Dr Yiyang Li

Abstract:

Photocatalytic water splitting is a promising method for green hydrogen production. Great progress has been made in photocatalyst activity after decades of study. Cationic doping is one of the most extensively studied photocatalyst optimization strategies. Diverse findings, both positive and negative effects, have been reported, reflecting the complexity of the system. Thus, a deep understanding of both the fundamentals and current progress is essential for the rational exploration and development of this strategy. In this Review , we start by providing a brief introduction to the principles of photocatalytic water splitting and the evaluation indices of photocatalytic efficiency. Following that, we present the fundamentals of cationic doping, with special attention to the underlying thermodynamics and its modification of the structure and electronic structure of metal oxide photocatalysts. Building on this basis, we highlight recent progress in understanding how cationic doping affects fundamental steps in photocatalytic water splitting, with a focus on light absorption and charge transport. Finally, we summarize the current challenges and research gaps in the field.

Abstract:

The catalytic decomposition of ammonia under mild conditions is a promising route for green hydrogen production. However, conventional dissociative ammonia decomposition pathways over metal sites are suffering from the Brønsted−Evans−Polanyi (BEP) constraint which establishes an inverse correlation between atomic N binding energy and the N-H bond dissociation energy. Herein, we report a ruthenium-supported nitrogen-doped cerium oxide (Ru/N-CeO2) catalyst that breaks this limitation and exhibits significantly enhanced catalytic activity compared to its undoped counterpart. Furthermore, we reveal that N dopants can act as independent active sites, enabling an associative mechanism distinct from the conventional Ru-driven pathway. Comprehensive isotopic labelling experiments together with computational techniques elucidate the reaction mechanism over the N site and reveal a distinct correlation between the location of the active site and catalytic activity. The proximal N site exhibits the highest activity, challenging the conventional view that activity is dominated by metal–support interfacial sites. While N doping is a commonly used approach for surface modification, our findings show that it can also alter the reaction mechanism by introducing new active sites. These insights offer valuable guidance for the rational design of catalytic supports in ammonia decomposition and open new directions for catalytic systems limited by scaling relationships in heterogenous catalysis.

Abstract:

We report the isolation and characterization of the first example of a crystallized high-valent Ag3+-containing polyoxometalate (POM) complex, Cs7K4[P2W19AgIIIO69(OH2)]·17H2O (1), as a “catalyst bearing catalyst” capable of catalyzing the formation of the high-valent Ni3+-containing POMs in the presence of peroxydisulfate. The oxidation state and exotic chemical behaviors of Ag in 1 were confirmed by crystallographic, spectroscopic, and electrochemical characterizations. The Ag3+/Ag+ redox pair embedded in 1 showed good electrochemical reversibility and the ability to accelerate electron transfer, contributing to the observed catalytic activity of 1 in both formation of other high-valent metal-containing POMs and electrochemical oxidative C–H activation.

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.