Weitao Qiu

Recent advances in metal nitrides as high-performance electrode materials for energy storage devices

Energy storage devices are the key components for successful and sustainable energy systems. Some of the best types of energy storage devices right now include lithium-ion batteries and supercapacitors. Research in this area has greatly improved electrode materials, enhanced electrolytes, and conceived clever designs for device assemblies with the ever-increasing energy and power density for electronics. Electrode materials are the fundamental key components for energy storage devices that largely determine the electrochemical performance of energy storage devices. Various materials such as carbon materials, metal oxides and conducting polymers have been widely used as electrode materials for energy storage devices, and great achievements have been made. Recently, metal nitrides have attracted increasing interest as remarkable electrode materials for lithium-ion batteries and supercapacitors due to their outstanding electrochemical properties, high chemical stability, standard technological approach and extensive fundamental importance. This review analyzes the development and progress of metal nitrides as suitable electrode materials for lithium-ion batteries and supercapacitors. The challenges and prospects of metal nitrides as energy storage electrode materials are also discussed.

Three dimensional architectures: design, assembly and application in electrochemical capacitors

Currently, supercapacitors (SCs) are considered to be one of the most promising energy storage devices, mainly due to their unique properties such as high output power, long cycling stability, and fast charge/discharge capability. Nevertheless, the low energy density of SCs still limits their promotion in practical applications. Given this, designing three dimensional (3D) architectures for SC electrodes is perceived as an efficient strategy because well-constructed 3D structures could enable reduced “dead surface”, good electron transport kinetics, hierarchical porous channels and short ionic diffusion distances. This review aims to describe the current progress of different synthetic processes with respect to the preparation of 3D SC electrodes and focuses on both template-assisted strategies and non-template strategies. We summarize recently proposed methods, novel structures, and electrochemical performances for these 3D electrodes. The advantages and disadvantages accompanying them are also analyzed. Finally, we discuss the challenges and prospects of the fabrication of 3D SC electrodes.

A monolithic metal-free electrocatalyst for oxygen evolution reaction and overall water splitting

Herein, a three-dimensional monolithic and metal-free N-doped porous carbon cloth electrocatalyst was fabricated. Owing to the increased surface area and N-doping, the self-supporting electrocatalyst could effectively catalyze the oxygen evolution reaction, and was also utilized as the anode for an alkaline electrolyzer for the first time with a considerably low overpotential.

Three-dimensional nickel nitride (Ni3N) nanosheets: free standing and flexible electrodes for lithium ion batteries and supercapacitors

The search for suitable electrode materials for electrochemical storage devices has led to the development of new electrode materials. Metal nitrides are regarded as an attractive and promising class of electrode materials for high-performance energy storage devices because they exhibit excellent electrical conductivity over the corresponding metal oxides and have considerably higher capacity than carbon based materials. Moreover, designing of different electrode nanostructures has been demonstrated to effectively improve the storage performance of energy storage devices. Hence, three dimensional (3D) nickel nitride (Ni3N) nanosheets were successfully fabricated on a carbon cloth by a simple hydrothermal and post annealing process that can be used directly as electrode storage materials for flexible lithium ion batteries and supercapacitors. Due to the electrode, architectures that demonstrated fast electron transport via direct connection to the flexible substrate and facile ion diffusion paths that ensured the participation of every nanosheet in the ultrafast electrochemical reaction, the 3D flexible Ni3N/carbon composites cloth exhibited a high capacity or capacitance and possessed an excellent rate performance.

A review of the development of full cell lithium-ion batteries: The impact of nanostructured anode materials

Lithium-ion batteries have emerged as the best portable energy storage device for the consumer electronics market. Recent progress in the development of lithiumion batteries has been achieved by the use of selected anode materials, which have driven improvements in performance in terms of capacity, cyclic stability, and rate capability. In this regard, research focusing on the design and electrochemical performance of full cell lithium-ion batteries, utilizing newly developed anode materials, has been widely reported, and great strides in development have been made. Nanostructured anode materials have contributed largely to the development of full cell lithium-ion batteries. With this in mind, we summarize the impact of nanostructured anode materials in the performance of coin cell full lithium-ion batteries. This review also discusses the challenges and prospects of research into full cell lithium-ion batteries.

Vanadium Nitride Nanowire Supported SnS2 Nanosheets with High Reversible Capacity as Anode Material for Lithium Ion Batteries

The vulnerable restacking problem of tin disulfide (SnS2) usually leads to poor initial reversible capacity and poor cyclic stability, which hinders its practical application as lithium ion battery anode (LIB). In this work, we demonstrated an effective strategy to improve the first reversible capacity and lithium storage properties of SnS2 by growing SnS2 nanosheets on porous flexible vanadium nitride (VN) substrates. When evaluating lithium-storage properties, the three-dimensional (3D) porous VN coated SnS2 nanosheets (denoted as CC-VN@SnS2) yield a high reversible capacity of 75% with high specific capacity of about 819 mAh g(-1) at a current density of 0.65 A g(-1). Remarkable cyclic stability capacity of 791 mAh g(-1) after 100 cycles with excellent capacity retention of 97% was also achieved. Furthermore, discharge capacity as high as 349 mAh g(-1) is still retained after 70 cycles even at a elevated current density of 13 A g(-1). The excellent performance was due to the conductive flexible VN substrate support, which provides short Li-ion and electron pathways, accommodates large volume variation, contributes to the capacity, and provides mechanical stability, which allows the electrode to maintain its structural stability.

