Cu2S/Ni3S2 ultrathin nanosheets on Ni foam as a highly efficient electrocatalyst for oxygen evolution reaction

It is an inevitable choice to find efficient and economically-friendly electrocatalysts to reduce the high overpotential of oxygen evolution reaction (OER), which is the key to improve the energy conversion efficiency of water splitting. Herein, we synthesized Cu₂S/Ni₃S₂ catalysts on nickel foam (NF) with different molar ratios of Ni/Cu by a simple two-step hydrothermal method. Cu₂S/Ni₃S₂-0.5@NF (CS/NS-0.5@NF) effectively reduces the overpotential of OER, displaying small overpotentials (237 mV@100 mA cm^?2 and 280 mV@500 mA cm^?2) in an alkaline solution, along with a low Tafel slope of 44 mV dec^?1. CS/NS-0.5@NF also presents an excellent durability at a relatively high current density of 100 mA cm^?2 for 100 h. The excellent performance is benefited by the prominent structural advantages and desirable compositions. The nanosheet has a high electrochemical active surface area and the porous structure is conducive to electrolyte penetration and product release. This work provides an economically-friendly Cu-based sulfide catalyst for effective electrosynthesis of OER.     

In-situ synthesis of N/S co-doped Cu-based graphene-like nanosheets as high efficiency electrocatalysts for oxygen reduction reaction

Heteroatom-doped transition metal electrocatalysts supported on carbon materials are widely-recognized as the promising catalysts for oxygen reduction reaction (ORR). Here, we describe the one-pot method of preparing the Cu-based PAT₁-Cu_x/KB catalyst with Cu/N/S doped graphene-like nanosheets. For the obtained catalyst, Cu²⁺ ions catalyzed the polymerized 2-aminothiazole organic monomers into nanosheet and simultaneously in-situ doped Cu, N, S atoms into the carbon matrix. The amount of Cu²⁺ ions affected the geometry structure, as well as the formation of Cu–N structure and C–S–C bond of PAT₁-Cu_x/KB catalyst. Cu₂S crystals with ORR catalytic ability were also generated in the catalysts. The Cu–N structure in the catalyst regulates the d-electron density of inert copper through the synergistic effect of electronic connection between copper and nitrogen atoms. N and S doped in the carbon skeleton changes the spin density and charge distribution of near carbon atoms. Therefore, PAT₁-Cu_0.33/KB catalyst with graphene-like nanosheets, Cu–N structure, C–S–C bond, and Cu₂S crystals exhibits excellent activities with E_1/2 = 0.84 V and high limit-current density of 5.25 mA cm⁻² for ORR.     

Copper induced phosphide for enhanced electrochemical hydrogen evolution reaction

Research on highly efficient catalysts for electrochemical hydrogen evolution reaction (HER) remains a challenge. In this work, we successfully wrap copper (Cu) inside of copper phosphide (Cu₃P) nanoparticle to form a copper/copper phosphide (Cu/Cu₃P) core/shell structure attached on carbon nanotubes (CNTs) for enhanced HER activity in acid. The average size of the core/shell particles is around 25 nm, with about 5 nm of Cu₃P as the outer layer. The catalytic activity of the core/shell structure is significantly promoted compared to the metallic Cu and Cu₃P pure phases nanoparticles on CNTs, requiring overpotentials of 84 and 161 mV to achieve 10 and 100 mA cm⁻² of current density, respectively. The core/shell structure also presents high HER durability and stability, with the polarization curve overlapped after 5000 cycles of CVs and steady current density at 25 mA cm⁻² for as long as 10 h. To account for the promoted HER performance, the Cu/Cu₃P structure is fully investigated by physical and electrochemical characterizations and density functional theory (DFT) calculations. The DFT results depict that the neutralized the adsorption Gibbs free energy of hydrogen atoms (ΔG_H1) is induced by the electronic interactions between metallic Cu and phosphide phase.     

