• 2D Hexagonal Boron Nitride (2D-hBN) Explored as a Potential Electrocatalyst for the Oxygen Reduction Reaction

      Khan, Aamar F.; Brownson, Dale A. C.; Ji, Xiaobo; Smith, Graham C.; Banks, Craig E.; Manchester Metropolitan University (Khan, Brownson, Banks); University of Chester (Smith); Central South University Changsha (Ji) (Wiley, 2016-09-28)
      Crystalline 2D hexagonal Boron Nitride (2D-hBN) is explored as a potential electrocatalyst towards the oxygen reduction reaction (ORR) when electrically wired via a drop-casting approach upon a range of carbon based electrode surfaces; namely, glassy carbon (GC), boron-doped diamond (BDD), and screen-printed graphitic electrodes (SPEs). We consider the ORR in acidic conditions and critically evaluate the performance of unmodified and 2D-hBN modified electrodes, implementing coverage studies (commonly neglected in the literature) in order to ascertain the true impact of this novel nanomaterial. The behaviour of 2D-hBN towards the ORR is shown to be highly dependent upon both the underlying carbon substrate and the coverage/mass utilised. 2D-hBN modified SPEs are found to exhibit the most beneficial response towards the ORR, reducing the peak potential by ca. 0.28 V when compared to an unmodified/bare SPE. Such improvements at this supporting substrate are inferred due to favourable 2D-hBN interaction with ridged surfaces exposing a high proportion of edge regions/sites, where conversely, we show that relatively smooth substrate surfaces (such as GC) are less conducive towards successful 2D-hBN immobilisation. In this paper, we reveal for the first time (in the specific case of using a rough supporting substrate) that 2D-hBN gives rise to beneficial electrochemical behaviour towards the ORR. Unfortunately, this material is not considered an electrocatalyst for use within fuel cells given that the estimated number of electrons transferred during the ORR ranges between 1.90–2.45 for different coverages, indicating that the ORR at 2D-hBN predominantly produces hydrogen peroxide. 2D-hBN does however have potential and should be explored further by those designing, fabricating and consequently electrochemically testing modified electrocatalysts towards the ORR.
    • Atomic-layer-deposited aluminum and zirconium oxides for surface passivation of TiO 2 in High-Efficiency Organic Photovoltaics

      Vasilopoulou, Maria; Georgiadou, Dimitra G.; Soultati, Anastasia; Boukos, Nikos; Gardelis, Spyros; Palilis, Leonidas C.; Fakis, Mihalis; Skoulatakis, Georgios; Kennou, Stella; Botzakaki, Martha A.; et al. (Wiley, 2014-06-23)
      The reduction in electronic recombination losses by the passivation of surfaces is a key factor enabling high-efficiency solar cells. Here we investigate a strategy to passivate surface trap states of TiO 2 films used as cathode interlayers in organic photovoltaics (OPVs) through applying alumina (Al2O3) or zirconia (ZrO2) insulating nanolayers by thermal atomic layer deposition (ALD). Our results suggest that the surface traps in TiO 2 are oxygen vacancies, which cause undesirable recombination and high electron extraction barrier, reducing the open-circuit voltage and the short-circuit current of the complete OPV device. It was found that the ALD metal oxides enable excellent passivation of the TiO2 surface followed by a downward shift of the conduction band minimum. OPV devices based on different photoactive layers and using the passivated TiO2 electron extraction layers exhibited a significant enhancement of more than 30% in their power conversion efficiencies (PCEs) as compared to their reference devices without the insulating metal oxide nanolayers as a result of significant suppression of charge recombination and enhanced electron extraction rates at the TiO2/ALD metal-oxide/organic interface.
    • Impact of Functionalized Polystyrenes as the Electron Injection Layer on Gold and Aluminum Surfaces: A Combined Theoretical and Experimental Study

      Papadopoulos, Theodoros A.; Li, Hong; Kim, Eung-Gun; Liu, Jie; Cella, James A.; Heller, Christian M.; Shu, Andrew; Kahn, Antoine; Duggal, Anil; Brédas, Jean-Luc; et al. (Wiley, 2014-06-06)
      At metal/organic interfaces, insertion of an organic monolayer can significantly modify the surface properties of the substrate, especially in terms of charge injection across the interface. Here, we study the formation of an insulating monolayer of morpholine or amine-functionalized polystyrene on Al(111) and Au(111) surfaces and its impact on surface work-function and charge injection. First principles calculations based on density functional theory have been carried out and point to a significant decrease of the work-function for the modified metal surfaces, in very good agreement with ultraviolet photoemission spectroscopy measurements performed on the Au(111) surface. In addition, a bilayer cathode consisting of a thin film of high work-function metal, such as Al and Au, and a layer of amine-functionalized polystyrene is also fabricated and tested in organic light-emitting diodes. Such bilayer structures exhibit substantially enhanced efficiency when compared to controls without the functionalized polymers. Our combined theoretical and experimental investigation gives insight into how a thin layer of a commodity polymer can be used to transform rather high work-function metals into high-performance cathodes providing efficient electron injection.
    • Improved Stability of Polymer Solar Cells in Ambient Air via Atomic Layer Deposition of Ultra-Thin Dielectric Layers

