Redox Chemistry of Molybdenum Trioxide for Ultrafast Hydrogen‐Ion Storage

Abstract

Hydrogen ions are ideal charge carriers for rechargeable batteries due to their small ionic radius and wide availability. However, little attention has been paid to hydrogen‐ion storage devices because they generally deliver relatively low Coulombic efficiency as a result of the hydrogen evolution reaction that occurs in an aqueous electrolyte. Herein, we successfully demonstrate that hydrogen ions can be electrochemically stored in an inorganic molybdenum trioxide (MoO3) electrode with high Coulombic efficiency and stability. The as‐obtained electrode exhibits ultrafast hydrogen‐ion storage properties with a specific capacity of 88 mA hg−1 at an ultrahigh rate of 100 C. The redox reaction mechanism of the MoO3 electrode in the hydrogen‐ion cell was investigated in detail. The results reveal a conversion reaction of the MoO3 electrode into H0.88MoO3 during the first hydrogen‐ion insertion process and reversible intercalation/deintercalation of hydrogen ions between H0.88MoO3 and H0.12MoO3 during the following cycles. This study reveals new opportunities for the development of high‐power energy storage devices with lightweight elements.

Opportunities and challenges for aqueous metal-proton batteries

“…The conversion reaction (MoO 3 + 0.88H + + 0.88e À / H 0.88 MoO 3 ) occurs during the first reduction process, and a reversible intercalation/de-intercalation reaction (H 0.88 MoO 3 À 0.76H + À e À 4 H 0.12 MoO 3 ) takes place in the following cycles (Figure 6B). 54 The MoO 3 electrode delivers a capacity of 88 mAh g À1 at 1 C (1 C = 200 mA g À1 ), and the Coulombic efficiency is in the range of 97%-99% from the fifth cycle at 5 C.…”

“…(B) Charging/discharging curves at 1 A g À1 (left) and schematic illustrations of the reaction mechanism (right) of the MoO 3 electrode. Adapted with permission from Wang et al54 Copyright 2018, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.…”

Aqueous OH−/H+ Dual‐Ion Zn‐Based Batteries

“…Compared to WO 3 , MoO 3 shows a b value of 0.5, implying the diffusion‐limited behavior of H + ions in MoO 3 [41b] . Besides, the ex‐situ XRD experiments (Figure 5f) reveal a conversion reaction of the MoO 3 electrode into H 0.88 MoO 3 during the first H + ions insertion process due to the strong bonding force between H + and terminated oxygen, and a reversible intercalation/deintercalation of hydrogen ions between H 0.88 MoO 3 and H 0.12 MoO 3 during the following cycles.…”

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

“…α-MoO 3 , with a unique bilayered structure and multivalent redox center Mo (VI, V, IV, III) (Figure 1), has been studied as a proton host material with fast kinetics and large capacities for battery applications. [18][19][20] Recently, the science behind the fast proton transfer properties of α-MoO 3 was unveiled by Yamada group 21 . Due to the dense oxide-ion arrays of MoO 3 (O-O distance < 3 Å), inserted proton can chemically bond with one lattice oxygen and form one or more hydrogen bonds with other lattice oxygens, building a dense hydrogen bond network.…”