Electrosynthesis of hierarchical Cu2O–Cu(OH)2 nanodendrites supported on carbon nanofibers/poly(para-phenylenediamine) nanocomposite as high-efficiency catalysts for methanol electrooxidation

The development of highly efficient catalysts using inexpensive and earth-abundant metals is a crucial factor in a large-scale commercialization of direct methanol fuel cells (DMFCs). In this study, we explored a new catalyst based on copper nanodendrites (CuNDs) supported on carbon nanofibers/poly (para-phenylenediamine) (CNF/PpPD) nanocomposite for methanol oxidation reaction (MOR). The catalyst support was prepared on a carbon paste electrode by electropolymerization of para-phenylenediamine monomer on a drop-cast carbon nanofibers network. Afterwards, CuNDs were electrodeposited on the nanocomposite through a potentiostatic method. The morphology and the structure of the prepared nanomaterials were characterized by transmission electron microscope, scanning electron microscope, energy dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscope. The results suggested that a three-dimensional nanodendritic structure consisting of Cu₂O and Cu(OH)₂ formed on the hybrid CNF/PpPD nanocomposite. The catalytic performance of CuNDs supported on CNF, PpPD and CNF/PpPD was evaluated for MOR under alkaline conditions. The CNF/PpPD/CuNDs exhibits a highest activity (50 mA cm^?2) and stability toward MOR over 6 h, with respect to CNF/CuNDs (40 mA cm^?2) and PpPD/CuNDs (36 mA cm^?2). This inexpensive catalyst with high catalytic activity and stability is a promising anode catalyst for alkaline DMFC applications.     

Bandgap control of p-n heterojunction of Cu–Cu2O @ ZnO with modified reduced graphene oxide nanocomposites for photocatalytic hydrogen evolution

Here, we describe the in-situ synthesis of multicomponent ZnO-based photocatalysts for hydrogen production. We fabricated ZnO coupled with Cu–Cu₂O nanoparticles and modified reduced graphene oxide (mRGO) to ameliorate hydrogen production. The simultaneous introduction of mRGO and Cu–Cu₂O enhanced the generation rate of photocatalytic hydrogen to 3085.02 μmol g^?1 h^?1 due to significant alteration of the electronic structure. The bandgap energy of the prepared catalysts decreased from 3.2 eV for pristine ZnO to 2.64 eV for a composite containing 15% Cu–Cu₂O. The optimal designed heterostructure efficiently separates photo charge carriers and prevents charge carriers’ recombination by accelerating charge transfer with the help of mRGO and metallic Cu and as a result leading to efficient hydrogen yields.     

Bifunctional iron doped CuS catalysts towards highly efficient overall water electrolysis in the alkaline electrolyte

Efficient catalysts towards overall water electrolysis in alkaline electrolytes were highly desirable for the hydrogen production technology. The surface electronic states of copper in CuS nanocrystal catalysts were modified by iron doping through a simple wet-chemical method. The iron-doped CuS catalysts displayed drastically enhanced catalytic activities for overall water electrolysis in the strong alkaline electrolyte of 1 M KOH after a simple cyclic voltammetry activation. The optimized catalytic performance for overall water electrolysis was achieved in the CuFe_0.6S_1.6 catalyst, which exhibited a low overpotential of ?237 mV for HER and 302 mV for OER to reach 10 mA cm^?2. The high activities for overall water electrolysis in CuFe_0.6S_1.6 were induced by the enhanced charge transfer from Cu to S via iron doping, which not only modified the surface electronic state of copper but also enhanced charge transfer during the electrochemical reactions. Moreover, the catalysts displayed satisfying stability for over 20 h at a high current density of 300 mA cm^?2 for both HER and OER, showing great potential for industrial water electrolysis.     

