High-pressure Hydrothermal Method Research Articles

Electric-Field Manipulation of Magnetic Chirality in a Homo-Ferro-Rotational Helimagnet.

Ferro-rotational (FR) materials, renowned for their distinctive material functionalities, present challenges in the growth of homo-FR crystals (i.e., single FR domain). This study explores a cost-effective approach to growing homo-FR helimagnetic RbFe(SO4)2 (RFSO) crystals by lowering the crystal growth temperature below the TFR threshold using the high-pressure hydrothermal method. Through polarized neutron diffraction experiments, it is observed that nearly 86% of RFSO crystals consist of a homo-FR domain. Notably, RFSO displays remarkable stability in the FR phase, with an exceptionally high TFR of ≈573K. Furthermore, RFSO exhibits a chiral helical magnetic structure with switchable ferroelectric polarization below 4K. Importantly, external electric fields can induce a single magnetic domain state and manipulate its magnetic chirality. The findings suggest that the search for new FR magnets with outstanding material properties should consider magnetic sulfates as promising candidates.

High-pressure hydrothermal dope Ce into MoVTeNbOx for one-step oxidation of propylene to acrylic acid

A high-pressure hydrothermal method was employed to introduce Ce element facilely into MoVTeNbOx catalysts in 0.5 h. It was indicated that Ce atoms were doped into the framework of MoVTeNbOx without changing the unique crystal structure of MoVTeNbOx. The introduction of Ce could facilitate the formation of oxygen vacancies and improve the redox ability of surfacial V. However, it was worth noting that the doping amount of Ce was negatively related to the content of M1 active phase. Within a certain range, the catalytic performance could be improved by sacrificing an appropriate amount of M1 phase. In the conversion of propylene to acrylic acid, the highest yield of 58.2% was obtained under catalyst MoVTeNbCeOx (V: Ce =1: 0.05) at 380 °C with the M1 phase content of 81.6%. The appropriate amount of Ce doping improved the propylene conversion by more than 20% compared to undoped. Moreover, the changes in Gibbs free energy of the rate-limiting step of direct oxidation of propylene before and after Ce doping were evaluated by Density functional theory (DFT). It is illustrated that the doping of Ce is thought to affect the main reason for the reduction of Gibbs free energy.

Green and effective route to convert chromium-free leather waste into protein retarding material for building gypsum

Leather manufacturing generates a large amount of leather solid waste, among which the effective treatment of leather waste scraps rich in protein resources has always been a challenge for the tanning industry. In this paper, a green and convenient method was devised for the first time to prepare protein retarding material (PRM) for gypsum from chrome-free tanned leather waste. Aldehyde tanned leather scraps as the main chrome-free leather waste were directly hydrolyzed through high-pressure hydrothermal treatment without any chemicals to obtain PRM. Compared with chemical treatment (acid or alkaline hydrolysis), high-pressure hydrothermal method avoided the decrease of protein product purity due to without the help of acid and alkali. The results showed that PRM obtained from leather waste had a significant effect on prolonging the initial setting time and delaying the release of hydration heat of gypsum. With the dosage or molecular weight of PRM increased, this retarding effect on gypsum was more remarkable. SEM, XRD, and FTIR analysis indicated that the presence of PRMs inhibited the hydration process of gypsum hemihydrate to gypsum dihydrate. Through polypeptide-calcium chelation, PRMs could bind free Ca2+ ions dissolved from gypsum to delay them from participating in the hydration reaction. The larger molecular weight or the more dosage of PRM, the stronger ability to bind calcium ions in gypsum. Chemical structure characterization and molecular dynamics simulation of PRM-Ca chelate further proved that PRMs mainly through carboxyl groups on molecular chain combined with Ca2+ in gypsum system to inhibit hydration reaction, thereby fulfilling the retardation demand. This study indicated that PRM from leather scraps can be a promising candidate for gypsum retardation, which provides a path for the efficient utilization of leather waste.

