Nickel Phosphate Research Articles

Binder free hydrothermally synthesized nickel phosphate hydrate microplates on nickel foam for supercapacitors

In this study, the nickel phosphate hydrate (NiPh) microplates are deposited on 3D Ni-foam by a facile hydrothermal method. The microstructures of NiPh electrodes vary with hydrothermal reaction time (2, 4 and 6 h) at the constant reaction temperature. The structural, morphological and electrochemical characterizations of the NiPh electrodes were systematically studied. X-ray diffraction (XRD) study reveals a monoclinic crystal system of NiPh material with an I2/m space group. The scanning electron microscopy (SEM) analysis shows plates like microstructures. The electrochemical measurements of NiPh electrodes were carried out in 1 M KOH electrolyte in −0.2 to 0.55 V vs SCE potential window. NiPh (deposited at 2 h reaction time) electrode shows the specific capacitance of 855.11 F/g (178.18 mAh/g) at 10 mA/cm2 current density. It is speculated that NiPh deposited on Ni-foam can be an efficient electrode material for energy storage applications.

Anion engineering guided MOF-to-hollow nickel phosphate transformation enabling robust electrochemical platforms for detection of hydrogen peroxide and hydrazine

Rationally designing of transition metal phosphate (TMP) with charming structure and exploiting their electroanalytic functionalities are of great potential and challenging. Herein, in-situ adoption of MOF as the framework and skillfully regulation of the evolution process through the mass ratios of sodium phosphate (namely as both etchants and reactants) and Ni-MOFs led to the configuration of a series of nickel phosphate (NiP) counterparts with well-defined structures and definable compositions, and further their bifunctional sensing performance for H2O2 and N2H4 were investigated, where the ratio of 4:3 prepared NiP, with pure ingredient, amorphous states and 2D scaly nanosheets uniformly decorated 3D hollow scaffolds, collectively reveals rich electrocatalytic sites, shorten ion transfer/diffusion channels and excellent electrical conductivity, thus affording an significant enhancement for its electrochemical behaviors, especially its low detection limit (27.9 nM and 45.1 nM) and wide measurable range (0.001–2.6 mM and 0.005–4.5 mM) for H2O2 and N2H4, respectively. Additionally, its powerful anti-interference and recognition for H2O2 and N2H4 in water samples verify the practicality of our electrochemical platforms. Our design establishes the promising strategy for engineering of new class MOF-derived diversified functionally materials for electroanalytical application and beyond.

High areal energy density and super durable aqueous rechargeable NiCo//Zn battery with hierarchical structural cobalt–nickel phosphate octahydrate as binder-free cathode

Aqueous rechargeable Zn-based alkaline batteries combine the advantages of battery-level energy density and capacitance-level power density, showing bright prospects.However, their energy density and cycling life were restricted by the low areal capacity and poor cycling tolerance of cathodes. Herein, bimetallic cobalt–nickel phosphate octahydrate (NCP) with hierarchical structure was prepared in situ on nickel foam by a simple one-step hydrothermal method. The NCP cathode achieved an ultrahigh areal capacity (3.2 mAh/cm2), which was far more than twice that of the single metallic cobalt/nickel phosphate octahydrate due to its larger surface area, smaller electrode/electrolyte interface resistance, higher electrochemical reaction activity and kinetics process. The NCP//Zn battery showed much higher areal energy density of 5.42 mWh/cm2 and peak power density of 129.68 mW/cm2 than most aqueous Zn-based batteries currently reported. The cycling durability of NCP//Zn battery increased from 58.59% to 98.31% after 2000 cycles by coating carbon material on electrode and adding potassium phosphate buffer salt into electrolyte. Quasi-solid NCP-C//Zn batteries can still charge a mobile phone even under hammer strokes, demonstrating excellent safety and promising energy storage applications. This work might shed light on the construction of phosphate based energy storage devices with high energy density, power density and long life.

