Facile electrodeposited amorphous Co–Mo–Fe electrocatalysts for oxygen evolution reaction

A new type of superior activity and highly cost-effective amorphous electrocatalyst Co–Mo–Fe on nickel foam (NF) supports is prepared by facile one-step rapid electrodeposition. The amorphous electrocatalyst Co–Mo–Fe/NF shows excellent oxygen evolution reaction (OER) performance, with a small overpotential of 218 mV at 10 mA cm^?2 current density in 1 M KOH. It only needs overpotential of 252 mV at 50 mA cm^?2 current density in 1 M KOH, and the Tafel slope is 45 mV dec^?1. The results show that the doping of Fe significantly improves the oxygen evolution capacity of the Co–Mo–Fe system. The synergistic effect of the three metals and the doping of the third metal iron make the oxygen evolution active sites of the whole system increase significantly. This provides a feasible direction for the oxygen evolution reaction of cobalt transition metal.     

Amine and Carbon-pretreated nickel–molybdenum disulfide as bifunctional electrocatalysts for hydrogen and oxygen gas evolution

We report the synthesis and characterization of a variety of nickel molybdenum disulfide (NiMoS₂) materials as efficient bifunctional electrocatalysts for both the hydrogen evolution and oxygen evolution reactions (HER and OER, respectively). These catalysts were obtained from pretreated ammonium tetrathiomolybdate (ATM) using ethylenediamine (EDA), diethylenetriamine (DETA), or carbon nanotubes (CNT), which were further reacted with Ni(NO₃)₂. All the materials were characterized by scanning electron microscopy (SEM) and powder X-ray diffraction (pXRD), and all materials were evaluated as both HER and OER electrocatalysts. The NiMoS₂ synthesized from DETA-pretreatment exhibits the best HER catalytic performance with the lowest overpotential of 0.151 V, while the CNT-modified NiMoS₂ shows the lowest OER overpotential of 0.310 V. All the pretreated NiMoS₂ electrocatalysts show significantly improved catalytic activity compared to the one prepared directly from pristine ATM precursor.     

Effect of microstructure on the electrocatalytic activity for hydrogen evolution of amorphous and nanocrystalline Zr–Ni alloys

Rapidly quenched Zr₂Ni amorphous and nanocrystalline ribbons were studied as electrocatalysts for hydrogen evolution in 6 M KOH. Linear polarization, potentiostatic hydrogen charge/discharge and EIS measurements at various potentials were carried out for the Zr alloys with different microstructure with the aim to extract information about the mechanism of hydrogen evolution and absorption and estimate the kinetic parameters of the hydrogen evolution reaction (HER). Though the melt-spun Zr₆₇Ni₃₃ alloys with varying microstructure do not show substantially different catalytic activity for HER, it could be clearly demonstrated that the nanocrystalline material reveals better catalytic performance than the entirely amorphous and nano-/amorphous alloys with the same chemical composition. It was found that all studied Zr–Ni alloys absorb hydrogen under the conditions of the hydrogen evolution experiments, as the amount of the absorbed hydrogen depends to a large degree on the alloys microstructure as well as on the applied potential during the HER experiment. The diffusion coefficient of hydrogen into the amorphous Zr₆₇Ni₃₃ alloy, as well as the thickness of the hydrided layer were found to be noticeably larger than those of the nanocrystalline alloy at the same conditions of hydrogen charging. Therefore the improved electrocatalytic properties of the nanocrystalline alloy could only be explained by its favorable microstructure (e.g. higher density of defects) and weaker hydrogen absorption into the nanostructured material under the conditions of the HER.     

