Ni Molar Ratio Research Articles

Observed kinetics for the production of diethyl carbonate from CO2 and ethanol catalyzed by CuNi nanoparticles supported on activated carbon

Monometallic and bimetallic Cu:Ni catalysts with different Cu:Ni molar ratios (3:1, 2:1, 1:1, 1:2, 1:3) were synthesized by wetness impregnation on activated carbon and characterized by TPR (temperature programmed reduction), XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy). The synthesized catalysts were evaluated in the gas phase production of diethyl carbonate from ethanol and carbon dioxide. The largest catalytic activity was obtained over the bimetallic catalyst with a Cu:Ni molar ratio of 3:1. Its improved activity was attributed to the formation of a Cu–Ni alloy on the surface of the catalyst, evidenced by XPS and in agreement with a previous assignment based on Vegard law and TPR analysis. During the reaction rate experiments, it observed the presence of a maximum of the reaction rate as a function of temperature, a tendency also reported for other carbon dioxide–alcohol reactions. It showed that the reaction rate-temperature data can be adjusted with a reversible rate equation. The initial rate as a function of reactant partial pressure data was satisfactorily adjusted using the forward power law rate equation and it was found that the reaction rate is first order in CO2 and second order in ethanol.

3D Nickel–Manganese bimetallic electrocatalysts for an enhanced hydrogen evolution reaction performance in simulated seawater/alkaline natural seawater

In this paper, we report an inexpensive one-step synthesis of self-supported 3D nickel-manganese (NiMn) bimetallic coatings and their application for the hydrogen evolution reaction in simulated seawater (1 M KOH + 0.5 M NaCl) and alkaline natural seawater (1 M KOH + natural seawater). These binary coatings were electrodeposited on a titanium substrate using a facile electrochemical deposition method by a dynamic hydrogen bubble template technique. The as-deposited NiMn coatings with variable Mn amounts produce typical globular and unique porous architecture with abundant pores of different sizes. The activity of these fabricated catalysts towards the hydrogen evolution reaction was investigated by linear sweep voltammetry towards simulated seawater and alkaline natural seawater at different temperatures. The surface morphology and composition of the catalysts were also characterized by scanning electron microscopy and inductively coupled plasma optical emission spectroscopy. The as-prepared NiMn/Ti electrocatalyst, which was electrodeposited using a chemical bath containing Ni2+ and Mn2+ ions with a molar ratio of Ni2+:Mn2+ = 1:5, exhibits excellent hydrogen evolution activity in simulated seawater with an ultra-low overpotential of 64.2 mV to reach a current density of 10 mA cm−2. It is noteworthy that this NiMn/Ti electrocatalyst also achieves a current density of 10 mA cm−2 in alkaline natural seawater with a comparably low overpotential of 79.3 mV. The current densities increase by ca. 1.75–2.35 times with an increase in temperature from 25 °C to 75 °C for hydrogen evolution in both electrolytes. This bimetallic catalyst has shown excellent long-term stability at a constant potential of −0.23 V (vs. RHE) and a constant current density of 10 mA cm−2 for 10 h, which ensures higher durability and robustness for practical application of seawater splitting technology.

Fe-Co-Ni trimetallic Prussian blue analogs with tunable electrochromic energy storage properties

Prussian blue (PB) and its analogs (PBAs) have become a research hotspot in the fields of electrochemical energy storage and electrochromism due to their good reversible redox activity, and reversible color change response in different redox states. Herein, a series of trimetallic PBAs (Co/NiHCF with Co to Ni molar ratios of 1:0, 3:1, 1:1, 1:3, and 0:1) are synthesized by a facile co-precipitation method. In particular, the impact of Co to Ni molar ratio on the lithium storage and electrochromic properties of Co/NiHCF materials are systemically investigated. All five samples possess good crystallinity but the particle size decreases with the reduction of Co/Ni molar ratio. The color change, redox reaction potential, and lithium storage activity of the samples can be readily controlled by adjusting the molar ratio of Co to Ni. The lithium storage activity of the samples strengthens with the increase of Ni content in Co/NiHCF, accompanied by a decrease in redox potentials. With the increase of Ni content, the color of the Co/NiHCF film in the oxidation state changes from purple-red to orange, and finally to yellow; in the reduction state, the color of the film changes from green to light green and then to colorless. All the samples exhibit superior rate capability, excellent cycling stability, and short switching time (in the range of 1.6 to 4.3 s). The present work demonstrates a facile strategy for readily tunning the lithium storage activity, redox reaction potentials, and realizing rich color changes of PBA-based bifunctional materials.