Collagen hydrolyzed extract derived from leather waste as a multifunctional additive for the preparation of granular fertilizer

Effective treatment and high-valued utilization of chrome leather scraps have always been desired by all tanneries, which is of great significance for green and sustainable development of leather industry. In this paper, we first devised a green and effective approach to obtain collagen hydrolyzed extract (CHE) from chrome leather scraps, and then the obtained CHE was used in the granulation of pastoral soil to prepare CHE-Soil granular fertilizer. The results indicated that chrome leather scraps were effectively dechromed with sodium oxalate and then hydrolyzed by a high-pressure hydrothermal method without any chemical to obtain high-purity CHE. When the 4.5 wt%∼12.5 wt% CHE solution was introduced into the granulation process, the granulation rate of pastoral soil was up to 89.8%∼95.6%. However, the effective granulation rate was decreased due to the increase in large granule size (>5 mm). CHE-Soil granular fertilizer prepared by adding more CHE exhibited better surface roundness and more excellent crush resistance. Moreover, this type of granular fertilizer possessed excellent water retention and slow-released nutrient properties. Pine leaf peony cultivation experiments further showed that the presence of CHE-Soil granular fertilizer rapidly promoted plant growth and effectively increased the harvest of plants. This study indicated that CHE obtained from chrome leather scraps could be effectively used as a nutritious additive with adhesiveness to prepare the granular fertilizer for plant growth, which provides a novel idea for designing valorization methods of leather waste.

A Strategy Inspired by the Cicada Shedding Its Skin for Synthesizing the Natural Material NaFe3 S5 ·2H2 O.

Sulfide minerals hold significant importance in both fundamental science and industrial advancement. However, certain natural sulfide minerals, such as NaFe3 S5 ·2H2 O (NFS), pose great challenges for exploitation and synthesis due to their high susceptibility to oxidation. To date, no successful precedent exists for synthesizing NFS. Here, a novel approach to synthesizing low-cost and pollution-free NFS with high stability using the high-pressure hydrothermal method based solely on knowledge of its chemical formula is presented. Moreover, an innovative strategy inspired by the cicada's molting process to develop unstable natural materials is proposed. The mechanical, thermal, optical, electrochemical, and magnetic properties of the NFS are thoroughly investigated. The storage of lithium, sodium, and potassium ions is primarily concentrated in the gap between (0 0 1) crystal planes. Additionally, as a catalyst for hydrogen evolution reaction (HER) at 10mAcm-2 , micron-sized NFS exhibits an excellent overpotential of 6.5mV at 90°C, surpassing those of reported HER catalysts of similar size. This research bridges the gap in the sulfide mineral family, overcomes limitations of the high-pressure hydrothermal method, and paves the way for future synthesis of natural minerals, lunar minerals, and Martian minerals.

Crystal structure and catalytic performance for direst oxidation of propylene to acrylic acid of MoVTeNbOx prepared by high-pressure hydrothermal synthesis

MoVTeNbOx catalysts were prepared through a high-pressure hydrothermal method, in which the crystalline structure and properties of the catalysts were tuned by varying the system pressure (0-12.0 MPa). Results showed that the system pressure had a significant influence on the structure and catalytic performance of MoVTeNbOx. Under 3.0 MPa, MoVTeNbOx prepared possessed the highest content of M1 phase (90.6%) and V5+ content (60.7%), exhibiting a uniform short and thick needle-like morphology. Also, it showed excellent selectivity (79.1%) and yield (52.8%) to acrylic acid at the catalytic temperature of 380°C. However, under 4.4 and 11.6 MPa, the characteristic peaks of M1 shifted to a certain extent and the morphology changed from short and thick to slender. As a result, the V5+ content of M1 (001) plane decreased, resulting in a remarkable decline of the selectivity to acrylic acid. Moreover, DFT simulation results showed that the anti-bond orbital energy of V-O bond is the highest under 3.0 MPa, while further increase of pressure leads to obvious extrusion between atoms in the internal structure of MoVTeNbOx. Moreover, it was clear that the lower the anti-bond orbital energy of V-O bond, the lower the selectivity to acrylic acid.

Hydrothermal single crystal growth and structural investigation of the stuffed tridymite family as NLO materials

The structures, crystal growth and preliminary NLO properties of a broad class of compounds known as the stuffed tridymites are investigated. The stuffed tridymites of the formula ABC O 4 , where A are the alkali metal ions and B and C are Group 13 and 14 metal ions, respectively, form an extensive series of structures, all of which are based on symmetry breaking of the parent tridymite (SiO 2 ) structure. In all cases the alkali ion resides in channels running parallel to the c- axis formed from six-membered rings of tetrahedra of the metal ions. A large array of structures can be formed though combinations of ordering of the B / C sites, staggered and eclipsed tetrahedra, up/down orientations of the tetrahedra relative to the c -axis, and distortions of the six-membered rings. These symmetry breaking steps can be mixed and matched to form many different structures, and nearly all are in polar acentric space groups. The primary cause of centrosymmetric crystal formation is disorder of the B / C sites. When the sites are well ordered most of the structures are acentric with polar axes. High quality single crystals of most products can be grown using a high pressure hydrothermal method. Preliminary NLO experiments indicate that the compounds are acentric, but have low NLO conversions, which is expected due to the low polarizability of the building blocks. The extremely high percentage of polar acentric structure types, and the ability to correlate the structures to systematic variations of the very large and flexible tridymite structural class, suggests that this can serve as a starting point for designing crystals with many other useful physical properties. • Stuffed tridymites of various compositions were synthesized hydrothermally. • Structural factors affecting symmetry reduction from parent tridymite were identified. • The family exhibits a high percentage of noncentrosymmetric structures. • Powder NLO data was measured on stuffed tridymites.

