Graphene-based sensors exhibit high sensitivity, fast response, and good selectivity towards toxic gases but have low mechanical stability. The combination of graphene and two-dimensional hexagonal boron nitride (h-BN) is expected to increase the mechanical stability and enhance the adsorption performance of these gas sensors. Using first-principles calculations, we demonstrate that two-dimensional graphene/h-BN double layers can be used as good substrates for gas sensors with a small lattice mismatch of only 1.78%. Moreover, the presence of a h-BN layer widens the band gap by about 38 meV and considerably increases the work function, thus positively affecting the gas adsorption performance. Although these graphene/h-BN heterostructures do not change the physical adsorption mechanism of these sensors concerning the graphene-based materials, these bilayers significantly enhance the sensitivity of these sensors for detecting CO₂, CO, NO, and NO₂ toxic gases. Particularly, compared to the pristine graphene-based materials, the gas adsorption energies of graphene/h-BN increased by up to 13.78% for the adsorption of NO, and the shortest distances between the graphene/h-BN substrates and adsorbed gas molecules decreased. We also show that the graphene/h-BN heterostructure is more selective towards NO_x gases while more inert towards CO_x gases, based on the different amounts of charge transferred from the substrate to the adsorbed gas molecules. Using the non-equilibrium Green functions in the context of density functional theory, we quantitatively associated these charge transfers with the reduction of the current passing through these scattering regions. These results demonstrate that graphene/h-BN heterostructures can be exploited as highly sensitive and selective room-temperature gas sensors for detecting toxic gases.

The electrochemical interface (EI) is the determining factor in the yield and mechanism of sustainable energy storage and conversion systems due to its intrinsic functionality as a dynamic junction with the symmetry breaking of the molecular arrangement for complex reaction fields of mass transport and heterogeneous electron transfer. At the EI, the externally applied potential stimulus drives the formation of the electrical double layer (EDL) and governs the adsorption of interfacial adsorbate species in aqueous electrolyte solutions. Water and its aqueous electrolyte systems are integral and quintessential elements in the technological innovation of various fields such as environmental sciences, electrocatalysis, photocatalysis, and biochemistry. Although deciphering the structure and orientation of water molecules at the electrode–electrolyte interface in a quantitative analysis is of utmost importance, assessing chemical phenomena at the buried EI was rather challenging due to the intricacy of selecting interface-specific methodologies. Based on the non-centrosymmetry of the interfaces’ electronic properties, sum-frequency generation (SFG) spectroscopy has been manifested to be specifically well suited for probing the EI with detailed and comprehensive characteristics of adsorbates’ chemical structures and electrochemical events. In this review, we holistically engage in a methodical and scrupulous assessment of the fundamental EDL models and navigate towards the connection of the renowned Stark effect and potential dependence of SFG spectra at heterogeneous electrode–electrolyte interfaces. We dissect the development, advantages, and available geometrical configurations of in situ SFG spectroscopy in harnessing the EI. A broad spectrum of applications in unraveling the water orientations and rationalizing the convoluted mechanism of fuel-generated electrocatalytic reactions with particular encumbrances and potential resolutions is underscored by leveraging SFG spectroscopy.

Geochemical fractionation, ecological risk evaluations, and pollution sources of heavy metals in a municipal watercourse system of Hai Duong province.

Comprehending and optimizing the electrified electrode-electrolyte interface is crucial for driving electrocatalytic reactions in sustainable green energy conversion and storage technologies, including fuel cells (FCs), electrolyzers, and batteries [1,2]. While the advent of non-precious heterogeneous electrocatalysts has facilitated novel alternatives to address the global challenges of the energy crisis, platinum (Pt)-based catalysts remain the most commonly employed noble material in hydrogen evolution and oxidation reactions (HER/HOR) and oxygen reduction reaction (ORR) [2]. Nonetheless, the selectivity and kinetics of these technologies are frequently hindered by complex adsorptive interactions of ad-species on the Pt surface, particularly chemisorbed adsorbates at the electrical double layer (EDL) [3]. Among aqueous anionic species, phosphate anions (H_nPO₄ ^(n-3), including H₂PO₄ ^-, HPO₄ ^2-, and PO₄ ^3-) are attributed to the surface-poisoning effect on high-temperature proton exchange membrane FCs (HT-PEMFCs) and phosphoric acid FCs (PAFCs) [4]. Second-harmonic generation (SHG) spectroscopy is considered inherently specific to probe the surface charge density and surface potential of water interfaces [5]. Herein, we unveil the microstructural complexity at the dynamic Pt-phosphate junction and disentangle the role of phosphate anions in interfacial properties by using the femtosecond (fs) SHG probing technique under potential-controlled conditions. By integrating a novel external thin-layer spectroelectrochemical cell with the SHG spectroscopic setup for in situ monitoring, the electronic properties of Pt-phosphate electrochemical interfaces (EIs) are detected across a wide range of applied potentials and buffered pH values (1.0 to 13).