Electrochemical oxygen evolution reaction efficiently boosted by thermal-driving core-shell structure formation in nanostructured FeNi/S, N-doped carbon hybrid catalyst

Microwave-Assisted Rational Designed CNT-Mn3 O4 /CoWO4 Hybrid Nanocomposites for High Performance Battery-Supercapacitor Hybrid Device

Extensive research interest in hybrid battery-supercapacitor (BSH) devices have led to the development of cathode materials with excellent comprehensive electrochemical properties. In this work, carbon nanotube (CNT)-Mn3 O4 /CoWO4 triple-segment hybrid electrode is synthesized by using a two-step microwave-assisted hydrothermal route. Systematic physical characterization revealed that, with the assistance of microwave, granular Mn3 O4 and spheroid-like CoWO4 with preferred orientation, and oxygen vacancies are stacked or arranged on CNTs skeletons to construct a rational designed hybrid nanocomposite with abundant heterointerfaces and interfacial chemical bonds. Electrochemical evaluations show that the synergistic cooperation in CNT-Mn3 O4 /CoWO4 resulted in an ultra-high specific capacity (1907.5 C g-1 /529.8 mA h g-1 at 1 A g-1 ), a wide operating voltage window (1.15 V), the satisfactory rate capability (capacity maintained at 1016.5 C g-1 /282.3 mA h g-1 at 15 A g-1 ), and excellent cycling stability (117.2% initial capacity retention after 13000 cycles at 15 A g-1 ). In addition, the assembled CNT-Mn3 O4 /CoWO4 //N doped porous carbon (NC) BSH device delivered a stable working voltage of 2.05 V and superior energy density of 67.5 Wh kg-1 at power density of 1025 W kg-1 , as well as excellent stability (92.2% capacity retained at 5 A g-1 for 12600 cycles). This work provides a new and feasible tactic to develop high-performance transition metal oxide-based cathodes for advanced BSH devices.

Hydrogen-Rich Pyrolysis from Ni-Fe Heterometallic Schiff Base Centrosymmetric Cluster Facilitates NiFe Alloy for Efficient OER Electrocatalysts

Binary metal nickel-iron alloys have been proven to have great potential in oxygen evolution reaction (OER) electrocatalysis, but there are still certain challenges in how to construct more efficient nickel-iron alloy electrocatalysts and maximize their own advantages. In this work, a heterometallic nickel-iron cluster (L = C₆₄ H₆₆ Fe₄ N₈ Ni₂ O₁₉ ) of Schiff base (LH₃  = 2-amino-1,3-propanediol salicylaldehyde) is designed as a precursor to explore its behavior in the pyrolysis process under inert atmosphere. The combination of TG-MS, morphology, and X-ray characterization techniques shows that the Schiff base ligands in the heterometallic clusters produces a strong reductive atmosphere during pyrolysis, which enable the two 3d metals Ni and Fe to form NiFe alloys. Moreover, Fe₂ O₃ /Fe_0.64 Ni_0.36 @Cs carbon nanomaterials are formed, in which Fe₂ O₃ /Fe_0.64 Ni_0.36 is the potential active material for OER. It is also found that the centrosymmetric structure of the heterometallic Schiff base precursor is potentially related to the formation of the Fe₂ O₃ /Fe_0.64 Ni_0.36 alloy@carbon structures. The Fe₂ O₃ /Fe_0.64 Ni_0.36 @C-800 provides 274 mV overpotential in 1 m KOH solution at 10 mA cm^-2 in OER. This work provides an effective basis for further research on Schiff base bimetallic doping-derived carbon nanomaterials as excellent OER electrocatalysts.