Role of citric acid in enhancing aromatic hydrogenation performance in Ni-HPW/SiO2 catalysts

In this study, we utilized a sol-gel method to prepare Ni-HPW/SiO2 catalysts with varying citric acid (CA):Ni molar ratios ranging from 0 to 5.0. The catalysts demonstrated different levels of activity in the hydrogenation of ethylbenzene, which correlated to their respective CA:Ni ratios. Introducing citric acid in the preparation process of nickel-based catalysts yielded mesopore formation and reduced NiO particle size, producing a more uniform NiO dispersion on SiO2, which was confirmed by BET, XRD, and TEM analyses. The results of H2-TPR, H2-TPD, NH3-TPD, and Py-IR analyses suggested that the addition of citric acid augmented the interaction between phosphotungstic acid (HPW), Ni species, and SiO2. Citric acid improved Ni species and HPW dispersion, fostering increased HPW-Ni species formation. This, in turn, generated additional electron-deficient Ni ions, stemming from semi-reduced HPW-Ni species, which acted as Lewis acid sites, enhancing Ni+ species effectiveness in activating aromatic rings. The better-dispersed, non-HPW-bound NiO, which, upon complete reduction to Ni, led to a substantial rise in H2 bond cleavage, thereby facilitating more hydrogen spillover. Overall, the infusion of citric acid into fabricating Ni-HPW/SiO2 catalysts sparked a significant surge in their aromatic hydrogenation ability.

One-step electrodeposited nickel phosphide electrode for pH-universal electrochemical hydrogen production

Herein, we describe the development and study of the relationship between the Ni molar ratio of amorphous nickel phosphide (Ni-P) electrodes synthesized via electrodeposition on Ni foam (NF) applied as a non-precious electrocatalyst for the Hydrogen Evolution Reaction (HER) in a pH-universal. The 3-Ni-P electrode displayed outstanding HER performance in alkaline, neutral, and acidic conditions with an overpotential of 69, 165, and 56 mV at –10 mA cm–2. Furthermore, the Ni-P films showed excellent stability under the different conditions studied. The optimized 3-Ni-P electrode performance was attributed to its granular structure with a large surface area, enabling good interaction with the electrolyte, which endorses the HER kinetics. These results are relevant concerning an adequate choice of stable catalyst material, easy to synthesize and capable of operating in a wide range of pH with high efficiency for HER.

Efficient transformation of plastic wastes to H2 and electromagnetic nanocarbon absorbents over molecular-level engineered 3D NiCo/MnO

The advancement in the pyrolysis-catalysis conversion of waste plastics is currently limited by three problematic issues, namely lack of efficient catalysts, ambiguous catalytic mechanism, and identification of a dedicated application of carbon nanocomposites. Herein, advanced bimetallic NiCo/MnO catalysts were developed via a molecular- and macroscale-level engineering strategy. The best conversion performance among all batches was achieved for a Co:Ni molar ratio of 1:1. When the plastic-to-catalyst ratio is 10.7:1, the H2 and carbon yields of polyethylene conversion reached 29.8 mmol/gplas and 42.2 wt%, respectively. Density functional theory simulations rationalized the activity of NiCo/MnO catalysts in the dehydrogenation of hydrocarbons. The resulting carbon nanocomposites demonstrated excellent electromagnetic absorption performance with an effective absorption bandwidth of the representative carbon nanocomposites/wax composite of 5.12 GHz and a minimal reflection loss lower than −45 dB. This work provides novel insights for developing advanced catalysts for the pyrolysis-catalysis conversion of waste plastics.

