Conversion of Spent Coffee Beans to Electrode Material for Vanadium Redox Flow Batteries

This study presents the application of pyrolyzed spent coffee beans as a potential electrode material to replace commercial bipolar graphite plate in vanadium redox flow batteries (VRB). The results indicate that the biochar obtained from spent coffee beans shows relatively good electrochemical charge transfer kinetics of vanadium redox reactions as well as generates higher energy and voltage efficiency in a static cell test when compared to TF6 bipolar graphite plate. Additionally, the biochar was activated via steam at various activation times to increase its surface area, and their effect on the kinetics of the electrochemical reactions was investigated. The activated carbon did not exhibit any improvement neither in electron transfer kinetics nor in the battery efficiency, despite their increased surface area. The performed studies demonstrate that the biochar obtained from spent coffee beans can be a low-cost electrode material for VRB with improved performance characteristics

Paper as sampling substrates and all-integrating platforms in potentiometric ion determination

In real-life situations, where samples such as wet soil, body fluids or foodstuff, contain high content of solids/impurities with a limited amount of liquid, sample collection within an adsorptive substrate prior ion determination emerges as a necessary step. For this reason, paper-based technology has been widely studied in development of potentiometric sensors and their application in determination of ions in various samples. Paper is easily available, inexpensive, capable of wicking fluids, disposable and biodegradable, thus provides clear benefits to be integrated with potentiometric ion sensors. In turn, potentiometric ion sensors are characterized by relatively cheap and compact design and, most importantly, by the ability to perform quick and easy ion determination. In this review, all aspects of application of paper substrates in potentiometry will be critically discussed. Those will include the application of paper substrates in paper-based sampling, fabrication of paper-based ion-selective and reference electrodes, and paper-based potentiometric devices.Economic Development Board (EDB)Ministry of National Development (MND)Nanyang Technological UniversityNational Environmental Agency (NEA)National Research Foundation (NRF)The authors would like to thank NEWRI (Nanyang Environment and Water Research Institute) and Singapore's Economic Development Board (EDB) for their financial support of this research. Undergraduate Research Experience on Campus Programme (URECA) is acknowledged for provided support. SCARCE is supported by the National Research Foundation, Prime Minister's Office, Singapore, the Ministry of National Development, Singapore, and National Environment Agency, Ministry of Sustainability and the Environment, Singapore under the Closing theWaste Loop R&D Initiative as part of the Urban Solutions & Sustainability e Integration Fund (Award No. USS-IF-2018-4)

Characterization of nano-layered solid-contact ion selective electrodes by simultaneous potentiometry and quartz crystal microbalance with dissipation

Nano-layered solid-contact potassium-selective electrodes (K⁺-ISEs) were explored as model ion-selective electrodes for their practical use in clinical analysis. The ultra-thin ISEs ought to be manufactured in a highly reproducible manner, potentially making them suitable for mass production. Thus, their development is pivotal towards miniaturised sensors with simplified conditioning/calibration protocols for point-of-care diagnostics. To study nano-layered ISEs, the ultra-thin nature of ISEs for the first time enabled to combine potentiometry-quartz crystal microbalance with dissipation (QCM-D) to obtain value-added information on the ISE potentiometric response regarding their physical state such as mass/thickness/viscoelastic properties/structural homogeneity. Specifically, the studies were focused on real-time observations of the ISE potentiometric response in relation to changes of their physicochemical properties during the ISE preparation (conditioning) and operation (including biofouling conditions) to identify the occurring processes that may accordingly be critical for potential instability of the ISEs, impeding their practical application. The K⁺-ISEs were prepared on a QCM-D gold sensor by electrodepositing poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) layer serving as an ion-to-electron transducer subsequently covered by a spin-coated poly(vinyl chloride) based K⁺-ion selective membrane (K⁺-ISM). The studies demonstrated that the performance of the nano-layered design of K⁺-ISEs is detrimentally affected by such processes as water layer formation accordingly causing the instability of the electrode potential. The changes in the ISE physical state such mass/viscoelastic properties associated with water layer formation and origin of the potential instability was already observed at the ISE conditioning stage. The potential instability of nano-layered ISEs limits their practical applicability, indicating the need of new solutions in designing ISEs, for instance, exploiting new water-resistant materials and modifying preparation protocols.Economic Development Board (EDB)Nanyang Technological UniversityThe authors would like to thank NEWRI (Nanyang Technological University) and Singapore’s Economic Development Board (EDB) for their financial support of this research

Bioelectrocatalytic reduction of oxygen at gold nanoparticles modified with laccase

To characterise bioelectrocatalytic oxygen reduction at gold nanoparticles (AuNPs) modified with Trametes hirsuta laccase (ThLc) combined electrochemical and quartz crystal microbalance measurements have been used. The electrodes with different degrees of AuNP-monolayer coverage, theta, have been studied. In every case of theta close to theoretically possible 44 ThLc molecules adsorbed at 22 nm diameter AuNP. The bioelectrocatalytic current was recalculated down to the current at a single AuNR Unexpectedly, the current at a single AuNP was higher when theta was higher. The maximum current reached at a single AuNP was 31.10(-18) A which corresponds to the enzyme turnover (k(cat)) 13 s(-1). This rate is lower than the homogeneous ThLc turnover (190 s(-1)) suggesting partial denaturation of ThLc upon adsorption or that some ThLc are not in DET contact with the electrode surfac