Ni Single Atoms and Ni Phosphate Clusters Synergistically Triggered Surface‐Functionalized MoS2 Nanosheets for High‐performance Freshwater and Seawater Electrolysis

Two‐dimensional metal dichalcogenides have been evidenced as potential electrocatalysts for hydrogen evolution reaction (HER); however, their application is limited by a poor oxygen evolution reaction (OER) activity due to insufficient number/types of multi‐integrated active sites. In this study, we report a novel bifunctional catalyst developed by simultaneous engineering of single nickel atoms (NiSA) and nickel phosphate clusters (NiPi) to synergistically trigger surface‐functionalized MoS2 nanosheets (NSs) resulting in high reactivities for both HER and OER. The NiSA‐NiPi/MoS2 NSs material exhibits a fairly Pt‐like HER behavior with an overpotential of 94.0 mV and a small OER overpotential of 314.0 mV to reach 10 mA cm−2 in freshwater containing 1.0 M KOH. Experimental results of the catalyst are well supported by theoretical study, which reveals the significant modulation of electronic structure and enrichment of electroactive site number/types with their reasonably adjusted free adsorption energy. For evaluating practicability, the NiSA‐NiPi/MoS2 NSs‐based electrolyzer delivers effective operation voltage of 1.62, 1.52, and 1.66 V at 10 mA cm−2 and superior long‐term stability as compared to Pt/C//RuO2 system in freshwater, mimic seawater, and natural seawater, respectively. The present study indicates that the catalyst is a promising candidate for the practical production of green hydrogen via water electrolysis.

Sono-chemical assisted synthesis of carbon nanotubes-nickel phosphate nanocomposites with excellent energy density and cyclic stability for supercapattery applications

Nickel phosphate (NiP) was synthesized by sono-chemical synthesis followed by calcination at 400 °C for 5 h. Synthesized NiP was blended with various concentrations (10, 30 and 50 wt%) of multiwalled carbon nanotubes (MWCNTs) to prepare the nanocomposites that were then characterized in terms of microstructure, morphology, composition, and electrochemical performance. Microscopic analysis showed the presence of uniformly distributed MWCNTs in NiP matrix in case of nanocomposites containing 50 wt% MWCNTS (NiP50CNT50) resulting in its better electrochemical performance than the other compositions. X-ray diffraction and Fourier transformed infra-red spectroscopic analysis also confirmed the synthesis of MWCNTs/NiP nanocomposites by showing that the characteristics peaks becoming broader and intense due to incorporation of CNTs. The electrochemical analysis of all the prepared nanocomposites presented that NiP50CNT50 has demonstrated the better specific capacity of 845 Cg−1 at 0.6 Ag−1. This composition also presented better asymmetric supercapacitor (ASC) device performance with specific capacity of 400 Cg−1 at 0.4 Ag−1, excellent energy density of 94.4 Wh kg−1 (at 340 W kg−1 power density) that decreases to 24.82 Wh kg−1 (at 10,200 W kg−1) which might be attributed to its higher surface area (32.4 m2/g) and adsorbed gas volume (168 cm3 g−1). ASC device showed a capacity retention of 95.5 % at 12 Ag−1 after 5000 charge/discharge cycles.

Hydrothermally synthesized nickel copper phosphate thin film cathodes for high-performance hybrid supercapacitor devices

Transition metal phosphate (TMP) based materials are developing as advanced type electrode materials for hybrid supercapacitors (SCs) due to their unprecedented conductivity, and rich redox activity. Attracted by these fabulous physicochemical characteristics of metal phosphates, binder-free nickel copper (Ni-Cu) phosphate thin films directly grown on stainless steel (SS) substrate by hydrothermal method. The morphological alteration from microplates like nickel phosphate to microrods like copper phosphate is detected with increasing copper content in Ni-Cu phosphate thin films. The optimal 1:1 ratio of nickel and copper in Ni-Cu phosphate (Ni1.62Cu1.35(PO4)2·H2O) thin film illustrates high specific capacitance (Cs) (capacity (Cc)) of 711 F g−1 (355.5 C g−1) at 1.5 A g−1. More significantly, a hybrid aqueous SC (HASC) and all-solid-state SC (HASSC) electrochemical energy storage devices (ESDs) have been fabricated. The HASC device showed superior Cs (85 F g−1 at 0.8 A g−1) with specific energy (SE) of 30 Wh kg−1 at 1.27 kW kg−1 specific power (SP). Additionally, HASSC device offers a higher Cs (52 F g−1 at 0.6 A g−1) with 18.53 Wh kg−1 SE at 1.64 kW kg−1 SP. Also, both HASC and HASSC devices exhibit excellent long-term durability of 84.81 and 80.83 %, respectively, after 5000 GCD cycles. Moreover, HASSC device brightens a panel of 201 red light-emitting diodes (LEDs) illustrating its commercial practicability to next-generation hybrid energy storage devices.

