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Chemical bonds fundamentally determine molecular properties and are prevalently characterized by various spectroscopic means such as infrared and Raman spectroscopies. However, the spatial resolution of these conventional approaches is insufficient to reveal nanoscale features. Recently, monochromated electron energy-loss spectroscopy (EELS) in the transmission electron microscope achieved a groundbreaking energy resolution of a few millielectronvolts and enabled direct observation of molecular vibrational spectrum with unmatched spatial resolution. Vibrational EELS is widely applicable to both organic and inorganic matter in the solid state or liquid phase. In this review, we introduce recent advancements and key concepts of this method, compare with other spectroscopic techniques, and discuss future developments for potential applications in research fields centered on catalysts, polymers, and live cells.

Summary The scalable preparation of high-purity monolayers is essential for practically integrating two-dimensional (2D) semiconductors in diverse technologies but remains a persistent challenge. Previous efforts to exfoliate 2D layered crystals by the organic ammonium intercalation usually produce few-layer nanosheets owing to a self-retarding effect that hinders the complete intercalation in neighboring layers. Herein, we report a unique “intercalation and separation” chemistry with a constant self-refreshing crystal surface that mitigates the self-retarding effect to ensure a complete intercalation of the bulk crystal, ultimately enabling high-yield solution-phase exfoliation of 2D semiconductor monolayers in excellent purity (e.g., monolayer purity of >95% for In2Se3 and InSe). Furthermore, we have assembled large-area organic/inorganic hybrid superlattices with diverse organic molecules and inorganic 2D monolayer crystals, thus creating a family of artificial superlattice materials with atomically modulated chemical compositions, widely tunable superlattice periodicities, and specifically tailorable electronic and thermal properties.

The atomic thin, vertically-stacked 2H-MoTe2/MoS2 heterostructures are successfully synthesized using the single step chemical vapor deposition (CVD) method and a magnet-assisted secondary precursor delivery tool. The second material (MoTe2) was grown in a well-controlled, unique and epitaxial 2H-stacking mode atop the first material (MoS2), starting from the edges. This led to the construction of a vertical p-n junction with a broadband photoresponse from the ultraviolet (UV, 200 nm) to the near-infrared (IR, 1100 nm) regions. The high crystallinity of MoTe2/MoS2 heterostructures with a modulation of sulfur and tellurium distribution is corroborated by multiple characterization methods, including Raman spectroscopy, photoluminescence (PL) spectroscopy and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Furthermore, the photoelectrical measurements exhibit a tremendous photoresponsivity with an external quantum efficiency (EQE) as high as 4.71 A/W and 532% at 1100 nm, while as 4.67 A/W and 1935% at 300 nm, one to two orders of magnitude higher than other exfoliated MoTe2 heterostructure devices have been reported so far. This synthetic method is a controllable stacking mode confined synthesis approach for 2D heterostructures, and paves the way for the fabrication of high-performance functional telluride-based broadband photodetectors.

For wide application of metal-air batteries, the key factor is the development of catalysts for air cathodes. In the present study, PdCo/C bimetallic nanocatalysts are prepared by a facile borohydride reduction method. To improve the activity and stability, the catalysts are heat-treated at 200 °C in H2/Ar atmosphere from 4 h to 24 h. The optimal heat-treatment time is found to be 8 h, at which the highest activity for both oxygen reduction reaction and oxygen evolution reaction is obtained. With the 8 h heat-treated PdCo/C catalyst, the rechargeable zinc-air battery exhibits a high power density of 180 mW cm−2 and retains stability for more than 50 h at a discharge-charge current density of 10 mA cm−2, while the magnesium-air battery obtains a power density of more than 200 mW cm−2 and remains stable within 8 h at a discharge current density of 65 mA cm−2.

This work aims to obtain a fundamental understanding of active sites near stone-wales (SW) defects rich nitrogen-doped graphene (DG) with specific coordination of carbon atom rings. It reveals that the SW rich defects (e.g., pentagon (5), pentagon—octagon—pentagon (i.e. 585), or pentagon-heptagon-heptagon-pentagon (5775) rings, appears correspondingly with carbon rings that brought active sites during catalytic reactions. Moreover, we anchored dual isolated metallic atoms (Ni/Fe) on DG support via linkers (O/N) called NiFe-DG. X-ray absorption spectroscopy indicates Ni/Fe metal single atoms are embedded via Fe-N4 and Ni-N4 coordination on DG surfaces. It exhibits high catalytic activity for oxygen reduction reaction (ORR) with an onset potential of 0.97 V, a half-wave potential of 0.86 V, and diffusion current density of 5.7 mA cm− 2, which is at par with commercial Pt/C. The catalyst shows superior stability, retained 82% of the initial current density even after 12 h under an applied potential of 0.86 V. Similarly, the oxygen evolution reaction (OER) overpotential of 358 mV was achieved at 10 mA cm− 2 with a lower Tafel slope value (76 mV/dec) than commercial Pt/C. It maintains 85% stability for 12 h at a constant potential of 1.588 V, shows better stability than commercial Pt/C.

Direct methanol fuel cells (DMFCs) have been recognized as a promising type of power sources to solve the energy shortage and environmental pollution from fossil energy consumption. However, their commercialization is still hindered by two major problems, the high cost of Pt-based catalysts and the crossover of methanol from anodes to cathodes. In the second problem, the methanol molecules can poison the Pt-based catalysts and lower the cell voltages by reacting with oxygen. Fe-based catalysts containing Fe–N–C active sites are well known as low-cost candidates that are promising to replace the Pt-based. But they cannot prevent the methanol molecules from reacting with oxygen. For the first time, we discovers a new enhancement of the electrocatalysis of Fe–N–C nanofiber catalysts induced by a synergy of methanol and oxygen-containing groups in the catalysts. Its mechanism is revealed by first-principles calculations of density functional theory and then proven experimentally. More significantly, the synergy-induced enhancement (SIE) is further improved experimentally by 40.8 times and reaches 21.60±0.05%. This indicates that the SIE has an enormous upside potential. Moreover, the methanol molecules in the SIE react with not oxygen but epoxy, reducing the harm of the reaction of methanol and oxygen in DMFCs. Further, the SIE has been employed in fuel cells and realized enhancement of current density by 3.0±0.5% in anion-exchange membrane DMFC and by 5.95±0.07% in H2–O2 anion exchange membrane fuel cell (AEMFC). Therefore, the new SIE can simultaneously solve both of the two problems and thus facilitate the DMFC commercialization for easing the crises of energy and pollution.