Stable Tetrasubstituted Quinone Redox Reservoir for Enhancing Decoupled Hydrogen and Oxygen Evolution

Abstract

Redox reservoirs (RRs) may be used to decouple the two halfreactions of water electrolysis, enabling the spatial and temporal separation of hydrogen and oxygen evolution. Organic RRs are appealing candidates for this application; however, their instability limits their utility. Here we show that a tetrathioether-substituted quinone, tetramercaptopropanesulfonate quinone (TMQ), exhibits significantly enhanced stability relative to anthraquinone-2,7disulfonate, the most effective organic RR reported previously. The enhanced stability, confirmed by symmetric flow-battery experiments under relevant conditions, enables the stable electrochemical production of H 2 and O 2 in a continuous-flow electrolysis cell. The reduced RR, tetramercaptopropanesulfonate hydroquinone, is not susceptible to decomposition, whereas the oxidized state, TMQ, undergoes slow decomposition, evident only after sustained operation (>60 h). The analysis of the byproducts provides the basis for a decomposition mechanism, establishing a foundation for the design of new organic RRs with even better performance.

Electrochemical Regeneration of Anthraquinones for Lifetime Extension in Flow Batteries

“…One such example is anthraquinone-2,7-disulfonic acid (AQDS) 10,16 that has a much lower fade rate of 0.1%/day in acid at room temperature, 17 but decomposes to anthrone (anthranol)-2,7-disulfonic acid (ADS) over cycling (Figure S12). 18 Our preliminary results confirm that ADS (both pure ADS and produced by cycling AQDS) can be chemically and electrochemically converted to AQDS (Figure S13, S14, S15). Thus this approach should reduce the overall fade rate of these negolytes, potentially enabling them to reach electrolyte lifetimes comparable to more recent studies utilising more complex and costly reactants.…”

Chemical and Electrochemical O2 Reduction on Earth-Abundant M-N-C Catalysts and Implications for Mediated Electrolysis

“…Mediated ORR systems represent an intersection between electrochemical and thermochemical reactions aerobic oxidation catalyst to achieve a mediated electrochemical ORR (Figure c), and it supported current densities much higher than those of previous mediated ORR systems. , The present study of M-N-C-catalyzed O 2 reduction by HQ1 provides unique insights into the relationship between the mediated and direct electrocatalytic ORR.…”

Redox-active benzoquinones as challenging “non-innocent” linkers to construct 2D frameworks and nanostructures with tunable physical properties

“…Among these ligands, quinone and its derivatives have been widely studied for their impressive redox properties. 46,47 Quinones are naturally occurring organic molecules forming conjugated six-membered cyclic diketones in ortho or para positions, namely, o -quinones and p -quinones, respectively. Quinones (Q) undergo reversible electron transfer reactions to form fully reduced hydroquinone QH 2 via an intermediate semiquinone radical species (Q˙ − ) (Scheme 1).…”