3D chrysanthemum-like g-C3N4/TiO2 as an efficient visible-light-driven Z-scheme hybrid photocatalyst for tetracycline degradation

Utilization of a solar-driven semiconductor as a photocatalyst to degrade antibiotic pollutants is a feasible and environmentally friendly technology. In this paper, 3D chrysanthemum-like g-C₃N₄/TiO₂ as a visible-light-driven hybrid photocatalyst with a Z-scheme heterostructure was firstly synthesized by the in situ hydrothermal synthesis method. Experiments proved that this 3D chrysanthemum-like g-C₃N₄/TiO₂ had better degradation performance toward tetracycline than TiO₂ and g-C₃N₄. In particular, when optimized g-C₃N₄/TiO₂-2 was applied for tetracycline removal (200 ml, 10 mg L^-1), the corresponding degradation efficiency could reach nearly 100% within 60 min. The improved photocatalytic activity was the result of better utilization of the heterostructure-induced visible light, more efficient charge transfer in the Z-scheme heterojunction as well as stronger redox capability. The Z-scheme degradation mechanism was supported by the trapping experiments of active species and ESR radical detection, and the whole photocatalytic process was controlled by the combined action of ˙O₂^-, h⁺ and ˙OH radicals. This study may be beneficial for the design of more efficient sunlight-driven hybrid photocatalysts and their applications in wastewater treatment.

Surface nitriding to improve the catalytic performance of FeNi3 for the oxygen evolution reaction

In the oxygen evolution reaction, optimized Fe/Ni–Nx@FeNi3 nanosheets exhibit an overpotential of 251 mV to achieve a current density of 10 mA cm−2 and an excellent durability of 210 h.

Heterostructure of core-shell IrCo@IrCoOxas efficient and stable catalysts for oxygen evolution reaction

Although researches on non-noble metal electrocatalysts have been made some progress recently, their performance in proton exchange membrane water electrolyzer is still incomparable to that of noble-metal-based catalysts. Therefore, it is a more practical way to improve the utilization of precious metals in electrocatalysts for oxygen evolution reaction (OER) in the acidic medium. Herein, nanostructured IrCo@IrCoO_xcore-shell electrocatalysts composed of IrCo alloy core and IrCoO_xshell were synthesized through a simple colloidally synthesis and calcination method. As expected, the hybrid IrCo-200 NPs with petal-like morphology show the best OER activities in acidic electrolytes. They deliver lower overpotential and better electrocatalytic kinetics than pristine IrCo alloy and commercial Ir/C, reaching a low overpotential (j = 10 mA cm^-2) of 259 mV (versus RHE) and a Tafel slope of 59 mV dec^-1. The IrCo-200 NPs displayed robust durability with life time of about 55 h in acidic solution under a large current density of 50 mA cm^-2. The enhanced electrocatalytic activity may be associated with the unique metal/amorphous metal oxide core-shell heterostructure, allowing the improved charge transferability. Moreover, the *OH-rich amorphous shell functions as the active site for OER and prevents the further dissolution of the metallic core and thus ensures high stability.

Coordination regulated pyrolysis synthesis of ultrafine FeNi/(FeNi)9S8 nanoclusters/nitrogen, sulfur-codoped graphitic carbon nanosheets as efficient bifunctional oxygen electrocatalysts

Design of advanced carbon nanomaterials with high-efficiency oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities is still imperative yet challenging for searching green and renewable energies. Herein, we synthesized ultrafine FeNi/(FeNi)₉S₈ nanoclusters encapsulated in nitrogen, sulfur-codoped graphitic carbon nanosheets (FeNi/(FeNi)₉S₈/N,S-CNS) by coordination regulated pyrolyzing the mixture of the metal precursors, dithizone and g-C₃N₄ at 800 °C. The as-prepared FeNi/(FeNi)₉S₈/N,S-CNS exhibited distinct electrocatalytic activity and stability for the ORR with positive onset (E_onset) and half-wave (E_1/2) potentials (E_onset = 0.97 V; E_1/2 = 0.86 V) and OER with the small overpotential (η = 283 mV) at 10 mA cm^-2 in the alkaline media, outperforming commercial Pt/C and RuO₂ catalysts. This research provides some constructive guidelines for preparing efficient, low-cost and stable nanocatalysts for electrochemical energy devices.

