Anhydrous Fast Proton Transport Boosted by the Hydrogen Bond Network in a Dense Oxide‐Ion Array of α‐MoO₃

Abstract

Developing high‐power battery chemistry is an urgent task to buffer fluctuating renewable energies and achieve a sustainable and flexible power supply. Owing to the small size of the proton and its ultrahigh mobility in water via the Grotthuss mechanism, aqueous proton batteries are an attractive candidate for high‐power energy storage devices. Grotthuss proton transfer is ultrafast owing to the hydrogen‐bonded networks of water molecules. In this work, similar continuous hydrogen bond networks in a dense oxide‐ion array of solid α‐MoO3 are discovered, which facilitate the anhydrous proton transport even without structural water. The fast proton transfer and accumulation that occurs during (de)intercalation in α‐MoO3 is unveiled using both experiments and first‐principles calculations. Coupled with a zinc anode and a superconcentrated Zn2+/H+ electrolyte, the proton‐transport mechanism in anhydrous hydrogen‐bonded networks realizes an aqueous MoO3–Zn battery with large capacity, long life, and fast charge–discharge abilities.

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

“…The remaining 1.0 H + can be extracted when applying a constant voltage at the end of deprotonation for 3 h (Figure S4, Supporting Information). The CV curves share large resemblances with that in a 32 mol kg −1 (m) ZnCl 2 + 1 m P 2 O 5 electrolyte in our previous study, [23] indicating the same H + intercalation mechanism in α-MoO 3 . More specifically, we ascribed the corresponding peaks observed for H x MoO 3 (1< x <2.5) in the subsequent cycles to the redox events of proton (de)intercalation, H 1 MoO 3 /H x MoO 3 and H x MoO 3 /H 2.5 MoO 3 (0< x <1.5); equations 1, 2, 3, and 4 are used to interpret the cathodic peaks (C1 and C2) and anodic peaks (A3 and A4), respectively, in agreement with previous electrochemical studies.…”

“…The unique proton transfer based on hydrogen bond networks in solid structures for fast proton transport in α‐MoO 3 and CuFe‐TBA could rationalize the persisting hydrogen generation under high current densities. Indeed, the proton diffusion barriers in α‐MoO 3 and CuFe‐TBA are < 0.3 eV, [ 19,23 ] resembling that in liquid water via the Grotthuss mechanism (< 0.4 eV), thanks to the dense oxide ion arrays (O‐O distance < 3 Å) in α‐MoO 3 and abundant structural water in CuFe‐TBA that facilitate the proton hopping. In contrast, Ni(OH) 2 , with O‐O distance of ≈3.18 Å, exhibit a much larger proton diffusion barrier of > 0.6 eV, [ 39 ] since the proton hopping barrier is positively related to the O‐O distance as evidenced by density functional theory (DFT) calculations (Figure S20, Supporting Information).…”

“…[ 49 ] A k‐point separation of ≈0.04 Å −1 was used in all calculations. Based on the calculated protonated structure, [ 23 ] the climbing image nudged elastic band (CI‐NEB) method was adopted to calculate proton diffusion pathways in a $$2\sqrt 2 \times 1 \times 2\sqrt 2 $$ supercell (Mo 32 O 96 ).…”

Intercalation Reaction of Molybdenum Trioxide Cathode for Rechargeable Ion Batteries

“…In recent studies, Ma et al [77] revealed the fast proton transport mechanism of the MoO 3 cathode through experiments and theoretical calculations. Similar to the Grotthuss proton transport mechanism of water molecules, protons form a hydrogen bond network in the α-MoO 3 cathode lattice of the ultra-concentrated double-ion electrolyte (32 mol kg À 1 ZnCl 2 and 1 mol kg À 1 P 2 O 5 /H 2 O).…”

“…In recent studies, Ma et al [77] . revealed the fast proton transport mechanism of the MoO 3 cathode through experiments and theoretical calculations.…”