Excellent catalytic activity of NiPd/C nanocatalysts for anodic oxidation of methanol in alkaline media

In this study, nanocatalyst NiPd was synthesized via a successful two-stage reduction process with NaBH4 and PVP. More specifically, the first stage involves NaBH4 reduction of Ni2+ ion to metallic Ni. Afterwards, Pd would be coated on the surface of the aformentioned Ni particles by reducing Pd2+ using the remaining NaBH4. The effect of experimental parameters on the synthesis and catalytic activity of the nanocatalysts, such as reaction temperature (30, 40, 50, 60, 70 °C), reaction time (60, 90, 120, 150, 180 minutes), Pd:Ni mole ratio (1:10, 3:10, 5:10, 7:10, 9:10). were investigated by X-ray diffraction (XRD), Energy dispersive spectroscopy (EDX), and transmission electron microscopy (TEM) were used to analyse the surface structure, composition and morphology of the catalyst samples. The catalytic activity and stability of the resulting NiPd/C catalysts were investigated towards the methanol oxidation reaction (MOR) in alkaline environment by cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The results showed that the highest catalytic activity was found for the sample synthesized at 50 °C with 120-minute reaction time and the Pd:Ni molar ratio of 5:10. The influence of KOH and methanol concentrations on the catalytic activity of NiPd/C for methanol oxidation reaction in alkaline medium was also investigated. The results demonstrated the promising potential of NiPd/C nanomaterials as catalyst materials for the anodic layer in direct methanol fuel cells (DMFCs).

Wheat-like Ni-coated core–shell silver nanowires for effective electromagnetic wave absorption

Nowadays, developing high-performance electromagnetic functional materials to eliminate the ever-increasing electromagnetic pollution problem is necessary for the complex electromagnetic environment. However, the materials with high electrical conductivity are prone to secondary electromagnetic pollution due to interface impedance mismatching. Herein, the wheat-like electrically conductive and magnetic silver nanowire@nickle (AgNW@Ni) composites were fabricated via a one-pot in-situ growth method. The electromagnetic properties of the composites could be regulated by adjusting different ratios of precursors, resulting in various morphological features of the nanowire as the core with different Ni shell thicknesses. When the Ag and Ni molar ratio was 1:1.1, the AgNW@Ni composite exhibited the optimal minimum reflection loss (RLmin) of −61.1 dB with an adequate effective absorption bandwidth (EAB) of 4.06 GHz owing to good impedance matching, abundant heterostructures, and synergistic electrical and magnetic losses. Even after three months, it still maintained an acceptable RLmin value of −39.7 dB and similar EAB, demonstrating its long-term operational stability. This unique composite is expected to be applied in more actual electromagnetic protection occasions.

Efficient Nitrate Generation through Electrochemical N2 Oxidation with Nickel Oxyhydroxide Decorated Copper Hydroxide Driven by Solar Cells.

Electrocatalytic nitrogen oxidation reaction (NOR) into nitrate under ambient conditions, as an alternative to replace traditional industrial method, is a promising artificial N2 fixation strategy, especially powered by renewable energy. Here, through skillfully balancing competitive relationships between NOR and oxygen evolution reaction (OER), the nickel oxyhydroxide decorated Cu(OH)2 hybrid electrocatalyst with Cu:Ni molar ratio of 1:1 is developed, which achieves outstanding Faradaic efficiency (FE) of 18.7% and yield rate of 228.24µmolh-1 gcat -1 at 2.0V versus reversible hydrogen electrode (RHE) in the electrolyte of 0.1m Na2 SO4 . Also, the hybrid catalyst maintained over five cycles (10h each cycle) with negligible decay in performance. The synergetic effect between the components of nickel oxyhydroxide and Cu(OH)2 is found to remarkably activate N2 and suppress the activity of competitive OER, which enhances NOR performance eventually. Moreover, the conversion efficiency of solar-to-nitrate (STN) with 0.025%wasobtained by coupling with a commercial solar cell. This work provides a novel avenue of rational catalysts design strategies and realizes solar-to-nitrate synthesis.

