The exploitation of lanthanide-induced NIR luminescence holds significant potential for advancing biosensing and imaging technologies because of its deeper imaging penetration depth and lower biosensing noise than visible light. However, the low quantum efficiency of light generation, along with the high cost and poor sensitivity of light detection for NIR-II photons, have largely constrained the application of NIR-II luminescence for bio-imaging and sensing. To overcome these challenges, we have developed a new strategy for NIR bioimaging and sensing by using Tm3+-doped NaYF4 upconversion nanoparticles (UCNPs) that emit NIR-I upconversion luminescence (UCL) at 808 nm under NIR-II excitation at 1208 nm. The 1208 nm excitation enables deeper imaging penetration due to negligible autofluorescence, thereby reducing biosensing noise, resulting in an enhanced signal-to-noise ratio (S/N) from a minimal noise background. Meanwhile, the NIR-I emission at 808 nm allows deep tissue penetration, while allowing highly sensitive detection of NIR-I photons using conventional detectors, which are much more accessible than NIR-II detection systems. The intrinsically weak NIR UCL signals were further amplified by up to 210-fold using a pioneering plasmonic approach, achieved by coupling UCNPs with periodic silver hole-cap nanoarrays (Ag-HCNAs). Three-dimensional finite-difference time-domain (3D-FDTD) simulations and lifetime analyses revealed substantial electric field enhancements under 1208 nm excitation and accelerated radiative decay at 808 nm, contributing to both excitation and emission enhancement. The potential use of Ag-HCNA-UCNP conjugates for fluorescence immunoassay platforms was further validated by immobilizing streptavidin-functionalized UCNPs (SA-UCNPs) onto biotinylated Bovine Serum Albumin (bBSA) pre-grafted substrates, resulting in up to a 113-fold increase in UCL intensity. This plasmonic-enhanced UCL platform offers significant advantages, including cost-effective detection of 808 nm emission using silicon-based detectors, an improved signal-to-noise ratio through enhanced tissue penetration, and reduced autofluorescence enabled by NIR-II excitation.

Understanding solid liquid interfaces at high spatial and chemical resolution is crucial for advancing electrochemical energy storage technologies, yet this remains a persistent challenge due to the lack of characterisation techniques that can capture dynamic processes and preserve fragile interfacial chemistries. In lithium ion batteries, interfacial phenomena such as lithium alloying, solid electrolyte interphase formation, and electrode degradation play a decisive role in capacity retention and failure mechanisms but are difficult to observe in their native state due to high mobility, reactivity, and low atomic number of lithium. Here, we use a recently introduced correlative operando characterisation approach that integrates electrochemical liquid cell transmission electron microscopy with cryogenic atom probe tomography to resolve the evolution of a platinum alloy anode at the solid liquid interface during electrochemical cycling. This correlative, cryo enabled workflow reveals spatially heterogeneous SEI formation, the presence of lithium carbonate rich inner SEI layers, and the retention of elemental lithium within the platinum electrode, most likely trapped along grain boundaries. Additionally, we observe the formation of mossy lithium structures and irreversible lithium loss through dead lithium accumulation. Our results provide direct mechanistic insight into lithium alloying and degradation pathways in alloy based anodes and establish a generalised platform for probing dynamic electrochemical interfaces with complementary structural and chemical sensitivity. The methodology is broadly applicable to next generation electrode materials and electrochemical devices where interfacial dynamics dictate performance and stability.

Li-mediated ammonia synthesis is – thus far – the only electrochemical method to decentralised ammonia production, an alternative to one of the largest thermal heterogeneous catalytic processes, for its unique selectivity on a solid electrode. However, it is burdened with intrinsic energy losses, operating at Li plating potential. In this work, we survey the periodic table to understand the fundamental features that make Li stand out. Through density functional theory calculations and experimentation on chemistries analogous to lithium (e.g. Na, Mg, Ca), we find that lithium is unique in several ways. It combines a stable nitride that readily decomposes to ammonia, with an ideal solid electrolyte interphase, balancing reagents at the reactive interface. We propose descriptors based on simulated formation and binding energies of key intermediates, and further on hard and soft acids and bases (HSAB principle) to generalize such features. The survey will help the community towards new electrochemical systems for nitrogen fixation.

