Colm O'DWyer

Enhancing conductivity is important for supercapacitor electrochemical behavior, and this is especially evident when using nonmetallic 3D printed cell components. Here, we study two different 3D‐printed cell types and examine the influence of the conductivity enhancement of the printed current collector and the slurry composition on the response of supercapacitor cells. Current collectors printed using vat polymerization and subsequently metallized, and similar collectors made using conductive polylactic acid by fused deposition modeling, are compared in a similarly designed printed coin cells. Various slurry mixtures of porous Mn ₃ O ₄ with carbon electrode materials and additives (single‐walled carbon nanotubes, graphene nanoplatelets (GNPs), and Super‐P) bound with PVDF are compared in both types of cell. Electrochemical analysis using cyclic voltammetry and galvanostatic charge–discharge measurements reveals that composite conductivity strongly influences charge storage behavior in 3D‐printed supercapacitors, while the conductivity of the current collector interface influences rate capability, ohmic losses, and long‐term cycling stability. Metallized Vat‐P printed current collectors, with smoother and entirely conductive interface with the composite material, offer improved voltammetric and galvanostatic stability and response for all slurries. Whereas FDM printed, rough PLA current collectors with sparsely distributed graphitic surface contacts to the electrode material, show poorer stability during long‐term cycling and rate tests.

Rechargeable batteries with customizable shapes and geometries that can be incorporated directly into the design of a device by 3D printing of functional materials could enable new smart devices for consumer electronics, medical devices, and connected living technologies. We report a 3D printing approach to a non-flammable all-plastic battery construction that operates as an aqueous Li-ion rechargeable battery. The battery cell is made using an extruder-type 3D printing method for the cell architecture, including graphene-impregnated conductive polylactic acid (PLA) current collectors within an acrylonitrile butadiene styrene (ABS) plastic cell, and an aqueous LiNO₃-containing polyvinylpyrrolidone-silica gel electrolyte for the cell chemistry, without any separator. LiCoO₂ cathodes and LiMn₂O₄ anode materials uniformly coated PLA current collectors allow operation within the water electrolysis window. These printed batteries exhibit good specific capacities of between 30 mAh g⁻¹ (1 C) to 90 mAh g⁻¹ (0.1 C) for at least 100 charge/discharge cycles, and gravimetric and volumetric energy densities of ∼110 Wh kg⁻¹ and 0.33 Wh L⁻¹, following a voltammetric priming step to enhance electrochemical stability during cycling. 3D printed cells can be printed to 4 mm thickness, as a donut-shaped rechargeable Li-ion battery, or as LEGO-brick series connections .

The use of earth‐abundant materials for novel electrodes for solar‐driven electrolysis will play a significant role in the future production of hydrogen as a green energy source. The choice of electrolyte will play a major role in how efficient and stable future photoelectrochemical cells (PEC) operate. A new approach to determining PEC efficiency using broadband acoustic resonance dissolution spectroscopy (BARDS) is investigated to analyze the real‐time production of hydrogen and oxygen at platinum electrodes in different electrolyte solutions. The parameters investigated include concentration of electrolyte, surface area of the electrode, and the potential applied to the cell. Herein, the suitability of neutral buffer as an electrolyte on a par with either acid or basic electrolytes is shown. This finding allows for the potential design of solar to hydrogen electrolysers which can operate under mild, neutral, and stable conditions using earth‐abundant materials for hydrogen production. It is also shown how BARDS can readily visualize and track gas evolution in real‐time and in situ in an open system without the need for gas collection. It is anticipated that the technique can be utilized in the future evaluation of newly developed electrode materials in terms of efficiency, stability, and life span.

