Microwave sintered porous CoCrFeNiMo high entropy alloy as an efficient electrocatalyst for alkaline oxygen evolution reaction

Developing efficient,stable and economical electrocatalyst for oxygen evolution reaction (OER) is a sig-nificant pathway to produce clean energy from water splitting.Herein,the promising and highly efficient porous CoCrFeNiMo high entropy alloys (HEAs) were prepared by microwave sintering using Mg space holder.Owing to unique properties of high entropy alloys and abundant active surface area,the porous CoCrFeNiMo-20 Mg exhibits excellent catalytic performance and prominent electrochemical stability with a low overpotential of 220 mV to reach current density of 10 mA cm-2,a small Tafel slope of 59.0 mV dec-1 and long-term durability for 24 h in 1.0 M KOH.The results of microstructure and element states indicate that crystal defects,porous structure and villous hydroxides are the reasons for high OER performance of the CoCrFeNiMo.This work not only provides a new way to prepare electrocatalysts,but also proves the important application of high entropy alloys in functional materials.     

Facile one-pot synthesis of nanocoral-like cerium-activated cobalt selenide: a highly efficient electrocatalyst for oxygen evolution reaction

The development of hydrogen production via environment-friendly and efficient electrochemical water splitting technology leans heavily on the exploitation of highly active and durable oxygen evolution reaction (OER) electrocatalysts. Herein, nanocoral-like cerium-activated cobalt selenide (Ce-CoSe₂) nanocomposites to enhance the OER catalytic activity have been successfully prepared by one-pot hydrothermal route via simply altering the cerium content. Owing to the ingenious introduction of cerium, as-prepared Ce-CoSe₂ electrode displays remarkable OER performance in comparison with CoSe₂. The nanocoral-like Ce-CoSe₂ catalyst prepared under optimal condition just needs low overpotential of 276 and 398 mV at 10 and 50 mA cm^?2, respectively. Additionally, it attains the current density of 255 mA cm^?2 at the potential of 2.0 V vs. RHE, and shows long-term stability during OER. This work offers a simple and feasible pathway for the design and construct of metal dichalcogenides for green and renewable hydrogen production by electrocatalytic water splitting.

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NiCo-LDH nanosheets strongly coupled with GO-CNTs as a hybrid electrocatalyst for oxygen evolution reaction

The rational fabrication of highly efficient electrocatalysts with low cost toward oxygen evolution reaction (OER) is greatly desired but remains a formidable challenge. In this work, we present a facile and straightforward method of incorporating NiCo-layered double hydroxide (NiCo-LDH) into GO-dispersed CNTs (GO-CNTs) with interconnected configuration. X-ray absorption spectroscopy (XAS) reveals the strong electron interaction between NiCo-LDH and the underlying GO-CNTs substrate, which is supposed to facilitate charge transfer and accelerate the kinetics for OER. By tuning the amount of CNTs, the optimized NiCo-LDH/GO-CNTs composite can achieve a low overpotential of 290 mV at 10 mA·cm⁻² current density, a small Tafel slope of 66.8 mV·dec⁻¹ and robust stability, superior to the pure NiCo-LDH and commercial RuO₂ in alkaline media. The preeminent oxygen evolution performance is attributed to the synergistic effect stemming from the merits and the intimate electron interaction between LDH and GO-CNTs. This allows NiCo-LDH/GO-CNTs to be potentially applied in an industrial non-noble metal-based water electrolyzer as the anodic catalysts.

     

Wet-chemistry synthesis of cobalt carbide nanoparticles as highly active and stable electrocatalyst for hydrogen evolution reaction

Transition metal carbide (TMC) nanomaterials are promising alternatives to Pt,and are widely used as heterogeneous electrocatalysts for the electrochemical hydrogen evolution reaction (HER).In this work,a bromide-induced wet-chemistry strategy to synthesize Co2C nanopartides (NPs) was developed.Such NPs exhibited high electrocatalytic activity (η =181 mV for j =-10 mA.cm-2) and long-term stability (no obvious performance decrease after 4,000 cycles) for the HER.This study will pave the way for the design and fabrication of TMC NPs via a wetchemistry method,and will have significant impacts on broader areas such as nanocatalysis and energy conversion.     

Fe-doped NiCo2O4 hollow hierarchical sphere as an efficient electrocatalyst for oxygen evolution reaction

We prepared porous Fe-doped nickel cobaltate (Fe-NiCo₂O₄) hollow hierarchical nanospheres through a facile self-templated synthetic strategy. Due to the porous hollow structure and composition, the Fe-NiCo₂O₄ presented vastly superior electrocatalytic activity for the oxygen evolution reaction (OER), compared with NiCo₂O₄ and the majority of other OER catalysts. With an aim of stimulating a current density of 10 mA·cm⁻², the Fe-NiCo₂O₄ catalyst needs an overpotential of 210 mV, which is on a par with the general properties of commercial IrO₂. In addition, the Fe-NiCo₂O₄ catalyst performed stably in long-term testing. The excellent activity and long-term stability showed that such catalysts have great promise for widespread application in the field of water splitting.     