Facile synthesis of copper selenide with fluffy intersected-nanosheets decorating nanotubes structure for efficient oxygen evolution reaction

Rational nanostructure design is the key point to prepare catalysts with superior catalytic performance, and tedious preparation method limits them large-scale application. Here, a Cu₂Se with fluffy intersected-nanosheets decorating nanotubes structure were prepared by a simple and rapid solution-immersion method at room temperature. The hollow hierarchical structure on a good conductor Cu foam (CF) enlarges surface available sites, enhances the conductivity of electrode materials, then endowing the catalyst with quick charge/mass transportation and favorable oxygen evolution reaction (OER) performance. In alkaline medium, our as-prepared Cu₂Se/CF electrode demonstrates high OER performance, especially for lower overpotential (200 mV at 10 mA cm⁻²) compared with the previously reported Cu-based catalysts. Moreover, the Cu₂Se catalyst could afford galvanostatic test of 10 mA cm⁻² test over 12 h and present superior OER tolerance. These results indicate that the Cu₂Se catalyst via cost efficiency and efficient solution-immersion method could be applied to large-scale efficient OER.     

The 3D ultra-thin Cu1-xNixS/NF nanosheet as a highly efficient and stable electrocatalyst for overall water splitting

In recent years, the exploration of efficient and stable noble-metal-free electrocatalysts is becoming increasingly important, used mainly for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In this work, a new ultrathin porous Cu_1-xNi_xS/NF nanosheets array was constructed on the 3D nickel skeleton by two-step method: hydrothermal method and vulcanization method. Through these two processes, Cu_1-xNi_xS/NF has a larger specific surface area than that of foamed nickel (NF) and Cu_1-xNi_xO/NF. The Cu_1-xNi_xS/NF materials show excellent catalytic activity by accelerating the electron transfer rate and increase the amount of H₂ and O₂ produced. The lower overpotential was obtained only 350 mV at 20 mA cm⁻² for OER, not only that, but also the same phenomenon is pointed out in HER, optimal Cu_1-xNi_xS/NF presents low overpotentials of 189 mV to reach a current density of 10 mA cm⁻² in 1.0 M KOH for HER. Both OER and HER shows a lower Tafel slope: 51.2 mV dec⁻¹ and 127.2 mV dec⁻¹, subsequently, the overall water splitting activity of Cu_1-xNi_xS/NF was investigated, and the low cell voltage was 1.64 V (current density 10 mA cm⁻²). It can be stable for 14 h during the overall water splitting reaction. These results fully demonstrate that Cu_1-xNi_xS/NF non-precious metal materials can be invoked become one of the effective catalysts for overall water splitting, providing a richer resource for energy storage.     

Okra-like hollow Cu0.15-CoP/Co3O4@CC nanotube arrays catalyst for overall water splitting

The manufacture of hydrogen energy by overall water splitting (OWS) has been broadly considered as a promising candidate for constant energy systems. Herein, we report an okra-like hollow Cu_0.15-CoP/Co₃O₄@CC nanotube arrays catalyst through a simple hydrothermal-phosphating method. As a noble-metal-free catalyst, it exhibits outstanding HER (hydrogen evolution reaction) catalytic activity with an overpotential of 13 mV to achieve 10 mA cm^?2 in 1 M KOH electrolyte. For OER (oxygen evolution reaction), it demands 225 mV to achieve 10 mA cm^?2. When okra-like hollow Cu_0.15-CoP/Co₃O₄@CC is used as both cathode and anode electrode materials, 1.487 V is required to reach 10 mA cm^?2 for OWS, better than numerous electrocatalysts that have been reported. Moreover, it displays excellent stability in a continuously 60 h i-t test, proving an enormous potential for large-scale applications. The theoretical calculation of density functional theory (DFT) further reveals that Cu doping can bring localized structure polarization and reduce the hydrogen adsorption free energy (ΔG_H1) on the interstitial sites, thus leading to a significant increase in catalytic activity.     

