To explore the capacitive charging mechanism of Ni3(HITP)2, this MOF was employed as an active electrode material in ex-situ supercapacitor experiments, for which NMR is performed after charging and disassembly of the supercapacitor (Figure ). In-situ NMR measurements, performed in real-time on a charging supercapacitor, were not possible due to lack of spectral resolution in the absence of magic-angle spinning (SI Figure ). Ex-situ F NMR spectra for all the electrodes showed the two expected resonances, corresponding to in-pore and ex-pore BF4 -anion environments (Figure , SI Figure ). Interestingly, a systematic shift of the in-pore resonance was also observed as the charging voltage was varied (Figure ). The experiments were conducted with 1 M NEt4BF4 in propylene carbonate (PC), a less volatile solvent, in addition to the original 1M NEt4BF4 in acetonitrile electrolyte (SI Figure ). Similar results were obtained for the two electrolyte systems, despite concerns about solvent evaporation with the acetonitrile-based electrolyte (SI Figure ). Figure : Studies on charging Ni3(HITP)2 supercapacitor electrodes with organic electrolytes. In the ex-situ experiments, symmetric supercapacitors with were held at a constant voltage for one hour as the current was monitored, and then disassembled, with NMR performed separately on each of the electrodes after disassembly. a) F solid-state NMR (9.4 T) spectra at 25 kHz MAS of ex-situ electrodes of Ni3(HITP)2 with 1 M NEt4BF4 in propylene carbonate (PC) compared to neat electrolyte; to obtain peak resolution for accurate fitting, a higher MAS rate of 25 kHz was required for samples with propylene carbonate solvents (SI Figure ). b) Correlation between in-pore chemical shift and electrode charge for 1M NEt4BF4 in deuterated acetonitrile (ACN), and propylene carbonate (PC). Measured in-pore ion population against specific electronic charge compared to theoretical scenarios in which all electrode charge storage is accounted for by exclusively (i) cation, or (ii) anion movement, with intercept fixed at the same value as the regression line for ease of comparison of their gradients, for an electrolyte of 1 M NEt4BF4 in c) propylene carbonate (PC) and d) deuterated acetonitrile (ACN) e) Top middle: Radial distribution function, g(r) as a function of distance between the boron atom of BF4 -and nickel in Ni3(HITP)2, the peak in the highlighted region corresponds to the pore-edge environment. Bottom row: QM/MM of simulated anion populations, highlighted in yellow, for 1 M NEt4BF4 electrolyte in Ni3(HITP)2, under negative charging (left), zero charge (middle), and positive charging (right). The isosurface level is 0.003 e bohr -3 . Simulations follow the cation-dominated charging mechanism observed experimentally. Simulated anion population symmetry is not fully maintained in 5 ns sampling time due to its strong binding affinity to the electrode. Two key anion sites are identified as pore centre (top left) and pore edge (top right).