The importance of constructing Triple-functional Sr2P2O7/Ni2P catalysts for smoothing hydrogenation Ring-rearrangement of Biomass-derived Furfural compounds in water

Rational design of catalysts with multi-function was of great importance for speeding mechanism-complicated heterogeneous reaction. Herein, a series of Sr-Ni-P catalysts characterized in (Sr2P2O7)m/Ni2P composite structure (Sr:Ni molar ratio m = 0.15–0.60) were prepared and investigated for hydrogenation ring-rearrangement of four biomass-derived Furfural compounds (FALs) to their Cyclopentanone derivatives (CPOs) in water. By properly manipulate m at 0.40, the superior and reproducible CPOs yields up to 96% were achieved under mild conditions in particular under low-pressure (0.1 MPa) H2. Chemical adsorption measurements disclosed that the attachment of Sr2P2O7 with Ni2P in nanoscale was crucial to construct triple-functional catalytic interface with modulated hydrogen activation (7.5–47.4 µmol/g), acid (196.4–327.3 µmol/g) and base (108.0–214.5 µmol/g) sites. H2-D2 exchange, H2-IR experiments and DFT simulation implied that H2 could be activated through heterolytic dissociation on Sr2P2O7 to participate in reaction; H218O, D2O, D2 isotope-label tracing experiments and DFT mechanism calculation further clarified that besides of H2, H2O was also frequently present in hydrogenation, ring opening, rearrangement and ring re-closing steps and acted as dual donors to provide H and O for CPO; in the favorable thermodynamic feature, a new pathway (with unsaturated dicarbonyl compound as key intermediate) achieved on Sr2P2O7/Ni2P was demonstrated to be more feasible than the reported pathway. The importance of the triple-functional Sr2P2O7/Ni2P catalytic interface for smoothing the aqueous hydrogenation transformation, in particular the function of base site for speeding the transformation was illustrated and discussed.

Bimetallic Cu–Ni core–shell nanoparticles anchored N-doped reduced graphene oxide as a high-performance bifunctional electrocatalyst for alkaline water splitting

Water electrolysis is regarded as the most promising method for developing sustainable energy technologies. However, low-cost bifunctional electrocatalysts with high efficacy and long-term stability are required to make this method economically viable. Core-shell nanoparticles, which comprise a thin layer of a catalytically active shell surrounding a subsurface core, have recently emerged as cutting-edge electrocatalysts for effective water electrolysis. Herein, we systematically fabricated distinct bimetallic Cu–Ni particles by tuning the Cu:Ni ratios, and then anchored them to an N-doped reduced graphene oxide (NRG) backbone for alkaline water splitting. A Cu:Ni molar ratio of 1:1 was determined to be optimal for forming an effective core–shell configuration, affording favorable adsorption energies toward reactants. The Cu–Ni(1:1) core–shell nanoparticles anchored NRG, termed Cu–Ni(1:1)@NRG, displayed excellent performance toward the H2 evolution reaction (HER) and oxygen evolution reaction (OER), with overpotentials at 10 mA cm−2 of 107 and 310 mV, respectively, versus a reversible hydrogen electrode (RHE). This current density (10 mA cm−2) was attained at a low cell voltage of 1.64 V when Cu–Ni(1:1)@NRG was used as the bifunctional electrocatalyst for alkaline water electrolysis. Furthermore, the Cu–Ni(1:1)@NRG electrocatalyst exhibited outstanding long-term stability in prolonged electrocatalytic studies at a constant current density.

Optimization of electromagnetic wave absorption properties of CoNi/MoSe2 composites with 3D flower-like by controlling the Co/Ni molar ratio

Developing composite materials with a rational composition structure has been a critical strategy to obtain superior electromagnetic (EM) wave absorption materials. CoNi/MoSe2 composites were synthesized by a two-step method in this work. Firstly, the flower-like MoSe2 was synthesized by hydrothermal method, and then the CoNi alloy was loaded on the MoSe2 surface by an electroless plating method. It is worth noting that in this paper, PdCl2 was not used for activation during the electroless plating process, and the flower-like structure of MoSe2 was not destroyed. In order to investigate the effect of different Co/Ni molar ratios on the absorption performance of the CoNi/MoSe2 composites, three samples with Co to Ni molar ratios of 1:3, 1:1, 3:1 and two other samples with only one metal (Ni or Co) were prepared. The analysis results show that the minimum reflection loss(RL) value of Ni/MoSe2 is −18.01 dB and the maximum effective absorption bandwidth(EAB) of Co/MoSe2 is 2.16 GHz. In comparison, the CoNi/MoSe2 composite exhibits the best EM wave absorption performance when the Co/Ni ratio is 1:3, and the minimum RL can reach −48.6 dB at a matching thickness of only 1.8 mm. And when the matching thickness is 1.4 mm, the broadest EAB is 3.76 GHz. Therefore, this work provides a new research idea for the design of broadband and efficient EM wave absorbers.

