Electronic Supplementary

Table 2. List of strains, associated species names, number of sequences per strains for each locus and results of automated annotation using ITS, LSU or both loci. Physiological similarities of strains within species names provided by curators or using ITS, LSU or both loci. In columns 5, 8 and 10, character " + " means that the predicted species name is the same as the one provided by the curators, otherwise the alternative name is provided (sometimes with a number after it if it is a sub-cluster within a given species). In columns 6, 9 and 11, character " + " means that the physiological similarities of strains are identical to the ones obtained using species name provided by the curators.


Section A. Supplementary Figures
The water uptake of 3 wt% MOF was calculated with various parameters of catalyst layer and TGA result as shown in Table S2.
The total weight of Pt (m Pt ) was calculated from the areal catalyst loading (0.25 mg cm -2 ).
m Pt = 0.25 mg cm -2 × 25 cm 2 = 6.25 mg The weight of carbon (m C ) was evaluated from the known Pt/C ratio (46% Pt and 54% C).
Since the mass ratio of ionomer to carbon was 1, the ionomer content (m ionomer ) is the same as the carbon weight.
Since the water uptake of Nafion at 30% RH was 3-5 wt%, 3,4 the amount of water in the ionomer of catalyst layer (m H2O@ionomer ) ranges 0.22-0.37mg.
m MOF = (m Pt + m C + m ionomer ) × 0.03 = 0.63 mg The water content in MOF (m H2O@MOF ) was calculated from the TGA result (11.3% weight loss for physisorbed water).We note that total water content in MOF (including chemisorbed ones) is higher than this value.

Fig. S2
Fig. S2 Nyquist plots of bare-MEA (0 wt%) and mof-MEA (3 wt%) at high current (25 A) measurements under 100% RH.The high current measurement emphasizes the mass transport resistance (the second semi-circle) which is related to the water flooding.The mass transport resistances of bare-MEA and mof-MEA are 98.4 and 179.2 mΩ cm 2 , respectively, suggesting the water flooding in the mof-MEA under 100% RH.

Fig. S3
Fig. S3 Nyquist plots with different MOF contents under conditions of OCV, H 2 /N 2 feed, and 30% RH.The high-frequency region is zoomed in for clarity.

Fig. S7
Fig. S7 Atomic charge of Nafion monomer and chain (for 10 repeating units) calculated from DFT calculation.

Fig. S8
Fig. S8 Model structures of the interface between MOF and Nafion chains.(a) The initial structure, and (b) interacted structure after 10ns of MD simulation.Upper grey atoms are MOF host framework, and lower cyan atoms are F in Nafion chains.Green and purple spheres are water molecules initially on the MOF and Nafion sides, respectively.

m
H2O@MOF = m MOF × 0.113 = 0.071 mg Increase in water uptake by adding 3 wt% MOF in the CL can be estimated as a follow.Increased weight percent of water = × 100 = 19.2-32.2% 2@  2@ Section C. Supplementary Note: Water state of the Nafion/MOF 3 wt% composite Water uptake (WU) of the sample was measured at room temperature by first drying the sample for 1 hour at 120 °C under vacuum and weighed it (W dry ).Then, the dried membrane was immersed in deionized water for 1 hour and reweighed after becoming fully hydrated (W wet ).The water uptake was calculated as a percentage using the following equation: WU =   -    × 100

Table S1
Various parameters for water absorption content calculation of MOF 3 wt%.

Table S2
The water state of Nafion/MOF 3 wt% composite.TableS3Summary of chemical durability results of MEA reported in the literature.

Table S4
The concentration of Zr element in cathode drain water measured from ICP-MS, both at the beginning and after 450 hr of continuous operation with a constant current.