Millisecond-timescale electrodeposition of platinum atom-doped molybdenum oxide as an efficient electrocatalyst for hydrogen evolution reaction

We present a straightforward method for one-pot electrodeposition of platinum atoms-doped molybdenum oxide (Pt·MoO_3−x) films and show their superior electrocatalytic activity in the hydrogen evolution reaction (HER). A ~15-nm-thick Pt·MoO_3−x film was prepared by one-pot electrodeposition at −0.8 V for 1 ms. Due to considerably different solute concentrations, the content of Pt atoms in the electrodeposited composite electrocatalyst is low. No Pt crystals or islands were observed on the flat Pt·MoO_3−x films, indicating that Pt atoms were homogeneously dispersed within the MoO_3−x thin film. The catalytic performance and physicochemical features of Pt·MoO_3−x as a HER electrocatalyst were characterized. The results showed that our Pt·MoO_3−x film exhibits 23- and 11-times higher current density than Pt and MoO_3−x electrodeposited individually under the same conditions, respectively. It was found that the dramatic enhancement in the HER performance was principally due to the abundant oxygen defects. The use of the developed one-pot electrodeposition and doping method can potentially be extended to various catalytically active metal oxides or hydroxides for enhanced performance in various energy storage and conversion applications.     

NiP2/FeP heterostructural nanoflowers interwoven by carbon nanotubes as highly efficient electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) for water splitting has a sluggish kinetics, thus significantly hindering the reaction efficiency. So far, it is still challenging to develop a cost-efficient and highly active catalyst for OER processes. To address such issues, we design and synthesize NiP₂/FeP heterostructural nanoflowers interwoven by carbon nanotubes (NiP₂/FeP@CNT) by a hydrothermal reaction followed by phosphating. The NiP₂/FeP@CNT catalyst delivers excellent OER performance: it displays an ultralow Tafel slope of 44.0 mV dec^?1 and a relatively low overpotential of 261 mV at 10 mA cm^?2, better than RuO₂ commercial catalyst; it also shows excellent stability without observable decay after 20-h cycling. The outstanding OER property is mainly attributed to its special 3D stereochemical structure of CNT-interwoven NiP₂/FeP heterostructural nanoflowers, which is highly conductive and guarantees considerable active sites. Such nanostructure greatly facilitates the charge transfer, which significantly improves its electrocatalytic activity. This work offers a simple method to synthesize non-precious transition metal-based phosphide electrocatalysts with a unique hierarchical nanostructure for water splitting.

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Flexible cobalt phosphide network electrocatalyst for hydrogen evolution at all pH values

High-performance electrocatalysts for water splitting at all pH values have attracted considerable interest in the field of sustainable hydrogen evolution.Herein,we report an efficient electrocatalyst with a nanocrystalline cobalt phosphide (CoP) network for water splitting in the pH range of 0-14.The novel flexible electrocatalyst is derived from a desirable nanocrystalline CoP network grown on a conductive Hastelloy belt.This kind of self-supported CoP network is directly used as an electrocatalytic cathode for hydrogen evolution.The nanocrystalline network structure results in superior performance with a low onset overpotential of ～45 mV over a broad pH range of 0 to 14 and affords a catalytic current density of 100 mA·cm-2 even in neutral media.The CoP network exhibits excellent catalytic properties not only at extreme pH values (0 and 14) but also in neutral media (pH =7),which is comparable to the behavior of state-of-the-art platinum-based metals.The system exhibits an excellent flexible property and maintains remarkable catalytic stability during continuous 100-h-long electrolysis even after 100 cycles of bending/extending from 100° to 250°.     

One-step scalable preparation of N-doped nanoporous carbon as a high-performance electrocatalyst for the oxygen reduction reaction

N-doped porous carbon materials have been prepared by a simple one-step pyrolysis of ethylenediaminetetraacetic acid (EDTA) and melamine in the presence of KOH and Co(NO₃)₂·6H₂O. The combination of the high specific area (1485 m²·g^?1), high nitrogen content (10.8%) and suitable graphitic degree results in catalysts exhibiting high activity (with onset and half-wave potentials of 0.88 and 0.79 V vs the reversible hydrogen electrode (RHE), respectively) and four-electron selectivity for the oxygen reduction reaction (ORR) in alkaline medium—comparable to a commercial Pt/C catalyst, but far exceeding Pt/C in stability and durability. Owing to their superb ORR performance, low cost and facile preparation, the catalysts have great potential applications in fuel cells, metal-air batteries, and ORR-related electrochemical industries.      

