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Plasmonic nanojunctions, consisting of adjacent metal structures with nanometre gaps, can support localised plasmon resonances that boost light matter interactions and concentrate electromagnetic fields at the nanoscale. In this regime, the optical response of the system is governed by poorly understood dynamical phenomena at the frontier between the bulk, molecular and atomic scales. Here, we report ubiquitous spectral fluctuations in the intrinsic light emission from photo-excited gold nanojunctions, which we attribute to the light-induced formation of domain boundaries and quantum-confined emitters inside the noble metal. Our data suggest that photoexcited carriers and gold adatom - molecule interactions play key roles in triggering luminescence blinking. Surprisingly, this internal restructuring of the metal has no measurable impact on the Raman signal and scattering spectrum of the plasmonic cavity. Our findings demonstrate that metal luminescence offers a valuable proxy to investigate atomic fluctuations in plasmonic cavities, complementary to other optical and electrical techniques., Metallic nanojunctions support localised plasmon resonances and boost light matter interactions, but dynamical phenomena are poorly understood. Here, the authors report intrinsic photoluminescence blinking from plasmonic nanojunctions, originating from light-induced atomic scale restructuring of the metal.

Efficient catalytic water splitting demands advanced catalysts to improve the slow kinetics of the oxygen evolution reaction (OER). Earth-abundant transition metal oxides show promising OER activity in alkaline media. However, most experimental information available is either from post-mortem studies or in-situ space-averaged X-ray techniques in the micrometer range. Therefore, the composition of the active centers under operando conditions is still under debate. In this work, we combine nanoscopic and spectroscopic measurements on the hydroxylation of molecular beam epitaxy (MBE)-prepared Ni and NiFe oxides nanoislands with operando local investigations of Ni and NiFe hydroxide electrocatalysts under OER conditions to reveal the nature of active centers of Ni and Fe-doped Ni oxides in 2D OER catalysts. Our results reveal that Fe doping increases the active surface area by island fragmentation and boosts the intrinsic activity by creating optimized active centers consisting of both Ni and Fe atoms. In addition, our findings show that operando characterization at the nanoscale is crucial to reveal the dynamic nature of the interface of 2D catalysts under reaction conditions.

While solar-to-fuel catalysis requires the careful transfer of electrons, there are still challenges understanding how electron spin contributes to reactivity. Here, authors employ chiral fused thiadiazole-helicenes to control spin polarization in oxygen evolution electrocatalysts., A sustainable future requires highly efficient energy conversion and storage processes, where electrocatalysis plays a crucial role. The activity of an electrocatalyst is governed by the binding energy towards the reaction intermediates, while the scaling relationships prevent the improvement of a catalytic system over its volcano-plot limits. To overcome these limitations, unconventional methods that are not fully determined by the surface binding energy can be helpful. Here, we use organic chiral molecules, i.e., hetero-helicenes such as thiadiazole-[7]helicene and bis(thiadiazole)-[8]helicene, to boost the oxygen evolution reaction (OER) by up to ca. 130 % (at the potential of 1.65 V vs. RHE) at state-of-the-art 2D Ni- and NiFe-based catalysts via a spin-polarization mechanism. Our results show that chiral molecule-functionalization is able to increase the OER activity of catalysts beyond the volcano limits. A guideline for optimizing the catalytic activity via chiral molecular functionalization of hybrid 2D electrodes is given.

The electrochemical reduction of CO2 (CO2RR) into multicarbon compounds is a promising pathway towards renewable chemicals. Structure-product selectivity studies highlight that copper (100) facets favour C2+ product formation. However, the atomic processes leading to the formation of (100)-rich Cu cubes remains elusive. Herein, we use Cu and graphene-protected Cu surfaces to reveal the differences in structure and composition of common Cu-based electrocatalysts, from nano to micrometer scales. We show that stripping/electrodeposition cycles lead to thermodynamically controlled growth of Cu2O micro/nanocubes, while multi-layered Cu nanocuboids form universally during CO2RR upon polarization-driven re-organization of Cu0 atoms. A synergy of electrochemical characterization by scanning tunnelling microscopy (EC-STM), operando EC-Raman and quasi-operando X-Ray Photoemission spectroscopy (XPS) allows us to shed light on the role of oxygen on the dynamic interfacial processes of Cu, and to demonstrate that chloride is not needed for the stabilization of cubic Cu nanostructures.