Preparation and coloring mechanism of cobalt-free black ceramic pigments from stainless steelmaking dust

In order to improve the recovery of Fe, Cr, Mn and Ni in stainless steel dust and efficiently recycle of stainless steel dust, this study supplies a novel method for the development of high-quality, low-cost and environmentally friendly cobalt-free black ceramic pigments. The results show that the optimal parameters for preparing the cobalt-free black ceramic pigments from stainless steelmaking dust are Fe/Cr/Mn/Ni molar ratio of 1:1:1:1 in the mixture of stainless steelmaking dust and chemical reagents, sintering temperature and holding time of 1125 °C and 30 min respectively, and cooling in the furnace to room temperature. Under this condition, the material undergoes high-temperature sintering reaction to produce Fe 3 O 4 , FeCr 2 O 4 and NiFe 2 O 4 , which results in the black color of prepared pigment. Meanwhile, the prepared pigments have uniform and superior coloring properties ( L* = +36.43, a* = +2.61, b*= +1.70 and C *= +3.11), which are better than those of commercial cobalt pigments.

Highly Dispersed Ni Nanoclusters Spontaneously Formed on Hydrogen Boride Sheets.

Hydrogen boride (HB) sheets are two-dimensional materials comprising a negatively charged hexagonal boron network and positively charged hydrogen atoms with a stoichiometric ratio of 1:1. Herein, we report the spontaneous formation of highly dispersed Ni nanoclusters on HB sheets. The spontaneous reduction reaction of Ni ions by the HB sheets was monitored by in-situ measurements with an ultraviolet-visible spectrometer. Acetonitrile solutions of Ni complexes and acetonitrile dispersions of the HB sheets were mixed in several molar ratios (the HB:Ni molar ratio was varied from 100:0.5 to 100:20), and the changes in the absorbance were measured over time. In all cases, the results suggest that Ni metal clusters grow on the HB sheets, considering the increase in absorbance with time. The absorbance peak position shifts to the higher wavelength as the Ni ion concentration increases. Transmission electron microscopy images of the post-reaction products indicate the formation of Ni nanoclusters, with sizes of a few nanometers, on the HB sheets, regardless of the preparation conditions. These highly dispersed Ni nanoclusters supported on HB sheets will be used for catalytic and plasmonic applications and as hydrogen storage materials.

Cu–Ni core–shell bimetallic cocatalyst decorated polymeric carbon nitride for highly efficient and selective methane production from photocatalytic CO2 reduction

The development of non-noble bimetallic cocatalysts for the efficient and selective CO2 photoreduction is extremely desirable yet challenging. Herein, we rationally synthesized a series of non-noble Cu–Ni bimetallic cocatalysts by varying the Cu and Ni molar ratios, and then, we decorated these cocatalysts on polymeric carbon nitride (CN) for photocatalytic CO2 reduction. Elemental distribution maps demonstrated that the Cu–Ni-11 bimetallic cocatalyst with a Cu:Ni molar ratio of 1:1 has a perfect core–shell configuration. Notably, this Cu–Ni-11 core–shell cocatalyst-decorated CN (Cu–Ni-11@CN) exhibited remarkable CO2 photoreduction activity for selective CH4 production, outperforming bare CN, Cu@CN, Ni@CN, and Cu–Ni-13@CN and Cu–Ni-31@CN catalysts with different metal proportions. Additionally, the Cu–Ni-11@CN catalyst was remarkably stable and durable over multiple test runs. The remarkable CO2 conversion activity and stability of the developed catalyst are predominantly due to the synergistic effect of the Cu–Ni-11 core–shell cocatalyst and CN, which affords significantly improved optical absorption, CO2 adsorption, and photoexcited charge separation. Therefore, the study results elucidate the rational design and development of non-noble bimetallic cocatalysts for photocatalytic CO2 conversion.