The nickel phosphate rods derived from Ni-MOF with enhanced electrochemical activity for non-enzymatic glucose sensing

In this work, spherical Ni-based metal-organic frameworks (Ni-MOFs) were used as precursors for preparing nanorod-like nickel phosphate (r-NiPO) with enhanced electro-catalytic properties in detection of glucose. It was found that the addition of nickel ion has a profound effect on construction of nickel phosphate with flower-like, rod-like, and ribbon-like structure in presence of H2PO2−. The r-NiPO consisted of multiple phases of nickel phosphate showed porous, interconnected structure and abundant active Ni(II)/Ni(III) pairs, which was beneficial to facilitate glucose oxidation. In comparison with Ni-MOF, r-NiPO exhibited the superior electrocatalytic property on oxidation of glucose because of the exposing more active Ni sites in r-NiPO than that of Ni-MOF precursor. r-NiPO modified glassy carbon electrode (r-NiPO/GCE) showed a good linear response to glucose from 1.0 μM to 3.0 mM with a high sensitivity of 3169 μA mM−1 cm−2. In addition, r-NiPO/GCE can be used to detect glucose in human serum with satisfactory recoveries (90–97%).

Rational Regulation of Crystalline/Amorphous Microprisms-Nanochannels Based on Molecular Sieve (VSB-5) for Electrochemical Overall Water Splitting.

Rational regulation of the composition and structure of electrocatalysts is crucial to the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a new electrocatalyst of nickel phosphate microprism (VSB/NiPO) is developed via a simple solvothermal reaction. The microprism is mainly composed of Versailles-Santa Barbara-5 (VSB-5, molecular sieve) with unique nanochannels, which contribute to accelerating mass transfer and exposing more active sites, thus displaying excellent HER activity. Subsequently, the crystallinity and electronic structure of the framework are modulated by incorporating Fe with the combination of calcination and impregnation. The nanochannels are converted to the amorphous arrangement, and the Ni centers are regulated to the higher valence. The resultant Fe-VSB/NiPO-500 exhibits a low OER overpotential of 227mV at 50mA cm-2 . Interestingly, an integrated electrolyzer assembled by VSB/NiPO(-) and Fe-VSB/NiPO-500(+) performs well for overall water splitting, which requires only 1.487V to achieve 10mA cm-2 , and remains stable at 100mA cm-2 over 100 h. This finding opens a new avenue for developing VSB-5 in the field of electrocatalysis.

Activation effect of nickel phosphate co-catalysts on the photoelectrochemical water oxidation performance of TiO2 nanotubes

We present exemplary fabrications of controlled Nickel phosphate (NiPi)/TiO2 nanotubes arrays (TNTs) in phosphate buffer for boosted photoelectrochemical (PEC) water splitting. The TNTs/NiPi composite electrodes revealed a considerably enhanced photocurrent density of 0.76 mA/cm2, up to 3-time enhancements than bare TNTs, mostly because of the enhanced charge separation, decreased carrier recombination, and improving kinetics of the water oxidation. Also, we demonstrated that the NiPi can assist the PEC features of TNTs over a varied region of pH values from 1 to 14. Incorporation of NiPi over the TNTs surface advances the light absorption features of the electrode, resulting in an enhanced photogenerated charge carrier; and promotes the reactive sites for water oxidation, which was proved by the double-layer capacitance. The TNTs/NiPi photoelectrode exhibited excellent photostabilization under continuous illumination for 5 h, and the photoconversion efficiencies were 0.45%, 3-fold enhancements than with bare TNTs under the illuminations. Overall, this work might offer an innovative approach to fabricating and designing efficient electrodes with superior contact interfaces among photoanodes and numerous co-catalysts.

Nanoarchitectured nickel phosphate integrated with graphene oxide for the toxicant diphenylamine detection in food samples

To date, numerous chemical substances are existing in food products, which cause some health issues in humans. Monitoring and controlling the level of toxicity in food for daily life is an important one. Hence, rapid and inexpensive detection methods are developed for the quantification of toxic chemicals. As a consequence, we have chosen the electrochemical sensing method for the detection of food toxicant diphenylamine (DPA). Herein, the flake-like structured nickel phosphate (NPO) is synthesized using the coprecipitation method and the preparation of NPO integrated graphene oxide (GO) by sonochemical treatment. As observed from electrochemical impedance spectra (EIS) analysis, the NPO/GO modified screen-printed carbon electrode (SPCE) has a lower charge transfer resistance (Rct) of 624 Ω and a fast electron transfer rate. The higher catalytic activity of NPO combined with a higher conductive and active surface area of GO through the electrostatic interaction is applied for the electrochemical determination of DPA. Using the differential pulse voltammetry (DPV) technique, the constructed NPO/GO/SPCE has a broad linear range (0.4 −680.8 μM), low LOD (12 nM), and good sensitivity (1.01 µA µM–1 cm–2) towards DPA sensing. Furthermore, the resultant sensor revealed good selectivity, cyclic and storage stability, repeatability, and reproducibility. The practical application of the DPA was estimated in food samples such as apple, grapes, and orange juice with satisfactory recovery.

