Anchoring Co3O4 nanoparticles on MXene for efficient electrocatalytic oxygen evolution

Rational design and controllable synthesis of efficient electrocatalysts for water oxidation is of significant importance for the development of promising energy conversion systems, in particular integrated photoelectrochemical water splitting devices. Cobalt oxide (Co₃O₄) nanostructures with mixed valences (II,III) have been regarded as promising electrocatalysts for the oxygen evolution reaction (OER). They are able to promote catalytic support of OER but with only modest activity. Here, we demonstrate that the OER performance of cubic Co₃O₄ electrocatalyst is obviously improved when they are anchored on delaminated two-dimensional (2D) Ti₃C₂ MXene nanosheets. Upon activation the overpotential of the hybrid catalyst delivers 300 mV at a current density of 10 mA cm^-2 in basic solutions, which is remarkably lower than those of Ti₃C₂ MXene and Co₃O₄ nanocubes. The strong interfacial electrostatic interactions between two components contribute to the exceptional catalytic performance and stability. The enhanced OER activity and facile synthesis make these Co₃O₄ nanocubes-decorated ultrathin 2D Ti₃C₂ MXene nanosheets useful for constructing efficient and stable electrodes for high-performance electrochemical water splitting.

Iridium Nanotubes as Bifunctional Electrocatalysts for Oxygen Evolution and Nitrate Reduction Reactions

One-dimensionally (1D) hollow noble meal nanotubes are attracting continuous attention because of their huge potential applications in catalysis and electrocatalysis. Herein, we successfully synthesize hollow iridium nanotubes (Ir NTs) with the rough porous surface by the 1-hydroxyethylidene-1, 1-diphosphonic acid-induced self-template method under hydrothermal conditions and investigate their electrocatalytic performance for oxygen evolution (OER) and nitrate reduction reactions (NO₃^-RR) in an acidic electrolyte. The unique 1D and porous structure endow Ir NTs with big surface areas, high conductivity, and optimal atom utilization efficiency. Consequently, Ir NTs exhibit significantly enhanced activity and durability for acidic OERs compared with commercial Ir nanocrystals (Ir c-NCs), which only require the overpotential of 245 mV to deliver the current density of 10 mA cm^-2. Meanwhile, Ir NTs also show higher electrocatalytic activity for NO₃^-RR than that of Ir c-NCs, such as a Faraday efficiency of 84.7% and yield rate of 921 μg h^-1 mg_cat^-1 for ammonia generation, suggesting that Ir NTs are universally advanced Ir-based electrocatalysts.

Microwave-assisted pyrolysis of Pachira aquatica leaves as a catalyst for the oxygen reduction reaction

In this study, biomimetic Mg-N x -C y from Pachira aquatica leaves were mixed with carbon black (L/C catalyst), in which the mixture was treated by a conventional microwave oven at 700 W and 2 min, exhibiting high catalytic activity for the oxygen reduction reaction (ORR). By using a microwave-assisted process, it not only offers a cheaper and faster way to synthesize the catalyst compared to the conventional furnace process but also avoids the decomposition of the N4-structure. Using the optimized conditions, the L/C catalyst exhibits an electron transfer number of 3.90 and an HO2 - yield of only 5% at 0.25 V vs. RHE, which is close to the perfect four electron-transfer pathway. Besides, the L/C catalyst offers superior performance and long-term stability up to 20 000 s. The L/C catalyst contains a high proportion of quaternary-type nitrogen, Mg-N x -C y , and -C-S-C- which can be the active sites for the ORR.

Ligand-assisted capping growth of self-supporting ultrathin FeNi-LDH nanosheet arrays with atomically dispersed chromium atoms for efficient electrocatalytic water oxidation

Self-supporting ultrathin FeNi-layered double hydroxide nanosheet arrays with atomically dispersed Cr atoms were firstly fabricated from stainless steel mesh by a facile ligand-assisted capping growth approach. Their unique nanostructure and a strong synergetic effect between the atomically dispersed Cr dopants and the active sites afford an exceptional OER activity.

