Revealing Electrolytic Ion Sorption in Layered Graphene Galleries through Low-Temperature Solid-State NMR

There is an ever-growing desire to use and store energyfrom sustainableresources. Pillared graphene materials offer high capacitive performancesin supercapacitors, presumably through enhanced electrolytic ion sorptionin their chemically engineered inter-layer graphene galleries. Herein,a judicious combination of the removal of excess electrolytes, isotopicenrichment of the pillar molecules, and the use of low temperatures(100 K) enables solid-state nuclear magnetic resonance spectroscopyto efficiently probe nuclear spin polarization exchange between theelectrolyte and the electrode. This provides the direct detectionof electrolyte ions in proximity to the gallery pillars, evidencingthe adsorption of ions in such two-dimensional galleries. However,when the ions are larger than the gallery d-spacing, they are notobserved to enter the galleries, and the total storage capacity isaccordingly reduced. This methodology provides a means to locate electrolyteions upon charging or discharging devices and thus will be invaluablein the quest for the design of materials with vastly improved powerdensities.