ZIF67@MoO3 NSs@NF composite electrocatalysts reinforced by chemical bonds and oxygen vacancy for efficient oxygen evolution reaction and overall water-splitting

A kind of composite electrocatalysts with the structure of MoO₃ nanosheets coated by ZIF67 nanocrystals and grown on the nickel foam substrate (ZIF67@MoO₃ NSs@NF) is prepared and mainly used as the electrode for oxygen evolution reaction (OER) and overall water splitting. The excellent electrocatalytic activity of ZIF67@MoO₃ NSs@NF are demonstrated. It can use the overpotential (?) of 178 mV and 386 mV respectively to drive 10 mA cm^?2 and 50 mA cm^?2. It is also observed that the ZIF67@MoO₃ NSs@NF electrode has the highest initial current density (45.7 mA cm^?2) at 1.618 V and can maintain more than 90% of the initial current density after 20,000 s. The ZIF67@MoO₃ NSs@NF electrode also shows the small HER overpotential of 135 mV at 10 mA cm^?2. Furthermore, the voltage of ZIF67@MoO₃ NSs@NF as a bifunctional overall water splitting catalysts is 1.58 V at 10 mA cm^?2, which is superior to another noble metal electric catalyst combination RuO₂/NF(+)//Pt–C/NF(?). And the ZIF67@MoO₃ NSs@NF(+)//ZIF67@MoO₃ NSs@NF(?) combination can maintain more than 90% of the initial current density after 65,000 s at 1.58 V. The main reason is the composite interface of MoO₃ NSs and ZIF67 phases with Co–O bonds, C–O–Mo bonds and oxygen vacancies defects facilitates the increase of the active sites and efficient electron transfer rate.     

Electrodeposition of NiS/Ni2P nanoparticles embedded in amorphous Ni(OH)2 nanosheets as an efficient and durable dual-functional electrocatalyst for overall water splitting

To develop earth-abundant and cost-effective catalysts for overall water splitting is still a major challenge. Herein, a unique “raisins-on-bread” Ni–S–P electrocatalyst with NiS and Ni₂P nanoparticles embedded in amorphous Ni(OH)₂ nanosheets is fabricated on Ni foam by a facile and controllable electrodeposition approach. It only requires an overpotential of 120 mV for HER and 219 mV for OER to reach the current density of 10 mA cm⁻² in 1 M KOH solution. Employed as the anode and cathode, it demonstrates extraordinary electrocatalytic overall water splitting activity (cell voltage of only 1.58 V @ 10 mA cm⁻²) and ultra-stability (160 h @ 10 mA cm⁻² or 120 h @50 mA cm⁻²) in alkaline media. The synergetic electronic interactions, enhanced mass and charge transfers at the heterointerfaces facilitate HER and OER processes. Combined with a silicon PV cell, this Ni–S–P bifunctional catalyst also exhibits highly efficient solar-driven water splitting with a solar-to-hydrogen conversion efficiency of 12.5%.     

The effective and stable Cu–C@SiO2 catalyst for the syntheses of methanol and ethylene glycol via selective hydrogenation of ethylene carbonate