A Co-MOF-derived oxygen-vacancy-rich Co3O4-based composite as a cathode material for hybrid Zn batteries

Through the integration of Zn-Co3O4 and Zn-air batteries at the cell level, a hybrid battery was assembled, which possessed a higher voltage and power density than a common Zn-air battery. In this hybrid battery, the cathode material is composed of oxygen-vacancy-rich Co3O4-x and N, S-co-doped carbon derived from a metal-organic framework; a Zn plate acts as the anode. With a current of 1 A g-1, the specific capacity of the cathode material achieves 144 mA h g-1. A four-electron process dominates the oxygen reduction reaction of the cathode material with a half wave potential of 0.78 V. In the oxygen evolution reaction, the η10 potential of the cathode material is merely 365 mV. When discharged at 1 mA cm-2, the hybrid Zn battery shows two discharge plateaus at 1.75 V and 1.11 V. Its specific capacity and energy density reach 711 mA h g-1 and 810 W h kg-1, respectively. This battery also inherits superior power density from the Zn-Co3O4 battery. Its peak power density occurs at 43.6 mW cm-2, and this value is obviously higher than that of the Zn-air battery built from the same cathode material. The hybrid battery also exhibits excellent stability with a capacity and charge-discharge voltage that are well maintained after long time periods. This study integrates two distinct batteries into one power source to develop a hybrid Zn battery, which possesses high voltage, specific capacity and superior power and energy densities.

ZIF-Derived Co9-xNixS8 Nanoparticles Immobilized on N-Doped Carbons as Efficient Catalysts for High-Performance Zinc-Air Batteries

Bimetallic sulfides have been attracting considerable attention because of their high catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction; thus, they are considered efficient catalysts for important energy conversion devices such as fuel cells and metal-air batteries. Here, the catalytic activity of a novel catalyst composed of Co_9-xNi_xS₈ nanoparticles immobilized on N-doped carbons (Co_9-xNi_xS₈/NC) is reported. The catalyst is synthesized using a Ni-adsorbed Co-Zn zeolitic imidazolate framework (ZIF) precursor (NiCoZn-ZIF). Because of the porous structure of ZIF and the high intrinsic activity of the bimetallic sulfide nanoparticles, the Co_9-xNi_xS₈/NC catalyst exhibits high half-wave potential 0.86 V versus reversible hydrogen electrode for ORR and outstanding bifunctional catalytic performance. When Co_9-xNi_xS₈/NC is applied as a cathode catalyst in zinc-air batteries, considerably higher power density of about 75 mW cm^-2 and discharge voltage are achieved compared to those of batteries with commercial Pt/C and other ZIF-derived catalysts. The zinc-air battery with the Co_9-xNi_xS₈/NC catalyst shows a high cyclability more than 170 cycles for 60 h with almost negligible decline at 10 mA cm^-2. Our work provides a new insight into the design of bimetallic sulfide composites with high catalytic activities.

Enhancing hydrogen evolution reaction through modulating electronic structure of self-supported NiFe LDH

NiFe-layered double hydroxide (NiFe LDH), as an efficient oxygen evolution reaction (OER) electrocatalyst, has emerged as a promising electrocatalyst for catalyzing overall water splitting in alkaline electrolyte.

Single-layer carbon-coated FeCo alloy nanoparticles embedded in single-walled carbon nanotubes for high oxygen electrocatalysis

Novel and durable single-layer carbon-coated FeCo alloy nanoparticles embedded in single-walled carbon nanotubes exhibit remarkable oxygen electrocatalysis, which advances realistic rechargeable zinc–air batteries with high efficiency.

Boosting oxygen electrocatalytic reactions with Mn3O4/self-growth N-doped carbon nanotubes induced by transition metal cobalt

Oxygen electrocatalytic activities in transition-metal atoms and/or heteroatom-doped carbon nanostructures are strongly dependent on their conductivity and electron configurations.

Improved ion-diffusion performance by engineering an ordered mesoporous shell in hollow carbon nanospheres

A new kind of hollow carbon nanosphere with an ordered mesoporous shell structure is prepared and demonstrated to have improved performances in practical application areas involving fast ion transport.

A one-step synthesis of hierarchical porous CoFe-layered double hydroxide nanosheets with optimized composition for enhanced oxygen evolution electrocatalysis

Hierarchical porous CoFe-LDHs composed of ultrathin nanosheets were prepared via a simple one-step precipitation process and exhibit excellent electrocatalytic activity and outstanding durability for OER in alkaline media.

