Abstract
A functionalised benzoquinone redox species is coupled to the hydrogen/proton reaction to achieve a respectable reversible redox fuel cell (RFC).
Highlights
The redox flow battery (RFB) is a suitable option for electricity storage due to its high energy efficiency, scalability and relative safety
The energy cost of a VRFB is $320 per kW h whilst the target set by the U.S Department of Energy (DOE) is $100 per kW h, with almost 50% of the price being dominated by the cost of the electrolyte.[20,21]
From 2009 onwards, when an RFB utilising organic chloranil redox material was demonstrated,[22] the implementation of organic redox active species has been explored owing to their ubiquity in nature and more economical price than their metal-based redox counterparts.[23]
Summary
Since the concept was rst presented by NASA in the 1970s, redox ow batteries (RFBs) have attracted attention because they have the potential to meet the requirements of durability for repeated charge/discharge, rapid response to changes in load or input and have a high capacity retention, a high roundtrip efficiency and reasonable capital costs.[1]. Paper radicals,[31,32] and viologens.[26] In this context, researchers at Harvard have pioneered the exploration of anthraquinone moieties which resulted in promising electrochemical activity at both low and high pH.[23,33] For instance, in their quinonebromide ow battery system, the workers functionalised the anthraquinone backbone with sulphonate groups (AQDS) to ensure better solubility at low pH.[23] In a separate investigation, ether-linked alkyl chains with solubilizing carboxylate functional groups were added onto an anthraquinone core to enable high chemical stability and high solubility (0.6 M at pH 12; 1.1 M at pH 14) in alkaline electrolytes.[34] selfdimerization of AQDS at high concentrations was reported subsequently for bisulphonated quinones.[35] The dimerization prevents the full-oxidation of the molecule, which means there will be unstable redox-active species in highly concentrated electrolytes.[36] Self-discharge mechanisms were brie y presented but not discussed as a function of operating time; the authors showed cell discharge at different current densities as a function of cycle number, which may not have revealed full capacity fading issues In this context, many organic redox couples and hydro-quinones (and hydro-anthraquinones) are known for their sensitivity towards molecular oxygen to regenerate the corresponding quinone with concomitant production of hydrogen peroxide. We employ a standard membrane-electrode assembly to determine how the system will operate under non-optimised conditions in order to compare with more established RFBs such that a means for optimising performance can be established by other workers in an attempt to achieve commercial outreach in a similar, if not better, manner to VRFBs
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