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

Afiliacje autorów:

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.

Afiliacje autorów:

Streszczenie:

The major hindrance to efficient electrocatalytic hydrogen generation from water electrolysis is the sluggish kinetics with corresponding large overvoltage of oxygen evolution reaction. Herein, we report a defective 2D NiCoMoS@Ni(CN)2 core-shell heterostructure derived from Hofmann-type MOF as an efficient and durable high-performance noble metal-free electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The sluggish oxygen evolution reaction was replaced with a more thermodynamically favourable HzOR, enabling energy-saving electrochemical hydrogen production with 2D NiCoMoS@Ni(CN)2 acting as a bifunctional electrocatalyst for anodic HzOR and cathodic hydrogen generation. Operating at room temperature, the two-electrode electrolyzer delivers 100 mA cm−2 from a cell voltage of just 257 mV, with strong long-term electrochemical durability and nearly 100% Faradaic efficiency for hydrogen evolution in 1.0 M KOH aqueous solution with 0.5 M hydrazine. The density functional theory (DFT) was employed to investigate the origin of catalytic performance and showed that high vacancy creation within the heterointerface endowed NiCoMoS@Ni(CN)2 with favourable functionalities for excellent catalytic performance.

Słowa kluczowe:

Defect engineering, Core-shell, Electrocatalyst, Hydrazine oxidation, Heterostructure

Afiliacje autorów:

Streszczenie:

Efficient and sustainable energy conversion depends on the rational design of single-atom catalysts. The control of the active sites at the atomic level is vital for electrocatalytic materials in alkaline and acidic electrolytes. Moreover, fabrication of effective catalysts with a well-defined surface structure results in an in-depth understanding of the catalytic mechanism. Herein, a single atom ruthenium dispersed in nickel-cobalt layered hydroxide (Ru-NiCo LDH) is reported. Through the precise controlling of the atomic dispersion and local coordination environment, Ru-NiCo LDH//Ru-NiCo LDH provides an ultra-low overpotential of 1.45 mV at 10 mA cm−2 for the overall water splitting, which surpasses that of the state-of-the-art Pt/C/RuO2 redox couple. Density functional theory calculations show that Ru-NiCo LDH optimizes hydrogen evolution intermediate adsorption energies and promotes O-O coupling at a Ru-O active site for oxygen evolution, while Ni serves as the water dissociation site for effective water splitting. As a potential model, Ru-NiCo LDH shows enhanced water splitting performance with potential for the development of promising water-alkaline catalysts.

Afiliacje autorów:

Streszczenie:

Oxygen vacancy (Vo) is ubiquitous, playing a critical role in tuning the electronic configuration and optimizing the adsorption of adsorbates in the oxygen evolution reaction (OER) process. However, fine control over the density and stabilization of Vo is a big challenge in the highly oxidizing environment of OER. Herein, we have fabricated bulk NiFeCo (layered double hydroxide) LDHs via the hydrothermal method and exfoliated them into thin sheets rich with Vo using high-energy Ar-plasma. We doped fluoride to simultaneously modulate the charge distribution of surrounding atoms and stabilize Vo by taking advantage of the extremely high electronegativity and similar ion diameter to oxygen of fluoride. The material exhibited OER activity with a low overpotential of 200 mV at 10 mA cm–2 and a Tafel slope of 34.6 mV dec–1. Density functional theory (DFT) calculations support the claim that Vo and fluoride substantially increase NiFeCo LDH OER activity by modifying the electronic structures of the catalytically active sites.

Słowa kluczowe:

Electrocatalyst, Double layered hydroxide, oxygen evolution reaction, oxygen vacancy, stabilization

Afiliacje autorów: