Tailoring Non‐Polar Groups of Quaternary Ammonium Salts for Inhibiting Hydrogen Evolution Reaction of Aluminum‐Air Battery

Abstract Aluminum‐air battery (AAB) with alkaline‐based aqueous electrolyte have attracted intensive research interests due to high‐capacity density, low cost, and high safety. However, severe hydrogen evolution reaction (HER) of Al anode in alkaline electrolyte extremely restricts its large‐scale application. In this work, ZnO with a group of quaternary ammonium salts (QAS, denoted as C1, C2, C4, C6, and C8 depending on the length of non‐polar group) are introduced into electrolytes to inhibit HER. It is revealing that capacity density initially increases with C1, C2, or C4, up to 2564 mAh g Al −1 with anodic utilization rate of 86.0%, and then follows by a decline (C6 and C8). The addition of QAS creates “physical‐hydrophobic interface” by non‐polar group owing to its electrophilic property and constructs “chemical‐hydrophobic interface” with polar group by reducing water activity. QAS also promotes the uniform growth of Zn‐based film, as a barrier against H 2 O. Thus, HER is effectively inhibited to improve the capacity density. With further increasing non‐polar group length (C6 or C8), the bonding status of the film deteriorates with enhanced H 2 O activity, leading to the recurrence of HER. This work explores the effect of non‐polar groups on inhibiting HER and opens the door to stable anodes for alkaline‐based batteries.