Comparative supercapacitive analysis of 2-methylimidazole derived cobalt nickel oxides (CoNiO2 and Co2NiO4) and subsequent fabrication of asymmetric supercapacitor devices

An attempt to pursue optimization study of a bi-metal organic framework derived cobalt nickel oxides has been demonstrated here to achieve best supercapacitive performance. The synthesis process was started with formation of Co-MOF by coordination of Co2+ metal ion with organic ligand 2-MeIM, following coordination of Ni2+ to the Co-MOF to construct Co2+ and Ni2+ dual metal coordinated organic cluster. The final oxides CoNiO2 (abbreviated as CNOa) and Co2NiO4 (abbreviated as CNOb), were obtained by breakdown of the organic moiety in a high temperature annealing process. While, the starting Co-MOF material yielded only Cs of 768 F g−1 (with 67% Cs retention after 8000 cycles) but the optimized CNOa with composition of Co: Ni molar ratio 1:1 revealed higher Cs of 1624 F g−1 with 86.5% Cs retention after 8000 cycles. The electrode material CNOb with Co:Ni molar ratio: 2:1 demonstrated Cs of 1329 F g−1 with 72.8% Cs retention. The superior specific capacitance, electrochemical reversibility and elevated cycle stability in CNOa was achieved from several positive virtues inherited in electrode material, such as: hierarchical nanoleaves with rough surface, bigger pore volume, thinner surface thickness of active material and definitely higher surface area. Two sets of asymmetric supercapacitor devices (CNOa//GNP, CNOb//GNP) were fabricated for comparison of the energy and power output. Superior energy density of 48.12 Wh Kg−1 was perceived from CNOa//GNP with commendable cycle stability of 92.8% whereas, CNOb//GNP delivered energy density of 40.18 Wh Kg−1 with 85.2% cycle stability experimented after 8000 GCD cycles.

Sm0.5Sr0.5Co1-xNixO3-δ-A Novel Bifunctional Electrocatalyst for Oxygen Reduction/Evolution Reactions.

The development of non-precious metal catalysts with excellent bifunctional activities is significant for air–metal batteries. ABO3-type perovskite oxides can improve their catalytic activity and electronic conductivity by doping transition metal elements at B sites. Here, we develop a novel Sm0.5Sr0.5Co1−xNixO3−δ (SSCN) nanofiber-structured electrocatalyst. In 0.1 M KOH electrolyte solution, Sm0.5Sr0.5Co0.8Ni0.2O3−δ (SSCN82) with the optimal Co: Ni molar ratio exhibits good electrocatalytic activity for OER/ORR, affording a low onset potential of 1.39 V, a slight Tafel slope of 123.8 mV dec−1, and a current density of 6.01 mA cm−2 at 1.8 V, and the ORR reaction process was four-electron reaction pathway. Combining the morphological characteristic of SSCN nanofibers with the synergistic effect of cobalt and nickel with a suitable molar ratio is beneficial to improving the catalytic activity of SSCN perovskite oxides. SSCN82 exhibits good bi-functional catalytic performance and electrochemical double-layer capacitance.

Doping of Ni in MIL-125(Ti) for enhanced photocatalytic degradation of carbofuran: Reusability of coated plates and effect of different water matrices

Nickel has been recently recognized as an efficient dopant to improve the electronic structure of metal-organic frameworks (MOFs). Herein, we prepared Ni-doped MIL-125(Ti) MOFs with different Ti: Ni molar ratios to evaluate the role of Ni in the improvement of photocatalytic degradation of carbofuran in different water matrices. The characterization of the TiNi MOF structure confirmed the successful incorporation of Ni2+ in the lattice structure of MIL-125(Ti). The molar ratio of 1:1 showed the highest degradation of carbofuran compared to pristine MIL-125(Ti) and mixed 2:1 TiNi MOF. We used the response surface methodology (RSM) to optimize the operating parameters of the photocatalytic reaction indicating that a pH of 11, irradiation intensity of 104.6 W/m2, and catalyst loading of 0.44 g/L were the optimal conditions. Furthermore, we employed the photocatalyst in a retained form by coating aluminum plates using polysiloxane to evaluate the reusability of the catalyst without needing a post-collection of nanoparticles. The effect of interfering species in different water matrices was investigated by conducting the photocatalytic reaction in different water backgrounds such as lake, tap, drain, and sea waters. The mechanism of photocatalytic oxidation was investigated by several scavenging experiments to identify the effective reactive oxidant species (ROS) and the degradation pathways were proposed by liquid chromatography coupled with tandem mass spectrometry LC/MS-MS. The toxicity of the generated intermediates was evaluated using the ecological structure activity relationships (ECOSAR) software.

