Regulating Hollow Carbon Cage Supported NiCo Alloy Nanoparticles for Efficient Electrocatalytic Hydrogen Evolution Reaction

A NiCo alloy particle-decorated TiO2 nanoarray as an efficient electrocatalyst for nitrite reduction to ammonia

Electrocatalytic nitrite (NO2-) reduction (NO2-RR) is a potential environmentally friendly method for producing NH3 efficiently. Herein, a hybrid catalyst with NiCo alloy particles uniformly decorated on a TiO2 nanograss array (NiCo-TiO2) is reported to display excellent NO2-RR performance. In alkaline media, NiCo-TiO2 possesses a large NH3 yield of 18 736.2 μg h-1 cm-2 at -0.4 V vs. RHE and a maximum FE of 97.5%. Utilizing NiCo-TiO2 as the cathode of a Zn-NO2- battery, it exhibits remarkable peak power density (6.49 mW cm-2) and a large NH3 yield (1911.4 g h-1 cm-2 at 20 mA cm-2). This work highlights the potential of catalysts based on alloy-metallic oxide hybrids for the electrochemical conversion of the NO2- pollutant into NH3.

A ratiometric electrochemical sensor based on Cu@Ni/MWCNTs for detection of chloramphenicol

A signal tag was successfully designed by means of two-step reduction approach, in which CuNi nanoparticles (CuNi NPs) uniformly distributed on the surface of multiwall carbon nanotubes (MWCNTs). This composites not only inherits excellent conductivity and surface area of MWCNTs, but also endows the material with superior electrocatalytic performance due to the introduction of CuNi NPs. Then, a ratiometric sensing platform coupled with built-in correction ability for convenient direct determination of chloramphenicol (CAP) was exploited, wherein Cu@Ni/MWCNTs were used as signal label and ferrocene (Fc) as internal reference. It is noteworthy that ratiometric measurement was performed by directly incorporating Fc into the electrolyte solution. The profound investigation into the sensing performance of the implemented sensor revealed that Cu@Ni/MWCNTs nanocomposites exhibit satisfactory electrocatalytic activity and stability. Additionally, the integration of the ratiometric strategy markedly enhanced the reliability and repeatability and exhibited decent performance in CAP determination varying from 0.1 to 10 μM. Overall, the corporation of Cu@Ni/MWCNTs with excellent electrocatalytic ability as well as elaborated ratiometric method makes it a valuable tool for future assaying an extensive range of substances.

Unique NiCo bimetal boosting 98% CH4 selectivity and high catalysis stability for photothermal CO2 hydrogenation

A highly dispersed NiCo alloy catalyst derived from NiCo bimetallic-organic framework nanosheets was synthesized for efficient photothermal catalysis for CO2 hydrogenation to methane. The NiCo bimetal catalyst achieves a CH4 production rate of 55.60 mmol g-1 h-1 with only a 18.82% decline in performance after 86 hours under atmospheric pressure at selected 290 °C and continuous flow reaction. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) reveals the synergistic and complementary roles of light and heat in photothermal catalysis. The thermochemical process drives the reverse water-gas shift reaction to form a *CO intermediate, a key intermediate for the formation of CH4, and light irradiation-generating strong near field from the surface plasma resonance of NiCo bimetals promotes the subsequent *CO hydrogenation step to form *CHO, the rate-determining step for the hydrogenation of CO2 into CH4. Meanwhile, density functional theory (DFT) calculations suggest that the NiCo bimetallic catalyst can also lower the energy barrier of *CO hydrogenation, facilitating the formation of *CHO.

Self-Powered Hydrogen Production via Laser-Coordinated NiCoPt Alloy Catalysts in an Integrated Zn-Hydrazine Battery with Hydrazine Splitting

This study proposes a novel approach for the rapid transformation of bimetallic NiCo-oxides into trimetallic NiCoPt alloys using a pulsed laser technique in an ethanol medium in the presence of Pt salts. The electrochemical results demonstrate the exceptional dual-functional activity of the optimized NiCoPt-10 alloy, effectively catalyzing both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR). Specifically, the NiCoPt-10 alloy presents a low overpotential of 90 mV at 10 mA·cm-2 for HER and a small working potential of 0.068 V versus the reversible hydrogen electrode (RHE) at 10 mA·cm-2 for HzOR. In situ Raman spectroscopy and theoretical calculations delivered insights into the dual-functional activity of the NiCoPt alloy. Consequently, the overall hydrazine splitting (OHzS) electrolyzer, employing a NiCoPt-10||NiCoPt-10 configuration, required only 0.295 V to deliver 10 mA·cm-2. Notably, using this dual-functional NiCoPt-10 catalyst as the cathode combined with Zn foil as the anode in a Zn-hydrazine (Zn-Hz) battery, achieved efficient hydrogen (H2) production with an energy efficiency of 97%. Furthermore, self-powered H2 production is realized by integrating the Zn-Hz battery with the OHzS electrolyzer, demonstrating its excellent potential for practical applications. Thus, this rapid synthetic strategy can aid in designing effective electrocatalysts for addressing challenges in H2 energy production.

