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An electrochemical nitrogen reduction reaction (ENRR) is considered a promising alternative for the traditional Haber-Bosch process. In this study, we present a method for improving the ENRR by controlling the wettability of the catalyst surface, suppressing the hydrogen evolution reaction (HER) while facilitating N

This review summarizes recent advances in synthesis strategies, structural engineering, and unique properties of transition metal nitrides, along with the critical discussion on electrode designs for supercapacitors to meet commercial standards.

The electrochemical approach for the feasible ammonia production via N2 fixation is well-thought-out to be an eco-friendly strategy to replace the polluting Haber Bosch process. However, the impeding activation barrier of strong N≡N and the competing hydrogen evolution reaction constrain the Faradaic efficiency of the electrochemical nitrogen reduction reaction. Therefore, the implication of innovative strategies for designing an active electrocatalyst remains a crucial criterion to deliver operational efficiencies during electrochemical reactions. This study proposes a unique fabrication of three-dimensional (3D)-architectured electrodes encompassed with cobalt-rich tungsten carbide (Co-WC) as an electrocatalyst using a 3D-printing technique for the efficient electrochemical nitrogen reduction reaction. Here, the cobalt acts as a binder between tungsten carbide particles after sintering, and the particles are bonded to each other. The 3D-printing process generates 3D-architectured Co-WC electrodes with an average particle size of 1–3 µm through precise control of printing parameters. The electrochemical performance of the 3D-architectured Co-WC electrode reveals a better selectivity for N2 reduction under ambient condition. Substantially, the 3D-architectured Co-WC electrodes demonstrate an improved ammonia yield rate of 34.61 μg h−1 cm−2 and Faradaic efficiency of 2.12% at an applied potential − 0.6 V (vs. RHE). 3D-printing techniques can be an effective design method for manufacturing 3D-architectured active material with superior performance and selectivity.

A key challenge in photoelectrochemical water-splitting is the development of photoanodes with improved chemically active and optically efficient. While various nanostructures in heterogeneous materials have been investigated as a potential electrode, existing structures/compositions are still insufficient to meet such demand. Here, we report a scalable strategy to fabricate photoanodes with a nanotubular structure using CdS–TiO2 heterogeneous composite as a model system. Precisely, a ~5 μm thick nanotubular CdS–TiO2 heterostructure is developed on fluorine-doped tin oxide glass by hydrothermal etching and successive ionic layer deposition process. An electron microscopy analysis confirms that the formation of TiO2 nanotubes in the preferential etching direction of [001] as well as uniform coating of the CdS light-absorber layer. We note that the CdS coated on TiO2 nanotubes shows a photocurrent density of 6.9 mA/cm2 at 1.23 VRHE, which is ~2 times higher than that of CdS- nanorod TiO2 heterostructured photoanode. The elemental and optical analysis reveals that the structural modification and sufficient CdS deposition captures a wide range of light absorption from 300 to 550 nm. Our results suggest that an effective fabrication method is applicable for electrodes in numerous energy conversion devices, providing an increase in surface area, light absorption, and chemical stability.

To enhance the efficiency of hydrogen production, bimetallic oxides with spinel structures, M2GeO4 (M = Fe, Co), were synthesized via a facile one-pot hydrothermal method and were used as electrocatalysts for urea-assisted water electrolysis. In alkaline electrolyte with urea, Fe2GeO4, which was used as the anode in the electrolysis cell, exhibited a lower potential (1.53 V (vs. RHE)) and a smaller Tafel slope (76 mV dec−1) Co2GeO4 (1.65 V (vs. RHE), 79 mV dec−1), indicating that Fe2GeO4 reduced the overall input potential to produce H2. The superior performance of Fe2GeO4 in the urea-added water electrolysis was attributed to the higher oxidation state of its metal cations, larger electrochemical active surface area, and lower charge transfer resistance than those of Co2GeO4. Hence, Fe2GeO4 showed 5.49 times higher H2 peak intensity than Co2GeO4, indicating higher efficiency of H2 production.