Facile fabrication of bifunctional SnO-NiO heteromixture for efficient electrocatalytic urea and water oxidation in urea-rich waste water

Heterostructured transition metal oxide hybrid have more attention in energy saving and environmental related field due to their higher electro-catalytic activity. In this work, we demonstrated SnO decorated with NiO nanocrystal electrocatalyst is successfully synthesized through solvothermal method and well characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. Physical characterizations confirm that spherical shape of SnO nanoparticles are homogeneously dispersed on the surface of NiO. The kinetic study of catalytic performance towards urea oxidation reaction were measured by liner sweep voltammetry and chronoamprometry. As proposed catalyst to facilitate the rate of urea oxidation reaction can increase by SnO doped NiO catalyst. The urea oxidation on SnO-NiO nanostructured modified electrode exhibits lower onset potential of 1.12 V and enhancement of current with tafel slope of 150 mV dec^-1. The obtained results demonstrated the synthesized SnO-NiO anode material could be promising electrode for urea-rich containing wastewater remediation and hydrogen production from wastewater.

Current trends and perspectives on emerging Fe-derived noble-metal-free oxygen electrocatalysts

This article discusses recent progress in the development of Fe-derived noble metal-free electrocatalysts, including the strategies used for design, synthesis, and assessment of their performance in alkaline conditions.

CoP and Ni2P implanted in a hollow porous N-doped carbon polyhedron for pH universal hydrogen evolution reaction and alkaline overall water splitting

Developing low-cost and highly active bifunctional electrocatalysts for water splitting is very important but still remains a challenge. Herein, a novel bifunctional electrocatalyst composed of CoP and Ni2P nanoparticles implanted in a hollow porous N-doped carbon polyhedron (CoP/Ni2P@HPNCP) is synthesized by carbonization of Co/Ni-layered double hydroxide@zeolitic imidazolate framework-67 (Co/Ni-LDH@ZIF-67) followed by an oxidation and phosphorization strategy. The introduction of LDH can not only promote the formation of a hollow porous structure to supply more active sites, but also generate the CoP/Ni2P nanoheterostructure to afford extra active sites and modulate the electronic structure of the catalyst. As a result, CoP/Ni2P@HPNCP exhibits excellent pH universal hydrogen evolution reaction activity and alkaline oxygen evolution reaction activity. Furthermore, the electrolytic cell assembled from bifunctional CoP/Ni2P@HPNCP requires a cell voltage of 1.59 V in 1.0 M KOH at 10 mA cm-2, revealing its potential as a high performance bifunctional electrocatalyst.

Concurrently Realizing Geometric Confined Growth and Doping of Transition Metals within Graphene Hosts for Bifunctional Electrocatalysts toward a Solid-State Rechargeable Micro-Zn-Air Battery

The simultaneous realization of confined growth and doping of transition metals within carbon hosts promises to deliver unusual bifunctional catalytic activity but still remains challenging due to the difficulty in achieving synchronous nucleation and diffusion of metallic ions in a single synthesis step. Herein, we present a simple synthesis strategy capable of concurrently realizing geometric confined growth and doping of transition metals within graphene hosts, demonstrated in Co,N-codoped graphene-confined FeNi nanoparticles (Co,N-GN-FeNi). The obtained Co,N-GN-FeNi can take full advantage of the hierarchy of interactions between the confined-grown FeNi nanoparticles (for high oxygen evolution reaction (OER) activity) and the Co,N-codoped graphene hosts (for high oxygen reduction reaction (ORR) activity). The overall structure is a rationally designed synergy that simultaneously realizes (i) adequate exposure of electroactive sites, (ii) effective protection against corrosion/aggregation of FeNi nanoparticles, and (iii) rapid transport of ions/electrons between the interfaces. As a result, Co,N-GN-FeNi exhibits excellent bifunctional electrocatalytic activity relying on a low ORR/OER subtraction (ΔE = 0.81 V). Subsequent combination with a planar electrode configuration and a solid polymer electrolyte further demonstrates the utilization of Co,N-GN-FeNi as air cathode bifunctional electrocatalysts in a solid-state rechargeable micro-Zn-air battery (SR-MZAB), which exhibits a large open-circuit voltage of 1.39 V, a high power density/specific capacity of 62.3 mW cm^-2/763 mAh g^-1, excellent durability (126 cycles/42 h), and mechanical flexibility. This work demonstrates an effective synthesis strategy for concurrently realizing geometric confined growth and doping of transition metals within carbon hosts, for enhanced bifunctional catalytic activity toward novel SR-MZABs with high energy efficiency, security, and flexibility for wearable micropower sources.