Nickel iron oxide is considered a benchmark nonprecious catalyst for the oxygen evolution reaction (OER). However, the nature of the active site in nickel iron oxide is heavily debated. Here we report direct spectroscopic evidence for the different active sites in Fe‐free and Fe‐containing Ni oxides. Ultrathin layered double hydroxides (LDHs) were used as defined samples of metal oxide catalysts, and18O‐labeling experiments in combination with in situ Raman spectroscopy were employed to probe the role of lattice oxygen as well as an active oxygen species, NiOO−, in the catalysts. Our data show that lattice oxygen is involved in the OER for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. Moreover, NiOO−is a precursor to oxygen for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. These data indicate that bulk Ni sites in Ni and NiCo oxides are active and evolve oxygen via a NiOO−precursor. Fe incorporation not only dramatically increases the activity, but also changes the nature of the active sites.

Immense field enhancement and nanoscale confinement of light are possible within nanoparticle-on-mirror (NPoM) plasmonic resonators, which enable novel optically-activated physical and chemical phenomena, and render these nanocavities greatly sensitive to minute structural changes, down to the atomic scale. Although a few of these structural parameters, primarily linked to the nanoparticle and the mirror morphology, have been identified, the impact of molecular assembly and organization of the spacer layer between them has often been left uncharacterized. Here, we experimentally investigate how the complex and reconfigurable nature of a thiol-based self-assembled monolayer (SAM) adsorbed on the mirror surface impacts the optical properties of the NPoMs. We fabricate NPoMs with distinct molecular organizations by controlling the incubation time of the mirror in the thiol solution. Afterwards, we investigate the structural changes that occur under laser irradiation by tracking the bonding dipole plasmon mode, while also monitoring Stokes and anti-Stokes Raman scattering from the molecules as a probe of their integrity. First, we find an effective decrease in the SAM height as the laser power increases, compatible with an irreversible change of molecule orientation caused by heating. Second, we observe that the nanocavities prepared with a densely packed and more ordered monolayer of molecules are more prone to changes in their resonance compared to samples with sparser and more disordered SAMs. Our measurements indicate that molecular orientation and packing on the mirror surface play a key role in determining the stability of NPoM structures and hence highlight the under-recognized significance of SAM characterization in the development of NPoM-based applications.

The electroreduction of CO

The electroreduction of CO2 (CO2RR) is a promising strategy towards sustainable fuels. Cu is the only earth-abundant catalyst capable of CO2-to-hydrocarbons conversion; yet, its dynamic structure under operando CO2RR conditions remains unknown. Here, we track the Cu structure operando by electrochemical scanning tunneling microscopy and Raman spectroscopy. Surprisingly, polycrystalline Cu surfaces reconstruct forming Cu nanocuboids whose size can be controlled by the polarization potential and the time employed in their in-situ synthesis, without the assistance of organic surfactants and-or halide anions. If the Cu-surface is covered by a graphene monolayer, smaller features with enhanced catalytic activity for CO2RR can be prepared. The graphene protecting layer soften the 3D morphological changes that Cu-based catalysts suffer when exposed to aggressive electrochemical environments, and allows us to track the kinetic roughening process. This novel strategy is promising for improving Cu long-term stability and, consequently, controlling product selectivity.

Transition metal dichalcogenides (TMDs) represent a class of semiconducting two-dimensional (2D) materials with exciting properties. In particular, defects in 2D-TMDs and their molecular interactions with the environment can crucially affect their physical and chemical properties. However, mapping the spatial distribution and chemical reactivity of defects in liquid remains a challenge. Here, we demonstrate large area mapping of reactive sulfur-deficient defects in 2D-TMDs in aqueous solutions by coupling single-molecule localization microscopy with fluorescence labeling using thiol chemistry. Our method, reminiscent of PAINT strategies, relies on the specific binding of fluorescent probes hosting a thiol group to sulfur vacancies, allowing localization of the defects with an uncertainty down to 15 nm. Tuning the distance between the fluorophore and the docking thiol site allows us to control Foster resonance energy transfer (FRET) process and reveal grain boundaries and line defects due to the local irregular lattice structure. We further characterize the binding kinetics over a large range of pH conditions, evidencing the reversible adsorption of the thiol probes to the defects with a subsequent transitioning to irreversible binding in basic conditions. Our methodology provides a simple and fast alternative for large-scale mapping of nonradiative defects in 2D materials and can be used for in situ and spatially resolved monitoring of the interaction between chemical agents and defects in 2D materials that has general implications for defect engineering in aqueous condition.