Environmental Research Institute - Journal Articles
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Item Asymmetrical optical response of opal photonic crystals with graded thickness(IOP Publishing, 2023-11-27) Grant, Alex; O'Dwyer, Colm; Irish Research CouncilThe influence of thickness gradient and structural order on the spectral response of opal photonic crystals (PhCs) grown by evaporation-induced self-assembly (EISA) are presented. SEM imaging and angle resolved optical transmission spectroscopy are used to investigate the evolution of the PBG along a thickness gradient for opals grown from five different colloidal sphere concentrations at two different evaporation rates. The degradation of structural order along the thickness gradient is demonstrated, the occurrence of which attenuates the PBG with the thinning of the opal film and results in asymmetrical angle-resolved transmission spectra. The asymmetry in transmission intensity becomes more pronounced for opals grown from lower volume fractions, where secondary Bragg reflections also appear at low incident angles.Item Operando color-coding of reversible lithiation and cycle life in batteries using photonic crystal materials(IOP Publishing, 2023-12-27) Lonergan, Alex; Gulzar, Umair; Zhang, Yan; O'Dwyer, Colm; Horizon 2020; Irish Research CouncilInnovative new materials are consistently emerging as electrode candidates from lithium-ion and emerging alternative battery research, promising high energy densities and high-rate capabilities. Understanding potential structural changes, morphology evolution, degradation mechanisms and side reactions during lithiation is important for designing, optimizing and assessing aspiring electrode materials. In-situ and operando analysis techniques provide a means to investigate these material properties under realistic operating conditions. Here, we demonstrate operando spectroscopic sensing using photonic crystal-structured electrodes that uses the optical transmission spectrum to monitor changes to the state of charge or discharge during lithiation, and the change to electrode structure, in real-time. Photonic crystals possess a signature optical response, with a photonic bandgap (or stopband) presenting as a structural color reflection from the material. We leverage the presence of this photonic stopband, alongside its intricate relationship to the electrode structure and material phase, to correlate electrode lithiation with changes to the optical spectrum during operation. We explore the optical and electrochemical behavior of a TiO2 anode in a lithium-ion battery, structured as a photonic crystal. The operando optical sensing demonstrated here is versatile and applicable to a wide range of electrochemical electrode material candidates when structured with ordered porosity akin to a photonic crystal structure.Item Three-dimensionally ordered macroporous amorphous C/TiO2 composite electrodes for lithium-ion batteries(IOP Publishing, 2024-02-09) Carroll, Aoife; Grant, Alex; Zhang, Yan; Gulzar, Umair; Ahad, Syed Abdul; Geaney, Hugh; O’Dwyer, Colm; Science Foundation Ireland; Irish Research Council; Horizon 2020A facile method utilizing colloidal templating and sucrose as a carbon precursor is used to synthesize highly ordered, porous inverse opal structures as C/TiO2 nanocomposites. Material characterization shows amorphous TiO2 and a large pore size of ∼400 nm allowing for enhanced electrolyte penetration. C/TiO2 inverse opals materials as electrodes in Li-ion battery half cells demonstrate discharge and charge capacities of ∼870 mAh g−1 and 470 mAh g−1, respectively, at a current density of 150 mA g−1. The enhanced capacities, which surpass theoretical limits for TiO2 and carbon based on intercalation reactions, are analyzed under voltammetric conditions to assess relative contributions to capacity from diffusion-limited intercalation and capacitive charge compensation reactions. The porous structure contributes to excellent capacity retention, rate performance and improved Coulombic efficiency (99.6% after 250 cycles), compared to individual carbon and TiO2 inverse opals.Item Comparing cycling and rate response of SnO2 macroporous anodes in lithium-ion and sodium-ion batteries(IOP Publishing, 2023-12-07) Grant, Alex; Carroll, Aoife; Zhang, Yan; Gulzar, Umair; Ahad, Syed Abdul; Geaney, Hugh; O'Dwyer, Colm; Science Foundation Ireland; Irish Research Council; Horizon 2020Tin oxide (SnO2) is a useful anode material due to its high capacity (1493 mAh g−1 and 1378 mAh g−1 vs Li/Li+ and vs Na/Na+, respectively) and natural abundance (tin is one of the thirty most abundant elements on Earth). Unfortunately, only moderate electrical conductivity and significant volume expansion of up to 300% for Li-ion, and as much as 520% for Na-ion can occur. Here, we use an ordered macroporous interconnected inverse opal (IO) architectures to enhance rate capability, structural integrity, and gravimetric capacity, without conductive additives and binders. Excellent capacity retention is shown during cycling vs Na/Na+ relative to Li/Li+. Cyclic voltammetry (CV) analysis, galvanostatic cycling, and differential capacity analysis extracted from rate performance testing evidence the irreversibility of the oxidation of metallic Sn to SnO2 during charge. This behavior allows for a very stable electrode during cycling at various rates. A stable voltage profile and rate performance is demonstrated for both systems. In a Na-ion half cell, the SnO2 retained >76% capacity after 100 cycles, and a similar retention after rate testing.Item The effect of TiO2 and GeO2 composite mixing on the behavior of macroporous Li-Ion battery anode materials(IOP Publishing, 2023-12-19) Carroll, Aoife; Grant, Alex; Zhang, Yan; Gulzar, Umair; Douglas-Henry, Danielle; Nicolosi, Valeria; O'Dwyer, Colm; Irish Research Council; Horizon 2020; Science Foundation IrelandHighly ordered, macroporous inverse opal structures can be made as TiO2/GeO2 nanocomposites with various GeO2 content and provide Coulombic and voltage stable response where the Ge content and its distribution influence the overall capacity at both slow and fast rates. These interconnected binder-free anodes were characterized using X-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy. The electrochemical response in half cells over 2000 cycles and various rates showed how the mixture affected key metrics for the material in battery cells. The data shows that a composite of intercalation and alloying compounds can provide good capacity (between theoretical maxima for either material alone) and excellent coulombic efficiency (>99%), even with low quantities of the higher capacity alloying compound. Compositional gradients or spatial heterogeneities in the distribution of one material in the composite are shown to affect capacity during cycling life, where a coulombically efficient increasing capacity is found as the higher capacity material becomes electrochemically active within the composite matrix as the material is modified during cycling.