Determining the nature of surface roughness and electrode structure on H₂ or O₂ bubble evolution rate and quantity, bubble trapping under photochemical, photoelectrochemical and electrolytic conditions is important for quantifying useful gas production during total water splitting. Controlled electrode systems involving design of surface area and porosity would also allow pathways to minimize trapped/redissolved gas bubble evolution and improve overall efficiency [1,2]. Water splitting oxides and semiconductors are available in almost any morphology, often less controlled. Defined thickness, morphology and porosity may be useful in quantifying the nature of gas evolution where the electrode structure and its influence are well controlled. We will use vat polymerization 3D printing to create ordered microlattice structures [3] from photopolymerized methacrylate-based resins. Vat polymerization provide excellent resolution and control in shape and structure fidelity, and we have used the method to create ordered porous structures for electrochemical applications such as rechargeable batteries and supercapacitors [4-12]. These microlattice structures are designed with various geometries to influence bubble traffic from gas nucleation and evolution during electrochemical and photoelectrochemical water splitting [13-15]. We will show how Ni, Au, NiO and TiO₂-coated 3D printed microelectrodes behave as water splitting electrodes as a function of the porous geometric structure. We will also show data from broadband acoustic resonance dissolution spectroscopy [16] that allows quantification of the bubble evolution and reabsorption in the electrolyte during electrolysis in the dark and under illumination, to show how electrode structure can influence the nature of bubble and gas evolution, bubble traffic and transport, reabsorption, and to decouple the intrinsic effect of surface area of the active coating from the larger length scale porous geometry of the overall electrode. References [1] K. T.Sullivan, C. Zhu, E. B. Duoss, A.E. Gash, D. B. Kolesky, J.D. Kuntz, J.A. Lewis, and C.M. Spadaccini, Adv. Mater. 28, 1934-1939 (2016) [2] X. Su, X. Li, C. Y. A. Ong, T. S. Herng, Y. Wang, E. Peng, J. Ding, Adv. Sci. 6, 1801670 (2019) [3] Zheng, X. et al. Science 344, 1373–1377 (2014) [4] A. Ambrosi and M. Pumera, Chem. Soc. Rev. 45, 2740-2755 (2016) [5] V. Egorov and C. O'Dwyer, Curr. Opin. Electrochem. 21, 201-208 (2020) [6] V. Egorov, U. Gulzar, Y. Zhang, S. Breen and C. O'Dwyer, Adv. Mater. 32, 2000556 (2020) [7] U. Gulzar, C. Glynn and C. O'Dwyer, Curr. Opin. Electrochem. 20, 46-53 (2020) [8] M. Ferguson, V. Egorov, Y. Zhang, U. Gulzar and C. O'Dwyer, Meet. Abstr. MA2024-01, 6 (2024) [9] M. Ferguson, V. Egorov, Y. Zhang, U. Gulzar and C. O'Dwyer, Meet. Abstr. MA2024-01, 771 (2024) [10] V. Egorov, U. Gulzar, C. O’Dwyer, ECS Adv. 2, 040508 (2023) [11] U. Gulzar, V. Egorov, Y. Zhang, and C. O'Dwyer, Adv. Energy Sustainability Res. 4, 2300029, (2023) [12] M. Ferguson, V. Egorov, Y. Zhang, U. Gulzar, C. O’Dwyer, ECS Adv. 3, 032501 (2024) [13] T. Y. Kou, et al., Adv. Energy Mater. 10, 2002955 (2020) [14] L. F. Arenas, C. P. de Leon, and F. C. Walsh, Electrochem. Commun. 77, 133–137 (2017) [15] R. A. Marquez, et al., ACS Appl. Mater. Interfaces 14, 42153–42170 (2022) [16] A. Kang, A. Alkhraije, S. McSweeney, A. Alfarsi, R. Ahmed, J. Krüse, C. O’Dwyer, and D. Fitzpatrick, ACS Appl. Energy Mater. 3, 2000-2009 (2020)

The rapid emergence of lithium‐ion batteries (LIBs) to satisfy our ever increasing energy demands will result in a significant future waste problem at their end of life. Lithium iron phosphate (LFP) as a cathode material is now widely used in LIBs with increasing market share. It is expected that there will be significant volumes of battery waste containing this material in the near future, and therefore it is important to develop methods for effectively repurposing this LFP waste to mitigate its impact on the environment. In this work we demonstrate the repurposing of LFP from spent LIBs as electrocatalysts for the oxygen evolution reaction (OER) which is critical to electrochemical water splitting and the production of green hydrogen. Our study has shown that the recovered LFP once immobilized onto a Ni substrate reconstructs into a mixed Fe/Ni oxide surface layer which is highly active for the OER. Promisingly, the LFP recovered from batteries that were cycled multiple times (up to 100 cycles) showed excellent electrocatalytic performance with a low Tafel slope of 58 mV dec⁻¹, overpotential values of 250 and 310 mV to reach 10 and 100 mA cm⁻², respectively and 24 h stability at over 200 mA cm⁻². This research provides potential motivation for recycling companies to isolate LFP from spent Li ion batteries for later use in water electrolysis technologies.