Chemically Lithiated TiO2 Heterostructured Nanosheet Anode with Excellent Rate Capability and Long Cycle-life for High-Performance Lithium Ion Batteries.

A new form of dual-phase heterostructured nanosheet comprised of oxygen-deficient TiO2/Li4Ti5O12 has been successfully synthesized and used as anode material for lithium ion batteries. With the three-dimensional (3D) Ti mesh as both the conducting substrate and the Ti(3+)/Ti(4+) source, blue anatase Ti(3+)/TiO2nanosheets were grown by a hydrothermal reaction. By controlling the chemical lithiation period of TiO2 nanosheets, a phase boundary was created between the TiO2 and the newly formed Li4Ti5O12, which contribute additional capacity benefiting from favorable charge separation between the two phase interfaces. Through further hydrogenation of the 3D TiO2/Li4Ti5O12 heterostructured nanosheets (denoted as H-TiO2/LTO HNS), an extraordinary rate performance with capacity of 174 mAh g(-1) at 200 C and outstanding long-term cycling stability with only an ∼6% decrease of its initial specific capacity after 6000 cycles were delivered. The heterostructured nanosheet morphology provides a short length of lithium diffusion and high electrode/electrolyte contact area, which could also explain the remarkable lithium storage performance. In addition, the full battery assembled based on the H-TiO2/LTO anode achieves high energy and power densities.

Cost-Effective Alkaline Water Electrolysis Based on Nitrogen- and Phosphorus-Doped Self-Supportive Electrocatalysts

Water splitting into hydrogen and oxygen in order to store light or electric energy requires efficient electrocatalysts for practical application. Cost-effectiveness, abundance, and efficiency are the major challenges of the electrocatalysts. Herein, this paper reports the use of low-cost 304-type stainless steel mesh as suitable electrocatalysts for splitting of water. The commercial and self-support stainless steel mesh is subjected to exfoliation and heteroatom doping processes. The modified stainless steel electrocatalyst displays higher oxygen evolution reaction property than the commercial IrO2 , and comparable hydrogen evolution reaction property with that of Pt. More importantly, an all-stainless-steel-based alkaline electrolyzer (denoted as NESSP//NESS) is designed for the first time, which possesses outstanding stability along with lower overall voltage than the conventional Pt//IrO2 electrolyzer at increasing current densities. The remarkable electrocatalytic properties of the stainless steel electrode can be attributed to the unique exfoliated-surface morphology, heteroatom doping, and synergistic effect from the uniform distribution of the interconnected elemental compositions. This work creates prospects to the utilization of low-cost, highly active, and ultradurable electrocatalysts for electrochemical energy conversion.

Defect Engineering of Bismuth Oxyiodide by IO3- Doping for Increasing Charge Transport in Photocatalysis.

Defect engineering is regarded as one of the most active projects to monitor the chemical and physical properties of materials, which is expected to increase the photocatalytic activities of the materials. Herein, oxygen vacancies and IO3- doping are introduced into BiOI nanosheets via adding NaH2PO2, which can impact the charge carrier dynamics of BiOI photocatalysts, such as its excitation, separation, trap, and transfer. These oxygen-deficient BiOI nanosheets display attractive photocatalytic activities of gaseous formaldehyde degradation and methyl orange under visible light irradiation, which are 5 and 3.5 times higher than the BiOI samples, respectively. Moreover, the comodified BiOI also displayed superior cycling stability and can be used for practical application. This work not only develops an effective strategy for fabricating oxygen vacancies but also offers deep insight into the impact of surface defects in enhancing photocatalysis.

Alkali-modified non-precious metal 3D-NiCo2O4 nanosheets for efficient formaldehyde oxidation at low temperature

Cost-effective catalysts for volatile organic compound (VOC) oxidation are critical to energy conversion and environmental protection. Herein, we developed new, low-cost and high-performance alkali-promoted 3D-NiCo2O4 nanosheet catalysts for HCHO oxidation at room temperature. Benefiting from the large surface area, high adsorption capacity and surface hydroxyls, the alkali-promoted 3D-NiCo2O4 nanosheet catalysts show substantially high catalytic activities for HCHO oxidation. The alkali-promoted 3D-NiCo2O4 nanosheets yield a remarkable HCHO conversion efficiency of 95.3% at room temperature, which is not achieved by any non-precious metal based catalysts at such low temperature. Additionally, the as-prepared alkali-promoted 3D-NiCo2O4 nanosheets retained excellent catalytic performance after 200 h, which can be applied to practical applications. This work provides a feasible approach to improve the efficiency of metal oxides for HCHO oxidation at low temperature.