Enhanced local electric fields are created by nanoparticles when pumped at wavelengths corresponding to Localised Surface Plasmon Resonance (LSPR) modes, leading to Metal Induced Fluorescence Enhancement (MIFE). This paper describes the fluorescent enhancement due to reproducible and tuneable Au nanostructures on glass substrates fabricated over large areas by colloidal lithography. Interparticle separation, particle resonance, and the fluorescent dye properties (quantum yield and emission/ excitation wavelengths) are all important factors influencing the fluorescent enhancement. A maximum fluorescence enhancement of 69 times from near infra-red (NIR) dye Alexa FluorÒ 790 was observed.

Performance improvements in electric vehicle batteries are needed in order to reduce their cost and encourage greater use.1 This improvement is dependent on the properties (e.g. specific capacity and stability) of the cathode active material in the electric vehicle’s lithium ion battery.1 Lithium Nickel Cobalt Manganese Oxide (NMC) is a layered transition metal oxide that shows great promise as an electrode in lithium ion batteries for electric vehicles, with a high theoretical specific capacity and good stability in the layered structure.2 As the nickel content of the cathode material increases, so does the discharge capacity, however this increase comes at the cost of significantly decreased capacity retention.1 The mechanisms that contribute to this degradation are complex and interlinking and many of them are accompanied by some form of gas evolution. For example, the solid electrolyte interphase (SEI) formation at the cathode evolves CO2, which is able to crossover and contribute to solid electrolyte interphase formation at the anode.1 Similarly, upon electrochemical cycling a reactive form of oxygen can be evolved from the NMC lattice, resulting in a cascade of parasitic reactions within a lithium-ion battery.2 Herein, we probe these gas evolving degradation mechanisms through the development and use of a novel type of electrochemistry mass spectrometry (EC-MS) with unprecedented time resolution and sensitivity.3,4 The new technique, known as on-chip EC-MS, employs a microfabricated membrane chip to precisely control the transfer of volatile species from an electrochemical cell to a mass spectrometer. Its design also allows instantaneous gas exchange, particularly useful to simulate cross talk phenomena. This work demonstrates the first application of this technique to the study of lithium-ion batteries; this study uses a new cell design to facilitate operando measurements of gas evolution in lithium-ion batteries to provide important insight into these complex mechanisms.4 More specifically, the effect of transition metal dissolution on the stability of the anodic SEI is investigated by monitoring ethylene evolution. Isotopic labelling studies are also performed to probe the evolution and consumption of CO2 that is evolved from the cathode. Complementary and correlative ex situ surface sensitive analysis (such as x-ray photoelectron spectroscopy and secondary ion mass spectrometry) are carried out in order to develop a holistic understanding of the complex reactivity and chemistry evolution of lithium-ion batteries during operation. References (1) Jung, R.; Metzger, M.; Maglia, F.; Stinner, C.; Gasteiger, H. A. Chemical versus Electrochemical Electrolyte Oxidation on NMC111, NMC622, NMC811, LNMO, and Conductive Carbon. J. Phys. Chem. Lett. 2017, 8 (19), 4820–4825. (2) Wandt, J.; Freiberg, A. T. S.; Ogrodnik, A.; Gasteiger, H. A. Singlet Oxygen Evolution from Layered Transition Metal Oxide Cathode Materials and Its Implications for Lithium-Ion Batteries. Mater. Today 2018, 21 (8), 825-833. (3) Trimarco, D. B.; Scott, S. B.; Thilsted, A. H.; Pan, J. Y.; Pedersen, T.; Hansen, O.; Chorkendorff, I.; Vesborg, P. C. K; Stephens, I. E. L. Enabling Real-Time Detection of Electrochemical Desorption Phenomena with Sub-Monolayer Sensitivity. Electrochim. Acta 2018, 268, 520–530. (4) Thornton D. B.; Cavalca F.; Aguadero A.; Ryan M.; Stephens I.E.; UK Patent filed 17 September 2021