La(Fe,Si)13-based alloys, with giant magnetocaloric effect, still encounter significant degradation issues prior to commercial viability. In this work, the corrosion behavior of ferro magnetic La(Fe,Si)13Hy was investigated with electrochemical linear polarization resistance measurements under conditions with zero, 1T parallel and perpendicular magnetic fields, mimicking practical application scenarios. The results demonstrated that both parallel and perpendicular magnetic fields had a suppressive effect on corrosion rates due to the combined influence of magnetohydrodynamic forces and magnetic field gradient forces. The inhibiting efficiency of the parallel field decreased with increasing exposure period, while that of the perpendicular field continued to increase over time. The magnetic field also affected the relative proportion of rust phases, and thereby the protectiveness of the rust layer. This highlights the importance of conducting experiments under service conditions to understand the degradation mechanisms of magnetic cooling devices.

Operando/in situ liquid cell transmission electron microscopy (LCTEM) allows for real time imaging of dynamic nanoscale liquid-based processes. However, due to the thick liquid cell of traditional LCTEM holders and thus scattering of the electron beam passing through the cell, the achievable spatial and chemical resolution is limited. Cryogenic atom probe tomography (cryo-APT) overcomes these limitations by offering (near-)atomic scale compositional analysis of frozen liquid-solid interfaces. However, APT provides limited structural analysis and has no capacity for dynamic or operando liquid cell studies. This work presents a novel workflow for site-specific cryo-APT sample preparation of liquid-solid interfaces from in situ electrochemical LCTEM micro-electro-mechanical systems (MEMS) chips. Using a cryogenic inert gas transfer suitcase and a cryogenic plasma-focused ion beam (PFIB), a MEMs nanochip containing a Li electrolyte from an electrochemistry LCTEM holder was successfully frozen, transferred to the cryo stage of a PFIB and prepared into APT needle samples containing the electrolyte-electrode interface at cryogenic temperatures, followed by cryogenic transfer to an atom probe for nanoscale compositional analysis. This correlative approach enables both dynamic nanoscale imaging and near atomic scale compositional analysis of air sensitive and reactive liquid-solid interfaces. This method enables reliable and reproducible APT sample preparation of these frozen interfaces from MEMs based nanochips and can hence be used across materials systems and energy-conversion or storage devices.

Although the Haber-Bosch process for industrial ammonia production is hailed by many as one of the most influential breakthroughs of the 20th century, its decarbonization and decentralization remain a critical challenge. One of the most promising and fast improving approaches is electrochemical nitrogen reduction mediated by lithium. However, the impact of electrolyte configuration on the formation of the solid electrolyte interphase (SEI) and its effect on selective nitrogen reduction is still elusive. In particular, the role of commonly added, supposedly sacrificial, proton donors on SEI chemistry and morphology remains a mystery. In this work, the impact of ethanol concentration in a 1 M LiNTf2 in THF electrolyte on SEI properties and nitrogen reduction is analyzed via a multipronged characterization approach. Post-mortem surface analysis via X-ray photoelectron spectroscopy shows a dependence in the relative proportion of LiF and Li2O on ethanol concentration, while depth profiling measurements via cluster source time-of-flight secondary ion mass spectrometry reveal increasing SEI electrolyte permeability at higher ethanol concentrations. Cryogenic electron microscopy measurements show a reduction in SEI thickness with increased ethanol concentration, as well as increased SEI homogeneity. Lithium metal is also observed only in the ethanol-free condition. Analysis of bulk SEI components via titration corroborates the observation of lithium metal in cryo-microscopy measurements, as well as showing an increase in bulk Li2-xOHx content with ethanol concentration. A narrow 'Goldilocks' region is revealed, where the SEI has just the right properties for efficient nitrogen reduction.

