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Abstract Alkaline iron (Fe) batteries are attractive due to the high abundance, low cost, and multiple valent states of Fe but show limited columbic efficiency and storage capacity when forming electrochemically inert Fe₃O₄on discharging and parasitic H₂on charging. Herein, sodium silicate is found to promote Fe(OH)₂/FeOOH against Fe(OH)₂/Fe₃O₄conversions. Electrochemical experiments,operandoX‐ray characterization, and atomistic simulations reveal that improved Fe(OH)₂/FeOOH conversion originates from (i) strong interaction between sodium silicate and iron oxide and (ii) silicate‐induced strengthening of hydrogen‐bond networks in electrolytes that inhibits water transport. Furthermore, the silicate additive suppresses hydrogen evolution by impairing energetics of water dissociation and hydroxyl de‐sorption on iron surfaces. This new silicate‐assisted redox chemistry mitigates H₂and Fe₃O₄formation, improving storage capacity (199 mAh g⁻¹in half‐cells) and coulombic efficiency (94 % after 400 full‐cell cycles), paving a path to realizing green battery systems built from earth‐abundant materials. 

Aqueous Li-ion batteries (ALIBs) are an important class of battery chemistries owing to the intrinsic non-flammability of aqueous electrolytes. However, water is detrimental to most cathode materials and could result in rapid cell failure. Identifying the degradation mechanisms and evaluating the pros and cons of different cathode materials are crucial to guide the materials selection and maximize their electrochemical performance in ALIBs. In this study, we investigate the stability of LiFePO₄(LFP), LiMn₂O₄(LMO) and LiNi_0.8Mn_0.1Co_0.1O₂(NMC) cathodes, without protective coating, in three different aqueous electrolytes, i.e., salt-in-water, water-in-salt, and molecular crowding electrolytes. The latter two are the widely reported “water-deficient electrolytes.” LFP cycled in the molecular crowding electrolyte exhibits the best cycle life in both symmetric and full cells owing to the stable crystal structure. Mn dissolution and surface reduction accelerate the capacity decay of LMO in water-rich electrolyte. On the other hand, the bulk structural collapse leads to the degradation of NMC cathodes. LMO demonstrates better full-cell performance than NMC in water-deficient aqueous electrolytes. LFP is shown to be more promising than LMO and NMC for long-cycle-life ALIB full cells, especially in the molecular crowding electrolyte. However, none of the aqueous electrolytes studied here provide enough battery performance that can compete with conventional non-aqueous electrolytes. This work reveals the degradation mechanisms of olivine, spinel, and layered cathodes in different aqueous electrolytes and yields insights into improving electrode materials and electrolytes for ALIBs. 

NiO_x/CeO₂catalysts were synthesized under various pretreatment conditions. Different pretreatment conditions significantly influenced the activity of the NO reduction by CO reaction.