Instytut Podstawowych Problemów Techniki

Streszczenie:

A promising approach to catalysis in various electrochemical applications is engineering of heterostructures with enhanced active sites and interfacial electron transfer processes. In this study, conductive NiCo2S4 was interfaced with layered MoS2 as bifunctional electrode material for asymmetric supercapacitors and hydrogen generation through water splitting. The creation of opposite charges within the heterostructure components facilitates the adsorption of OH− and H+ ions, thereby boosting the bifunctional potentials. The constructed NiCo2S4/MoS2 electrode showed excellent specific capacitance of 1488.9 F g−1 at 1.0 A g−1 current density and capacity retention of 93 % after 30-fold rise in current density. The asymmetric supercapacitor exhibits superior energy density of 63 Wh kg−1 at power density 7.56 kW kg−1 compared to similar electrode materials reported in literature. The hydrogen evolution performance of the electrode materials in alkaline media produced a low overpotential (79.95 mV at 10 mA cm−2) and small Tafel slope (59 mV dec−1) that are comparable to the state-of-the-art Pt/C. Density functional theory calculation reveals a fast electron transfer from NiCo2S4 to MoS2 leading to creation of positively charged surface and negatively charged surface at NiCo2S4 and MoS2 respectively that facilitate the adsorption of OH− and H+ ions. This study offered a promising high active and stable non platinum advanced electrode bifunctional catalyst for energy storage supercapacitor and energy conversion hydrogen generation.

Słowa kluczowe:

Heterostructure, NiCo2S4, MoS2, Supercapacitor, HER

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Streszczenie:

The anodic substitution of a sluggish oxygen evolution reaction with a more energy-saving hydrazine oxidation reaction has the potential to greatly reduce energy consumption for hydrogen production. However, the underlying mechanism of the hydrazine oxidation reaction remains ambiguous, and the existing hydrazine splitting generally requires an external power source to drive the anodic and cathodic reactions, which is not suitable for outdoor applications. In this study, we have developed a heterostructure sulfide-based catalyst that effectively catalyzes both hydrazine oxidation and hydrogen evolution reactions. Through in situ Raman spectroscopy, we have confirmed that the breakage of the nitrogen-nitrogen single bond is a pathway for the hydrazine oxidation reaction. The enhanced electrocatalytic performance is attributed to the increased active sites and accelerated electron transfer within the heterostructures, which reduced the energy barrier, thereby enabling the fabricated electrolyzer using the g-C3N4/Ni(CN)2@NiS catalyst to deliver 200 mA cm−2 with a low voltage of 0.31 V. The assembled electrolyzer can be powered by a g-C3N4/Ni(CN)2@NiS anode-equipped direct hydrazine fuel cell, achieving self-powered hydrogen production with faradaic efficiency of more than 97 %.

Słowa kluczowe:

Functional electrod, Carbon nitride, Hydrogen generation, Hydrazine

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Streszczenie:

The urea oxidation reaction (UOR) is characterized by a lower overpotential compared to the oxygen evolution reaction (OER) during electrolysis, which facilitates the hydrogen evolution reaction (HER) at the cathode. Charge
distribution, which can be modulated by the introduction of a heterostructure, plays a key role in enhancing the adsorption and cleavage of chemical groups within urea molecules. Herein, a facile all-room temperature synthesis of functional heterojunction NiCo2 S4 /CoMo 2 S4 grown on carbon cloth (CC) is presented, and the as-prepared electrode served as a catalyst for simultaneous hydrogen evolution and urea oxidation reaction. The Density
Functional Theory (DFT) study reveals spontaneous transfer of charge at the heterointerface of NiCo 2 S4 /CoMo 2 S4 , which triggers the formation of localized electrophilic/nucleophilic regions and facilitates the adsorption of electron donating/electron withdrawing group in urea molecules during the UOR. The NiCo2 S4 /CoMo 2 S4 // NiCo 2 S4 /CoMo 2 S4 electrode pair required only a cell voltage of 1.17 and 1.18 V to deliver a current density of 10 and 100 mA cm−2 respectively in urea electrolysis cell and display very good stability. Tests performed in real urine samples show similar catalytic performance to urea electrolytes, making the work one of the best transition
metal-based catalysts for UOR applications, promising both efficient hydrogen production and urea decomposition.

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Słowa kluczowe:

ChemRAWN,electrocatalysis,electrochemical oxidation,ethanol,gold nanoparticles,nanobrush,nanowires,polyindole

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Streszczenie:

In this work we apply N+ ion irradiation on vertically aligned carbon nanotube (VACNT) arrays in order to increase the number of connections and joints in the CNT network. The ions energy was 50 keV and fluence 5 × 10^17 ions cm^−2. The film was 160 μm thick. SEM images revealed the ion irradiation altered the carbon bonding and created a sponge-like, brittle structure at the surface of the film, with the ion irradiation damage region extending ~4 μm in depth. TEM images showed the brittle structure consists of amorphous carbon forming between nanotubes. The significant enhancement of mechanical properties of the irradiated sample studied by the cyclic nanoindentation with a flat punch indenter was observed. Irradiation on the VACNT film made the structure stiffer, resulted in a higher percentage recovery, and reduced the energy dissipation under compression. The results are encouraging for further studies which will lead to create a class of materials - ion-irradiated VACNT films - which after further research may find application in storage or harvesting energy at the micro/nanoscale.

Słowa kluczowe:

vertically aligned carbon nanotubes, ion irradiation, nanoindentation

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Słowa kluczowe:

Electrocatalysis, Ascorbic acid, Polyindole, Gold nanoparticles, Nanobrush, Hard-template synthesis

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