The electrochemical response of symmetric carbon-based supercapacitor devices made using two 3D-printing techniques, Vat-P (vat polymerization) and FDM (fused deposition modeling), shows how the printing method dominates the overall cell response. Despite possessing excellent cycle life, the conductive poly(lactic acid) (PLA) FDM printed current collectors suffer from relatively high resistance and suppressed capacitance linked to current collector material resistivity. Here, we examine in situ methods to influence the interfacial conductivity of the FDM current collectors by surface modification. Both dimethylformamide (DMF) and aqueous potassium hydroxide (KOH) treatments are investigated to compare solvent decomposition and electrolyte presoaking for this purpose. Using a single-walled carbon nanotube and graphene nanoplatelet carbon composite slurry on FDM current collectors in Vat-P 3D-printed cell casings, the supercapacitor cells show that the DMF treatment method has worse capacitance but better retention over 1 million cycles compared to the untreated FDM current collector cells. Pretreatment in a solution of 6 M aqueous KOH, identical to the cell electrolyte, markedly improves the effective current collector conductivity and interface with the active material, with a five-fold improvement in capacitance at the expense of less cycling stability. This is possible because the KOH treatment provides a 10-fold reduction in the FDM current collector resistance, which correlates with the improved cyclic voltammetric response. Galvanostatic charge-discharge tests reveal a deteriorated long-term cycling stability and rate capability despite better interfacial conductivity with the active material. In-situ presoaking that allows a degree of depolymerization at the surface relieves the conductive additive within the PLA to improve electrochemical interfacial activity and identifies the trade-off between improved capacitance and long-term cycling stability for common electrolytes in PLA-based 3D printed aqueous supercapacitors.

Porosity, composition, and electrode thickness play a vital role in lithium-sulfur (Li-S) batteries. They can be difficult to control and can make the link between morphology and its performance more complex. We evaluated the utilization of sulfur during the discharge process in carbon-sulfur composite with varying porosity, carbon encapsulant type and relative mixture ratios, the distribution of sulfur utilization between the upper and lower voltage plateau of the discharge, and the overall rate capability of sulfur electrodes. Chronoamperometry was used as a simple and fast technique to obtain high resolution rate curves while the distribution of charge between upper and lower plateaux was thoroughly investigated using galvanostatic cycling. Our results suggest that discharge capacity associated with the upper higher voltage plateau of the Li-S discharge curve is limited by the maximum concentration of polysulfide species inside the electrolyte-filled pores of the sulfur electrode, not by the porosity. By varying the type of carbon material composited with sulfur, electrode morphologies unique to those encapsulants have a significant impact on the deposition of lithium sulphide, and the overall rate capability is strongly linked to changes in electrode morphology where the porosity, carbon-sulfur ratio are varied for each type of carbon encapsulant.

Metal oxide thin films are critically important materials for modern technologies, particularly semiconductor thin films in transistors and optoelectronic applications. Many metal oxide thin films attract interest for their electronic bandgap, charge carrier mobility, optical opacity, luminescence, low cost, relative abundance, and environmentally-friendly production. Additionally, these properties are often tuneable via particle size, film density, surface morphology, film deposition, growth method, hetero-interface engineering or ion-doping. The n-type semiconducting zinc oxide (ZnO) is an important material, possessing a variety of useful properties including an intrinsically wide direct bandgap, high electron mobility, relatively high exciton binding energy, high optical transparency, demonstrated metal-ion doping, a range of different particle morphologies and deposition methods, electro/photoluminescence, low cost, and a variety of existing green synthesis methods. Here, these aspects of ZnO and some related compound semiconducting oxides are reviewed, focusing on how the unique properties of these metal oxides make them suitable for a range of different applications from thin film transistors, high mobility oxide interfaces, transparent conductive oxides, photoanodes photodetectors, chemical sensors, photocatalysts, superlattice electronics, and more. The properties and deposition methods and their impact on functionality will be discussed alongside their role in sustainable optoelectronics.