The lithium-mediated method of electrochemical nitrogen reduction, pioneered by Tsuneto et al1 then verified by Andersen et al2, is currently the sole paradigm capable of unequivocal electrochemical ammonia synthesis. Such a system could allow the production of green, distributed ammonia for use as fertiliser or a carbon-free fuel. However, despite great improvements in Faradaic efficiency and stability since just 20193, fundamental understanding of the mechanisms governing nitrogen reduction and other parasitic reactions is lacking. Lithium Ion Battery (LIB) research can provide insight; since both lithium-mediated electrochemical ammonia synthesis and LIBs utilise an organic solvent and lithium salt, both form a Solid Electrolyte Interphase (SEI), which is electronically insulating but ionically conducting, at the electrode surface. In LIBs, this is necessary to stabilize and cycle low potential materials4. In lithium-mediated ammonia synthesis, the SEI could also have a critical role in controlling the access of protons and other key reactants to the catalytically active sites and promoting greater selectivity toward nitrogen reduction to ammonia5. While some characterisation of the SEI has been carried out for the lithium-mediated nitrogen reduction system6, the literature still lacks holistic studies which aim to carefully characterise the bulk electrolyte and SEI components and link them to system performance. In this work we use insight from battery science to tackle a significant stability problem in lithium-mediated nitrogen reduction. The traditional electrolyte employed by Tsuneto et al. was 0.2 M LiClO4 in a 99:1 tetrahydrofuran to ethanol mix. While this system can produce ammonia, the working electrode potential becomes more negative over time. Our initial investigations show that this problem stems from an unstable SEI which becomes increasingly organic. Simply by raising the concentration of LiClO4 in the electrolyte, we vastly improve stability, as shown in figure 1(a), and boost Faradaic efficiency. Bulk electrolyte salt solvation properties are investigated through Raman spectroscopy, as shown in figure 1(b). Here we observe the emergence of a shoulder at around 930 cm-1 with increasing LiClO4 concentration, which we assign to the emergence of Contact-Ion-Pairs (CIPs) through comparison to Density Functional Theory calculations. These CIPs mean that perchlorate anion degradation products are more abundant in the formed SEI, as shown in our X-Ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass spectrometry results. This more inorganic SEI protects the electrolyte against further degradation, preventing the working electrode drift to more negative potentials. We then link this behaviour to a peak observed in the Faradaic efficiency of ammonia synthesis at 0.6 M LiClO4 by also considering decreasing N2 solubility and diffusivity, as well as a more ionically conductive SEI, in an increasingly concentrated electrolyte. We also present never-before seen cross-sectional images of the SEI using cryogenic Focussed Ion Beam milling and Scanning Electron Microscopy, further aiding understanding of how salt solvation affects the morphology of the formed SEI and system performance. Our results emphasise the need to consider SEI properties in electrolyte design for lithium-mediated nitrogen reduction, as well as the need to balance desirable SEI properties with desirable bulk electrolyte properties. Tsuneto, A., Kudo, A. & Sakata, T. Efficient Electrochemical Reduction of N 2 to NH 3 Catalyzed by Lithium . Chemistry Letters vol. 22 851–854 (1993). Andersen, S. Z. et al. A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements. Nature 570, 504–508 (2019). Westhead, O., Jervis, R. & Stephens, I. E. L. Is lithium the key for nitrogen electroreduction? Science. 372, 1149–1150 (2021). Peled, E. & Menkin, S. Review—SEI: Past, Present and Future. J. Electrochem. Soc. 164, A1703–A1719 (2017). Singh, A. R. et al. Electrochemical Ammonia Synthesis—The Selectivity Challenge. ACS Catal. 7, 706–709 (2017). Li, K. et al. Enhancement of lithium-mediated ammonia synthesis by addition of oxygen. Science. 1597, 1593–1597 (2021). Figure 1

No abstract