Zeolite Imidazole Framework-Derived Hollow Nickel-Cobalt Layered Double Hydroxide Intercalated with Metalloporphyrin for Enhanced Oxygen Evolution Reaction

The design of highly efficient, stable, and nonprecious-metal-based electrocatalysts for the oxygen evolution reaction (OER) has been a major research topic in the field of hydrogen production from electrolytic water splitting. In this work, a novel hierarchical hollow NiCo layered double hydroxide (NiCo LDH) with Cu-TCPP (TCPP = tetrakis(4-carboxyphenyl)-porphyrin) intercalation (denoted as X-CT/LR, where X is the amount of Cu-TCPP addition) was successfully fabricated by using zeolite imidazole framework-67 (ZIF-67) as a template. Among them, 1-CT/LR has superior OER activity and stability, requiring only a low overpotential of 204 mV to reach a current density of 10 mA/cm2. The experimental results show that the introduced Cu-TCPP, in addition to being an active center itself, also acts as an electron transfer medium in the interlayer to enhance the conductivity of the material. Meanwhile, the hierarchical hollow structure and interlayer domain-limiting effect of NiCo LDH also ensure the dispersion and stabilization of Cu-TCPP, which is favorable to give full play to the synergistic catalytic effect of the two components. This work provides a facile strategy to obtain a nonprecious-metal-based OER electrocatalyst for water splitting.

Facile Aqueous Route to Large-Scale Superhydrophilic TiO2-Incorporated Graphitic Carbon Nitride-Coated Ni(OH)2 and Ni2P Nano-Architecture Arrays as Efficient Electrocatalysts for Enhanced Hydrogen Production

Water splitting by an electrochemical method to generate hydrogen gas is an economic and green approach to resolve the looming energy and environmental crisis. Designing a composite electrocatalyst having integrated multichannel charge separation, robust stability, and low-cost facile scalability could be considered to address the issue of electrochemical hydrogen evolution. Herein, we report a superhydrophilic, noble-metal-free bimetallic nanostructure TiO2/Ni2P coated on graphitic polyacrylonitrile carbon fibers (g-C/TiO2/Ni2P) using a facile hydrothermal method followed by phosphorylation. In an aqueous-based route, PAN is dissolved in water in the presence of ZnCl2, followed by wet-spinning to prepare scalable PAN/ZnCl2 fibers. The nitrogen-contained porous graphitic carbon fibers are prepared via the pyrolysis of PAN/ZnCl2 fibers; now ZnCl2 acts as a volatile porogen to form porous matrix structures. Finally, the as-prepared graphitic carbon fibers are electrochemically activated by incorporating TiO2/Ni2P active sites. The materials formed in this work show excellent electrocatalytic activity for the hydrogen evolution reaction. The as-synthesized g-C/TiO2/Ni2P catalyst shows a low overpotential, its electrocatalytic activity is improved, and its efficiency is better than that of the commercial Pt/C catalyst. At a current density of -10 mA/cm2, the g-C/TiO2/Ni2P catalyst shows an overpotential of 55 mV, while the commercial Pt/C catalyst shows an overpotential of 77 mV. Our work provides a facile aqueous scalable route with no need for noble metals that can be considered as a potential alternative for the commercial Pt/C catalyst.

In situ fabrication of Ni3S2/Cu2S heterojunction on nickel foam as a highly efficient and durable electrocatalyst for overall water splitting

The development of cost-efficient bifunctional electrocatalysts is significant for overall water splitting. Herein, we report the in situ fabrication of heterogeneous NF/Ni3S2/Cu2S-X (where X refers to Cu2+ concentrations of 50, 75, and 100 mM) on nickel foam (NF) using an electrodeposition-hydrothermal method. The in situ electrodeposited metallic Cu0 layers on the NF conferred higher stability to the resulting bimetallic sulfide of Ni3S2/Cu2S. In alkaline media (1 M KOH), the optimized NF/Ni3S2/Cu2S-75 exhibited ultra-low overpotentials of 108 and 166 mV during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 10 mA·cm-2. For overall water splitting, the catalyst showed a significantly low cell voltage of 1.50 V and long stabilization time (≥150h)at15mA·cm-2. Density functional theory calculations revealed that the formation of Ni3S2/Cu2S heterojunction reduced the Gibbs free energy of hydrogen adsorption (ΔGH*) on the S site, thus facilitating H2 generation. This study serves as a guide for tailoring transition metal-based catalysts with enhanced activity and long-term durability, thereby contributing to highly efficient water electrolysis for large-scale hydrogen production.