Fe-doped Co3O4 polycrystalline nanosheets as a binder-free bifunctional cathode for robust and efficient zinc–air batteries

Self-standing Fe-Co₃O₄@CC bifunctional electrocatalysts enabled high-performance Zn–air batteries with a power density of 268.6 mW cm⁻² and superior cycling stability.

Selective C–C coupling of terminal alkynes under an air atmosphere without base over Cu–NX–C catalysts

Highly dispersed copper nanoparticles supported on mesoporous nitrogenated carbon were synthesized and exhibited superior catalytic activity towards aerobic oxidative coupling of terminal alkynes.

Promoting toluene oxidation by engineering octahedral units via oriented insertion of Cu ions in the tetrahedral sites of MnCo spinel oxide catalysts

Toluene oxidation was promoted by engineering octahedral units via oriented insertion of Cu ions in the tetrahedral sites of MnCo spinel oxide catalysts.

Nanowrinkled Carbon Aerogels Embedded with FeN x Sites as Effective Oxygen Electrodes for Rechargeable Zinc-Air Battery

Rational design of single-metal atom sites in carbon substrates by a flexible strategy is highly desired for the preparation of high-performance catalysts for metal-air batteries. In this study, biomass hydrogel reactors are utilized as structural templates to prepare carbon aerogels embedded with single iron atoms by controlled pyrolysis. The tortuous and interlaced hydrogel chains lead to the formation of abundant nanowrinkles in the porous carbon aerogels, and single iron atoms are dispersed and stabilized within the defective carbon skeletons. X-ray absorption spectroscopy measurements indicate that the iron centers are mostly involved in the coordination structure of FeN₄, with a minor fraction (ca. 1/5) in the form of FeN₃C. First-principles calculations show that the FeN _x sites in the Stone-Wales configurations induced by the nanowrinkles of the hierarchically porous carbon aerogels show a much lower free energy than the normal counterparts. The resulting iron and nitrogen-codoped carbon aerogels exhibit excellent and reversible oxygen electrocatalytic activity, and can be used as bifunctional cathode catalysts in rechargeable Zn-air batteries, with a performance even better than that based on commercial Pt/C and RuO₂ catalysts. Results from this study highlight the significance of structural distortions of the metal sites in carbon matrices in the design and engineering of highly active single-atom catalysts.

Carbon-Based Nanomaterials as Sustainable Noble-Metal-Free Electrocatalysts

Nowadays, due to the worldwide growth demand of energy, over consumption of fossil fuel as well as their accompanying increased negative environmental impacts, the development of renewable energy systems, such as fuel cells and water electrolyzers, is becoming one of the "holy grail" for researchers. However, their large-scale applications have been severely limited by precious and unsustainable noble-metal electrocatalysts. Hence, it is highly desirable to develop robust electrocatalysts composed exclusively of low-cost and earth-abundant elements, to reduce or replace expensive and scarce noble-metals. Carbon-based nanomaterials, including heteroatoms-doped carbons and carbon-encapsulated metal materials, have recently attracted great interests because they show remarkable electrocatalytic performance and long-term stability for energy-related reactions, such as oxygen reduction reaction (ORR), hydrogen and oxygen evolution reactions (OER), hydrazine oxidation reaction (HzOR), etc. This review summarizes the recent progress in heteroatoms-doped carbon and carbon-encapsulated metal materials, highlighting the promise as cost-efficient electrocatalysts. Finally, a prospective on the future development of these promising materials is offered.

Zinc-air batteries: are they ready for prime time?

Zn-air batteries are under revival. They have large theoretical energy density and potentially very low manufacturing cost compared to the existing Li-ion technology. However, their full potential has not been fulfilled due to challenges associated with air cathodes and Zn anodes. In this minireview, we present the current status and technical hurdles of Zn-air batteries and discuss the possible direction of their future improvements. We show that in contrast to tremendous efforts on the design and development of efficient cathode electrocatalysts over recent years, the pursuit of stable and cyclable Zn anodes is equally important but receives far less attention than deserved. We therefore call for a shift of future research focus from cathode electrocatalysts to Zn anodes in order to make this century old technology a truly commercial reality.

Effects of vanadium pentoxide with different crystallinities on lithium ion storage performance

V₂O₅ anode materials with low crystallinity release better electrochemical performance than that of V₂O₅ with high crystallinity.