Electrodeposited Ni–Co–S nanosheets on nickel foam as bioelectrochemical cathodes for efficient H2 evolution

High overpotential and soaring prices of the cathode electrode are the bottlenecks for the development of microbial electrolysis technology for hydrogen production. In this study, a novel one-step electrodeposition method has been attempted to fabricate electrodeposited cathodes in situ growth of Ni–Co–S, Ni–S, Co–S catalyst on nickel foam (NF) to reduce the overpotential of electrodes. Finally, a uniform nanosheet with a high specific surface area and more active sites is formed on the NF surface, resulting in a lower overpotential than plain NF. At 0.8 V, the Co–S/NF cathode produces a favorable 42% increase in hydrogen yield (0.68 m³·m⁻³·d⁻¹), 40% upsurge in current density (10.6 mA/cm³) and 39% rise of cathodic recovery rate (58.0 ± 3.2%) than bare NF, followed by Ni–Co–S/NF and Ni–S/NF cathode. All the electrodeposited electrodes demonstrate enhanced current density and reduced electron losses, thereby achieving efficient hydrogen production. These innovative varieties of electrodes are highly advantageous as they are relatively inexpensive and easy to manufacture with great potential in reducing costs and further real time application in large scale.     

Modulated amorphous Fe–Ni–P nanosphere chains anchored on graphene aerogel grafted nickel foam: High-performance electrocatalyst for oxygen evolution reaction

Substrate materials with large special surface area and high conductibility play a crucial role in preparing promising oxygen evolution reaction (OER) catalysts. Herein, binder-free Fe–Ni–P nanospheres anchored on graphene aerogel grafted nickel foam (FNP/GA@NF) are assembled with different molar ratios of Fe/Ni. GA@NF with prominent conductivity supplies ample accessible sites to amorphous Fe–Ni–P nanospheres to attach and offers a strong skeleton guaranteeing long-term stability during OER process. As revealed via spectroscopic measurement, tremella-like nanospheres arranged in a nanochain structure have been observed on the surface of GA@NF. Such a nanochain provides abundant paths for freely electronic transformation leading to faster kinetics. Besides, FNP/GA@NF possesses distinguished electrocatalytic activities in 1.0 M KOH solution. Especially, when the molar ratio is 3:2, FNP/GA@NF catalyst requires overpotentials of only 320 and 413 mV to arrive current density of 50 and 100 mA cm^?2. Furthermore, by the reason of robust framework, it shows superior durability even up to 24 h chronoamperometry test. This work opens an evolutive direction to construct binderless substrates to improve conductivity and catalytic activity of non-noble catalysts for OER.     

Electrodeposited nickel–zinc alloy nanostructured electrodes for alkaline electrolyzer

Over the last decade, as a consequence of the global decarbonization process, the interest towards green hydrogen production has drastically increased. In particular a substantial research effort has focused on the efficient and affordable production of carbon-free hydrogen production processes. In this context, the development of more efficient electrolyzers with low-cost electrode/electrocatalyst materials can play a key role. This work, investigates the fabrication of electrodes of nickel-zinc alloys with nanowires morphology cathode for alkaline electrolyzers. Electrodes are obtained by the simple method of template electrosynthesis that is also inexpensive and easily scalable. Through the analysis of the morphological and chemical composition of nanowires, it was found that the nanowires composition is dependent on the concentration of two metals in the deposition solution. Electrocatalytic tests were performed in 30% w/w potassium hydroxide aqueous solution at room temperature. In order to study the electrodes stability, mid-term galvanostatic test was also carried out. All electrochemical tests show that nanowires with about 44.4% of zinc have the best performances. Particularly, at ?50 mAcm^?2, these electrodes have an overpotential 50 mV lower than pure Ni nanowire. NiZn nanowires show also a good stability over time without noticeable signs of performance decay.     

Structure engineering of amorphous P–CoS hollow electrocatalysts for promoted oxygen evolution reaction

Oxygen evolution reaction (OER) is a key process involved in many energy-related conversion systems. An ideal OER electrocatalyst should possess rich active sites and optimal binding strength with oxygen-containing intermediates. Although numerous endeavors have been devoted to the modification and optimization of transition-metal-based OER electrocatalysts, they are still operated with sluggish kinetics. Herein, an ion-exchange approach is proposed to realize the structure engineering of amorphous P–CoS hollow nanomaterials by utilizing the ZIF-67 nanocubes as the precursors. The precise structure control of the amorphous hollow nanostructure contributes to the large exposure of surface active sites. Moreover, the introduction of phosphorus greatly modifies the electronic structure of CoS₂, which is thus favorable for optimizing the binding energies of oxygenated species. Furthermore, the incorporation of phosphorus may also induce the formation of surface defects to regulate the local electronic structure and surface environment. As a result of this, such P–CoS hollow nanocatalysts display remarkable electrocatalytic activity and durability towards OER, which require an overpotential of 283 mV to afford a current density of 10 mA cm^?2, outperforming commercial RuO₂ catalyst.     