Leaf-veins-inspired nickel phosphate nanotubes-reduced graphene oxide composite membranes for ultrafast organic solvent nanofiltration

Organic solvent nanofiltration (OSN) membranes provide extraordinary opportunities for environment friendly and cost-competitive solvent recovery in petrochemical and pharmaceutical purifications. Currently, membranes that based on two-dimensional (2D) materials are extremely attractive in ultrafast molecular separations owing to the atomic thickness and remarkable physicochemical properties of the 2D nanosheets. Inspired by the structures and functions of vessel element that transport water in leaf veins, nickel phosphate nanotubes-reduced graphene oxide (NPTs-rGO) ultrathin laminar membrane is successfully prepared for ultrafast organic solvent nanofiltration. The in-situ synthetic NPTs can not only contribute to the size-dependent ultrafast molecular separation of the rGO membrane by providing additional molecular transport pathways as well as enlarging the interlayer space of the rGO layer, but also enhance the stability of the resultant membrane. The optimum membrane exhibits a methanol permeance of 670 L m −2 h −1 bar −1 and a high rejection toward molecules greater than 2 nm (MWCO: 650 Da). More importantly, the NPTs-rGO membrane shows promising anti-swelling property under OSN operating conditions. Inspired by leaf veins, this strategy provides insight into designing high-performance lamellar membranes with tubular-channel network, which may promote the fabrication and application of lamellar membranes in OSN. • Inspired by leaf veins, nickel phosphate nanotubes-reduced graphene oxide (NPTs-rGO) composite was applied to develop organic solvent nanofiltration (OSN) membrane. • The OSN performance of the resultant membrane was markedly improved. • The NPTs in the membrane could create tubular transport pathways for solvent. • The resultant NPTs-rGO membrane has superior anti-swelling stability and mechanical strength.

Nickel and sodium phosphate composite with wall putty substantive as energy saving decorating material

The phosphate containing inorganic mixture has been synthesized and various measurement techniques are used to characterize it. Composite mixtures of this mixture are synthesized with assimilation of wall putty. The differential scanning calorimetry of mixture is studied in two thermal cycles from 298 K to 223 K at 10 K min−1 in normal atmosphere and found endothermic behavior after a cycle. The specific heat capacity (C p) of 4.42% composite mixture is found exhibit lower C p value as compared to wall putty by 20% at 343 K. The C p of wall putty is 4.96 Jg−1K−1 at 300 K while C p of 4.42% and 12.11% composite mixture are 2.70 Jg−1K−1 and 4.00 Jg−1K−1 at 300 K, respectively. This composite mixture could be used in exterior walls of the buildings instead of wall putty alone. So, coating material of 4.42% mixture keeps the buildings cooler than expected.

A Highly Efficient Nickel Phosphate Electrocatalyst for the Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF), one of biomass-derived platform compounds, is an attractive route to produce 2,5-furandicarboxylic acid (FDCA), an important monomer of bio-based polyesters. Here, we successfully synthesized a highly efficient and stable nickel phosphate (Ni3 (PO4)2) electrocatalyst by a simple hydrothermal method for the electrocatalytic oxidation of HMF to FDCA, in which the yield of FDCA reached 94.2% and the Faraday efficiency was 93.5% in 0.1 M KOH. Compared with nickel hydroxide (Ni (OH)2), the introduction of phosphorus enhanced the charge transfer ability of Ni-based catalysts by EIS and Tafel slope analysis. At the same time, the Ni2+ species in Ni3(PO4)2 was more likely to be oxidized to active nickel species than that in Ni (OH)2 from XPS and in situ Raman results. Moreover, in situ attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) over Ni3(PO4)2 were carried out to study the changes of nickel phosphate during the electrocatalytic oxidation of HMF. According to ATR-SEIRAS, XPS, and Raman results, it can be concluded that Ni2+ species under applied potential in KOH solution was transformed to the high-valence nickel species/Ni3+ species with P–OH and the ring-shaped P–O group. In addition, the phosphorus group was also involved in the electrocatalytic oxidation of HMF. Based on these evidences, a complete electrocatalytic oxidation process of HMF to FDCA on Ni3(PO4)2 was proposed.

