As mentioned above, an abrupt increase of the gravimetric capacitance is noted for HTC-750 compared to the other carbons prepared at lower temperatures. We attribute this to the significant pore opening at 750 ºC which gives rise to the sample with the highest BET surface area (2689 m 2 g -1 ) in the series and a significant number of pores below 1 nm in diameter and around 2 nm in diameter (Figure , Table ). This is likely due to the more dramatic etching of the carbon framework at 750 ℃ by KOH and the formation of potassium-containing compounds at this temperature (i.e. K2CO3 and K2O). Importantly, in addition to providing a measurement of the sizes of the graphene-like domains, our NMR experiments measure another key property of the nanoporous carbons; the electrolyte ion adsorption capacity. Indeed, the integrals of the in-pore resonances relate to the number of ions which can access the carbon nanopores in the absence of applied potential. Deconvolution of the NMR spectra of the electrolyte-saturated carbon samples shows that the gravimetric capacitance showed some correlation with the ion adsorption capacity (Figure ), with HTC-750 having the largest ion adsorption capacity in the series (1.6 mmol g -1 ). The volumetric capacitance is also correlated with the ion adsorption capacity of the carbons in the absence of an applied potential (Figure ), though for volumetric capacitance the correlation is less obvious (Figure ). We hypothesise that the opening of the pores facilitates more pathways for ions to access the defective sites, where the charges are stored. However, an excessively high BET surface area is not always desirable, as it lowers the volumetric capacitance, though HTC-750 exhibits a similar volumetric capacitance to HTC-600 and HTC-650 (Figure , Figure ). Moreover, comparing HTC-600 and HTC-750, the BET surface area normalised capacitance is around two times larger for HTC-600, than that of HTC-750 (Figure ), highlighting the more efficient charge storage in HTC-600.