Institute of Fundamental Technological Research

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.

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

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.

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.

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