Electronic Modulation in Cu Doped NiCo LDH/NiCo Heterostructure for Highly Efficient Overall Water Splitting.

Layered double hydroxides (LDHs), promising bifunctional electrocatalysts for overall water splitting, are hindered by their poor conductivity and sluggish electrochemical reaction kinetics. Herein, a hierarchical Cu-doped NiCo LDH/NiCo alloy heterostructure with rich oxygen vacancies by electronic modulation is tactfully designed. It extraordinarily effectively drives both the oxygen evolution reaction (151 mV@10 mA cm-2) and the hydrogen evolution reaction (73 mV@10 mA cm-2) in an alkaline medium. As bifunctional electrodes for overall water splitting, a low cell voltage of 1.51 V at 10 mA cm-2 and remarkable long-term stability for 100 h are achieved. The experimental and theoretical results reveal that Cu doping and NiCo alloy recombination can improve the conductivity and reaction kinetics of NiCo LDH with surface charge redistribution and reduced Gibbs free energy barriers. This work provides a new inspiration for further design and construction of nonprecious metal-based bifunctional electrocatalysts based on electronic structure modulation strategies.

Insight into Electrochemical Performance of Nitrogen-Doped Carbon/NiCo-Alloy Active Nanocomposites.

Nanocomposites containing Ni or Co or NiCo alloy and nitrogen-doped carbon with diverse ratios have been prepared and utilized as active elements in supercapacitors. The atomic contents of nitrogen, nickel, and cobalt have been adjusted by the supplement amount of Ni and Co salts. In virtue of the excellent surface groups and rich redox active sites, the NC/NiCo active materials exhibit superior electrochemical charge-storage performances. Among these as-prepared active electrode materials, the NC/NiCo1/1 electrode performs better than other bimetallic/carbon electrodes and pristine metal/carbon electrodes. Several characterization methods, kinetic analyses, and nitrogen-supplement strategies determine the specific reason for this phenomenon. As a result, the better performance can be ascribed to a combination of factors including the high surface area and nitrogen content, proper Co/Ni ratio, and relatively low average pore size. The NC/NiCo electrode delivers a maximum capacity of 300.5 C g-1 and superior capacity retention of 92.30% after 3000 unceasing charge-discharge cycles. After assembling it into the battery-supercapacitor hybrid device, a high energy density of 26.6 Wh kg-1 (at 412 W kg-1 ) is achieved, comparable to the recent reports. Furthermore, this device can also power four light-emitting-diode (LED) demos, suggesting the potential practicability of these N-doped carbon compositing with bimetallic materials.

N-Doped Carbon Confined NiCo Alloy Hollow Spheres as an Efficient and Durable Oxygen Electrocatalyst for Zinc-Air Batteries.

Exploring cost-efficient/durability bifunctional electrocatalysts are of upmost importance for the practical application of metal-air batteries. However, preparing bifunctional electrocatalysts with the above three advantages remains conceptually challenging. This work reports the preparation of N-doped carbon confined NiCo alloy hollow spheres (NiCo@N-C HS) as bifunctional oxygen electrocatalyst for Zn-air battery with a higher energy density (788.7 mWh gZn -1 ) and outstanding cycling stability (over 200 h), which are more durable than the commercialized Pt/C+RuO2 -based device. Electrochemical results and theoretical calculation demonstrate that the synergy in the NiCo@N-C accelerates the electronic transmission for improving activation of O2 * and OH* intermediates and optimizing reacted free energy pathways, while the hollow structures exposure more active sites for improving the reaction kinetics and enhancing the activity of ORR/OER reaction. This work provides crucial understanding for constructing low-cost transition metal-based catalyst to overcome the efficiency and durability barriers of metal-air batteries for widespread applications.

NiCo alloy/C nanocomposites derived from a Ni-doped ZIF-67 for lightweight microwave absorbers.

In this work, we prepared NiCo alloy/C with rhombic dodecahedron structure and superior microwave absorption performance by using ZIF-67 as the raw material. The rhombic dodecahedron NiCo alloy/C was with rough particles on the surface was photographed by field emission scanning electron microscopy. By adjusting the doping amount of Ni and the temperature of pyrolysis, improved the impedance matching of NiCo alloy/C. Specifically, NiCo alloy/C exhibits a minimum reflection loss of -65.48 dB at 13.48 GHz, while the thickness is 1.63 mm. Defects introduced in the Ni doping process and the special rhombic dodecahedral structure can cause multiple loss mechanisms. Therefore, this NiCo alloy/C composite has the potential to be a potential microwave absorber material with lightweight and high microwave absorption properties.