The co-production of ethylene glycol and methanol via ethylene carbonate hydrogenation derived from CO₂ has attracted great concerns because of the promising chemical utilization of CO₂ in large-scale. Copper-based catalysts are widely concerned in hydrogenation of ester due to the high catalytic efficiency and low cost, but the stability of copper-based catalyst is poor and needs to be further improved. In this study, the modification Cu–C@SiO₂-R catalyst with graphite oxide was prepared by using Cu₃(BTC)₂ as the precursor and ammonia evaporation method, and was applied in ethylene carbonate hydrogenation to synthesis ethylene glycol and methanol. Furthermore, the catalysts were characterized in detail. The results showed that the Cu–C@SiO₂-R catalyst was modified with graphite oxide, the average size of Cu particles was 2.9 nm and Cu particles had good dispersion. In addition, both Cu–C@SiO₂-R and Cu@SiO₂-R catalysts had similar ratio of Cu⁺/(Cu⁰+Cu⁺). In a batch reactor, under 453 K, 5 MPa, 4 h, the catalytic efficiency was 80.0% EC conversion 92.2% EG and 70.8% MeOH selectivity showing excellent catalytic performance capability of Cu–C@SiO₂-R catalyst. In long-term experiment, the Cu–C@SiO₂-R catalyst showed excellent stability after using for 264 h. The activity was 0.63 g_EC g_cat^?1 h^?1, and 100.0% EC conversion 99.9% EG and 85.8% MeOH selectivity could be achieved in a fixed bed. After the long-term experiment, the Cu⁺/(Cu⁺+Cu⁰) ratio in Cu–C@SiO₂-R catalyst kept at around 0.48. In contrast, the Cu⁺/(Cu⁺+Cu⁰) ratio in Cu@SiO₂-R catalyst decreased sharply from 0.48 to 0.38. The stability of the structure and the balance of valence of Cu were considered to be responsible to the stability of Cu–C@SiO₂-R catalyst, because the graphite oxide not only kept the Cu⁺/(Cu⁰+Cu⁺) ratio stability, but also restrained the aggregation of Cu particles and loss of copper. This work provides an in-depth understanding of the stabilization mechanism of Cu and can be a reference for the industrial application of ethylene carbonate hydrogenation.     

Assembly of Fe7S8 and Co9S8 nanosheets coupled with Cu(OH)2 nanorods as highly efficient oxygen evolution catalyst

Traditional fossil fuels can be replaced with hydrogen, and electrolysis of water is thought to be one of the most efficient ways to produce hydrogen that is also pollution-free. The oxygen evolution reaction (OER), which is thought to be the bottleneck of the entire water decomposition, is a result of the intricate electrochemical mechanism and the slow kinetic process. In this paper, Cu(OH)₂ forerunners with nanorods structure were combined on copper froth by straightforward submersion technique. Then, in a standard three-electrode system Fe₇S₈ and Co₉S₈ nanosheets with 3D structures were assembled on Cu(OH)₂ precursors by electrodeposition. At an alkaline environment of 1 M KOH, Cu(OH)₂/CF requires an overpotential of only 235 mV when the current density reaches 10 mA cm^?2, which is lower than that of other reported catalysts. In addition, Fe₇S₈–Co₉S₈@Cu(OH)₂/CF also showed excellent OER performance after long-term stability test, because bimetallic synergism can adjust the electronic structure of the catalyst and optimize its electrical conductivity. A feasible method for the design of a highly efficient oxygen evolution catalyst based on copper foam is reported in this paper.     

Carbon nanotube-copper oxide-supported palladium anode catalysts for electrocatalytic enhancement in formic acid oxidation

Pd/xCuO–10CNT (x = 1, 2, 3, 4) catalysts were synthesized using an improved polyol method. Uniformly prepared catalyst structures and chemical compositions of the catalysts delivered a high oxidation performance. The prepared catalysts were characterized via transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The formation of homogenous active Pd metal and CuO nanoparticle-modified CNT surfaces was found. Meanwhile, the electrocatalytic activity and the long-term stability performance of the prepared catalysts toward formic acid oxidation reaction (FAOR) were also employed via cyclic voltammogram (CV) and chronoamperometry (CA), respectively. Prominently, the prepared Pd/xCuO–CNT nanocomposite catalyst presented an outstanding electrocatalytic performance with a higher maximum forward peak current density (26.9 mA cm^?2) than those of catalysts Pd/CNT (3.4 mA cm^?2) and Pd/C (2.3 mA cm^?2) toward FAOR in the H₂SO₄ electrolyte, representing high conductivity CNT, and dispersed Pd nanoparticles with a large active surface area, on the CuO-CNT support. Additionally, the prepared catalysts also had outstanding stability and an excellent CO poisoning tolerance through the modified Pd structures on CuO-supported CNT. The insertion of CuO onto the CNT surface before Pd loading provided additional electrochemical active sites due to the enhanced geometric and bifunctional system. CuO supports the adsorption of oxygen-containing species (OH_ads) on the catalyst surface, and the electron effect among Pd and Cu metals is beneficial for charge transfer.     