Bimetallic iron–copper and iron–nickel nano-catalysts over ceria support for medium temperature shift reaction

Iron/ceria catalysts promoted by copper or nickel, were studied in medium temperature shift (MTS) reaction for hydrogen production and purification. Samples were characterized by X-Ray Diffraction (XRD), N₂ adsorption-desorption (BET), temperature programmed reduction (TPR), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), and transmission electron microscope (TEM) analysis. Among xFe/CeO₂ (x = 2, 5, 8, 10 wt%) samples, 8Fe/CeO₂ showed the best performance, due to appropriate amount and good dispersion of active phase on the support (45% CO conversion at 390 °C). Then, to enhance the CO conversion, 2% of Ni or Cu were added to the catalyst. However CO conversion using Cu promoter was lower than Ni containing one, (25 and 45%, at 300 °C, respectively.), but due to better reducibility and lack of methane production, copper was selected as promoter. Eventually, the effect of Cu loading (2, 4, 8, 12 wt %) was also investigated, and 8Fe–8Cu/CeO₂, with >80% CO conversion at 390 °C, showed the best performance with appropriate stability.     

Enhanced activity of Pd/α-MnO2 for electrocatalytic oxygen evolution reaction

This work describes the application of α-MnO₂ and Pd/α-MnO₂ as electrocatalysts in the oxygen evolution reaction (OER). Characterization data revealed that the Pd²⁺ precursor has been oxidized during the synthesis, and the resulting Pd⁴⁺ ions have unprecedently replaced the lattice framework Mn³⁺ ions of α-MnO₂. Furthermore, formation of PdO nanoparticles was also observed. Lower OER overpotential at j = 10 mA cm^?2 (636 mV) was obtained for Pd/α-MnO₂ in relation to α-MnO₂ (700 mV), what is in alignment with the lower charge transfer resistance of Pd/α-MnO₂ (4.9 kΩ cm²) compared to α-MnO₂ (10.4 kΩ cm²). Lower Tafel slope (73 mV dec^?1) and higher TOF (2.87 × 10^?4 s^?1) at overpotential of 350 mV was obtained for Pd/α-MnO₂ in relation to α-MnO₂ (Tafel of 77 mV dec^?1 and TOF of 1.94 × 10^?4 s^?1), indicating a faster electron transfer kinetics promoted by Pd. Pd/α-MnO₂ was stable at j = 14 mA cm^?2 for 6 h.     

Facile synthesis of bimetallic Ni–Fe phosphide as robust electrocatalyst for oxygen evolution reaction in alkaline media

Bimetallic Ni–Fe phosphide electrocatalysts were in-situ synthesized through direct phosphorization of metal salts on carbon cloth (CC). The Fe dopant remarkably enhances the OER performance of Ni₂P in alkaline medium through the electronic structure modulation of Ni. The (Fe_0.5Ni_0.5)₂P/CC electrode, composed of uniform films coated on carbon fibers, delivers a low overpotential of 260 mV with a small Tafel slope of 45 mV·dec⁻¹ at the current density of 100 mA cm⁻², outperforming most reported non-noble electrocatalysts and commercial RuO₂ electrocatalyst. The (Fe_0.5Ni_0.5)₂P/CC also displays superior electrochemical stability at high current density. An appropriate Fe dopant level facilitates the in-situ transformation of Ni–Fe phosphides into active NiFeOOH during alkaline OER. This work simplifies the synthesis procedure of metal phosphides.     