Novel Hydrogel-Derived Bifunctional Oxygen Electrocatalyst for Rechargeable Air Cathodes.

The commercialization of Zn-air batteries has been impeded by the lack of low-cost, highly active, and durable catalysts that act independently for oxygen electrochemical reduction and evolution. Here, we demonstrate excellent performance of NiCo nanoparticles anchored on porous fibrous carbon aerogels (NiCo/PFC aerogels) as bifunctional catalysts toward the Zn-air battery. This material is designed and synthesized by a novel K2Ni(CN)4/K3Co(CN)6-chitosan hydrogel-derived method. The outstanding performance of NiCo/PFC aerogels is confirmed as a superior air-cathode catalyst for a rechargeable Zn-air battery. At a discharge-charge current density of 10 mA cm-2, the NiCo/PFC aerogels enable a Zn-air battery to cycle steadily up to 300 cycles for 600 h with only a small increase in the round-trip overpotential, notably outperforming the more costly Pt/C+IrO2 mixture catalysts (60 cycles for 120 h). With the simplicity of the synthetic method and the outstanding electrocatalytic performance, the NiCo/PFC aerogels are promising electrocatalysts for Zn-air batteries.

Enhancing oxygen reduction reaction performance through eco-friendly chitosan gel-assisted molten salt strategy: Small NiCo alloy nanoparticles decorated with high-loading single Fe-NX.

We developed an effective and eco-friendly strategy using chitosan gel-molten salt to achieve high loading (2.23 At. %) of single Fe-NX as assistive active sites. These sites were combined with small NiCo alloy NPs distributed on porous carbon aerogels to boost the ORR performance. The FeSAs-NiCo alloy@N-C sphere exhibits exceptional mass activity and specific activity of 3.705 A.mg-1 and 8.79 mA.cm-2(ECSA), respectively, at 0.85 V versus RHE. It has a superior onset potential of 1.08 V versus RHE, surpassing that of its nanoparticle Fe counterpart and NiCo alloy@N-C sphere. The significant improvement in ORR performance of the FeSAs-NiCo alloy@N-C sphere could be attributed to the positive effects of increased lattice strain due to the single atoms of Fe-NX hybridized with small NiCo alloy NPs. The chitosan gel-assisted molten salt strategy and assistive active sites of Fe-NX hybridized with NiCo alloy NPs regulate the electronic properties of the FeSAs-NiCo alloy@N-C sphere, both geometrically via lattice strain mismatch and electronically through shifting of the d-band center. This could influence the binding energies for oxygen and/or oxygen reduction intermediate adsorption/desorption. The additional improvement in the ORR performance of the FeSAs-NiCo alloy@N-C sphere also benefits from having a lower electrochemical activation energy.

MOF-Derived Hollow Carbon Supported Nickel-Cobalt Alloy Catalysts Driving Fast Polysulfide Conversion for Lithium-Sulfur Batteries.

Transition-metal compounds can be used as electrocatalysts to expedite polysulfide conversion effectively in lithium-sulfur batteries. However, insufficient conductivity and tedious preparation process still limit their practical applications. In this work, NiCo alloy nanoparticles embedded in hollow carbon spheres (NiCo@HCS) are fabricated via a facile, template-free strategy from the NiCo-metal-organic framework (MOF) precursor and used as electrocatalysts for separator modification. NiCo@HCS can not only improve the adsorption capacity of polysulfides by d-band deviation to the Fermi level but also reduce the energy barrier in the process of catalytic polysulfide conversion. Due to favorable three-dimensional (3-D) morphology, improved adsorption, and promoted kinetics of NiCo@HCS, the battery containing the NiCo@HCS-modified separator gives a starting capacity of 1377 mAh g-1 at 0.2C, which is retained by 72% over 500 charge/discharge operations at 1.0C current density. Moreover, the battery's start capacity reaches 1180 mAh g-1 (5.9 mAh cm-2) with a high sulfur content of 5.0 mg cm-1 at 0.2C.

Mesoporous NiCo alloy/reduced graphene oxide nanocomposites as efficient hydrogen evolution catalysts.