Cu2-xSe@CuO core-shell assembly grew on copper foam for efficient oxygen evolution

Hydrogen production from electrolyzed water is a mature technology and has great development prospects in terms of energy conversion and utilization. However, the kinetically sluggish oxygen-evolution reaction becomes the limiting step in the electrolysis of water. Copper-based materials have been reported as a good choice to catalyze the oxygen evolution reaction, but their performance is poor. We describe a Cu_2-xSe@CuO/copper foam core–shell structure from the in situ electrochemical oxidation of Cu₂Se/copper foam to promote the oxygen-evolution reaction performance. The presence of a semi-metallic Cu_2-xSe core and nanostructured CuO shell at a current density of 10 mA cm⁻² requires a low overpotential of 253 mV. The Tafel slope was only 73 mV dec⁻¹. The preparation of Cu_2-xSe@CuO on three-dimensional copper foam facilitates the reaction.     

Effect of synthesis method on the oxygen reduction performance of Co–N–C catalyst

In recent years, Co, N co-doped carbon (Co–N–C) materials as oxygen reduction reaction (ORR) catalysts have attracted great attention because of their good ORR stability as well as decent activity. Co-doped zeolitic imidazolate framework-8 (Co@ZIF-8) as the precursor for synthesizing Co–N–C has attracted great interest recently. Co@ZIF-8 synthesis method may affect the properties of the as-synthesized Co@ZIF-8 precursors, which will surely affect the properties and ORR performance of Co@ZIF-8-derived Co–N–C catalysts. Herein, three methods, viz. room-temperature stirring method, reflux method, and hydrothermal method, were used to synthesize Co@ZIF-8 precursors. Physical characterization shows that the synthesis method has a great influence on the textural properties, composition, and graphitization degree of the as-synthesized Co–N–C catalysts. Electrochemical characterization shows that Co–N–C-R synthesized with reflux method exhibits an onset potential (E_onset) of 0.905 V, a half-wave potential (E_1/2) of 0.792 V and a limiting current density (J_L) of 5.85 mA cm^?2 in acidic media, which are higher than those of Co–N–C–S (E_onset = 0.870 V, E_1/2 = 0.770 V, J_L = 4.71 mA cm^?2) and Co–N–C–H (E_onset = 0.892 V, E_1/2 = 0.785 V, J_L = 4.68 mA cm^?2) synthesized with room-temperature stirring method and hydrothermal method, respectively. The better ORR activity observed on Co–N–C-R can be attributed to its larger graphitization degree and larger mesopore volume. Catalytic stability test shows that Co–N–C-R has negligible activity loss after 5000 potential cycles. This work demonstrates that reflux method is a more suitable method for synthesizing Co–N–C catalysts for ORR.     

High active and ultra-stable bifunctional FeNi/CNT electrocatalyst for overall water splitting

Efficient non-noble metal catalysts are desirable to greatly improve the efficiency of anodic oxygen evolution and cathodic hydrogen evolution reactions. Herein, iron-nickel/carbon nanotube composites are synthesized as efficient bifunctional electrocatalysts for water splitting. The catalyst is homogeneously distributed, while the formation of iron-nickel alloy is confirmed. Because of the synergism of iron and copper and the contribution of carbon nanotubes, the Fe–Ni/CNT electrocatalyst shows excellent oxygen evolution reaction performance with the overpotential of 221 mV at 10 mA cm^?2 and maintains stable at 0.48 V for 150 h. It expedites overall water splitting at 10 mA cm^?2 with 1.50 V and show excellent stability at 20 mA cm^?2 for 65 h, providing great potential for large-scale applications.     