Texturing, i.e., preferentially oriented deposition of a film with a specific crystallographic direction, enables the manipulation of the charge transport properties and surface reactivity of photoelectrodes for solar water-splitting. The advancement of solar water-splitting systems under neutral conditions is a vital strategy to reduce the economic and ecological traits of the prevailing strong acid or alkaline-based solar water-splitting systems. However, the photoelectrodes have to endure cumulative barriers in neutral media to convalesce the performance of the neutral solar water-splitting system. The implication of texturing in materials enforces the synergistic effect that is essential to confine the barriers to improve the performance of the photoelectrodes in eco-friendly neutral pH conditions. Here, we synthesized tungsten trioxide (WO3) films to achieve a columnar-type nanostructure with (0 2 0) texture, through a laser ablation deposition. Specifically, we modulated both deposition temperature and working pressure, enabling the (0 2 0) textured deposition of films, as well as the fine-tuning of the surface morphology. With optimized fabrication conditions, the (0 2 0)-textured WO3 film (thickness: 3.6 µm) showed improved photoelectrochemical water-oxidation performance, and the photocurrent density was ~3 mA/cm2 at 1.23 V versus reversible hydrogen electrode in an economic and ecological neutral condition. The WO3 films were further characterized using various methods, namely a UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and Hall Effect measurements. Based on the measured film characteristics, we attributed enhanced charge transport and transfer characteristics to the (0 2 0)-texturing, and the formation of the optimal amount of oxygen vacancies.

The electrochemical reaction that involves the splitting of water into hydrogen and oxygen gas is the superior technique for sustainable energy conversion and storage without the environmentally damaging effects of fossil fuels. To date, a large number of electrocatalysts have been used for electrochemical water splitting (EWS). Nowadays, the quest for a universal pH stable bifunctional electrocatalyst that can efficiently enhance the hydrogen and oxygen evolution reactions (HERs and OERs) is gaining significant interest in the research community. This approach avoids the divergence in the pH of the electrolyte for OER and HER activity and effectively reduces the difficulty and system cost in practical EWS. This article highlights engineering strategies and challenges in designing prospective universal pH-stable electrocatalysts with feasible OER and HER pathways for full water splitting over a wide pH range.

The development of sustainable energy conversion and storage systems is on demand to ease the energy needs and restrict environmental pollution. Here, we account a unique multifunctional flake-like CoS deposited over the flexible carbon cloth (CoS@CC) by a facile hydrothermal technique. The single-phase hexagonal structured CoS@CC with high crystallinity was identified through the XRD analysis. The morphological feature portrays the uniform distribution of flake-like CoS over carbon cloth. The electrocatalytic properties of the prepared flake-like CoS (CoS@CC) suggests improved electroactivity of requiring minimal overpotentials of 280 mV (OER) and 264 mV (HER) to accomplish a pre-eminent current density of 20 mA cm−2. In addition, a lab-scale water splitting system was projected to achieve a current density of 10 mA cm−2 with a low cell voltage of 1.65 V. In view to driving the fabricated water splitting system, a flexible (CoS@CC||rGO) supercapattery was fabricated to deliver an improved specific energy of 38 Wh kg−1 at a superior specific power of 533 W kg−1. Therefore, the prepared CoS@CC electrode with improved flexibility, useful catalytic activity, expressive kinetics, and resilient strength serves as a multifunctional material for prospective energy conversion and storage systems.

The integration of energy conversion and storage systems such as electrochemical water splitting (EWS) and rechargeable zinc-air battery (ZAB) is on the vision to provide a sustainable future with green energy resources. Herein, a unique strategy for decorating 3D tetragonal CoMn

Turning trash into treasure, the present work divulges the preparation of onion-like porous carbon derived out of the most malignant invasive weed, the Prosopis juliflora. The pods of the Prosopis juliflora are treated hydrothermally and chemically activated using KOH. The effect of activation temperature on the pore formation is investigated to obtain the desired porous carbon. The prepared porous carbon (J–800) has a significant specific surface area of 967 m2 g−1 with unique morphology of onion-like nanostructures and provided a sensible specific capacitance of 274 F g−1 at 1.3 A g−1 in H2SO4 electrolyte. Further, the performance of the device is effectually enhanced by adding KI as redox additive. Interestingly, the increased cell voltage (1.4 V) and improved cell capacitance of 588 F g−1 is obtained. Ultimately, a superior energy density of 35.7 Wh kg−1 at an enhanced power density of 971 W kg−1 is also obtained in the redox additive based aqueous electrolyte. A detailed investigation of the surface storage mechanism is discussed, and the stability of the prepared supercapacitors is also demonstrated. Thus, the most eradicable eco-threat P. juliflora is successfully reformed into an efficient electrode material for the energy storage application.

