3D nanorhombus nickel nitride as stable and cost-effective counter electrodes for dye-sensitized solar cells and supercapacitor applications

Recent progress in graphene and its derived hybrid materials for high-performance supercapacitor electrode applications

Graphene, the most fascinating 2D form of carbon with closely packed carbon atoms arranged in a layer, needs more attention in various fields. For its unique electrical, mechanical, and chemical properties with a large surface area, graphene has been in the limelight since its first report. Graphene has extraordinary properties, making it the most promising electrode component for applications in supercapacitors. However, the persistent re-stacking of carbon layers in graphene, caused by firm interlayer van der Waals attractions, significantly impairs the performance of supercapacitors. As a result, many strategies have been used to get around the aforementioned problems. The utilization of graphene-based nanomaterials has been implemented to surmount the aforementioned constraints and considerably enhance the performance of supercapacitors. This review highlights recent progress in graphene-based nanomaterials with metal oxide, sulfides, phosphides, nitrides, carbides, and conducting polymers, focusing on their synthetic approach, configurations, and electrochemical properties for supercapacitors. It discusses new possibilities that could increase the performance of next-generation supercapacitors.

Metal nitrides for seawater electrolysis

Electrocatalytic high-throughput seawater electrolysis for hydrogen production is a promising green energy technology that offers possibilities for environmental and energy sustainability. However, large-scale application is limited by the complex composition of seawater, high concentration of Cl- leading to competing reaction, and severe corrosion of electrode materials. In recent years, extensive research has been conducted to address these challenges. Metal nitrides (MNs) with excellent chemical stability and catalytic properties have emerged as ideal electrocatalyst candidates. This review presents the electrode reactions and basic parameters of the seawater splitting process, and summarizes the types and selection principles of conductive substrates with critical analysis of the design principles for seawater electrocatalysts. The focus is on discussing the properties, synthesis, and design strategies of MN-based electrocatalysts. Finally, we provide an outlook for the future development of MNs in the high-throughput seawater electrolysis field and highlight key issues that require further research and optimization.

Sputter-Deposited Binder-Free Nanopyramidal Cr/γ-Mo2N TFEs for High-Performance Supercapacitors

Due to their outstanding power density, long cycle life and low cost, supercapacitors have gained much interest. As for supercapacitor electrodes, molybdenum nitrides show promising potential. Molybdenum nitrides, however, are mainly prepared as nanopowders via a chemical route and require binders for the manufacture of electrodes. Such electrodes can impair the performance of supercapacitors. Herein, binder-free chromium (Cr)-doped molybdenum nitride (Mo₂N) TFEs having different Cr concentrations are prepared via a reactive co-sputtering technique. The Cr-doped Mo₂N films prepared have a cubic phase structure of γ-Mo₂N with a minor shift in the (111) plane. While un-doped Mo₂N films exhibit a spherical morphology, Cr-doped Mo₂N films demonstrate a clear pyramid-like surface morphology. The developed Cr-doped Mo₂N films contain 0-7.9 at.% of Cr in Mo₂N lattice. A supercapacitor using a Cr-doped Mo₂N electrode having the highest concentration of Cr reveals maximum areal capacity of 2780 mC/cm², which is much higher than that of an un-doped Mo₂N electrode (110 mC/cm²). Furthermore, the Cr-doped Mo₂N electrode demonstrates excellent cycling stability, achieving ~ 94.6% capacity retention for about 2000 cycles. The reactive co-sputtering proves to be a suitable technique for fabrication of binder-free TFEs for high-performance energy storage device applications.

Recent Advances on Pt-Free Electro-Catalysts for Dye-Sensitized Solar Cells

Since Prof. Grätzel and co-workers achieved breakthrough progress on dye-sensitized solar cells (DSSCs) in 1991, DSSCs have been extensively investigated and wildly developed as a potential renewable power source in the last two decades due to their low cost, low energy-intensive processing, and high roll-to-roll compatibility. During this period, the highest efficiency recorded for DSSC under ideal solar light (AM 1.5G, 100 mW cm-2) has increased from ~7% to ~14.3%. For the practical use of solar cells, the performance of photovoltaic devices in several conditions with weak light irradiation (e.g., indoor) or various light incident angles are also an important item. Accordingly, DSSCs exhibit high competitiveness in solar cell markets because their performances are less affected by the light intensity and are less sensitive to the light incident angle. However, the most used catalyst in the counter electrode (CE) of a typical DSSC is platinum (Pt), which is an expensive noble metal and is rare on earth. To further reduce the cost of the fabrication of DSSCs on the industrial scale, it is better to develop Pt-free electro-catalysts for the CEs of DSSCs, such as transition metallic compounds, conducting polymers, carbonaceous materials, and their composites. In this article, we will provide a short review on the Pt-free electro-catalyst CEs of DSSCs with superior cell compared to Pt CEs; additionally, those selected reports were published within the past 5 years.

Advanced Inorganic Nitride Nanomaterials for Renewable Energy: A Mini Review of Synthesis Methods

Inorganic nitride nanomaterials have attracted widespread attention for applications in renewable energy due to novel electrochemical activities and high chemical stabilities. For different renewable energy applications, there are many possibilities and uncertainties about the optimal nitride phases and nanostructures, which further promotes the exploration of controllable preparation of nitride nanomaterials. Moreover, unlike conventional nitrides with bulk or ceramic structures, the synthesis of nitride nanomaterials needs more accurate control to guarantee the target nanostructure along with the phase purity, which make the whole synthesis still a challenge to achieve. In this mini review, we mainly summarize the synthesis methods for inorganic nitride nanomaterials, including chemistry vapor deposition, self-propagation high-temperature synthesis, solid state metathesis reactions, solvothermal synthesis, etc. From the perspective of nanostructure, several novel nitrides, with nanostructures like nanoporous, two-dimensional, defects, ternary structures, and quantum dots, are showing unique properties and getting extensive attentions, recently. Prospects of future research in design and synthesis of functional inorganic nitrides are also discussed.