Hairy sphere-like Ni9S8/CuS/Cu2O composites grown on nickel foam as bifunctional electrocatalysts for hydrogen evolution and urea electrooxidation

The urea solution electrolysis has become more attractive than water splitting, because it not only produces clean H₂ via the cathodic hydrogen evolution reaction (HER) with lower cell voltage, but also treats sewage containing urea through anodic urea oxidation reaction (UOR). However, lack of efficient electrocatalysts for HER and UOR has limited its development. Herein, hairy sphere -like Ni₉S₈/CuS/Cu₂O composites were synthesized on nickel foam (NF) in situ by a two-step hydrothermal method. The Ni₉S₈/CuS/Cu₂O/NF exhibited good electrocatalytic activity for both HER (?0.146 V vs. RHE to achieve 10 mA cm^?2) and UOR (1.357 V vs. RHE to achieve 10 mA cm^?2). Based on the bifunctional properties of Ni₉S₈/CuS/Cu₂O/NF, a dual-electrode urea solution electrolytic cell was constructed, which only needed a low voltage of 1.47 V to reach a current density of 10 mA cm^?2, and displayed a good stability during a 20-h test. In addition, the reason for the good catalytic activity of Ni₉S₈/CuS/Cu₂O/NF was analyzed and the UOR mechanism was discussed in detail. Our research shows that Ni₉S₈/CuS/Cu₂O/NF is a very promising low-cost dual-function electrocatalyst, which can be used for high-efficiency electrolysis of urea solution to produce hydrogen and treat wastewater.     

Electrosynthesis of eco-friendly electrocatalyst based nickel-copper bimetallic nanoparticles supported on poly-phenylenediamine with highest current density and early ethanol oxidation onset potential

Bimetallic catalysts have been investigated as the most efficient materials to accelerate the chemical transformations at the anode in Direct Ethanol Fuel Cells. A comparative study is presented here to synthesize Ni–Cu bimetallic nanoparticles for the ethanol oxidation reaction on three conducting polymers: poly-ortho-phenylenediamine, poly-meta-phenylenediamine, and poly-para-phenylenediamine. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electrochemical Impedance Spectroscopy (EIS) were used to analyze the modified electrodes. A series of bimetallic Ni–Cu nanoparticles with tunable ratios were successfully synthesized by simply changing the concentrations of Nickel and Copper. It has been confirmed that the best Ni/Cu molar ratio was 25% in the aspect of catalytic performance. The electrocatalyst exhibited an excellent catalytic activity with an anodic current of 70.5 mA cm^?2 at the lowest onset potential of 0.39 V with impressive stability. Ni₄Cu₁/PpPD should be considered as a good alternative to noble metal anode catalyst.     

Spatially confined growth of ultrathin NiFe layered double hydroxide nanosheets within carbon nanofibers network for highly efficient water oxidation

The rational design of catalysts with low cost, high efficient and robust stability toward oxygen evolution reaction (OER) is greatly desired but remains a formidable challenge. In this work, a one-pot, spatially confined strategy was reported to fabricate ultrathin NiFe layered double hydroxide (NiFe-LDH) nanosheets interconnected by ultrafine, strong carbon nanofibers (CNFs) network. The as-fabricated NiFe-LDH/CNFs catalyst exhibits enhanced OER catalytic activity in terms of low overpotential of 230 mV to obtain an OER current density of 10 mA cm^?2 and very small Tafel slope of 34 mV dec^?1, outperforming pure NiFe-LDH nanosheets assembly, commercial RuO₂, and most non-noble metal catalysts ever reported. It also delivers an excellent structural and electrocatalytic stability upon the long-term OER operation at a large current of 30 mA cm^?2 for 40 h. Furthermore, the cell assembled by using NiFe-LDH/CNFs and commercial Pt/C as anode (+) and cathode (?) ((+)NiFe-LDH/CNFs||Pt/C(?)) only requires a potential of 1.50 V to deliver the water splitting current of 10 mA cm^?2, 130 mV lower than that of (+)RuO₂||Pt/C(?) couple, demonstrating great potential for applications in cost-efficient water splitting devices.