Our peak assignments were further supported by integration of the NMR spectra at variable loadings (SI Figure ). At the lowest loading, the in-pore environment dominates, but upon increasing the solvent loading this peak grows slowly compared to the proposed ex-pore environment, which dominates at higher electrolyte loadings where the in-pore environment i.e. the electrolyte-accessible porosity of the MOF, becomes saturated. A series of analogous adsorption experiments on Ni3(HITP)2 composite electrode film gave rise to the same two environments, following the same trend on variation of electrolyte loading (SI Figure ). Having, made these initial assignments, the ion dynamics of the system were investigated. Interestingly, the peak assigned as 'ex-pore' shifts towards the neat electrolyte peak at increasing electrolyte loading (Figure , SI Figure ). This change in chemical shift could not be accounted for purely by those expected for variation in the local electrolyte concentration (SI Figure ), which suggests this peak is impacted by fast exchange on the NMR timescale between truly unconfined electrolyte in the 'ex-pore' environment, and a smaller proportion of electrolyte which is influenced by the MOF, likely close to the pore openings such that it is easily accessible for exchange. Exchange spectroscopy (EXSY) was used to further reveal the slow exchange between in-pore and ex-pore environments, which manifests as cross peaks appearing on a timescale of tens of milliseconds (Figure ). Despite these various exchange contributions, the adsorption experiments on Ni3(HITP)2 confirmed the presence of two key environments, in-pore and ex-pore, analogous to those seen in adsorption NMR studies on activated porous carbons. Interestingly, the 'in-pore' BF4 -peak for Ni3(HITP)2 is positively shifted from the neat electrolyte resonance, quantified by Δδ = δin-pore -δneat = +3.9 ppm (Figure ). This contrasts with the negative Δδ values seen in NMR studies of ion adsorption in porous carbons, where ring current shielding effects dominate the Δδ values, leading to a nucleus independent chemical shift. As a result, in porous carbons, the observed Δδ remains constant when varying the NMR active nucleus studied, or the electrolyte components. In MOFs, other non-covalent binding interactions may dominate the chemical shifts, with one possibility in Ni3(HITP)2 being hydrogen-bond interactions between the BF4 -anions and the N-H moiety of the HITP linker. To investigate the origin of the observed Δδ values in Ni3(HITP)2, both the studied NMR active nucleus and the electrolyte anion were independently varied (Figure , SI Table ). Studying the same sample in the original electrolyte of 1 M NEt4BF4/d3ACN with 11 B NMR as a second probe of BF4 -, the two peaks are no longer well-resolved (Figure ). On deconvolution Δδ for the B spectrum was found to be just +0.7 ppm (SI Table ). The significant difference in the F and B Δδ values for Ni3(HITP)2 is in contrast to previous findings on porous carbons. Indeed, previous work on a microporous carbidederived-carbon showed very similar F and B Δδ values of +5.5 ppm and +5.7 ppm respectively. These shifts are dominated by a ring-current shift, which is assumed to be similar on average for both nuclei due to the rapid rotation of the BF4 -anion in the electrolyte. Therefore, the observed nucleusdependent effects in Ni3(HITP)2 suggest a different dominant chemical shift mechanism compared to porous carbons. F solid-state NMR (9.4 T) spectra of Ni3(HITP)2 soaked with 1 M NEt4TFSI/d3ACN compared to neat electrolyte d) F and e) B simulated NMR spectra of tetrafluoroborate anion close to Ni3(HITP)2 MOF fragment compared to in bulk acetonitrile. Spectra are schematic to show the simulated chemical shift, the line width is not indicative of the peak width. f) F solid-state NMR (9.4 T) spectra of Ni3(HITP)2 soaked with 1 M NaSO3CF3/DMF compared to neat electrolyte. All experimental spectra used Ni3(HITP)2 Sample A and are recorded in the quantitative regime with an MAS rate of 5 kHz.