Transformation Behavior of Iron Minerals in High-Iron Red Mud During High-Pressure Hydrothermal Reduction.

Nowadays, the comprehensive utilization of red mud is still a difficult problem. Using starch as the reducing agent, the "high-pressure hydrothermal reduction method" is used to separate and recover sodium, aluminum, and iron in high-iron red mud in one step in an alkaline hydrothermal system. This article focuses on the hydrothermal reduction behavior of the iron ore phase. The results showed that starch formed a strong reduction system through degradation under alkaline hydrothermal conditions, in which Fe2O3 was first partially dissolved and reduced to form Fe[OH]+, then Fe[OH]+ further reacted with Fe2O3 to form Fe3O4. At a temperature of 260°C, a C/S (calcium to silicon ratio) of 3.5, a Na2O concentration of 250g/L, Whigh-iron red mud/Wstarch = 10, the Fe reduction rate was 98.46%, and the transformation slag at a magnetic field strength of 1800 Gs resulted in a magnetic iron concentrate powder with a TFe grade of 65.75%.

High-pressure hydrothermal synthesis of MoVTeNbOx with high surface V5+ abundance for oxidative conversion of propane to acrylic acid

A series of MoVTeNbOx-mixed metal oxides were synthesized by high-pressure hydrothermal method. The effects of temperature and time during the preparation process on the structure and catalytic performance of MoVTeNbOx were investigated. It was demonstrated that high content of M1 phase (94.5%) MoVTeNbOx with typical needle-shape morphology and high surface abundance of V5+ (68.9%) could be fabricated by high-pressure hydrothermal method in a short time (30–60 min) without hydrogen peroxide post-treatment. The catalytic results of propane selective oxidation showed that the MoVTeNbOx sample synthesized at 200 °C for 30 min possessed the highest surface V5+ abundance and largest proportion of terminating (001) plane, displaying the highest selectivity (74.1%) for acrylic acid. Moreover, the prepared MoVTeNbOx showed excellent stability in high temperature continuous reaction.

High-yield preparation of molybdenum disulfide/polypyrrole hybrid nanomaterial with non-covalent interaction and its supercapacitor application

• High-yield of molybdenum disulfide (MoS 2 ) nanosheets could be prepared by simple grinding and sonochemical exfoliation. • Polypyrrole/MoS 2 (MPY) hybrid was synthesized via a chemical oxidative polymerization according to pyrrole content. • Non-covalent Mo–N bonding of MPY made it possible to have lowered interfacial resistance and improved surface conductivity. • MPY electrodes showed enhanced specific capacitance and electrochemical stability for pseudocapacitive behavior. Molybdenum disulfide (MoS 2 ) incorporated with a conducting polymer can be a promising nanomaterial for use as low-cost electrodes in supercapacitors. MoS 2 nanosheets are generally prepared by the high-pressure hydrothermal method, which has a few drawbacks such as low exfoliation yield, safety issues, and long-time processing. Herein, we report a simple and effective method for the high-yield (~72.5%) preparation of a MoS 2 /polypyrrole (MPY) hybrid nanomaterial via sonochemical exfoliation of ground bulk MoS 2 in a polar aprotic solvent and subsequent chemical oxidative polymerization of pyrrole (PY) onto the MoS 2 nanosheets. The strong non-covalent Mo–N bonding lowers the interfacial resistance, and the morphology of polypyrrole (PPY) can be easily controlled by varying the PY content. The MPY hybrid nanomaterial exhibited a maximum surface conductivity of 991 S sq., which is very high compared to that of pristine MoS 2 nanosheet (~3.6 × 10 –7 S sq.). When used in supercapacitors, the specific capacitance of the hybrid nanomaterial is 312 F g –1 . Thus, improved capacitance retention with increase in the scan rate and enhanced diffusion process during electrochemical reactions result in good supercapacitor performance, which is important for the mass production of energy-storage devices.