      Polydorou, Ermioni; Botzakaki, Martha A.; Sakellis, Ilias; Soultati, Anastasia; Kaltzoglou, Andreas; Papadopoulos, Theodoros A.; Briscoe, Joe; Drivas, Charalabos; Seintis, Kostas; Fakis, Mihalis; et al. (Wiley, 2017-07-12)
      Polymer solar cells have attracted tremendous interest in the highly competitive solar energy sector, due to the practical advantages they exhibit, such as being lightweight, flexible, and low cost, in stark contrast to traditional photovoltaic technologies. However, their successful commercialization is still hindered by issues related to device instability. Here, atomic layer deposition (ALD) is employed to deposit conformal ultrathin dielectrics, such as alumina (Al2O3) and zirconia (ZrO2), on top of ZnO electron extraction layers to address problems that arise from the defect-rich nature of these layers. The deposition of dielectrics on ZnO significantly improves its interfacial electronic properties, manifested primarily with the decrease in the work function of ZnO and the concomitant reduction of the electron extraction barrier as well as the reduced recombination losses. Significant efficiency enhancement is obtained with the incorporation of six ALD cycles of Al2O3 into inverted devices, using photoactive layers, that consist of poly(3-hexylthiophene):indene-C60-bisadduct or poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b] thiophenediyl}):[6,6]-phenyl-C70-butyric acid methyl ester. More importantly, upon performing lifetime studies (over a period of 350 h), a strong improvement in polymer solar cell stability is observed when using the ALD-modified ZnO films.
    • Next Generation Additive Manufacturing: Tailorable Graphene/Polylactic(acid) Filaments Allow the Fabrication of 3D Printable Porous Anodes for Utilisation within Lithium-Ion Batteries

      Foster, Christopher W.; Zou, Guo-Qiang; Jiang, Yunling; Down, Michael P.; Liauw, Christopher M.; Ferrari, Alejandro Garcia-Miranda; Ji, Xiaobo; Smith, Graham C.; Kelly, Peter J.; Banks, Craig E.; et al. (Wiley, 2019-04-02)
      Herein, we report the fabrication and application of Li-ion anodes for utilisation within Li-ion batteries, which are fabricated via additive manufacturing/3D printing (fused depo- sition modelling) using a bespoke graphene/polylactic acid (PLA) filament, where the graphene content can be readily tailored and controlled over the range 1–40 wt. %. We demon- strate that a graphene content of 20 wt. % exhibits sufficient conductivity and critically, effective 3D printability for the rapid manufacturing of 3D printed freestanding anodes (3DAs); simplifying the components of the Li-ion battery negating the need for a copper current collector. The 3DAs are physicochemcally and electrochemically characterised and possess sufficient conductivity for electrochemical studies. Critically, it is found that if the 3DAs are used in Li-ion batteries the specific capacity is very poor but can be significantly improved through the use of a chemical pre-treatment. Such treatment induces an increased porosity, which results in a 200-fold increase (after anode stabilisation) of the specific capacity (ca. 500 mAhg-1 at a current density of 40 mAg-1). This work significantly enhances the field of additive manufacturing/3D printed graphene based energy storage devices demonstrating that useful 3D printable batteries can be realised
    • Next-Generation Additive Manufacturing of Complete Standalone Sodium-Ion Energy Storage Architectures

      Down, Michael P.; Martinez-Perinan, Emiliano; Foster, Christopher W.; Lorenzo, Encarnacion; Smith, Graham C.; Banks, Craig E.; Manchester Metropolitan University (Down, Martinez-Perinan, Foster, Banks), Universidad Autonoma Madrid (Lorenzo), University of Chester (Smith) (Wiley, 2019-02-10)
      The first entirely AM/3D-printed sodium-ion (full-cell) battery is reported herein, presenting a paradigm shift in the design and prototyping of energy- storage architectures. AM/3D-printing compatible composite materials are developed for the first time, integrating the active materials NaMnO2 and TiO2 within a porous supporting material, before being AM/3D- printed into a proof-of-concept model based upon the basic geometry of commercially existing AA battery designs. The freestanding and completely AM/3D-fabricated device demonstrates a respectable performance of 84.3 mAh g-1 with a current density of 8.43 mA g-1; note that the structure is typically comprised of 80% thermoplastic, but yet, still works and functions as an energy-storage platform. The AM/3D-fabricated device is critically benchmarked against a battery developed using the same active materials, but fabricated via a traditional manufacturing method utilizing an ink-based/doctor-bladed methodology, which is found to exhibit a specific capacity of 98.9 mAh m-2 (116.35 mAh g-1). The fabrication of fully AM/3D-printed energy-storage architectures compares favorably with traditional approaches, with the former providing a new direction in battery manufacturing. This work represents a paradigm shift in the technological and design considerations in battery and energy-storage architectures
    • The past, present and future of indoor air chemistry

      Bekö, Gabriel; Carslaw, Nicola; Fauser, Patrick; Kauneliene, Violeta; Nehr, Sascha; Phillips, Gavin; Saraga, Dikaia; Schoemaecker, Coralie; Wierzbicka, Aneta; Querol, Xavier; et al. (Wiley, 2020-04-25)
      This is an editorial contribution to the Journal Indoor Air on the future direction of indoor air chemistry research.