Correlating In-pore Anion Population in the Absence of Applied Potential to Electrochemical Performance. F NMR adsorption experiments, analogous to those previously described, were subsequently evaluated as a tool to predict the electrochemical performance of Ni3(HITP)2 samples. Two samples with contrasting BET SSAs, sample A at 852 m 2 g -1 , and sample B at 309 m 2 g -1 , were selected and made into composite electrode films for further BET measurements (Figure ), NMR adsorption experiments (Figure ), and electrochemical performance tests (Figure , SI Table ). Adsorption experiments were performed at high electrolyte loadings to saturate the porosity of the MOF and probe the electrolyte-accessible in-pore volume (SI Table ). Sample A was found to have a higher in-pore anion population (defined by mmol of in-pore anions per gram of MOF), evident from the larger integral of the in-pore peak in adsorption experiments (Figure ). Furthermore, we note a difference in the peak shape of the ex-pore environments between the two samples which we attribute to differences in ion exchange rates. Importantly, Sample A demonstrated a higher gravimetric capacitance measured from galvanostaticcharge-discharge (GCD) experiments (SI Table ), which was also supported by a larger cyclic voltammogram (CV) area for a symmetric supercapacitor cell (Figure ). The CVs for both samples over a cell voltage window of 1.0 V qualitatively resemble the electric double-layer behaviour previously reported for this system. However, with a gravimetric capacitance of 160 F g -1 at a current density of 0.05 A g -1 (0.3 mA cm -2 ), Sample A exceeds the electrochemical performance reported in the literature for the same system (up to 111 F g -1 at a current density of 0.05 A g -1 ), and competes closely with the gravimetric capacitance of Ni3(HITP)2 with aqueous sodium sulfate electrolyte (170 F g -1 at a current density of 0.1 mA cm -2 ) reported by Nguyen et al. With a gravimetric capacitance of 62 F g -1 , Sample B falls within the range reported by Borysiewicz et al.. The batch-to-batch variation observed in electrochemical performance may be linked to variations in MOF morphology, as has previously been reported for Ni3(HITP)2. Morphology differences would also be expected to give rise to changes in exchange rate between the in-pore and ex-pore environments, which would explain the significant difference in peak-shape of the ex-pore environment. F solid-state NMR (9.4 T) spectra at 5 kHz MAS of Ni3(HITP)2 composite films of sample A and B at saturated electrolyte loading volumes of 1 M NEt4BF4/d3ACN, compared to neat electrolyte spectrum; differences in intensity of the in-pore peak are highlighted c) CVs at 5 mV s -1 of symmetric supercapacitors with Ni3(HITP)2 samples A and B as the active electrode material. The small faradaic contribution prominent in the CV for Sample A is attributed to the previously reported quasi-reversible oxidation process of the MOF, reported to be likely centred on the linker molecule. Correlations between d) BET SSA and gravimetric capacitance, e) In-pore anion population and gravimetric capacitance, and f) In-pore anion population and BET SSA for the five Ni3(HITP)2 composite film samples studied. All samples reflect a single gas sorption measurement except sample E which is represented as an average of two measurements. Gravimetric capacitances at a current /density 0.05 A g -1 were measured from galvanostatic-charge-discharge (GCD) experiments.