Cancrinite synthesis from natural kaolinite by high pressure hydrothermal method: Application to the removal of Cd2+ and Pb2+ from water

Abstract Zeolites were synthesized from natural Tunisian clay by hydrothermal treatment under high pressure (100 MPa H2O pressure) at different gradients of temperature in high pressure autoclaves. The natural clay was first heated at 650 °C (HC-heated clay) and then transformed to an amorphous phase at 650 °C by adding different amount of NaOH. By increasing temperature and NaOH content, low-density frameworks zeolites like faujasite are transformed into more stable zeolites having higher density frameworks like cancrinite due to dissolution and recrystallisation steps. Cancrinite (Na8(H20)2CO3[Al6Si6O24]) (IZA-code: CAN) was successfully synthesized with a good purity. The synthesized CAN was characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The removal performance of heavy metal ions (Cd2+, Pb2+) from solution by pure CAN and clays has been studied. The kinetics of adsorption of Cd2+ and Pb2+ are very fast: equilibrium is reached within 2 min at 298 K. The capacity of adsorption of CAN is higher for Pb2+ (192 mg g−1) than for Cd2+ (68 mg g−1). Adsorption equilibrium of Cd2+ and Pb2+ on CAN were well represented by Langmuir equation although the thermodynamic study reveals a more complex mechanism: thermodynamic parameters, such as equilibrium constant, free energy, entropy and enthalpy for adsorption were obtained from the experimental data, including adsorption microcalorimetry.

Differences of Characteristics and Performance with Bi3+ and Bi2O3 Doping Over TiO2 for Photocatalytic Oxidation Under Visible Light

Bi-doped TiO2 photocatalysts were synthesized by sol with a high-pressure hydrothermal method and developed for the photocatalytic degradation of formaldehyde under the visible light irradiation and ambient temperature. According to characterization, some Bi-doped TiO2 can be transformed into the distinctive crystals phase of Bi4Ti3O12, which was crucial for improving activity. The excess Bi2O3 doping into TiO2, such as Bi2O3–N/TiO2 and Bi2O3–C/TiO2, generated a mixed oxides with Bi2O3 and Bi4Ti3O12, was not beneficial to increase the activity of HCHO oxidation, whereas Bi3+/TiO2 composed of TiO2 and Bi4Ti3O12 displayed a higher activity with good stability. It is noteworthy that Bi3+/TiO2 didn’t show the lowest binding energy. However, it exhibited a lower PL intensity, higher adsorption, and activity due to the uniform particulates, high surface areas, and the strong interaction between TiO2 and Bi4Ti3O12, attributing to create superoxide radical anion (.O2−) and hydroxyl radical (.OH). The present results of Bi3+/TiO2 indicated that HCHO could be effectively oxidized from 1.094 to 0.058 mg/m3 (94.7%) under visible light irradiation within 36 h. The current research made effort to draw out the existing state of Bi, which can be better, Bi3+ or Bi2O3, doped in the TiO2.

Modified activated carbon catalytic reduction of dissolved oxygen in reclaimed water

ABSTRACT Dissolved oxygen (DO) is the main corrosive substance in the transport process of urban reclaimed water by pipelines, and it can be removed by catalytic reduction. Activated carbon (AC) has been conventionally used as a carrier for catalysts. This paper focuses on the effect of modification conditions of AC on the catalytic performance for DO removal by hydrazine. The catalytic performance of modified AC (MAC) samples by single and combinatory methods has been investigated. The results showed that the combinatory method was better than the single method, and the MAC by combinatory method of high-pressure hydrothermal method followed by metal salt solution impregnation method could remarkably promote the catalytic activity for DO removal. The prepared catalyst GS270-5-Ni-60-3 had the optimal catalytic activity at the conditions of reaction temperature of 30°C, pH 10 and the initial DO concentration of 5.31 mg/L, and the DO removal rate could reach 98.74%. Meanwhile, the samples of AC and MAC were characterized using BET, SEM and FTIR technologies. The experimental results showed that the high-pressure hydrothermal method could significantly improve the pore structure of AC, and the clogging of AC was not obvious by impregnation modification. Furthermore, the surface group of MAC also has a certain influence on the DO removal in reclaimed water.