Performance evaluation of a low-cost, novel vanadium nitride xerogel (VNXG) as a platinum-free electrocatalyst for dye-sensitized solar cells

A vanadium nitride xerogel (VNXG) was synthesised by a simple and effective method of ammonialising a vanadium pentoxide xerogel at a higher temperature. Xerogel-structured materials possess salient features such as high surface area, tunable porosity and pore size that result in enhancing the catalytic activity by a fast electron-transport pathway and increase electrolyte diffusion channels. Metal nitrides are reported as promising alternate low-cost counter electrodes to replace the conventional and expensive platinum (Pt) counter electrode. Though few studies are reported on aerogel-based CEs for DSSCs, the present work is the first attempt to synthesize and evaluate the performance of xerogel-structured metal nitrides as counter electrode materials for dye-sensitized solar cells. The synthesized material was well characterized for its structural and morphological characteristics and chemical constituents by photoelectron spectroscopy. Finally, the VNXG was tested for its electrocatalytic performance as a choice of counter electrodes for dye-sensitized solar cells (DSSCs). The photo-current studies were performed under standard 1 SUN, class AAA-simulated illumination with AM1.5G. The consolidated results revealed that the vanadium nitride xerogel exhibited good photocatalytic activity and low charge transfer resistance. This identified it as a promising low-cost counter electrode (CE) material for dye-sensitized solar cells. The photo-current conversion efficiency of the vanadium nitride xerogel CE-based DSSC reached 5.94% comparable to that of the conventional thermal decomposed Pt CE-based DSSC, 7.38% with the same iodide/triiodide electrolyte system. Moreover, the 28 days stability study of VNXG CE DSSCs provided an appreciably stable performance with 37% decrement in the PCE under the same test condition.

Cost-Effective Synthesis of Efficient CoWO4/Ni Nanocomposite Electrode Material for Supercapacitor Applications

In the present study, the synthesis of CoWO4 (CWO)-Ni nanocomposites was conducted using a wet chemical method. The crystalline phases and morphologies of the Ni nanoparticles, CWO, and CWO-Ni composites were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDAX). The electrochemical properties of CWO and CWO-Ni composite electrode materials were assessed by cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) tests using KOH as a supporting electrolyte. Among the CWO-Ni composites containing different amounts of Ni1, Ni2, and Ni3, CWO-Ni3 exhibited the highest specific capacitance of 271 F g-1 at 1 A g-1, which was greater than that of bare CWO (128 F g-1). Moreover, the CWO-Ni3 composite electrode material displayed excellent reversible cyclic stability and maintained 86.4% of its initial capacitance after 1500 discharge cycles. The results obtained herein demonstrate that the prepared CWO-Ni3 nanocomposite is a promising electrode candidate for supercapacitor applications.

3D porous nanostructured Ni3N-Co3N as a robust electrode material for glucose fuel cell

Metal nitrides are broadly applicable in the field of electrochemistry due to their excellent electrical properties. In this study, a 3D nanostructured Ni₃N-Co₃N catalyst was prepared by using a versatile urea glass method, and was tested as an anode catalyst for a glucose fuel cell. The synthesized Ni₃N-Co₃N exhibits uniform particle dispersion in structure, morphology, and composition, and has a interpenetrating three-dimensional network structure. Notably, the Ni₃N-Co₃N significantly improved the catalytic activity of glucose oxidation compared to Ni₃N, Co₃N, and conventional activated carbon electrodes. The superior electrochemical performance could be attributed to its porous structure and unique properties, which provided a fast transport network for charge and mass transfer as well as good synergetic effect. The glucose fuel cell equipped with a Ni₃N-Co₃N anode achieved 30.89 W m^-2 power and 97.66 A m^-2 current densities at room temperature. This investigation provides potential directions for the design of cost-effective bimetallic catalysts for a wide range of glucose fuel cell applications.

Recent Progress in the Design and Synthesis of Nitrides for Mesoscopic and Perovskite Solar Cells

With growing concerns about global warming and the energy crisis, a variety of photovoltaic devices have attracted worldwide attention as alternative energy sources. Among them, organic-inorganic hybrid photovoltaics, typically mesoscopic and perovskite solar cells, are promising, owing to their potential for low-cost energy production, which mainly comes from unlimited combinations of materials optimized for each step of solar energy conversion. However, the commercialization of organic-inorganic hybrid solar cells is hampered by costly electrocatalysts or hole-transport materials. Currently, state-of-the-art dye- or quantum-dot-sensitized solar cells and perovskite solar cells necessitate noble metals and high-price polymeric materials. In an attempt to resolve this issue, various kinds of metal compounds have been investigated, and nitrides have been actively reported to possess a number of favorable properties for the aforementioned purpose, such as excellent electrical conductivity and superb electrocatalytic performance. Herein, the use of nitrides as cost-effective electrocatalysts or hole-transport materials in organic-inorganic hybrid solar cells is reviewed. Nitrides with a variety of morphologies and scales are discussed, together with the synergistic effect in the case of diverse composites. In addition, prospects and challenges for applying nitride materials are briefly suggested.

A high-performance asymmetric supercapacitor designed with a three-dimensional interconnected porous carbon framework and sphere-like nickel nitride nanosheets

The novel asymmetric supercapacitor was assembled based on a three-dimensional (3D) interconnected porous carbon framework as the negative electrode and 3D sphere-like nickel nitride nanosheets as the positive electrode in aqueous electrolyte.