Molybdenum carbides embedded on carbon nanotubes for efficient hydrogen evolution reaction

Plasma Functionalization of Multi-Walled Carbon Nanotubes for Ammonia Gas Sensors

The role of plasma functionalization of multi-walled carbon nanotubes (MWCNTs) for room-temperature ammonia gas sensors was investigated. Plasma functionalization of MWCNTs with maleic anhydride was carried out at various durations. The active material of the gas sensor was investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was shown that the formation of functional groups on the surface of carbon nanotubes led to an increase in the ammonia sensor response by two to four times. The increase in functionalization duration induced the rise of O/C from 0.28 to 0.335, an increase in sensor resistance, and the distortion of the shape of the I-V curves.

Hierarchical Bimetallic Ni-Co-P Microflowers with Ultrathin Nanosheet Arrays for Efficient Hydrogen Evolution Reaction over All pH Values

Designing efficient nonprecious catalysts with pH-universal hydrogen evolution reaction (HER) performance is of importance for boosting water splitting. Herein, a self-template strategy based on Ni-Co-glycerates is developed to prepare bimetallic Ni-Co-P microflowers with ultrathin nanosheet arrays. The highly porous core-shell structure gives rise to affluent mass transfer channels and availably prevents the aggregation of nanosheets, while the ultrathin nanosheets are favorable for producing abundant active sites. Besides, the produced CoP/NiCoP heterostructure in the bimetallic Ni-Co-P catalyst has excellent HER performance in a wide pH range. The as-prepared catalyst shows low potentials of 90, 157, and 121 mV to deliver a current density of 10 mA cm^-2 in 0.5 M H₂SO₄, 0.5 M PBS, and 1 M KOH solution, respectively. Meanwhile, negligible overpotential decay is achieved in the polarization curves after a long-term stability determination. This work supplies a promising strategy for developing pH-universal HER electrocatalysts based on solid-state metal alkoxides.

Chemical and Structural Analysis of Carbon Materials Subjected to Alkaline Oxidation

Redox species such as transition metals may, unknowingly, integrate carbon materials that are produced (or supplied) for the assembling of electrodes in batteries, supercapacitors, and fuel cells. The extent to which these species alter the electrochemical profile of carbons and affect the performance and/or degradation of energy storage systems is still not fully appreciated. Alkaline oxidation (or fusion) is a promising approach to disintegrate nanocarbons for the subsequent study of their chemical composition by routine analytical tools. In this work, three commercial carbon powders, relevant for electrochemical applications and bearing varied textural orientation (point, radial, and planar), were selected to evaluate the versatility of fusion as a pretreatment process for elemental analysis. Additionally, the interaction of the flux, a lithium borate salt, with the carbons was elucidated by examining their post-fusion residues. The degree of structural degradation varied and, generally, the doping with Li and/or B (whether substitutional or interstitial) was low to nonexistent. With future developments, fusion could become a relevant pretreatment method to analyze the composition of carbon materials, even when complex mixtures (e.g., cycled battery electrodes) and larger batch scales are considered.

Uniformly Decorated Molybdenum Carbide/Nitride Nanostructures on Biomass Templates for Hydrogen Evolution Reaction Applications

Natural fibrils derived from biomass were used as a template to synthesize uniformly decorated nanoparticles (10-12 nm) of molybdenum carbide (Mo₂C) and molybdenum nitride (Mo₂N) supported on carbon. The nanoparticles have been synthesized through the carburization and nitridation of molybdenum on cotton fibrils, using a high-temperature solid-state reaction. The catalyst exhibits an onset potential of 110 mV and an overpotential of 167 mV to derive a cathodic current density of 10 mA cm^-2. The electrocatalyst also demonstrates excellent long-term durability of more than 2500 cycles in acidic media with a Tafel slope value of 62 mV dec^-1.

Enhancing hydrogen evolution activity by doping and tuning the curvature of manganese-embedded carbon nanotubes

Doping heteroatoms (Mn and N) and tuning the curvature of carbon nanotubes could efficiently elevate the C p-band center, lower the absolute electrode potential, and thus enhance the HER performance.

A Quasi-Solid-State Flexible Fiber-Shaped Li-CO2 Battery with Low Overpotential and High Energy Efficiency

The rapid development of wearable electronics requires a revolution of power accessories regarding flexibility and energy density. The Li-CO₂ battery was recently proposed as a novel and promising candidate for next-generation energy-storage systems. However, the current Li-CO₂ batteries usually suffer from the difficulties of poor stability, low energy efficiency, and leakage of liquid electrolyte, and few flexible Li-CO₂ batteries for wearable electronics have been reported so far. Herein, a quasi-solid-state flexible fiber-shaped Li-CO₂ battery with low overpotential and high energy efficiency, by employing ultrafine Mo₂ C nanoparticles anchored on a carbon nanotube (CNT) cloth freestanding hybrid film as the cathode, is demonstrated. Due to the synergistic effects of the CNT substrate and Mo₂ C catalyst, it achieves a low charge potential below 3.4 V, a high energy efficiency of ≈80%, and can be reversibly discharged and charged for 40 cycles. Experimental results and theoretical simulation show that the intermediate discharge product Li₂ C₂ O₄ stabilized by Mo₂ C via coordinative electrons transfer should be responsible for the reduction of overpotential. The as-fabricated quasi-solid-state flexible fiber-shaped Li-CO₂ battery can also keep working normally even under various deformation conditions, giving it great potential of becoming an advanced energy accessory for wearable electronics.