Ni foam electrode solution impregnated with Ni-Fe X (OH) Y catalysts for efficient oxygen evolution reaction in alkaline electrolyzers

Oxygen evolution reaction (OER) is a demanding step within the water splitting process for its requirement of a high overpotential. Thus, to overcome this unfavourable kinetics, an efficient catalyst is required to expedite the process. In this context, we report on Ni foam functionalised with low cost iron (Fe) and iron hydroxide (Fe(OH)_X), wet chemically synthesized as OER catalysts. The prepared catalyst based on iron hydroxide precipitate shows a promising performance, exhibiting an overpotential of 270 mV (at a current density of 10 mA cm⁻² in 1 M KOH solution), an efficient Tafel slope of ∼50 mV dec⁻¹ and stable chronopotentiometry. The promising performance of the anode was further reproduced in the overall water splitting reaction with a two electrode cell. The overall reaction requires a lower potential of 1.508 V to afford 10 mA cm⁻², corresponding to 81.5% electrical to fuel efficiency.

Modification of Ni foam electrode by FeCl₃·6H₂O and HCl, towards superior oxygen-evolving electrocatalyst for water splitting process.

A robust Mn@FeNi-S/graphene oxide nanocomposite as a high-efficiency catalyst for the non-enzymatic electrochemical detection of hydrogen peroxide

Exploring high-efficiency, stable, and cost-effective electrocatalysts for electrochemical activities is greatly desirable and challenging. Herein, a newly designed hybrid catalyst with manganese-doped FeNi-S encapsulated into graphene oxide (Mn@FeNi-S/GO) with unprecedented electrocatalytic activity was developed by simple one-step heat treatment followed by sonication. X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and N₂ sorption isotherm demonstrated the successful formation of Mn@FeNi-S/GO. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) further confirmed the kinetic-favourable adsorption of hydrogen peroxide (H₂O₂) onto the surface sites of Mn@FeNi-S/GO. Additionally, the synergetic effects between Mn@FeNi-S and GO are regarded as significant contributors to an efficient electron transfer path, and they promote the capture of H₂O₂ in hybrid catalysts. Under an optimal condition, a biosensor-based Mn@FeNi-S/GO electrode exhibits a high sensitivity of 8.929 μA μM^-1 cm^-2 and a detection limit of 8.84 nM with a wide detection range for H₂O₂ and excellent selectivity; also, it is capable of online monitoring H₂O₂ derived from apple juice and human blood serum.

In situ growth of Fe and Nb co-doped β-Ni(OH)2 nanosheet arrays on nickel foam for an efficient oxygen evolution reaction

Fe, Nb co-doped β-Ni(OH)₂ electrode exhibited excellent OER performance with an overpotential of 294 mV at 100 mA cm⁻².

Phosphorus/nitrogen co-doped and bimetallic MOF-derived cathode for all-solid-state rechargeable zinc–air batteries

The bimetallic FeNi-MOFs are employed to fabricate P–FeNi and N–carbon co-doped bifunctional catalyst. Due to the enhanced catalytic performance, the peak power density of all-solid-state zinc–air battery is 159 mW cm⁻².

Chemical Structure of Fe-Ni Nanoparticles for Efficient Oxygen Evolution Reaction Electrocatalysis