Nanometre to micrometre scale interfacial processes control CO2 mineralisation in silicate rocks targeted for carbon sequestration. Understanding the chemical mechanisms prompted by the addition of CO2 into aqueous-rock systems is necessary to design and manage industrial scale mineralisation operations. This work presents a synthesis of the past two decades of research on chemical processes taking place at the solid mineral interface, and how they drive or inhibit ex-situ or in-situ mineralisation. Studies cited in this review focus on samples representative of mafic or ultramafic rocks, their constituent mineral phases, and the calcium silicate wollastonite. Key findings include 1) Mechanical passivation is not caused solely by silica formation, a variety of chemical species can inhibit reactions by forming pervasive layers, including the target carbonate phase. 2) The functionality of engineered carrier solutions primarily derives from sodium bicarbonate which provide a pH buffering effect, excess CO32– ions, and limit mass transport resistance from Si-rich passivating compounds. 3) Non-uniform mineralisation is exhibited in whole rocks and can be attributed to the inherent pore characteristics and heterogeneous distribution of grain sizes that produce micro-environments of preferential carbonation in natural mafic rock samples. 4) Thin water films facilitate a coupled dissolution-re-precipitation mechanism in water-bearing supercritical (CO2-rich) environments. 5) Mineralisation in both aqueous and supercritical CO2 systems generates product layers of comparable morphology, consisting of interstratified carbonate-silica growths. Yet, experiments involving a wet supercritical CO2 phase tend to generate carbonates at lower temperature conditions indicating enhanced reactivity or a more porous passivating layer.

Glioblastoma (GBM) is an extremely infiltrative brain cancer that is impossible to fully remove surgically and almost always recurs at the borders of the resection cavity. There is increasing focus on inducing cancer cell death using magneto-mechanical therapy (MMT), which involves energy conversion of an external low-frequency magnetic field into mechanical forces using magnetic nanoparticles. Here, we combined MMT with enhanced radiotherapy (RT)─the standard of care treatment for GBM─to increase the efficiency of treatment using gold-iron nanowires (AuFe NWs). The magnetic iron component of the nanowires mechanically rotates, inducing cellular damage, and the gold scatters X-rays due to its high atomic number, enhancing the local RT dose. We show that reproducible synthesis of AuFe NWs with different ratios of gold:iron can be achieved using a hard-template electrochemical method, controlling composition by tuning the deposition current. Ratios with best-performing iron percentages were selected for computational modeling to predict which frequency should be applied in vitro on a GBM cell line. In vitro testing, using a cell metabolism assay, and the optimal frequency and gold:iron ratio, demonstrated that applying MMT alongside RT resulted in a synergistic effect, reducing cell viability significantly by ∼60% (as compared with a 30% reduction for RT, with/without AuFe NWs), and a 20% reduction for MMT (with AuFe NWs). The increased efficacy of RT, post-MMT, was attributed to the higher association of the nanowires with the cells following application of the magnetic field and local membrane damage.

A single nanoparticle (NP) capable of simultaneously performing multiple bioimaging and therapeutic functions is an innovative approach to advance the field of cancer diagnostics and treatment. Here we report a facile synthesis approach to produce magnetic-plasmonic core-shell nanostars. These NPs consist of an Fe3O4 core, silica intermediate shell, and outer spiky gold nanostar shell. Remarkably, these core-shell NPs exhibit outstanding magnetisation and tuneable localized surface plasmon resonance (LSPR) spanning from visible to Near Infrared (NIR) wavelengths. Through incorporation of Indocyanine Green (ICG) and subsequent coating with bovine serum albumin (BSA), the obtained NPs demonstrate dual imaging capabilities in the form of magnetic resonance imaging (MRI) which offers high spatial resolution and deep tissue penetration and Surface-Enhanced Raman Scattering (SERS) which can provide the ultrasensitive molecular detection which MRI lacks. More significantly, they also exhibit significant potential to be used in photothermal therapy (PTT). These multi-functional NPs show minimal cytotoxicity when exposed to cells even at high concentrations, positioning them as promising candidates for future in vivo studies centred around imaging-guided photothermal therapy.

