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During the Electrochemical Energy and Water Summit, held during the ECS Fall 2014 Meeting in Cancun, Mexico, we proposed the idea for the PowerPAD, a concept for an eco-friendly, biodegradable paper-based redox power source for water monitoring in low resource settings and the idea was awarded funding in the Science for Solving Society’s Problems Challenge. The concept leverages recent advances in microfluidic co-laminar flow cells with flow-through porous electrodes [1] and paper-based fuel cell structures [2], as shown in Fig. 1. In electrochemical energy conversion systems, various organic materials are used as fuel in electrochemical power sources such as direct methanol fuel cells or direct formic acid fuel cells. However, oxidation/reduction reactions involving these fuels often require precious metal catalysts such as platinum or palladium [2-3] as well as complex ion-conducting polymers, both of which are expensive and non-disposable and hence unsuitable for the present application. A more affordable and sustainable solution may be reached with microbial and enzyme-based fuel cells. However, their power output is generally much lower than the target application requirements and their biocatalysts often have limited stability and durability [4]. Recently, the use of organic species in aqueous flow batteries has been reported for large-scale energy storage [5-6]. The quinone redox species are soluble in aqueous electrolytes, have rapid kinetics on pure carbon electrodes and do not require any catalysts. These characteristics make them a potential candidate for the requirements of the PowerPAD concept. In this work, we will present our experimental results for the electrochemical characterization of potential redox couples and the discharge performance. As a screening approach, the potential candidates were ex-situ tested in various supporting electrolytes using cyclic voltammetry techniques. A glassy carbon electrode, a platinum wire electrode and a saturated calomel electrode were used as working electrode, counter electrode and reference electrode, respectively, in a three electrode electrochemical cell throughout the measurements. The aim of the measurements was to investigate the open circuit potential and qualitatively assess the kinetics of the half-cell candidate species on bare carbon electrodes and the effect of different supporting electrolytes. Next, the species were tested in a co-laminar flow cell (CLFC) with flow-through porous electrodes, in order to measure the discharge performance. Details about the cell design and fabrication can be found elsewhere [7-8]. These membrane-less CLFCs utilize a co-laminar diffusion interface to provide reactant streams separation and thereby enable the flexibility of the choice of different supporting electrolytes at the two electrodes. It was found that the operation in mixed-media electrolytes enables high open circuit cell voltage and high performance output. The results of this study were carried on and tested later in a paper-based proof-of-concept device providing the departing point for a new generation of biodegradable power sources that would have a positive environmental impact. Acknowledgements: The funding for this research provided by the Electrochemical Society and the Bill & Melinda Gates Foundation is highly appreciated. Additional support from the Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI) and British Columbia Knowledge Development Fund (BCKDF) is also acknowledged. J.P.E. thanks support from Marie Curie International Outgoing Fellowship (APPOCS) within the 7th European Community Framework. References: [1] Kjeang E., et al., J. Am. Chem. Soc.,2008, 130(12), 4000-4006. [2] Esquivel J. P., et al., Energy Environ. Sci., 2014, 7(5), 1744-1749. [3] Ortiz-Ortega E., et al., Lab Chip , 2014, 14(24), 4596-4598. [4] Lee J.W. and Kjeang E., Biomicrofluidics, 2010, 4(4), p. 041301. [5] Huskinson B., et al., Nature, 2014, 505, 195-198. [6] Yang B., et al., J. Electrochem. Soc., 2014, 161, A1371-A1380. [7] Ibrahim, O.A., et. al., J. Electrochem. Soc., 2015, 162(7), p. F639-F644. [8] Ibrahim, O. A., et al., Electrochim. Acta, 2016, 187, p. 277-285. Figure 1 |