In this work, a facile single-step hydrothermal technique is used to prepare a spherically concomitant foamy NiCoP as positrode for supercapatteries. Similarly, the nitrogen-doped carbon nanofibers are prepared by simple electrospinning technique to use as negatrode. The prepared materials are raptly examined through primary studies for both energy conversion and storage applications. Fascinatingly, NiCoP electrode encourages oxygen evolution reaction, and the carbon nanofiber electrode emboldens hydrogen evolution reaction with the minimum overpotential of 257 mV and 160 mV, respectively. In addition, a supercapattery is designed and operated at a full voltage window of 1.6 V using the fusion of carbon nanofiber as the negatrode and the cutting-edge NiCoP as the positrode, which presents a superior energy (56 Wh kg−1) and an improved power density (5333 W kg−1) with a long cyclic stability (5000 cycles). Finally, the fabricated supercapattery device is used to power the constructed hybrid water electrolyser that requisites a low cell voltage of 1.71 V to afford a current density of 10 mA cm−2. Overall, the prepared electrodes reveal its superiority of handling the multifunctional challenges for both water electrolyzer and supercapatteries.

Carbon-based materials are considered to be promising cadidates for energy storage systems because of their superior conductivity, low price, and high specific surface area. Moreover, heteroatom-doped graphene or graphitic carbons are prepared by various methods for modulating their physicochemical properties, improving their wettabililty, and achieving favorable pseudocapacity for use in electrochemical supercapacitors. Here we report a simple solvent-free scale-up technique to synthesis fluorine-doped graphene oxide (FGO) by direct plasma treatment of graphene oxide (GO) powder at ambient pressure. The FGO enabled fast electrochemical charge transfer and provided a large number of active sites for redox reactions during supercapacitor operation, and the mechanisms were thoroughly studied by various electrochemical analyses. As a result, fabricated symmetric supercapacitor using FGO electrodes exhibited a maximum power density (~3200 W/kg) and energy density (~25.87 Wh/kg) with superior cycle stability (20000 cycles) without capacitance loss. Furthermore, the computational calculation results clarified the roles of semi-ionic C–F bonding of FGO: huge charge accumulation on the electrodes and superior electrical conductivity. Thus, our study demonstrates a facile strategy to develop promising functionalized materials, which can enhance the viability of supercapacitor for the next generation of energy storage systems.

Herein, discrete gamma-KCoPO4 nanocrystals were prepared by a facile, green and fast sol-gel route. The lattice parameters as well as positional and displacement parameters of atoms in the average gamma-KCoPO4 structure with a space group of P2(1)/n were calculated using full profile Rietveld refinement. Monodispersed quadrangular gamma-KCoPO4 nanocrystals with improved phase purity and crystallinity were found through XRD patterns and HRTEM images. Subsequently, the prepared gamma-KCoPO4 nanocrystals were tested as electrode material for supercapatteries in aqueous electrolytes. The gamma-KCoPO4 electrode shows superior specific charge capacity of 309 C g(-1) at 1 mV s(-1) in 1 M KOH, compared to 1 M NaOH (222 C g(-1)) and 1 M LiOH (77 C g(-1)). Further, it exhibits improved electrochemical activity by delivering an impressive specific charge capacity of 100 C g(-1) at a current of 0.6 mA cm(-2) in an aqueous electrolyte medium with acceptable capacity retention. A lab-scale supercapattery was assembled resembling the commercial device. The fabricated device delivered an enhanced specific energy of 28 W h kg(-1) and a specific power of 1600 W kg(-1) and prolonged cycle life of about 5000 cycles.

Featured with superior structural stability and highest redox potential, the olivine LiCoPO4 parades itself as a conceit battery-type material. To deploy its foot in the field of hybrid supercapacitors a series of LiCoPO4 with three contrasting morphologies were achieved. The evolution of morphology from clustered microspheres to elongated rods and multifaceted submicronic particles has an appreciative effect on the particle size and electrochemical properties. Endowed with distinct qualities such as high crystallinity, and multifaceted morphology, LiCoPO4 prepared at alkaline pH provides a superior specific capacity of 381 C g−1 (1060 F g−1) at 1 mV s−1 and a maximum discharge specific capacity of 253 C g−1 (631 F g−1) at 0.6 mA cm−2. The fabricated hybrid supercapacitor using prepared LiCoPO4 at the pH-12 condition as a battery type positive electrode and Fe2O3 as the negative electrode provides a grander energy density of 18 Wh kg−1 at an enhanced power density of 443 W kg−1 with a sustained cyclic performance for about 5000 cycles.