The selectivity and geometric current density of copper-based electrodes for electrochemical CO2 reduction (CO2RR) have been significantly improved, yet research is striving to improve the intrinsic activity of these materials. The accurate quantification of active sites is vital to benchmark the intrinsic activity of the catalysts for electrochemical CO2 reduction to facilitate activity improvements. Herein, we propose a method to determine the active sites using CO displacement in potassium phosphate buffer at 10 °C. Comparing this method with the electrochemical surface area (ECSA), measured by double-layer capacitance, the most used technique in this field, we demonstrate that CO displacement provides a much more accurate quantification of the number of active sites. By normalizing current density vs the CO displacement active sites, we find electropolished copper foil has the highest intrinsic activity towards CO2RR. We also reveal there is a clear relationship between surface roughness and chained products.

To advance the development of all-solid-state Na-ion batteries (ASSNIBs), optimal Na solid-state electrolyte (SSE) materials must meet critical requirements, including high ionic conductivity (>10−3 ​S ​cm−1), low electronic conductivity (<10−10 ​S ​cm−1), and cost-effectiveness (<$50 ​kg−1). In this study, we present a mixed-anion strategy for designing SSEs containing earth-abundant elements only. Density functional theory (DFT) and bond valence site energy (BVSE) calculations show that Na2ZrO3 offers better electrochemical stability but poor Na ​+ ​conductivity compared to Na2ZrCl6. Mixed-anion SSE Na2ZrCl6-4xO2x has the potential for combining the strengths of high electrochemical stability of the oxide and high ionic conductivity of the halide. The optimal composition Na2ZrCl3O1.5 synthesized by a mechanochemical method exhibits a high ionic conductivity of 5.17 ​× ​10−5 ​S ​cm−1 at room temperature, nearly an order of magnitude improvement over Na2ZrCl6 and orders of magnitude higher than that of Na2ZrO3. This enhancement is attributed to the more disordered phase within Na2ZrCl3O1.5. Cost analysis reveals that Na2ZrCl6-4xO2x can be produced at a large scale and low cost (≤£25.53/kg). These findings pave the way for the mixed-anion strategy for developing high-performing SSE materials for ASSNIBs.

Since its verification in just 2019, there have been numerous high-profile papers reporting improved efficiency of the lithium-mediated electrochemical nitrogen reduction system to make ammonia. However, the literature lacks a cohesive investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we vary electrolyte salt concentration and observe a transition from an unstable working electrode potential to working electrode potential stability and peak in Faradaic efficiency of 7.8 ± 0.5 % at 0.6 M LiClO4. The behaviour is linked to the formation of Solvent Separated Ion Pairs in the electrolyte through Raman spectroscopy. Time of Flight Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy reveal a more inorganic, and therefore more stable, SEI layer with increasing salt concentration. A drop in Faradaic efficiency is seen at concentrations higher than 0.6 M LiClO4, which is attributed to a combination of a loss in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by Electrochemical Impedance Spectroscopy.

The durability of La(Fe, Si)13-based magnetocaloric alloys in magnetic cooling devices present challenges mainly due to the material's susceptibility to corrosion in water-related heat transfer fluids. This study proposes an electrophoretic deposition method to deposit graphene oxide coatings on LaFe13.9Si1.4 thin plates under various applied voltages. The results show that the coating prepared at 5 V significantly enhanced corrosion resistance, achieving an inhibition efficiency of 36 %. Additionally, the LaFe13.9Si1.4-GO sample exhibited no reduction in the maximum magnetic entropy change. This study demonstrates that graphene oxide coatings can serve as effective corrosion-resistant coatings for La-Fe-Si magnetocaloric alloys, offering guidance to ensure the integrity of magnetic cooling devices over long term.

Nanoporous Cu produced by chemical dealloying is a promising catalyst for electrochemical CO2 reduction owing to its tunable chemistry, morphology, and surface defect sites. However, how dealloying controls the atomic-scale structure of Cu ligaments and how these features govern catalytic behavior remain unclear, particularly in nanostructured catalysts under realistic operating conditions. Here, we synthesize nanoporous Cu by dealloying Cu20Zn80 in H3PO4 at different temperatures, enabling control over ligament sizes from the nanoscale to the microscale. Nanoporous Cu outperforms polycrystalline Cu for CO reduction, with the sample dealloyed at 15 °C reaching 60

Commercial lithium-ion battery (LIB) electrodes traditionally comprise a homogeneous layer of stochastically mixed constituent materials. However, a significant barrier to cell performance is attributed to the architecture of the electrode; the trade-off between useful capacity and rate capability limits the cell performance during fast charging or discharging. This study develops a continuum model to emulate the behaviour of these electrodes. It presents optimal electrode thickness and active material (AM) volume fraction values that maximise cell performance for slurry-cast electrodes. Finally, the study demonstrates that by patterning the electrode architecture, volumetric energy density can be significantly improved, subject to manufacturing constraints, and provides quantitative design guidelines for future study.