Interface Engineering Induced by Low Ru Doping in Ni/Co@NC Derived from Ni-ZIF-67 for Enhanced Electrocatalytic Overall Water Splitting

Electrochemical water splitting is a promising approach for hydrogen evolution reactions (HER); however, the oxygen evolution reaction (OER) remains a major bottleneck due to its high energy requirements. High-performance electrocatalysts capable of facilitating HER, OER, and overall water splitting (OWS) are highly needed to improve OER kinetics. In this work, we synthesized a trimetallic heterostructure of Ru, Ni, and Co incorporated into N-doped carbon (denoted as Ru/Ni/Co@NC) by first synthesizing Ni/Co@NC from Ni-ZIF-67 polyhedrons via high-temperature carbonization, followed by Ru doping using the galvanic replacement method. Benefiting from increased active surface sites, modulated electronic structure, and enhanced interfacial synergistic effects, Ru/Ni/Co@NC exhibited exceptional electrocatalytic performance for both HER and OER processes. The optimized Ru/Ni/Co@NC catalyst, with a minimal Ru mass ratio of ∼2.07%, demonstrated significantly low overpotential values of 34 mV for HER and 174 mV for OER at a current density of 10 mA/cm2 with corresponding Tafel slope values of 33.42 and 34.39 mV/dec, respectively. Further, the optimized catalyst was loaded onto carbon paper and used as anode and cathode materials for alkaline water splitting. Interestingly, a low cell voltage of just 1.44 V was obtained. The enhanced electrolytic performance was further elaborated by density functional theory (DFT) calculations, which confirmed that Ru doping in Ni/Co introduced additional active sites for H*, enhancing adsorption/desorption abilities for HER (ΔGH* = -0.30 eV), lowering water dissociation barrier (ΔGb = 0.49 eV) and reducing the energy barrier for the rate-determining step of OER (O* → OOH*) to 1.62 eV in an alkaline environment. These findings reflect the significant potential of ZIF-67-based catalysts in energy conversion and storage applications.

Integrating Sulfur Doping with a Multi-Heterointerface Fe7S8/NiS@C Composite for Wideband Microwave Absorption

Heterointerface engineering is presently considered a valuable strategy for enhancing the microwave absorption (MA) properties of materials via compositional modification and structural design. In this study, a sulfur-doped multi-interfacial composite (Fe7S8/NiS@C) coated with NiFe-layered double hydroxides (LDHs) is successfully prepared using a hydrothermal method and post-high-temperature vulcanization. When assembled into twisted surfaces, the NiFe-LDH nanosheets exhibit porous morphologies, improving impedance matching, and microwave scattering. Sulfur doping in composites generates heterointerfaces, numerous sulfur vacancies, and lattice defects, which facilitate the polarization process to enhance MA. Owing to the controllable heterointerface design, the unique porous structure induced multiple heterointerfaces, numerous vacancies, and defects, endowing the Fe7S8/NiS@C composite with an enhanced MA capability. In particular, the minimum reflection loss (RLmin) value reached -58.1 dB at 15.8 GHz at a thickness of 2.1 mm, and a broad effective absorption bandwidth (EAB) value of 7.3 GHz is achieved at 2.5 mm. Therefore, the Fe7S8/NiS@C composite exhibits remarkable potential as a high-efficiency MA material owing to the synergistic effects of the polarization processes, multiple scatterings, porous structures, and impedance matching.

Design and fabrication of intermetallic NiCo electrocatalysts for the alkaline HER

The design and fabrication of highly efficient electrocatalysts are crucial for reducing energy consumption, improving hydrogen production rates, and prolonging the service life of alkaline electrolyzers. In this study, intermetallic L10-NiCo electrocatalysts were designed using DFT calculations and fabricated through a one-step solid-state reaction method. The DFT calculations indicated that L10-NiCo presented a lower H adsorption Gibbs free energy and a moderate H2O dissociation barrier compared to the commonly used Ni catalyst and disordered NiCo alloy. Increasing the solid-state reaction temperature facilitated the formation of intermetallic L10-NiCo. Electrocatalytic tests for the alkaline HER demonstrated that the ECSA of L10-NiCo nanoparticles increased to 2.3 times, the overpotential decreased by 19%, the electrocatalytic activity increased to 1.5 times, and the stability improved to 2.2 times compared to those of the Ni nanoparticles. This research provides insights into the design and fabrication of highly efficient catalytic electrodes for alkaline electrolyzers.

