Yunxuan Zhao

Bio: Yunxuan Zhao is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Photocatalysis & Catalysis. The author has an hindex of 26, co-authored 51 publications receiving 4017 citations. Previous affiliations of Yunxuan Zhao include Nanjing University & Nanjing University of Information Science and Technology.

Alkali-Assisted Synthesis of Nitrogen Deficient Graphitic Carbon Nitride with Tunable Band Structures for Efficient Visible-Light-Driven Hydrogen Evolution.

Abstract: A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx ) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea. In situ introduced nitrogen vacancies significantly redshift the absorption edge of g-C3 Nx , with the defect concentration depending on the alkali to nitrogen precursor ratio. The g-C3 Nx products show superior visible-light photocatalytic performance compared to pristine g-C3 N4 .

Tuning Oxygen Vacancies in Ultrathin TiO2 Nanosheets to Boost Photocatalytic Nitrogen Fixation up to 700 nm

Abstract: Dinitrogen reduction to ammonia using transition metal catalysts is central to both the chemical industry and the Earth's nitrogen cycle. In the Haber-Bosch process, a metallic iron catalyst and high temperatures (400 °C) and pressures (200 atm) are necessary to activate and cleave NN bonds, motivating the search for alternative catalysts that can transform N2 to NH3 under far milder reaction conditions. Here, the successful hydrothermal synthesis of ultrathin TiO2 nanosheets with an abundance of oxygen vacancies and intrinsic compressive strain, achieved through a facile copper-doping strategy, is reported. These defect-rich ultrathin anatase nanosheets exhibit remarkable and stable performance for photocatalytic reduction of N2 to NH3 in water, exhibiting photoactivity up to 700 nm. The oxygen vacancies and strain effect allow strong chemisorption and activation of molecular N2 and water, resulting in unusually high rates of NH3 evolution under visible-light irradiation. Therefore, this study offers a promising and sustainable route for the fixation of atmospheric N2 using solar energy.

Defect‐Engineered Ultrathin δ‐MnO2 Nanosheet Arrays as Bifunctional Electrodes for Efficient Overall Water Splitting

Abstract: Recently, defect engineering has been used to intruduce half-metallicity into selected semiconductors, thereby significantly enhancing their electrical conductivity and catalytic/electrocatalytic performance. Taking inspiration from this, we developed a novel bifunctional electrode consisting of two monolayer thick manganese dioxide (δ-MnO2) nanosheet arrays on a nickel foam, using a novel in-situ method. The bifunctional electrode exposes numerous active sites for electrocatalytic rections and displays excellent electrical conductivity, resulting in strong performance for both HER and OER. Based on detailed structure analysis and density functional theory (DFT) calculations, the remarkably OER and HER activity of the bifunctional electrode can be attributed to the ultrathin δ-MnO2 nanosheets containing abundant oxygen vacancies lead to the formation od Mn3+ active sites, which give rise to half-metallicity properties and strong H2O adsorption. This synthetic strategy introduced here represents a new method for the development of non-precious metal Mn-based electrocatalysts for eddicient energy conversion.

Layered‐Double‐Hydroxide Nanosheets as Efficient Visible‐Light‐Driven Photocatalysts for Dinitrogen Fixation

Abstract: Semiconductor photocatalysis attracts widespread interest in water splitting, CO2 reduction, and N2 fixation. N2 reduction to NH3 is essential to the chemical industry and to the Earth's nitrogen cycle. Industrially, NH3 is synthesized by the Haber-Bosch process under extreme conditions (400-500 °C, 200-250 bar), stimulating research into the development of sustainable technologies for NH3 production. Herein, this study demonstrates that ultrathin layered-double-hydroxide (LDH) photocatalysts, in particular CuCr-LDH nanosheets, possess remarkable photocatalytic activity for the photoreduction of N2 to NH3 in water at 25 °C under visible-light irradiation. The excellent activity can be attributed to the severely distorted structure and compressive strain in the LDH nanosheets, which significantly enhances N2 chemisorption and thereby promotes NH3 formation.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Abstract: Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Emerging Two-Dimensional Nanomaterials for Electrocatalysis

Abstract: Over the past few decades, the design and development of advanced electrocatalysts for efficient energy conversion technologies have been subjects of extensive study. With the discovery of graphene, two-dimensional (2D) nanomaterials have emerged as some of the most promising candidates for heterogeneous electrocatalysts due to their unique physical, chemical, and electronic properties. Here, we review 2D-nanomaterial-based electrocatalysts for selected electrocatalytic processes. We first discuss the unique advances in 2D electrocatalysts based on different compositions and functions followed by specific design principles. Following this overview, we discuss various 2D electrocatalysts for electrocatalytic processes involved in the water cycle, carbon cycle, and nitrogen cycle from their fundamental conception to their functional application. We place a significant emphasis on different engineering strategies for 2D nanomaterials and the influence these strategies have on intrinsic material performance, ...

Self-Supported Transition-Metal-Based Electrocatalysts for Hydrogen and Oxygen Evolution

Abstract: Electrochemical water splitting is a promising technology for sustainable conversion, storage, and transport of hydrogen energy. Searching for earth-abundant hydrogen/oxygen evolution reaction (HER/OER) electrocatalysts with high activity and durability to replace noble-metal-based catalysts plays paramount importance in the scalable application of water electrolysis. A freestanding electrode architecture is highly attractive as compared to the conventional coated powdery form because of enhanced kinetics and stability. Herein, recent progress in developing transition-metal-based HER/OER electrocatalytic materials is reviewed with selected examples of chalcogenides, phosphides, carbides, nitrides, alloys, phosphates, oxides, hydroxides, and oxyhydroxides. Focusing on self-supported electrodes, the latest advances in their structural design, controllable synthesis, mechanistic understanding, and strategies for performance enhancement are presented. Remaining challenges and future perspectives for the further development of self-supported electrocatalysts are also discussed.

Transition Metal Oxides as Electrocatalysts for the Oxygen Evolution Reaction in Alkaline Solutions: An Application-Inspired Renaissance

Abstract: Water splitting is the essential chemical reaction to enable the storage of intermittent energies such as solar and wind in the form of hydrogen fuel. The oxygen evolution reaction (OER) is often considered as the bottleneck in water splitting. Though metal oxides had been reported as OER electrocatalysts more than half a century ago, the recent interest in renewable energy storage has spurred a renaissance of the studies of transition metal oxides as Earth-abundant and nonprecious OER catalysts. This Perspective presents major progress in several key areas of the field such as theoretical understanding, activity trend, in situ and operando characterization, active site determination, and novel materials. A personal overview of the past achievements and future challenges is also provided.

Recent progress made in the mechanism comprehension and design of electrocatalysts for alkaline water splitting

Abstract: Alkaline water splitting is an attractive method for sustainable hydrogen production. Owing to the sluggish kinetics of alkaline water reduction and oxidation, it is crucial to understand the mechanism of the hydrogen evolution reaction/oxygen evolution reaction (HER/OER) and construct efficient electrocatalysts based on the structure–activity relationship. This review describes the fundamentals of the alkaline HER and OER, the design of noble and nonnoble HER electrocatalysts with low energy barriers, OER electrocatalysts based on binding energy, electronic structure, lattice oxygen, and surface reconstruction as well as the recent developments of bifunctional HER/OER electrocatalysts. Future perspectives towards alkaline water splitting electrocatalysts are also proposed.