Iridium oxide is the state-of-the-art electrocatalyst for water oxidation in polymer electrolyte membrane (PEM) electrolysers, crucial for green hydrogen production. Despite its extensive industrial use, the water oxidation mechanism on this metal oxide and the key factors controlling the reaction rate remain unclear. Understanding these controls at a fundamental level on such benchmark metal oxides is vital for designing more active and stable electrocatalysts for water oxidation in PEM electrolysers. In this talk, I will present our research on probing oxygen evolution reaction (OER) relevant species on iridium-based catalysts. This involves a combination of time-resolved operando optical spectroscopy, soft and hard X-ray absorption spectroscopy (XAS), and electrochemical mass spectrometry. Initially, I will discuss the intermediate and catalytically active states of iridium oxides. This is based on correlating optically detected states with oxygen molecular products identified through on-chip electrochemical mass spectrometry. Subsequently, I will demonstrate how we used optical spectroscopy to quantify these states as a function of potential. The nature of these states, including the Ir oxidation state and surface adsorbates on iridium sites, will be elucidated using a combination of time-resolved Ir-L edge XAS, O-K edge XAS, and supported by Density Functional Theory (DFT). With these quantification results of active species for OER, I will compare the intrinsic kinetics of two state-of-the-art iridium oxide structures - amorphous IrO x versus crystalline rutile IrO 2 . [1] The effect of the electrolyte on the intrinsic activity of iridium oxides will also be discussed. [2] Finally, based on this molecular-level understanding, I will present a modified volcano model for OER catalyst design. This model considers the impact of adsorbate-adsorbate interactions on binding energetics, demonstrating critical design principles for high intrinsic activity OER catalysts. The authors acknowledge the funding support from the Imperial College-Chinese Scholarship Council Studentship and bp-ICAM 92, which made this research possible. [1] Caiwu Liang, Reshma Rao, Karine Svane et al. Unravelling the effects of active site densities and energetics on the water oxidation activity of iridium oxides, 07 March 2023, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-2605628/v1] [2] Caiwu Liang, Yu Katayama, Yemin Tao, Asuka Morinaga, Benjamin Moss, Verónica Celorrio, et al. Role of electrolyte pH on water oxidation for iridium oxides. ChemRxiv. Cambridge: Cambridge Open Engage; 2023

Understanding the effect of non-covalent interactions of intermediates at the polarized catalyst-electrolyte interface on water oxidation kinetics is key for designing more active and stable electrocatalysts. Here, we combine operando optical spectroscopy, X-ray absorption spectroscopy and surface-enhanced infrared absorption spectroscopy to probe the effect of non-covalent interactions on OER activity of IrOx in acidic and alkaline electrolyte. Our results suggest the active species for OER (Ir4.x+-*O) binds much stronger in alkaline compared with acid at low coverage, while the repulsive interactions between these species is higher in alkaline electrolyte. These differences are attributed to the larger fraction of water within the cation hydration shell at the interface in alkaline electrolytes compared to acidic electrolytes, which can stabilise oxygenated intermediates and facilitate long-range interactions between them. Quantitative analysis of the state energetics shows that although the *O intermediates bind more strongly than optimal in alkaline electrolyte; the larger repulsive interaction between them results in significant weakening of *O binding with increasing coverage, leading to similar energetics of active states in acid and alkaline at OER-relevant potentials. By directly probing the electrochemical interface with complementary spectroscopic techniques, our work goes beyond conventional computational descriptors of OER activity to explain the experimentally observed OER kinetics of IrOx in acidic and alkaline electrolytes.