Cu Regulating the Bifunctional Activity of Co-O Sites for the High-Performance Rechargeable Zinc-Air Battery

The rational design of cost-effective and highly active electrocatalysts becomes the crucial energy storage technology to boost the kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), which hinders the large-scale application of metal-air batteries under the situation of increasingly pressing energy anxiety. Herein, the Co-based ZIF introduced the moderate amount of Cu2+-derived Cu/Co metal nanoparticles (NPs) embedded in carbon frameworks after high-temperature calcination. The Co-O bond on the surface of Co nanoparticles is modulated by adjacent Cu nanoparticles with the surface Cu-O bonds. The resulted increase of the Co2+/Co3+ ratio in 0.1CuCo-NC enhances the ORR/OER bifunctional catalytic kinetics along with the ΔE of 0.639 V. In situ Raman spectra of the catalyst on the three-electrode system as well as in the driven zinc-air battery (ZAB) show that the Co-O active sites regulated by Cu nanoparticles with Cu-O bonds maintain a periodic lattice expansion and compression during discharging and charging. The zinc-air battery based on 0.1CuCo-NC has a peak power density of up to 198.3 mW cm-2, a mass-specific capacity of 798.2 mAh g-1, and a cycling stability of 923 h at room temperature. This work makes up the research gap of a Co-based metal-organic framework (MOF)-derived catalyst regulated by a transition metal.

Electronic Structure Regulated Nickel-Cobalt Bimetal Phosphide Nanoneedles for Efficient Overall Water Splitting

Transition metal phosphides (TMPs) have been widely studied for water decomposition for their monocatalytic property for anodic or cathodic reactions. However, their bifunctional catalytic activity still remains a major challenge. Herein, hexagonal nickel-cobalt bimetallic phosphide nanoneedles with 1-3 μm length and 15-30 nm diameter supported on NF (NixCo2-xP NDs/NF) with adjusted electron structure have been successfully prepared. The overall alkaline water electrolyzer composed of the optimal anode (Ni0.67Co1.33P NDs/NF) and cathode (Ni1.01Co0.99P NDs/NF) provide 100 mA cm-2 at 1.62 V. Gibbs Free Energy for reaction paths proves that the active site in the hydrogen evolution reaction (HER) is Ni and the oxygen evolution reaction (OER) is Co in NixCo2-xP, respectively. In the HER process, Co-doping can result in an apparent accumulation of charge around Ni active sites in favor of promoting HER activity of Ni sites, and ΔGH* of 0.19 eV is achieved. In the OER process, the abundant electron transfer around Co-active sites results in the excellent ability to adsorb and desorb *O and *OOH intermediates and an effectively reduced ∆GRDS of 0.37 eV. This research explains the regulation of electronic structure change on the active sites of bimetallic materials and provides an effective way to design a stable and effective electrocatalytic decomposition of alkaline water.

First Reusable Catalyst for the Reductive Coupling Reaction of Organohalides with Aldehydes

In this study, we simulate the reductive coupling (Barbier-Grignard-type) reaction of organohalides with aldehydes using a new reusable catalyst. In this regard, bimetallic alloys of NiCo encapsulated in melamine-based dendrimers (MBD) immobilized on magnetic nanoparticles symbolized as γ-Fe2O3-MBD/NiCo were designed and synthesized. The structure and properties of the catalyst were studied by a variety of techniques such as Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), energy-dispersive spectrometry (EDS) mapping, and inductively coupled plasma (ICP). The presence of NiCo nanoalloys was confirmed by XRD and XPS analysis, TEM images, and EDS mapping. Various secondary alcohols were produced in good to high yields by reductive coupling of different types of aldehydes and organohalides in the presence of HCO2K as a nonmetallic reducing agent in aqueous media catalyzed by γ-Fe2O3-MBD/NiCo. In these reactions, the high catalytic performance of γ-Fe2O3-MBD/NiCo was achieved in comparison to monometallic counterparts due to the synergistic cooperative effect of Co and Ni in the NiCo nanoalloys. Magnetic and hydrophilic properties of the catalyst facilitate the catalyst recyclability for seven runs. The reusability of γ-Fe2O3-MBD/NiCo, use of water as an environmentally friendly solvent, ease of processing, and absence of metal additives make this process an excellent choice for the reductive coupling reaction to produce secondary alcohols from aldehydes. This is the first report on these kinds of reactions using a reusable catalyst.