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Page 6 of 17 Li et al. Chem Synth 2023;3:30 https://dx.doi.org/10.20517/cs.2023.16

Scheme 1. Synthesis routes to (A) MIL-53 (Al); (B) MIL-68 (Al); and (C) MIL-100 (Al) with different precursors and thus to MIL-53-
800, MIL-68-800, and MIL-100-800 by pyrolysis at 800 °C.

Supplementary Table 1 and Supplementary Figure 2 summarize the surface area and pore volume
information of samples before and after pyrolysis at 700, 800, and 900 °C. Notably, the surface area and pore
volume of MIL-53 (Al) and MIL-68 (Al) decrease after pyrolysis at 700 °C due to the collapse of ordered
[49]
micropores . However, the surface area and pore volume of MIL-100 (Al) increase owing to the stable
trimesic acid ligand that could relieve the collapse of the MIL-100 (Al) structure. By increasing the pyrolysis
temperature from 700 to 800 °C, the Al-MIL-derived porous carbon materials achieve higher surface area
and pore volume for the reason of the gasification of carbon atoms. When the temperature rises to 900 °C,
the surface area of MIL-53-900 and MIL-68-900 drops from 1566 to 413 and 1053 to 240 m g , and pore
-1
2
-1
3
volume from 2.33 to 0.68 and 2.16 to 0.26 cm g , respectively. The sharp decrease in the surface area and
pore volume reflects the high collapse of the particle structure [50-52] . The MIL-100-900 also shows a decrease
in surface area and pore volume, but not as high as MIL-53-900 and MIL-68-900. That is because the
trimesic acid ligands in the spatial configuration of MIL-100 (Al) help to resist high temperature to keep
structural stability, which is commonly observed during the pyrolysis of ZIF series materials [19,53] . To obtain
enough pore space for Se loading and high surface area for electrochemical reactions, the samples from
three Al-MOFs calcined at 800 °C showing the highest BET surface area and the pore volume were selected
for Se confinement.

The morphologies of MOF-derived porous carbon materials are examined by SEM and TEM [Figure 1].
The morphology of MIL-53-800 remained intact after calcination compared with MIL-53 (Al)
[Supplementary Figure 3A]and shows a massive porous structure with particle size ranging from several
hundred nanometers to several micrometers [Figure 1A]. The TEM image [Figure 1B and its inset] presents
the particle size and some empty space surrounded by carbon, which is consistent with the SEM result.
Figure 1C confirmed the continuous amorphous carbon network with a microporous structure. The
morphology of MIL-68-800 shows that the pyrolysis generates a highly porous structure [Figure 1D and E].
Compared with the original TEM morphology of MIL-68 (Al) in Supplementary Figure 3B, the big particle
size of MIL-68-800 was composed of small carbon aggregates of 10-20 nm, where exists an interparticle
mesopores structure. The micropores of MIL-68-800 can be observed in Figure 1F. MIL-100 (Al) showed a
typical octahedron crystal structure with a size of 200-500 nm [Supplementary Figure 3C], and this
morphology is still maintained after pyrolysis at 800 °C [Figure 1G]. Both mesopores and micropores were
observed in Figure 1H and I. Consequently, the original morphologies can still be maintained after the
pyrolysis of MOFs under appropriate conditions.