Electrolyzer Design for Flexible Decoupled Water Splitting and Organic Upgrading with Electron Reservoirs

Abstract

Robust proton-independent electron reservoirs of (ferrocenylmethyl) trimethylammonium chloride and Na 4 [Fe(CN) 6 ] are utilized to separate H 2 evolution from O 2 evolution with much lower voltage inputs than that of conventional water-splitting electrolysis. Such decoupled water splitting can be readily driven by photovoltaics with small photovoltages in near-neutral solution under natural sunlight irradiation. The electron reservoirs can facilitate sustainable H 2 production from decoupled water splitting and further integrate H 2 evolution with organic upgrading, yielding two value-added products (H 2 and 2,5furandicarboxylic acid).

Recent Progress in Decoupled H2 and O2 Production from Electrolytic Water Splitting

“…Based on the above consideration, Sun et al recently reported an alternative strategy of utilizing Na 4 [Fe(CN) 6 ] as a low‐cost proton‐independent redox mediator for decoupled water splitting in alkaline electrolytes . Na 4 [Fe(CN) 6 ] has a great solubility in alkaline electrolyte (1.0 M KOH) and rapid electron transfer kinetics on electrode.…”

“…b) Linear sweep voltammograms of a Co−P working electrode with (red) and without (blue) 0.3 M Na 4 [Fe(CN) 6 ] in the counter chamber. c) Linear sweep voltammograms of a Ni foam working electrode with (red) and without (black) 0.3 M Na 3 [Fe(CN) 6 ] in the counter chamber in the absence (red and black) and presence (green) of 10 mM HMF in the working chamber . Reproduced with permission from Ref.…”

“…Besides strongly acidic or alkaline conditions, which are corrosive environments for electrolyzers and also prohibit biological enzymes as potential electrocatalysts, neutral electrolyte has been widely recognized as an attractive medium for water splitting electrolysis . Taking advantage of the rapid, reversible, and stable redox properties of ferrocene, Sun et al reported a ferrocene derivative, (ferrocenylmethyl)trimethylammonium chloride (FcNCl), as a suitable proton‐independent redox mediator for decoupled water splitting under near neutral condition (0.5 M Na 2 SO 4 ) . Despite the insoluble nature of the parent ferrocene in aqueous solution, the ammonium salt FcNCl has a great solubility in water (up to 4.0 M).…”

“…c) Comparison of the measured and calculated amount of generated H 2 during electrolysis at −1.8 V. d) Linear sweep voltammograms of Ni foam as the working electrode with 0 (black) and 50 mM (red) FcNCl + (the oxidized form of FcNCl) in the counter chamber. e) Comparison of the measured and calculated amount of O 2 during electrolysis at 1.7 V . Reproduced with permission from Ref.…”

Recent Advances in Electrochemical Hydrogen Production from Water Assisted by Alternative Oxidation Reactions

“…On the one hand, such an innovative electrolysis system could lower the voltage input and exclude the formation of H 2 /O 2 gas mixture and reactive oxygen species due to the replacement of OER with thermodynamically more favorable anodic oxidation reactions . On the other hand, value‐added anodic products instead of O 2 can be potentially produced at the anode side of the system by choosing suitable feedstock chemicals, maximizing the return of energy investment …”