Bimetallic iron-nickel-based nanocatalysts are perhaps the most active for the oxygen evolution reaction (OER) in alkaline electrolytes. Recent developments in literature have suggested that the ratio of iron and nickel in Fe-Ni thin films plays an essential role in the performance and stability of the catalysts. In this work, the metallic ratio of iron to nickel was tested in alloy bimetallic nanoparticles. Similar to thin films, nanoparticles with iron-nickel atomic compositions where the atomic iron percentage is ≤50% outperformed nanoparticles with iron-nickel ratios of >50%. Nanoparticles of Fe₂₀Ni₈₀, Fe₅₀Ni₅₀, and Fe₈₀Ni₂₀ compositions were evaluated and demonstrated to have overpotentials of 313, 327,, and 364 mV, respectively, at a current density of 10 mA/cm². While the Fe₂₀Ni₈₀ composition might be considered to have the best OER performance at low current densities, Fe₅₀Ni₅₀ was found to have the best current density performance at higher current densities, making this composition particularly relevant for electrolysis conditions. However, when stability was evaluated through chronoamperometry and chronopotentiometry, the Fe₈₀Ni₂₀ composition resulted in the lowest degradation rates of 2.9 μA/h and 17.2 μV/h, respectively. These results suggest that nanoparticles with higher iron and lower nickel content, such as the Fe₈₀Ni₂₀ composition, should be still taken into consideration while optimizing these bimetallic OER catalysts for overall electrocatalytic performance. Characterization by electron microscopy, diffraction, and X-ray spectroscopy provides detailed chemical and structural information on as-synthesized nanoparticle materials.

Bonding state synergy of the NiF2/Ni2P hybrid with the co-existence of covalent and ionic bonds and the application of this hybrid as a robust catalyst for the energy-relevant electrooxidation of water and urea

Among the energy-relevant electrochemical reactions, the electrochemical water and urea oxidation reactions are very significant for solving the increasing energy crisis and environmental pollution. Herein, the NiF2/Ni2P hybrid catalyst, in which covalent and ionic bonds co-existed, was found to be a very active catalyst for these electrochemical reactions occuring during the electrolysis of water. The bonding states of the covalent and ionic bonds were verified by the crystal structure and surface chemical state revealed by spectral analysis. As a bifunctional catalyst for the electrooxidation of water and urea, the NiF2/Ni2P hybrid structure demonstrated higher catalytic activity, kinetics and stability in the catalytic reaction than the individual components NiF2 and Ni2P under the same conditions. Specifically, an overpotential as low as 283 mV could drive the benchmark current density of 10 mA cm-2 for the oxygen evolution reaction, significantly lower than the overpotential required for the NiF2 (393 mV) and Ni2P materials (342 mV); the maximum current density for urea electrooxidation could reach 157.35 mA cm-2 at 1.53 V, which was much higher than those of NiF2 (23.55 mA cm-2) and Ni2P (102.72 mA cm-2). The catalytic performance also outperformed those of the recently reported similar advanced catalysts, and the high performance could be attributed to the highly exposed active sites, rough surface area, excellent charge transfer ability, and especially, the synergistic effects between the covalent and ionic bonds in the catalyst system. Using a commercial Pt/C catalyst as a cathode, the cell potential for urea-assisted water electrolysis could be reduced to 1.5 V to obtain the current density of nearly 40 mA cm-2 in a two-electrode system (Pt/C||NiF2/Ni2P), about 300 mV less than that required for water electrolysis in the general alkaline electrolyte. The current study demonstrates the significance of bonding state synergy in an advanced catalyst for water electrolysis and sheds some light on catalyst development in energy chemistry.

Fluoridated Iron-Nickel Layered Double Hydroxide for Enhanced Performance in the Oxygen Evolution Reaction

Layered double hydroxides (LDHs) are very promising but still far from satisfactory for catalyzing the electrochemical oxygen evolution reaction (OER) in water electrolysis. Herein, it was found that the catalytic performance of iron-nickel LDHs for OER can be largely boosted by a facile and controllable fluoridation approach at low temperatures. Temperature dependence of the crystal structure and surface chemical state was observed for the simple fluoridation of the iron-nickel LDH. However, no significant surface roughness and electrochemical active surface area increases were found, which was probably owing to the structure change from nanosheets to nanorods. Significant improvements in the performance, including the catalytic activity, stability, efficiency, and kinetics, were found compared with the pristine iron-nickel LDH. Specifically, iron-nickel fluoride obtained at 250 °C afforded the lowest overpotential of 225 mV (no iR correction) to drive 10 mA cm^-2 loaded on an inert glassy carbon electrode with a small Tafel slope of 79 mV dec^-1 , outperforming the noble-metal IrO₂ catalyst and most of the similar Fe-Ni based catalysts. The performance improvement could be mainly attributed to the phase-structure transfer from metal-O bonding in the FeNi-LDHs to metal-F bonding after fluoridation, which means it is easier to form the real active sites of Fe-doped high-valence Ni-(oxy)hydroxide over the iron-nickel fluoride surface.