Ni/Ce co-doping δ-MnO2 nanosheets with oxygen vacancy for enhanced electrocatalytic oxygen evolution reaction

The design and manufacture of strongly engaged, low-cost, and resilient oxygen evolution reaction (OER) electrocatalysts is the most challenging task in electrochemical hydrolysis. Herein, Ce and Ni co-doped MnO₂ (NiCe/MnO₂) nanosheets (NSs) with oxygen vacancy (V_O) and abundant active sites have been prepared in one step employing a defect strategy. The co-doping of Ce/Ni on the one hand reduced the catalyst particle size and increased the specific surface area, which promoted the exposure of more active sites. On the other hand, heteroatom doping altered the species the crystalline surface, stimulating the formation of Vo and thus activating the catalyst performance simultaneously. The OER performance of NiCe/MnO₂ NSs was significantly enhanced over the pure δ-MnO₂, with an overpotential of 170 mV (10 mA cm^?2), which was verified by density functional theory. This work shows a straightforward and practical method for making non-precious metal electrocatalysts with high electrochemical hydrolysis performance.     

In-situ generate robust Fe–Ni derived nano-catalyst featuring surface reconstruction for enhanced oxygen evolution reaction

Oxygen evolution reaction (OER) catalysts with highly efficient and cost-effective are cardinal for hydrogen production through water electrolysis. Herein, a novel strategy based on the theory of molecular crystallization and atomic diffusion is described to construct the FeOOH@Ni₃(NO₃)₂(OH)₄/NF. It requires an overpotential of 248 mV at the current density of 100 mA cm^?2 for OER. The in-situ Raman spectroscopy test exploring the catalytic actives unravels that NiOOH is one of the real active species and a small amount of NiFe₂O₄ is generated during OER process. The analysis of the mechanism shows that NiOOH converted from the intermediate product of Ni(OH)₂ derived from Ni₃(NO₃)₂(OH)₄ in the process of OER. NiOOH and FeOOH mainly work together contributing to boosting intrinsic catalytic activity. This work may provide a new insight into fabricating strategy for other nano-catalysts. The in-situ Raman measurement provides a valid and reliable means to probe into the catalytic active site and catalytic mechanism in the catalytic process.     

MgO as promoter for electrocatalytic activities of Co3O4–MgO composite via abundant oxygen vacancies and Co2+ ions towards oxygen evolution reaction

Oxygen evolution reaction (OER) is known as bottleneck problem during the water splitting process due to high energy barrier and non-availability of efficient nonprecious electrocatalysts. The cobalt oxide (Co₃O₄) in the spinel phase has limited OER activity and stability in the alkaline media. For this purpose, we have carried out the synthesis of Co₃O₄–MgO (CM) composite by wet chemical method and it offers abundant oxygen vacancies and Co²⁺ concentration for the efficient OER reaction. The effect of different amounts of MgO on the OER activity of Co₃O₄ was also studied. Despite inactivity of MgO towards OER, it creates high density of oxygen vacancies and favored the formation Co²⁺ ions at the surface, thus accelerated the OER kinetics. The physical studies were performed to investigate the morphology, crystalline structure, surface information and chemical composition using several analytical techniques. The optimized CM-0.1 composite produced an overpotential of 274 mV at 10 mAcm⁻² which is lower in value than the pristine Co₃O₄. The significant enhancement in the OER activity was verified by the large value of electrochemical active surface area values 12.8 μFcm⁻² and the low charge transfer resistance of 45.96 Ω for the optimized CM-0.1 composite. The use of abundance materials for the synthesis of CM composite revealed an enhanced OER performance, suggesting the dynamic role of MgO, therefore it could be used for improving the electrochemical properties of extended range of metal oxides for specific application especially energy conversion and storage devices.     

Template confined construction of Fe–NiCoP/NiCoP/NF heterostructures for highly efficient electrocatalytic oxygen evolution reaction

Rational design of oxygen evolution reaction (OER) electrocatalysts with advance nanostructures and composition superiority is an urgent need to promote electrocatalytic property. In this research, we fabricate Fe–NiCoP/NiCoP/NF electrocatalyst for OER via the interfacial scaffolding strategy with Prussian-blue-analogue (PBA) followed by low-temperature phosphating. The cube-on-sheet multimetallic-TMPs-based nanoarchitecture of Fe–NiCoP/NiCoP/NF exhibits outstanding OER performance, which only requires the overpotential of 201 mV to achieve a current density of 10 mA cm⁻² and possesses good durability up to 50 h in 1.0 M KOH solution. The superior OER property of Fe–NiCoP/NiCoP/NF is mainly characteristic to the rich composition that optimizes the electronic structure and the cube-on-sheet multimetallic-TMPs-based nanoarchitecture which can facilitate more effective active sites exposure and ultimately promote charge transfer at the same time. This research provides a new strategy for the construction of advanced nanoarrays structure and the improvement of the electrocatalytic performance of polymetallic phosphides, which offers its promising applications especially in energy storage and conversion technology.     