Water electrolysis is a clean and efficient route for producing high-purity hydrogen. Developing highly efficient, stable and inexpensive electrocatalysts to replace Pt is currently a major challenge for the widespread application of water splitting. Herein, we report a facile and novel strategy for the synthesis of mesoporous NiCo alloy nanoparticle/reduced graphene oxide (MNiCo/rGO) composites via electroless deposition technique. Owing to the synergistic interaction of Ni and Co, the mesoporous structure of NiCo alloy, and the optimized combination of the mesoporous NiCo with rGO, the obtained optimal MNi63Co37/rGO5 catalyst exhibits outstanding electrocatalytic performance for hydrogen evolution reaction (HER) with a low overpotential of 115 mV to reach the current density of 10 mA cm-2, and a small Tafel slope of 45 mV dec-1, as well as a high durability in alkaline solution. These remarkable merits make it a favorable alternative to noble metal Pt-based catalysts for HER, thereby further promoting the development of non-noble metal electrocatalysts.

N-Doped Graphene-Decorated NiCo Alloy Coupled with Mesoporous NiCoMoO Nano-sheet Heterojunction for Enhanced Water Electrolysis Activity at High Current Density.

Developing highly effective and stable non-noble metal-based bifunctional catalyst working at high current density is an urgent issue for water electrolysis (WE). Herein, we prepare the N-doped graphene-decorated NiCo alloy coupled with mesoporous NiCoMoO nano-sheet grown on 3D nickel foam (NiCo@C-NiCoMoO/NF) for water splitting. NiCo@C-NiCoMoO/NF exhibits outstanding activity with low overpotentials for hydrogen and oxygen evolution reaction (HER: 39/266 mV; OER: 260/390 mV) at ± 10 and ± 1000 mA cm-2. More importantly, in 6.0 M KOH solution at 60 °C for WE, it only requires 1.90 V to reach 1000 mA cm-2 and shows excellent stability for 43 h, exhibiting the potential for actual application. The good performance can be assigned to N-doped graphene-decorated NiCo alloy and mesoporous NiCoMoO nano-sheet, which not only increase the intrinsic activity and expose abundant catalytic activity sites, but also enhance its chemical and mechanical stability. This work thus could provide a promising material for industrial hydrogen production.

NixCoy Nanocatalyst Supported by ZrO2 Hollow Sphere for Dry Reforming of Methane: Synergetic Catalysis by Ni and Co in Alloy.

NixCoy/H-ZrO2 catalysts composed of highly dispersed NixCoy nanoparticles supported by mesoporous ZrO2 hollow sphere are synthesized by templating and impregnation processes. According to thermogravimetric analysis, X-ray photoelectron spectroscopy, and dry reforming results, a synergetic reaction mechanism is proposed to explain the better performance of alloy catalysts compared to Ni/H-ZrO2 or Co/H-ZrO2. In dry reforming of methane (DRM) reaction, Ni and Co act as catalysts for CH4 cracking and CO2 reduction, respectively, and the induced carbon deposits on Ni can be oxidized by the active oxygen left on Co, which regenerate the metal surface for the following reaction. Among all the alloy catalysts, the Ni0.8Co0.2/H-ZrO2 catalyst presents the highest activity and stability because the strong metal-support interaction prevents the sintering of nanocatalysts at high temperature and the hollow structure enhances the mass transportation of reactants and products. More importantly, Ni and Co can synergistically balance the speed of CH4 cracking and CO2 reduction, which effectively avoid coke accumulation/catalyst oxidation and ensure fast and stable conversion for DRM reaction.

Bimetallic Metal-Organic Framework Derived Metal-Carbon Hybrid for Efficient Reversible Oxygen Electrocatalysis.

Development of cost-effective electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is key to enabling advanced electrochemical energy conversion technologies. Here, a novel nitrogen-doped metal-carbon hybrid (NiCo/CN) with a unique 3D hierarchical structure, consisting of uniformly distributed bimetallic nanoparticles encapsulated by partially graphitized N-doped carbon shells, is fabricated by a one-step pyrolysis of a nanoscale metal-organic framework as precursor, which exhibits excellent activity for both ORR and OER. The surface chemical changes on the carbon hybrid probed by X-ray photoelectron spectroscopy (XPS) reveal the presence of favorable electronic interaction at the metal-nitrogen-carbon interface. Remarkably, the NiCo/CN catalyst prepared at high temperature (800°C) manifests a comparable performance to a commercial Pt/C catalyst for the ORR, but also superior stability, path selectivity and methanol tolerance. On the other hand, the E onset (1.48 V vs. reversible hydrogen electrode) and E j = 10 mA/cm 2 of NiCo/CN-800 for OER is very close to the state-of-the-art noble catalyst RuO2 (Eonset = 1.46 and E j = 10 mA/cm 2 ) along with superior stability over 20 h of operation. The excellent catalytic property is attributable to the unique nanostructure, high porosity and the constructive synergistic effects of the elements M, N, and C.