Rational design of hierarchically porous Fe-N-doped carbon as efficient electrocatalyst for oxygen reduction reaction and Zn-air batteries

The rational design and construction of hierarchically porous nanostructure for oxygen reduction reaction (ORR) electrocatalysts is crucial to facilitate the exposure of accessible active sites and promote the mass/electron transfer under the gas-solid-liquid triple-phase condition. Herein, an ingenious method through the pyrolysis of creative polyvinylimidazole coordination with Zn/Fe salt precursors is developed to fabricate hierarchically porous Fe-N-doped carbon framework as efficient ORR electrocatalyst. The volatilization of Zn species combined with the nanoscale Kirkendall effect of Fe dopants during the pyrolysis build the hierarchical micro-, meso-, and macroporous nanostructure with a high specific surface area (1,586 m²·g⁻¹), which provide sufficient exposed active sites and multiscale mass/charge transport channels. The optimized electrocatalyst exhibits superior ORR activity and robust stability in both alkaline and acidic electrolytes. The Zn-air battery fabricated by such attractive electrocatalyst as air cathode displays a higher peak power density than that of Pt/C-based Zn-air battery, suggesting the great potential of this electrocatalyst for Zn-air batteries.

     

Natural tea-leaf-derived,ternary-doped 3D porous carbon as a high-performance electrocatalyst for the oxygen reduction reaction

To commercialize fuel cells and metal-air batteries, cost-effective, highly active catalysts for the oxygen reduction reaction (ORR) must be developed. Herein, we describe the development of low-cost, heteroatom (N, P, Fe) ternary-doped, porous carbons (HDPC). These materials are prepared by one-step pyrolysis of natural tea leaves treated with an iron salt, without any chemical and physical activation. The natural structure of the tea leaves provide a 3D hierarchical porous structure after carbonization. Moreover, heteroatom containing organic compounds in tea leaves act as precursors to functionalize the resultant carbon frameworks. In addition, we found that the polyphenols present in tea leaves act as ligands, reacting with Fe ions to form coordination compounds; these complexes acted as the precursors for Fe and N active sites. After pyrolysis, the as-prepared HDPC electrocatalysts, especially HDPC-800 (pyrolyzed at 800 °C), had more positive onsets, half-wave potentials, and higher catalytic activities for the ORR, which proceeds via a direct four-electron reaction pathway in alkaline media, similar to commercial Pt/C catalysts. Furthermore, HDPC-X also showed enhanced durability and better tolerance to methanol crossover and CO poisoning effects in comparison to commercial Pt/C, making them promising alternatives for state-of-the-art ORR electrocatalysts for electrochemical energy conversion. The method used here provides valuable guidelines for the design of high-performance ORR electrocatalysts from natural sources at the industrial scale.

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Electrical and magnetic properties of nanomaterials containing iron or cobalt nanoparticles

We have prepared nanocomposites consisting of narrowly sized metal-containing nanoparticles embedded in a polyethylene matrix and have established conditions for the fabrication of thick films and bulk materials from the synthesized polymer powders. Dielectric permittivity and resistivity measurements demonstrate that the electrical properties of the nanocomposites depend significantly on the nanoparticle size and content.The microwave absorption and permittivity of the materials are shown to vary little in a broad frequency range. The magnetization (including the remanent one) of the cobalt-containing nanomaterials is higher than that of the iron-containing samples.     

Ketjenblack carbon supported amorphous manganese oxides nanowires as highly efficient electrocatalyst for oxygen reduction reaction in alkaline solutions

A composite air electrode consisting of Ketjenblack carbon (KB) supported amorphous manganese oxide (MnOx) nanowires, synthesized via a polyol method, is highly efficient for the oxygen reduction reaction (ORR) in a Zn-air battery. The low-cost and highly conductive KB in this composite electrode overcomes the limitations due to low electrical conductivity of MnOx while acting as a supporting matrix for the catalyst. The large surface area of the amorphous MnOx nanowires, together with other microscopic features (e.g., high density of surface defects), potentially offers more active sites for oxygen adsorption, thus significantly enhancing ORR activity. In particular, a Zn-air battery based on this composite air electrode exhibits a peak power density of ～190 mW/cm2, which is far superior to those based on a commercial air cathode with Mn3O4 catalysts.     

PdCo alloys@N-doped porous carbon supported on reduced graphene oxide as a highly efficient electrocatalyst for hydrogen evolution reaction

Journal of Materials Science - Water splitting is considered as one of the recommendable techniques to realize clear and renewable hydrogen production. However, it suffers from lacking efficient...