One‐pot synthesis of the fluorocarbon quantum dots for sensitively detecting Fe 3+

In this work, the novel method of generating fluorocarbon quantum dots (FQDs) in aqueous solution is demonstrated. The FQDs were synthesised by milk at high temperature and high-pressure hydrothermal method, which were the only raw material. They synthesised high fluorescence, green FQDs. The Fe 3+ was added to FQDs, the fluorescence signal was quenched effectively. The fluorescence of FQDs showed a good linear relationship with the change of Fe 3+ concentration (50-700 μmol/l), and FQDs selected Fe 3+ to complete detection. Finally, the authors applied the prepared FQDs to the real samples to detect the Fe 3+ in the water. The iron ions belong to the Yellow River water, which is detected about 90.6-107%, and it is indicated that this method can be applied to detect iron ions in actual water samples. They successfully used milk to synthesis the FQDs, and it had high selectivity for Fe 3+ . So the authors' think the FQDs has great potential in the field.

Ca10Na10[Te9O42](H2O): a hydrothermally synthesized quaternary tellurium(vi) oxide containing edge-sharing octahedral trimers.

A new tellurium(vi) oxycompound, Ca10Na10[Te9O42](H2O), was synthesized by a high-temperature, high-pressure hydrothermal reaction at 550 °C, its structure determined by single-crystal X-ray diffraction, and further characterized by energy dispersive, infrared, and X-ray photoelectron spectroscopy. The compound crystallizes in the centrosymmetric trigonal space group R3[combining macron]c (no. 167) with a = 9.743(2), c = 66.337(13) Å, and Z = 6. The structure consists of discrete linear edge-sharing octahedral trimers with the composition Te3O1410-, which is a new type of finite Te-O oligomer with Te6+ only. The large complex anions form a hexagonal close-packed lattice with the octahedral and tetrahedral interstices being filled with Ca2+ and Na+ cations and water molecules. The octahedral trimers in every other h.c.p. layer rotate around the 31 screw axis for 120°; therefore the unit cell has a very long c axis. This work is one of the few examples of the synthesis of metal tellurates by supercritical hydrothermal techniques.

High-Temperature, High-Pressure Hydrothermal Synthesis and Characterization of an Acentric Borate Fluoride: Ba2B5O9F·0.5H2O.

A new borate fluoride, Ba2B5O9F·0.5H2O, has been synthesized by high-temperature, high-pressure hydrothermal method, characterized by a combination of techniques and its structure determined by single-crystal X-ray diffraction. The compound crystallizes in the noncentrosymmetric space group P4̅ n2 (No. 118) and powder SHG measurements were performed to confirm the absence of a center of symmetry. Its crystal structure is formed of a new fundamental building block which shares oxygen atoms with neighboring blocks to form a 3D borate framework with 12- and 8-ring channels where the Ba2+ cations, F- anions, and water molecules are located. The structure is compared with those of minerals and synthetic borate fluoride and chlorides with similar framework compositions. The 11B MAS NMR experimental results are in accord with those from crystal structure analysis and the resonances in the spectrum are assigned. The presence of water was confirmed by IR spectroscopy, and its content and the thermal decomposition products were determined by thermogravimetric analysis and powder X-ray diffraction.

Single crystal synthesis of δ-(Al,Fe)OOH

Single crystals of δ-AlOOH, δ-(Al 0.953 ,Fe 0.047 )OOH, and δ-(Al 0.878 ,Fe 0.122 )OOH with dimensions up to ~0.4–0.6 mm were synthesized by the high-pressure hydrothermal method. Synthesis experiments were performed at 21 GPa and 1470 K for 4 h using a Kawai-type multi-anvil apparatus. The crystals of δ-AlOOH, δ-(Al 0.953 ,Fe 0.047 )OOH, and δ-(Al 0.878 ,Fe 0.122 )OOH were colorless, yellowish green, and brown, respectively. Mossbauer spectra showed 95–100% Fe 3+ /∑Fe at the octahedral site in δ-(Al,Fe)OOH. Chemical compositions of δ-(Al 0.953 ,Fe 0.047 )OOH and δ-(Al 0.878 ,Fe 0.122 )OOH are homogeneous with Fe/(Al+Fe) of 0.0469(8) and 0.122(3), respectively. Unit-cell parameters of δ-AlOOH are consistent with those of previous studies, and they increase with Fe/(Al+Fe). These results confirm that δ-AlOOH can form a solid solution with ɛ-FeOOH. The crystals contained a small number of fluid inclusions. The syntheses of large single crystals of δ-(Al,Fe)OOH will facilitate investigation of their phase stability, physical properties including elasticity and elastic anisotropy, behavior of hydrogen bonding, and spin state of Fe, which will improve models of the water and oxygen cycles in the deep Earth.