Development of a plastic membrane containing micro-hole(s) for a potential bio-sensing application

In this work, a poly (methyl methacrylate) membrane containing micro-holes (MHs) as a prototype of a simple sensing platform of a lab-on-a-chip device has been developed for a potential analysis of clinical fluidic samples. A four probe electrochemical impedance spectroscopy (EIS) setup, with two electrodes placed on each side of the membrane, was adopted for monitoring the MH impedance (Fig. 1a). The setup was used to investigate, if EIS is suitable to sense the trapping of an analyte inside the MHs. Latex micro-beads with a diameter of 10 mu m were used to test clogging of the MHs. Additionally, finite element model simulations were performed using Comsol Multiphysics software to theoretically evaluate the sensitivity field of the EIS measurement along the MHs. (C) 2017 The Authors. Published by Elsevier Ltd

Conversion of Spent Coffee Beans to Electrode Material for Vanadium Redox Flow Batteries

This study presents the application of pyrolyzed spent coffee beans as a potential electrode material to replace commercial bipolar graphite plate in vanadium redox flow batteries (VRB). The results indicate that the biochar obtained from spent coffee beans shows relatively good electrochemical charge transfer kinetics of vanadium redox reactions as well as generates higher energy and voltage efficiency in a static cell test when compared to TF6 bipolar graphite plate. Additionally, the biochar was activated via steam at various activation times to increase its surface area, and their effect on the kinetics of the electrochemical reactions was investigated. The activated carbon did not exhibit any improvement neither in electron transfer kinetics nor in the battery efficiency, despite their increased surface area. The performed studies demonstrate that the biochar obtained from spent coffee beans can be a low-cost electrode material for VRB with improved performance characteristics

Impact of molecular linker size on physicochemical properties of assembled gold nanoparticle mono-/multi-layers and their applicability for functional binding of biomolecules

In this work the impact of molecular inter-linker size on gold nanoparticle (AuNP) mono-/multilayer structural properties, density and homogeneity has been investigated. These characteristics are of great importance for functional binding of biomolecules. Positively charged high or low molecular weight inter-linkers, poly-L-lysine (PLL) or N-(6-mercapto)hexylpyridinium (MHP), were used to attach negatively charged AuNPs on a planar gold surface as well as to further interlink into a multilayer structure via layer-by-layer deposition. The inter-particle interaction within the assembled AuNP films was adjusted by the ionic strength in the AuNPs dispersions. The AuNP layer density and structural/viscoelastic properties were evaluated by the quartz crystal microbalance with dissipation (QCM-D) technique. The validity of the commercial Voigt model, specifically developed for quantitative QCM-D data analysis of homogeneous viscoelastic films, was evaluated by a model independent analysis when comparing the assembled AuNP films with a homogeneous layer of a mucin from bovine submaxillary glands. Both AuNP mono- and multilayers, attached/interlinked via long flexible PLL molecules assembled to denser and more soft/viscous structures compared to those interlinked by short MHP compounds. Thus, PLL-interlinked AuNP mono-/multilayer structures were further investigated as a platform for laccase enzyme functional adsorption via qualitative assessment of bioelectrochemical characteristics of the enzyme

Impact of molecular linker size on physicochemical properties of assembled gold nanoparticle mono-/multi-layers and their applicability for functional binding of biomolecules

In this work the impact of molecular inter-linker size on gold nanoparticle (AuNP) mono-/multilayer structural properties, density and homogeneity has been investigated. These characteristics are of great importance for functional binding of biomolecules. Positively charged high or low molecular weight inter-linkers, poly-L-lysine (PLL) or N-(6-mercapto)hexylpyridinium (MHP), were used to attach negatively charged AuNPs on a planar gold surface as well as to further interlink into a multilayer structure via layer-by-layer deposition. The inter-particle interaction within the assembled AuNP films was adjusted by the ionic strength in the AuNPs dispersions The AuNP layer density and structural/viscoelastic properties were evaluated by the quartz crystal microbalance with dissipation (QCM-D) technique. The validity of the commercial Voigt model, specifically developed for quantitative QCM-D data analysis of homogeneous viscoelastic films, was evaluated by a model independent analysis when comparing the assembled AuNP films with a homogeneous layer of a mucin from bovine submaxillary glands. Both AuNP mono- and multilayers, attached/interlinked via long flexible PLL molecules assembled to denser and more soft/viscous structures compared to those interlinked by short MHP compounds. Thus, PLL-interlinked AuNP mono-/multilayer structures were further investigated as a platform for laccase enzyme functional adsorption via qualitative assessment of bioelectrochemical characteristics of the enzyme. (C) 2019 Elsevier Inc. All rights reserved