Hybrid niobium and titanium nitride nanotube arrays implanted with nanosized amorphous rhenium–nickel: An advanced catalyst electrode for hydrogen evolution reactions

The scalable application of high-performance electrocatalysts with fine nanostructures for hydrogen evolution reactions (HER) depends on the development of durable and active electrode supports. Transition metal nitrides are considered as candidates due to their high conductivity, favorable catalytic activity, and excellent chemical stability in acidic or alkaline aqueous solutions. The present work proposed to fabricate self-ordered hybrid niobium–titanium (Nb–Ti) nitride nanotube arrays (NNAs) on Nb–Ti alloy panels by an anodization and subsequent nitridation process. Results showed that the highly ordered NNA is composed of mixed Nb₄N₅ and TiN and has merits of super hydrophilicity, outstanding corrosion resistance, and high conductivity. On the basis of the successful synthesis of Nb–Ti NNA, the nano–sized amorphous rhenium–nickel (Re–Ni) alloy was electrodeposited onto the NNA support, forming the Re–Ni/NNA composite electrode. Electrochemical tests exhibited that the Re–Ni/NNA composite electrode can provide a current density of 50 mA cm⁻² in 1.0 M KOH at a potential of −0.18 V vs. RHE and maintain stability in a testing period of 100 h. This superior HER performance is attributed to the combination of Re–Ni particles and Nb–Ti NNA support, which can benefit the diminution of charge transfer resistance and the improvement of catalytic activity.     

Hollow Fe/Ni–CoTe@NCFs nanoarchitecture derived from MOF@MOF as high-efficiency electrocatalysts for boosting oxygen evolution reaction

To improve the oxygen evolution reaction (OER) catalytic efficiency of non-noble-metal-based catalysts, researchers have made great endeavors to adjust the compositions, morphologies and configuration of material. In this work, a dual-metal-organic frameworks (MOFs)-assisted fabrication hierarchical and hollow N-doped carbon nanoframes (NCFs) decorated with Fe/Ni-codoped CoTe nanocomposite catalyst (Fe/Ni–CoTe@NCFs) is reported. Starting from MOF-in-MOF composite precursors, the design and fabrication of Fe/Ni–CoTe by the strategies: i.e, hydrothermal precipitation, chemical etching and low-temperature tellurization, and high-temperature pyrolysis steps. Newly designed catalyst (Fe/Ni–CoTe@NCFs) performs superior OER catalytic activity to afford 10 mA cm⁻² at the overpotential of 287 mV with a small Tafel slope of 52.3 mV dec⁻¹. The frame-like hollow core-shell nanostructures with ample channels into the internal volume and high double-layer capacitance provide the large catalytic active surface area and increase more actives sites. The cooperative effects between alloy and metal telluride, as well as hollow carbon shell promote the activity of OER. Therefore, this study offers a catalyst with great potential for OER and provides the possibility for the application of transition metal tellurides in electrocatalysis.     

Interface engineering and heterometal doping Co–Mo/FeS for oxygen evolution reaction

