For the first time, a new ErCl3 alkaline aqueous pseudo capacitor system was demonstrated by designing
commercial ErCl3 salt electrode in alkaline aqueous electrolyte, where the materials synthesis and subsequently
integrating into practical electrode structures occur at the same spatial and temporal scale.
Highly electro active ErOOH colloids were in-situ crystallized via electric field assisted chemical coprecipitation
of ErCl3 in potassium hydroxide aqueous electrolyte. These electro active ErOOH colloids absorbed by carbon black
and PVDF matrix were highly redox-reactive with higher cation utilization ratio of 86 % and specific
capacitance values of 1811 F/g, exceeding the one-electron redox theoretical capacitance (Er3+MEr2+).
We believe that additional two-electron (Er2+MEr) or three-electron (Er3+MEr) reactions can occur in
our designed ErCl3 alkaline aqueous pseudo capacitor system. The specific electrode configuration with
ErOOH colloids grown among the carbon black/PVDF matrix can create short ion diffusion and electron
transfer length to enable the fast and reversible Faradaic reactions. This work shows promising for finding
high-performance electrical energy storage systems via designing the colloidal state of electroactive
cations with the utilization of in-situ crystallization route.