Tuning H2O-Engaged Redox Reaction Pathway via Water Orientation in Aqueous Batteries

Aqueous battery research has long focused on ionic behavior during reactions but has largely neglected the essential role of reactive water, hindering the mechanistic understanding and limiting breakthroughs in battery performance. Herein, we establish an H2O-engaged perspective in aqueous electrochemistry and identify unfavorable interfacial water orientation as the fundamental degradation mechanism for H2O-engaged redox. In situ spectroscopy, synchrotron radiation analyses, and theoretical simulations demonstrate that N vacancies in the constructed WN artificial interface elevate the work function and positively shift the point of zero charge, thereby inducing interfacial water into an H-down configuration. The energy barrier for the O-H bond cleavage and proton release can be lowered, boosting H2O-engaged Mn2+ oxidation reaction (MnOR) and facilitating uniform planar MnO2 deposition. As a result, the developed Zn-MnO2 aqueous batteries enable a high capacity of 20 mAh cm-2 with 666.7 mAh cm-3, an ultrahigh rate capability of 160 C, and a cycling lifespan over 10,000 cycles. These findings establish interfacial water orientation as a pivotal reaction coordinate for H2O-engaged redox electrochemistry and provide a general mechanism-guided strategy for designing next-generation robust aqueous batteries.