Aqueous zinc batteries are highly attractive for large-scale storage applications owing to their inherent safety, low-cost, and durability. Yet, their advancement is hindered by a dearth of positive host materials (cathode) due to sluggish diffusion of Zn 2+ inside solid inorganic frameworks. Here, we report a novel organic host, tetrachloro-1,4-benzoquinone (also called: p-Chloranil), which due to its inherently soft crystal structure can provide reversible and efficient Zn 2+ storage. It delivers a high capacity of ≥200 mAh g-1 with a very small voltage polarization of 50 mV in a flat plateau around 1.1 V, which equate to an attractive specific energy of > 200 Wh kg-1 at an unparalleled energy efficiency (~95%). As unraveled by density functional theory (DFT) calculations, the molecular columns in p-Chloranil undergo a twisted rotation to accommodate Zn 2+ , thus restricting the volume change (-2.7%) during cycling. In-depth characterizations using operando X-ray

Aqueous Zn-ion batteries, which are being proposed as large scale energy storage solutions due to their unparalleled safety and cost advantage, are comprised of a positive host (cathode) material, a metallic zinc anode, and a mildly acidic aqueous electrolyte (pH ~ 3 -7). Typically, the charge storage mechanism is believed to be reversible Zn 2+ (de)intercalation in the cathode host, with the exception of α-MnO2, for which multiple vastly different and contradicting mechanisms have been proposed. However, our present study, combining electrochemical, operando X-ray diffraction (XRD), electron microscopy in conjunction with energy dispersive X-ray spectroscopy (EDX), and in situ pH evolution analyses on two oxide hosts -tunneled α-MnO2 and layered V3O7•H2O vis-à-vis two non-oxide hostslayered VS2 and tunneled Zn3[Fe(CN)6]2, suggests that oxides and non-oxides follow two dissimilar charge storage mechanisms. While the oxides behave as dominant proton intercalation materials, the non-oxides undergo exclusive zinc intercalation.Stabilization of the H + on the hydroxyl terminated oxide surface is revealed to facilitate the proton 2 intercalation by a preliminary molecular dynamics simulation study. Proton intercalation for both oxides leads to the precipitation of layered double hydroxide (LDH) -Zn4SO4(OH)6•5H2O with ZnSO4/H2O electrolyte and a triflate anion (CF3SO3 -) based LDH with Zn(SO3CF3)2/H2O electrolyte -on the electrode surface. The LDH precipitation buffers the pH of the electrolytes to a mildly acidic value, sustaining the proton intercalation to deliver large specific capacities for the oxides. Moreover, we also show that the stability of the LDH precipitate is crucial for the rechargeability of the oxide cathodes, revealing a critical link between the charge storage mechanism and the performance of the oxide hosts in aqueous zinc batteries.

Based on constant Fermi-level molecular dynamics and a proper alignment scheme, we perform simulations of the Pt(111)/water interface under variable bias potential referenced to the standard hydrogen electrode (SHE). Our scheme yields a potential of zero charge μ of ∼0.22 eV relative to the SHE and a double layer capacitance C of ≃19 μF cm, in excellent agreement with experimental measurements. In addition, we study the structural reorganization of the electrical double layer for bias potentials ranging from -0.92 eV to +0.44 eV and find that O configurations, which are dominant at potentials above the pzc, reorient to favor H configurations as the measured potential becomes negative. Our modeling scheme allows one to not only access atomic-scale processes at metal/water interfaces, but also to quantitatively estimate macroscopic electrochemical quantities.

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