Improved oxygen evolution activity of IrO2 by in situ engineering of an ultra-small Ir sphere shell utilizing a pulsed laser

Noble metal-based catalysts are vital electrocatalysts for the oxygen evolution reaction (OER), which is a half reaction among multiple renewable energy-related reactions. To fully exploit their potential as efficient OER catalysts, we developed a fast one-step strategy to engineer a unique nanostructure for the benchmark catalyst IrO2 utilizing an ultra-fast pulse laser, through which a shell of ultra-small Ir spheres with a diameter of ca. 2 nm is in situ engineered around the IrO2 core. The creation of the Ir sphere shell not only increases the electrochemical surface area, but also improves the electrical conductivity of the electrocatalyst. The as-engineered IrO2@Ir architecture exhibits extremely high electrocatalytic activity towards the OER, revealing an overpotential of 255 mV at 10 mA cm-2 and Tafel slope of 45 mV dec-1. These values are much lower than those observed for the unmodified structure. Furthermore, the catalytic performance is the best among all the noble metal-based OER catalysts. This work may open a new avenue to efficiently improve the catalytic activity of noble metal-based catalysts and significantly advance the development in the energy industry.

Surface chemical state evaluation of CoSe2 catalysts for the oxygen evolution reaction

The critical condition for efficient metallic Co–Se bonding construction and its significance for the oxygen evolution reaction were demonstrated.

An Fe-doped NiTe bulk crystal as a robust catalyst for the electrochemical oxygen evolution reaction

An Fe doped NiTe bulk crystal was demonstrated to exhibit an extremely active and stable performance for the electrochemical oxygen evolution reaction.

A two-dimensional Ni(ii) coordination polymer based on a 3,5-bis(1′,2′,4′-triazol-1′-yl)pyridine ligand for water electro-oxidation

A two-dimensional Ni(ii) coordination polymer based on a novel 3,5-bis(1′,2′,4′-triazol-1′-yl)pyridine rigid ligand was proposed as a novel and efficient molecular catalyst for water oxidation.

Nanostructured carbons containing FeNi/NiFe2O4 supported over N-doped carbon nanofibers for oxygen reduction and evolution reactions

Non-precious metal-based electrocatalysts on carbon materials with high durability and low cost have been developed to ameliorate the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) for electrochemical energy applications such as in fuel cells and water electrolysis. Herein, two different morphologies of FeNi/NiFe₂O₄ supported over hierarchical N-doped carbons were achieved via carbonization of the polymer nanofibers by controlling the ratio of metal salts to melamine: a mixture of carbon nanotubes (CNTs) and graphene nanotubes (GNTs) supported over carbon nanofibers (CNFs) with spherical FeNi encapsulated at the tips (G/CNT@NCNF, 1 : 3), and graphene sheets wrapped CNFs with embedded needle-like FeNi (GS@NCNF, 2 : 3). G/CNT@NCNF shows excellent ORR activity (on-set potential: 0.948 V vs. RHE) and methanol tolerance, whilst GS@NCNF exhibited significantly lower over-potential of only 230 mV at 10 mA cm⁻² for OER. Such high activities are due to the synergistic effects of bimetallic NPs encapsulated at CNT tips and N-doped carbons with unique hierarchical structures and the desired defects.

Non-precious metal-based electrocatalysts on carbon materials with high durability and low cost have been developed to ameliorate the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER).

NOx removal by selective catalytic reduction with ammonia over hydrotalcite-derived NiTi mixed oxide

The speculated mechanism of the SCR reaction over the NiTi-LDO catalyst and the synergetic catalytic effect between Ni and Ti.