Interlayer Engineering of α-MoO3 Modulates Selective Hydronium Intercalation in Neutral Aqueous Electrolyte.

Among various charge-carrier ions for aqueous batteries, non-metal hydronium (H3 O+ ) with small ionic size and fast diffusion kinetics empowers H3 O+ -intercalation electrodes with high rate performance and fast-charging capability. However, pure H3 O+ charge carriers for inorganic electrode materials have only been observed in corrosive acidic electrolytes, rather than in mild neutral electrolytes. Herein, we report how selective H3 O+ intercalation in a neutral ZnCl2 electrolyte can be achieved for water-proton co-intercalated α-MoO3 (denoted WP-MoO3 ). H2 O molecules located between MoO3 interlayers block Zn2+ intercalation pathways while allowing smooth H3 O+ intercalation/diffusion through a Grotthuss proton-conduction mechanism. Compared to α-MoO3 with a Zn2+ -intercalation mechanism, WP-MoO3 delivers the substantially enhanced specific capacity (356.8 vs. 184.0 mA h g-1 ), rate capability (77.5 % vs. 42.2 % from 0.4 to 4.8 A g-1 ), and cycling stability (83 % vs. 13 % over 1000 cycles). This work demonstrates the possibility of modulating electrochemical intercalating ions by interlayer engineering, to construct high-rate and long-life electrodes for aqueous batteries.