Charge storage in supercapacitors is strongly related to the bond characteristics and electronic structure of electrode materials. Graphene-based materials are widely used in a supercapacitor due to the easily tunable properties and high surface/volume ratios. However, we claim that the typical covalent bond characteristics of 2D carbon materials originating from this 2pπ orbital is not very suitable to the application in supercapacitor. Here, we suggest an efficient way to improve the supercapacitor performance by tuning the covalency of bonding between the graphene-based electrode and potassium ion. We, for the first time, also introduce a simple solvent-free scale-up doping technique to prepare fluorine-doped graphene oxide (FGO) by direct plasma treatment on graphene oxide (GO) powder at ambient pressure. The FGO enabled fast electrochemical charge transfer and provided a large number of active sites for redox reactions during supercapacitor operation, and those mechanisms were thoroughly studied by various electrochemical analyses. As a result, the fabricated symmetric supercapacitor using FGO electrodes exhibited a maximum power density (~3200 W/kg) and energy density (~25.87 Wh/kg) with superior cycle stability (20000 cycles) without capacitance loss. Furthermore, the computational calculation results clarified the roles of semi-ionic C–F bonding of FGO: huge charge accumulation on the electrodes and superior electrical conductivity. Thus, our study demonstrates a facile strategy to develop promising functionalized materials, which can enhance the viability of supercapacitor for the next generation of energy storage systems.

The present work reports the preparation of olivine structured LiNiPO4 nanoparticles through sol-gel thermolysis method using three different chelating agents of citric acid (LiNi-C), l -ascorbic acid (LiNi-A) and D-sorbitol (LiNi-S). The flame temperature and enthalpy change of each reaction using the chelating agent is calculated. Further, the sharp X-ray diffraction peak reveals the phase pure and high crystalline nature of the prepared LiNiPO4 nanoparticles with the space group of Pnma (62) irrespective of the chelating agents. The four possible fundamental vibrations of phosphate anion PO43− are revealed through Fourier Transform Infrared Spectroscopy (FTIR) studies. The presence of elements such as Ni, P and O and its valence state is identified through X-Ray Photoelectron Spectroscopy analysis. The spherical shape particles with the uniform size distribution of LiNi –S is observed than the LiNi-C, LiNi-A particles through FESEM analysis. The redox peaks and plateau regions in the cyclic voltammetry (CV) and Galvanostatic charge-discharge (GCD) profiles infer the dominance of battery-type charge process rather than a capacitive mechanism. As a result, LiNiPO4 exhibits a maximum specific capacitance of 417 F g−1 at 2 mV s−1 and 357 F g−1 at 1 mA cm−2 in 1 M LiOH, which enables as a suitable cathode material for hybrid supercapacitor. Also, the assembled hybrid supercapacitor delivered a high energy density of 12.5 Wh kg−1 at 200 W kg−1 as well as a longer cycle life of 89% at a current density of 1 mA cm−2 over 2000 cycles is noticed. These results infer that LiNiPO4 could be used as a novel electrode material for hybrid supercapacitor application.

Battery type electrodes would replace the currently available pseudocapacitive electrodes by the cause of high energy density and long discharge time. In this regard, battery type carbon coated CoFe2O4 spherical nanoparticles is prepared by the facile hydrothermal method and tested as the possible negative electrode for supercapattery applications. The phase purity, electronic states of elements, and the presence of carbon is inferred through various sophisticated techniques. The calculated surface area of CoFe2O4 and carbon coated CoFe2O4 are found to be 9 and 26 m2 g−1, respectively. The morphological analysis confirms the formation of uniform CoFe2O4 nanospheres (∼25 nm) with a thin layer of carbon coating (∼2 nm). The amorphous carbon coating over CoFe2O4 nanosphere is identified via high-resolution transmission electron microscope. The observed peak and plateau regions in the cyclic voltammogram and galvanostatic charge/discharge curves reveals the battery-type charge storage behaviour of the material. The carbon coated CoFe2O4 delivers the maximum length capacitance of 9.9 F m−1 at 1 mV s−1 with a useful lifespan over 5000 cycles. The electrochemical impedance spectroscopy reveals that the carbon-coated CoFe2O4 delivers the low charge transfer resistance than CoFe2O4. Further, the fabricated supercapattery provides the energy density of 160 × 10−8 Wh cm−1 at a power density of 67.2 μW cm−1. As well as, the device shows 93% of coulombic efficiency and 75% of the specific capacitance retention over 11,000 cycles. Overall, it is believed that the carbon-coated CoFe2O4 can serve as a good candidate for flexible supercapatteries.

