High‐rate Decoupled Water Electrolysis System Integrated with α‐MoO₃ as a Redox Mediator with Fast Anhydrous Proton Kinetics

Abstract

Hydrogen is a promising alternative to fossil fuels that can reduce greenhouse gas emissions. Decoupled water electrolysis system using a reversible proton storage redox mediator, where the oxygen evolution reaction and hydrogen evolution reaction are separated in time and space, is an effective approach to produce hydrogen gas with high purity, high exibility, and low cost. To realize a fast hydrogen production in such a system, a redox mediator capable of releasing proton rapidly is required. Herein, α-MoO 3 , with an ultrafast proton transfer property that can be explained by a dense hydrogen bond network in the lattice oxygen arrays of H x MoO 3 , was examined in this work as a high-rate redox mediator for fast hydrogen production in acidic electrolytes. The α-MoO 3 redox mediator shows both a large capacity of 204 mAh g -1 and fast hydrogen production at a current rate of 1 A cm -2 (100 A g -1 ), outperforming most of the previously reported solid-state redox mediators.

Decoupled electrolysis for hydrogen production and hydrazine oxidation via high-capacity and stable pre-protonated vanadium hexacyanoferrate

“…As shown in Fig. 3b , most calculated b values for the anodic peaks and cathodic peaks exceed 0.8 (0.89, 0.98, 0.79 for anodic O 1 , O 2 , O 3 ; 0.86, 0.98, 0.84 for cathodic R 1 , R 2 , R 3 ), which signifies an ultra-fast proton insertion/de-insertion kinetics 17 , 37 , 38 .

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Breaking boundaries: advancements in solid-state redox mediators for decoupled water electrolysis

“…73,74 In 2023, Yamada and colleagues evaluated the potential of α-MoO 3 as an RM with this property. 39 Fig. 5d illustrates the schematic of its decoupled system.…”

Surpassing water-splitting potential in aqueous redox flow batteries: insights from kinetics and thermodynamics

“…By controlling electron mediation through these compounds, a higher level of selectivity is achieved, suppressing undesired chemical reactions and contributing to improved stability and cycle life. 103 RMs undergo reversible reduction and oxidation processes during electrochemical cycles, making them capable of reviving a depleted metallic anode. Criteria for a better performing RMs include a suitable redox potential, spontaneity for electron transfer, fast kinetics, high solubility, and greater stability.…”