The sluggish kinetics of the oxygen evolution reaction (OER) limits the development of water electrolysis technology and the long-term efficiency of hydrogen energy production. In addition, it is important to evaluate the reconstruction performance of OER catalysts for actual water electrolysis. We created a self-supported electrode with FeS film coated Fe foam as a substrate, ordered resoluble molybdate (MoO₄²⁻) anions in interlayers, and Co-doped as a catalytically active phase for the OER. The catalyst is capable of electrochemical self-reconstruction (ECSR). With the dissolution of molybdate and sulfur ions, the catalyst surface cobalt iron oxide (CoFe₂O₄) forms an active amorphous FeCoOOH, which is favorable for alkaline OER. We realized the introduction of new active sites in the catalyst reconstruction process. Finally, the composite CoFeO_x catalyst increased the specific surface area, promoted bubble transport, and enhanced electron mass transfer. The synergistic coupling effect of the catalyst makes it have excellent OER activity and stability. Remarkably, Co–Mo/FeS nanosheets afforded an electrocatalytic OER with a current density of 100 mA cm⁻² at a low overpotential of 321 mV. These discoveries open up new opportunities for the application of doping and template-directed surface reconfiguration, which holds promise as an effective electrocatalyst for the OER.     

Ni–Fe nanocubes embedded with Pt nanoparticles for hydrogen and oxygen evolution reactions

Electrochemical water-splitting is widely regarded as one of the essential strategies to produce hydrogen energy, while Metal-organic frameworks (MOFs) materials are used to prepare electrochemical catalysts because of its controllable morphology and low cost. Herein, a series of trimetallic porous Pt-inlaid Ni–Fe nanocubes (NCs) are developed with bifunctions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In the process of prepare the electrochemical catalysts, Pt nanoparticles are uniformly embedded in the Fe–Ni PBA cube structure, and ascorbic acid is employed as a reducing agent to reduce Pt²⁺ to Pt nanoparticles. In this work, the cubic structure of Fe–Ni PBA is maintained and the noble metal Pt nanoparticles are embedded. Remarkably, the formation of PBA cubes, Pt inlay and reduction are completed in one step, and Pt nanoparticles are embedded by a simple method for the first time. By employing acid etching method, a porous structure is formed on the PBA cube, which increases the exposed area of the catalyst and provides more active sites for HER and OER. Due to the porous structure, highly electrochemical active surface area and the embedded of highly dispersed Pt nanoparticles, the porous 0.6 Ni–Fe–Pt nanocubes (NCs) exhibits excellently electrocatalytic performance and durable stability to HER and OER. In this work, for HER and OER, the Tafel slopes are 81 and 65 mV dec⁻¹, the overpotential η at the current density of 10 mA cm⁻² are 463 and 333 mV, and the onset potential are 0.444 and 1.548 V, respectively. And after a 12-h i-t test and 1000 cycles of cyclic voltammetry (CV), it maintained high stability and durability. This work opens up a new preparation method for noble metal embedded MOF materials and provided a new idea for the preparation of carbon nanocomposites based on MOF.     

Core-shell structured metal organic framework materials derived cobalt/iron–nitrogen Co-doped carbon electrocatalysts for efficient oxygen reduction

Homogeneous dispersion of active sites and abundant pore structure for non-precious metal electrocatalysts are favorable for the oxygen reduction reaction (ORR) activity. Herein, a nitrogen-doped carbon core supported CoFe alloy-nitrogen co-doped carbon shell nanopolyhedron (NC@CoFe,N–CNP) electrocatalyst, which has rich pore structure and uniformly distributed active sites, is prepared through a facile thermal conversion of a ZIF-8 core and Fe,Co-ZIF shell composite precursor (ZIF-8@Fe,Co-ZIF) without any post-treatments. The existence of ZIF-8 core can maintain the structure of the ZIF-8@Fe,Co-ZIF composite controllable, avoiding the damage to the pore structure for fast mass transfer during pyrolysis. Meanwhile, the bi-metal iron and cobalt co-doping shell is more conducive for uniform dispersion of CoFe alloy particles than single one due to the interval effects, which can create various active sites and efficiently promote the ORR activity. As expected, the optimal NC@CoFe,N–CNP electrocatalyst exhibits an excellent catalytic activity with a high onset potential and half-wave potential (0.970 V and 0.865 V) compared to commercial Pt/C (0.934 V and 0.846 V). The kinetic current density of NC@CoFe,N–CNP reached to 7.99 mA cm^?2, which is higher than Pt/C (5.14 mA cm^?2) at 0.85 V. Furthermore, the NC@CoFe,N–CNP electrocatalyst demonstrates better electrochemical stability and anti-poisoning ability.