A unique multifunctional electrode made of well-defined highly crystalline Ni–P nanoparticles interweaved apiece to form sponge-like structure prepared by the single-step hydrothermal method. The distinct phases of interlinked nanospherical Ni–P compounds (Ni2P, Ni2P/Ni12P5, and Ni12P5) were obtained at 140 °C with different reaction time periods. The Ni2P exhibits supreme specific capacity of 206 mA h g–1 (1354 F g–1) at 5 mA cm–2, which seems to be the highest among the Ni2P reported so far. Biomass-derived activated carbon was prepared as a negative electrode (135 F g–1 at 1 mA cm–2) to fabricate a flexible supercapattery gadget, which delivered remarkable energy density and power density of 42 W h kg–1 and 2856 W kg–1 respectively, at 3 mA cm–2 even after 10000 cycles. The Ni–P coated carbon cloth has shown immense mechanical strength and durability, which was tempting to use for electrocatalytic application. Both oxygen evolution reaction and hydrogen evolution reaction trials resulted in the evoluti...

Biosynthesis of silver nanoparticles has received considerable attention due to their cost-effective, eco-friendly and medicinal values. In this study, silver nanoparticles (Ag NPs) were synthesised using the aqueous leaf extracts of Piper nigrum. TEM images revealed that the particle is spherical with 20–50 nm in size. Furthermore, to evaluate the toxicity of synthesized Ag NPs, fish Labeo rohita were exposed to two different concentrations (2.5 µg/L as the treatment I and 5 µg/L as treatment II) for 35 days, and antioxidant parameters and histology of gill, liver and kidney were examined. A biphasic response in the activity of glutathione S-transferases (GST) was observed in gill and liver of fish. GST activity in the kidney of fish was significantly increased when compared to control group. Glutathione reductase (GR) activity in organs/tissue of fish were found to be increased while peroxidase (POD) activity was significantly decreased. Histopathological changes such as hyperplasia, proliferation of epithelial cells and fusion of lamellae were observed in both the concentrations. In liver, necrosis, nuclear degeneration and dilation of sinusoids were observed. Subsequently, the representative effects of POD activity were assessed based on the Box–Behnken Equation, 3-D contour plot and ANOVA analysis through response surface methodology analysis.

For the fabrication of aqueous Li-ion hybrid supercapacitor, carbon coated LiCo1/3Ni1/3Mn1/3O2 (or LiCo1/3Ni1/3Mn1/3O2@C composite) is synthesized by polymeric precursor method with subsequent thermal decomposition procedures for carbon coating. Graphene like porous carbon is obtained by chemical activation from the biomass of Agave Americana. The XRD analysis reveals that LiCo1/3Ni1/3Mn1/3O2 is having a hexagonal layered structure and activated carbon exists in both amorphous and graphitic nature. The TEM image infers that LiCo1/3Ni1/3Mn1/3O2 particles having the non-uniform shape with sub-micron size and the LiCo1/3Ni1/3Mn1/3O2 particles are embedded into amorphous carbon cloud in the composite. The activated carbon shows the specific surface area of 1219 m2 g−1. Finally, the fabricated aqueous LiCo1/3Ni1/3Mn1/3O2@C‖AC hybrid supercapacitor delivers the specific capacitance of 56 F g−1 with good capacity retention even after 5000 cycles.

The integration of energy conversion and storage systems such as electrochemical water splitting (EWS) and rechargeable zinc-air battery (ZAB) is on the vision to provide a sustainable future with green energy resources. Herein, a unique strategy for decorating 3D tetragonal CoMn2 O4 on carbon cloth (CMO-U@CC) via a facile one-pot in situ hydrothermal process, is reported. The highly exposed morphology of 3D tetragons enhances the electrocatalytic activity of CMO-U@CC. This is the first demonstration of such a bifunctional activity of CMO-U@CC in an EWS system; it achieves a nominal cell voltage of 1.610 V @ 10 mA cm-2 . Similarly, the fabricated rechargeable ZAB delivers a specific capacity of 641.6 mAh gzn-1 , a power density of 135 mW cm-2 , and excellent cyclic stability (50 h @ 10 mA cm-2 ). Additionally, a series of flexible solid-state ZABs are fabricated and employed to power the assembled CMO-U@CC-based water electrolyzer. To the best of the authors' knowledge, this is the first demonstration of an in situ-grown binder-free CMO-U@CC as a flexible multifunctional electrocatalyst for a built-in integrated rechargeable ZAB-powered EWS system.