Research Update: Synthesis of sub-15-nm diameter silver nanowires through a water-based hydrothermal method: Fabrication of low-haze 2D conductive films

We synthesized ultra-thin Ag nanowire (Ag NWs) with sub-15 nm diameters and aspect ratios of 1000 through a water-based high-pressure hydrothermal method in the presence of a tetrabutylammonium dichlorobromide organic salt and glucose reducing agent. In the crystal growth stage, the diameter of the NWs could be controlled by adjusting the pressure, and 15-nm diameter wires were obtained at a pressure of 190 psi. These 2D conductive Ag NW network films showed an excellent optical performance with low haze value of ≤1.0% and 94.5% transmittance at a low sheet resistance of 20 Ω/sq.

Honeycomb-like S = 5/2 Spin-Lattices in Manganese(II) Vanadates.

New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn5(VO4)2(OH)4, was grown from Mn2O3 and V2O5 in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn6O(VO4)2(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn5(VO4)2(OH)4: C2/m, Z = 2, a = 9.6568(9) Å, b = 9.5627(9) Å, c = 5.4139(6) Å, β = 98.529(8)°; Mn6O(VO4)2(OH): P21/m, Z = 2, a = 8.9363(12) Å, b = 6.4678(8) Å, c = 10.4478(13) Å, β = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn5(VO4)2(OH)4 possesses complex honeycomb-type Mn-O layers, built from edge-sharing [MnO6] octahedra in the bc plane, with bridging vanadate groups connecting these layers along the a-axis. Mn6O(VO4)2(OH) presents a more complicated structure with both octahedral [MnO6] and trigonal bipyramidal [MnO5] units. A different pattern of planar honeycomb sheets are formed by edge-shared [MnO6] octahedra, and these sublattices are connected through edge-shared dimers of [MnO5] trigonal bipyramids to form corrugated sheets. Vanadate groups again condense the sheets into a three-dimensional framework. Infrared and Raman spectroscopies indicated the presence of OH groups and displayed characteristic Raman scattering due to vanadate groups. Temperature-dependent magnetic studies indicated Curie-Weiss behavior above 100 K with significant anti-ferromagnetic coupling for both compounds, with further complex magnetic behavior at lower temperatures. The data indicate canted anti-ferromagnetic order below 57 K in Mn5(VO4)2(OH)4 and below 45 K in Mn6O(VO4)2(OH). Members of another class of compounds, K2M3(VO4)2(OH)2 (M = Mn, Co), also containing a honeycomb-type sublattice, were also synthesized to allow a comparison of the structural features across all three structure types and to demonstrate extension to other transition metals.

Binary cobalt ferrite nanomesh arrays as the advanced binder-free electrode for applications in oxygen evolution reaction and supercapacitors

Abstract The porous CoFe 2 O 4 nanomesh arrays are successfully synthesized on nickel foam substrate through a high temperature and pressure hydrothermal method, following by the thermal post-treatment in air. The CoFe 2 O 4 nanomesh arrays own numerous pores and large specific surface area, which is in favor of exposing more active sites. In consideration of the structural preponderances and versatility of the materials, the CoFe 2 O 4 nanomesh arrays have been researched as the binder-free electrode materials for electrocatalysis and supercapacitors. When the CoFe 2 O 4 nanomesh arrays on nickel foam (CoFe 2 O 4 NM-As/Ni) directly act as the free-binder catalyst toward catalyzing the oxygen evolution reaction (OER) of electrochemical water splitting, CoFe 2 O 4 NM-As/Ni exhibits an admirable OER property with a low onset potential of 1.47 V(corresponding to the onset overpotential of 240 mV), a minimal overpotential ( η 10 = 253 mV), a small Tafel slope (44 mV dec −1 ), large anodic currents and long-term durability for 35 h in alkaline media. In addition, as an electrode of supercapacitors, CoFe 2 O 4 NM-As/Ni obtains a desired specific capacitance (1426 F/g at the current density of 1 A/g), remarkable rate capability (1024 F/g at the current density of 20 A/g) and eminent capacitance retention (92.6% after 3000 cycles). The above results demonstrate the CoFe 2 O 4 NM-As/Ni possesses great potential application in electrocatalysis and supercapacitors.