Effect of Preparation Conditions on the Morphology and Catalytic Performance of Nickel Phosphate Nanotubes

AbstractNickel phosphate nanotubes are synthesized by a hydrothermal method under different conditions with cetyltrimethyl ammonia bromide (CTAB) as a soft template and urea as an assistant agent. The structure and morphology are characterized by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X‐Ray powder diffraction (XRD), infrared (IR) spectroscopy, etc. Nickel phosphate nanotubes with different morphologies and structures are prepared at different pH values, crystallization time, molar ratios of Ni to P, CTAB to P, and urea to P. The TEM and SEM results show that the prepared nickel phosphate nanotubes seem like tremella or coral, which consist of nanotubes with a diameter of about 8 nm, length of about 200 nm, a rounded channel, and an open end. The formation process of nanotubes is deduced to be the self‐assembly of nickel phosphate growing along with CTAB. Nickel phosphate nanotubes show special catalytic performance in the isomerization reaction of epoxy propane. The reaction products are mainly propanal, allyl alcohol, and acetone, with a molar ratio of about 5:3:2 and the propylene oxide conversion and selectivity for propanal at 300 ℃ are 74.1% and 49.4%, respectively.

Three-dimensional hollow nickel phosphate microspheres with controllable hoya-like structure for high-performance enzymeless glucose detection and supercapacitor

Three-dimensional hollow hoya-like nickel phosphate (NiP) microspheres derived from nickel metal–organic frameworks (Ni-MOFs) are constructed and a series of calcinated temperatures are performed to investigate the temperature influence on the morphological and compositional evolutions, as well as electrochemical performance in detail. It is observed as-designed NiP calcinated at 450 °C is most beneficial for the enzymeless glucose sensor and supercapacitor applications outperforming its counterparts, delivering a noteworthy sensitivity (1373.7 A mM−1 cm−2) with a low detection limit of 160 nM, and satisfactory results in real human serum sample when utilized as a glucose sensor, while attaining a high specific capacity 1625F g−1 (1 A g−1) and exceptional rate performance (remaining 75.9% of its initial capacitance at 20 A g−1) for supercapacitor application. Here, the open structure configuration, interconnected flower-like nanosheets and amorphous state owing to NiP-450, like blooming “flowers”, make the active materials employed efficiently, ion/charge transferred rapidly and volume deformation decreased, significantly enhanced electrochemical properties, suggesting its competitive advantages in biosensor and supercapacitor research fields and capability as a promising candidate in future practical applications.

Facile synthesis of nickel phosphate nanorods as biomimetic enzyme with excellent electrocatalytic activity for highly sensitive detection of superoxide anion released from living cells

In this work, the superoxide dismutase (SOD) biomimetic enzyme based on nickel phosphate nanorods [Ni(PO4)NRs] was prepared by a simple and eco-friendly hydrothermal method. After further introduction of carboxylated multi-walled carbon nanotubes (C-MWCNTs), the obtained Ni(PO4)NRs/C-MWCNTs nanocomposites were utilized as the novel electrode materials to construct the electrochemical superoxide anion radicals (O2•−) biosensor with excellent electrical conductivity and unprecedented catalytic performance. The morphology of Ni(PO4)NRs/C-MWCNTs nanocomposite was examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman microscope, respectively. Under the optimum conditions, the proposed biosensor exhibits high sensitivity (5.67 × 104 μA/mM/cm2), low detection limit (0.097 μM at S/N = 3) and good selectivity to O2•−. In addition, the sensor can monitor O2•− released from MCF-7 cells with satisfactory results, which provides a great opportunity to apply it in the field of fundamental research and clinical diagnostics. Our results would promote Ni(PO4)NRs as the SOD biomimetic enzyme for designing biosensor and expand its various applications in biocatalysis and bioanalysis.

Selective production of lignin-derived monomers from corn stover by tuning the acid and hydrogenation sites of aluminum phosphate catalysts

This work is dedicated to the selective conversion of lignin. A nickel, tin, and sulfur-doped aluminum phosphate zeolite catalyst was developed for the selective production of lignin-derived monomers. The acidity and hydrogenation sites of this catalyst can be flexibly adjusted, and it exhibits a high yield (26.7%) for monomers with a nearly 68.8% conversion of lignin at 235 °C. The results show that Brønsted acid can increase the conversion of lignin and has a high selectivity for trans-ferulic acid, while Lewis acid and hydrogenation sites can promote the production of monomers with low oxygen content. The excellent stability and simple preparation method provide the possibility for the application of this depolymerization technology. This work could be a reference for the development of lignocellulosic biomass.

