability. The catalysts maintain their activity and structural integrity over multiple cycles, demonstrating both the feasibility and the durability of this innovative system. Achieving a solar‐to‐ammonia efficiency of 13% and an overall energy conversion efficiency of 6.3%, this breakthrough highlights the potential to decentralize ammonia production, enhancing accessibility and sustainability. This approach combines the benefits of thermal and photocatalytic processes, marking a significant advancement in ammonia synthesis technology.