Enhancement of the capacitance of rich-mixed-valence Co-Ni bimetal phosphide by oxygen doping for advanced hybrid supercapacitors

Tailoring of the electrode microstructure and its active components for the development of high-performance supercapacitors was rather indispensable to advance current technologies. Therefore, we fabricated a novel O-doped Co-Ni nanophosphide (O-CoxNiyP) with a porous structure. Our approach included the synthesis of 3D Co-Ni precursors with tunable Co/Ni ratio utilizing a phosphorization treatment. Our characterization results indicated that incorporating the optimized O content into CoxNiyP could tune its electronic structure and yield mixed valences of metals and P, which was beneficial to enhance electrochemical reactivity. The O-Co1Ni4P-based electrode with the 1:4 Co:Ni molar ratio manifested the best performance as demonstrated by its specific capacity, which was equivalent to 717.1 C/g (at 1 A/g). This value was significantly higher than those of other O-CoxNiyP family electrodes. The cycling stability of the electrode containing O-Co1Ni4P as an active material was found to be excellent: it demonstrated a 95.1% capacity retention after 5000 10 A/g cycles. We also assembled an asymmetric supercapacitor containing O-Co1Ni4P as a positive electrode material and commercial activated carbon as a negative electrode material. The device demonstrated very high energy density (47.5 Wh/kg) and 90.3% capacity retention after 10,000 cycles. These results established that our anion-doping method represented a novel strategy for improving the electrochemical performance of transition metal-based material. These discoveries were useful for energy storage applications.

Electrochemical Performance of Aluminum Doped Ni1−xAlxCo2O4 Hierarchical Nanostructure: Experimental and Theoretical Study

For electrochemical supercapacitors, nickel cobaltite (NiCo2O4) has emerged as a new energy storage material. The electrocapacitive performance of metal oxides is significantly influenced by their morphology and electrical characteristics. The synthesis route can modulate the morphological structure, while their energy band gaps and defects can vary the electrical properties. In addition to modifying the energy band gap, doping can improve crystal stability and refine grain size, providing much-needed surface area for high specific capacitance. This study evaluates the electrochemical performance of aluminum-doped Ni1−xAlxCo2O4 (0 ≤ x ≤ 0.8) compounds. The Ni1−xAlxCo2O4 samples were synthesized through a hydrothermal method by varying the Al to Ni molar ratio. The physical, morphological, and electrochemical properties of Ni1−xAlxCo2O4 are observed to vary with Al3+ content. A morphological change from urchin-like spheres to nanoplate-like structures with a concomitant increase in the surface area, reaching up to 189 m2/g for x = 0.8, was observed with increasing Al3+ content in Ni1−xAlxCo2O4. The electrochemical performance of Ni1−xAlxCo2O4 as an electrode was assessed in a 3M KOH solution. The high specific capacitance of 512 F/g at a 2 mV/s scan rate, 268 F/g at a current density of 0.5 A/g, and energy density of 12.4 Wh/kg was observed for the x = 0.0 sample, which was reduced upon further Al3+ substitution. The as-synthesized Ni1−xAlxCo2O4 electrode exhibited a maximum energy density of 12.4 W h kg−1 with an outstanding high-power density of approximately 6316.6 W h kg−1 for x = 0.0 and an energy density of 8.7 W h kg−1 with an outstanding high-power density of approximately 6670.9 W h kg−1 for x = 0.6. The capacitance retention of 97% and 108.52% and the Coulombic efficiency of 100% and 99.24% were observed for x = 0.0 and x = 0.8, respectively. First-principles density functional theory (DFT) calculations show that the band-gap energy of Ni1−xAlxCo2O4 remained largely invariant with the Al3+ substitution for low Al3+ content. Although the capacitance performance is reduced upon Al3+ doping, overall, the Al3+ doped Ni1−xAlxCo2O4 displayed good energy, powder density, and retention performance. Thus, Al3+ could be a cost-effective alternative in replacing Ni with the performance trade off.