High Energy Density in Combination with High Cycling Stability in Hybrid Supercapacitors.

Hybrid supercapacitors are considered the next-generation energy storage equipment due to their superior performance. In hybrid supercapacitors, battery electrodes need to have large absolute capacities while displaying high cycling stability. However, enhancing areal capacity via decreasing the size of electrode materials results in reductions in cycling stability. To balance the capacity-stability trade-off, rationally designed proper electrode structures are in urgent need and still of great challenge. Here we report a high-capacity and high cycling stability electrode material by developing a nickel phosphate lamination structure with ultrathin nanosheets as building blocks. The nickel phosphate lamination electrode material exhibits a large specific capacity of 473.9 C g-1 (131.6 mAh g-1, 1053 F g-1) at 2.0 A g-1 and only about 21% capacity loss at 15 A g-1 (375 C g-1, 104.2 mAh g-1, 833.3 F g-1) in 6.0 M KOH. Furthermore, hybrid supercapacitors are constructed with nickel phosphate lamination and activated carbon (AC), possessing high energy density (42.1 Wh kg-1 at 160 W kg-1) as well as long cycle life (almost 100% capacity retention after 1000 cycles and 94% retention after 8000 cycles). The electrochemical performance of the nickel phosphate lamination structure not only is commensurate with the nanostructure or ultrathin materials carefully designed in supercapacitors but also has a longer cycling lifespan than them. The encouraging results show the great potential of this material for energy storage device applications.

Plasma-enhanced atomic layer deposition of nickel and cobalt phosphate for lithium ion batteries.

A plasma-enhanced ALD process has been developed to deposit nickel phosphate. The process combines trimethylphosphate (TMP) plasma with oxygen plasma and nickelocene at a substrate temperature of 300 °C. Saturation at a growth per cycle of approximately 0.2 nm per cycle is observed for both the TMP plasma and nickelocene, while a continuous decrease in the growth per cycle is found for the oxygen plasma. From ERD, a stoichiometry of Ni3(P0.8O3.1)2 is measured, but by adding additional oxygen plasma after nickelocene, the composition of Ni3(P0.9O3.7)2 becomes even closer to stoichiometric Ni3(PO4)2. The as-deposited layer resulting from the process without the additional oxygen plasma is amorphous but can be crystallized into Ni2P or crystalline Ni3(PO4)2 by annealing under a hydrogen or helium atmosphere, respectively. The layer deposited with the additional oxygen plasma shows two X-ray diffraction peaks indicating the formation of crystalline Ni3(PO4)2 already during the deposition. The resulting PE-ALD deposited nickel phosphate layers were then electrochemically studied and compared to PE-ALD cobalt and iron phosphate. All phosphates need electrochemical activation at low potential first, after which reversible redox reactions are observed at a potential of approximately 2.5 V vs. Li+/Li. A relatively high capacity and good rate behavior are observed for both nickel and cobalt phosphate, which are thought to originate from either a conversion type reaction or an alloying reaction.

Conversion of Amorphous MOF Microspheres into a Nickel Phosphate Battery-Type Electrode Using the "Anticollapse" Two-Step Strategy.

Metal-organic frameworks (MOFs) have attracted great attention as templates for preparation of functional porous materials owing to their adjustable structures, rich porosity, and controllable components. However, collapsed templates during the conversion process hinder their application and synthesis of derivatives. In this study, we demonstrate a novel two-step etching strategy during which amorphous MOF microspheres are initially transformed into nickel hydroxide and then subsequently transformed into microspherical nickel phosphates. Through this strategy, the prepared nickel phosphates maintain the microspherical morphology of MOFs but with no MOF residuals, exhibiting ultrahigh specific surface area, uniform pore size, and good structural robustness. Examined as a supercapacitor electrode, they show an outstanding specific capacity of 820 C g-1 at 0.5 A g-1 and remarkable cycling stability of 88% capacity retention after 10 000 cycles. Moreover, an asymmetric supercapacitor constructed utilizing reduced graphene cross-linked with p-phenylenediamine oxide (PPD-rGO) as the cathode displays a preeminent energy density of 64.56 Wh kg-1 at a power density of 507 W kg-1. This strategy has important significance in guiding the preparation of high-performance MOF-derived electrodes.