Strategies for designing metal–organic frameworks with superprotonic conductivity

Superprotonic Conductivity of MOFs Confining Zwitterionic Sulfamic Acid as Proton Source and Conducting Medium

“…The study revealed the acidity of 10HSA@MOF‐808‐( b SA) 2 to be −0.2≤ H 0 (p K a )≤+2.8, which is very similar to pure HSA (p K a =1) (Figure S23). However, the proton conductivity achieved in MOFs using acidic guests with moderate acidity (such as H 3 PO 4 ) is in an order of 10 −2 S cm −1 [20] . Furthermore, the acidity of reported four SA − bound MOF‐808 (MOF‐808‐( b SA) 4 ) is much higher (−11.4≤ H 0 (p K a )≤−8.1) but exhibits a relatively low proton conductivity value of 7.89×10 −2 S cm −1 at 95 % RH and 60 °C [51] .…”

“…However, the proton conductivity achieved in MOFs using acidic guests with moderate acidity (such as H 3 PO 4 ) is in an order of 10 À 2 S cm À 1 . [20] Furthermore, the acidity of reported four SA À bound MOF-808 (MOF-808-(bSA) 4 ) is much higher (À 11.4 � H 0 (pK a ) � À 8.1) but exhibits a relatively low proton conductivity value of 7.89 × 10 À 2 cm À 1 at 95 % RH and 60 °C. [51] Hence, it can be stated that although acidity plays an important role in achieving high proton conductivity but is not the sole reason for very high proton conductivity in 10HSA@MOF-808-(bSA) 2 .…”

“…Several strategies have been applied to achieve superprotonic conductivity in MOFs [20–22] through functionalization, grafting or encapsulation of proton sources such as acids [23, 24] or molecules with proton hoping sites (PHS), such as imidazole, [25] histamine, [26] triazole, [27] or ionic liquids [28] that can work as proton‐conducting medium. In most superprotonic conductive MOFs with high (≈10 −1 S cm −1 order) proton conductivity, highly acidic molecules such as H 2 SO 4 are being used in an ex situ fashion as proton sources [29–37] .…”

“…[14][15][16] Therefore, proton conductivity in MOFs has been achieved mainly by targeting the increase of either proton sources (mostly acids) or the amount of proton-conducting media to promote a continuous hydrogen-bonded pathway for efficient proton transport, as evidenced by the humidity-dependent proton conductivity increase in most MOFs, through better pore filling. [17][18][19] Several strategies have been applied to achieve superprotonic conductivity in MOFs [20][21][22] through functionalization, grafting or encapsulation of proton sources such as acids [23,24] or molecules with proton hoping sites (PHS), such as imidazole, [25] histamine, [26] triazole, [27] or ionic liquids [28] that can work as proton-conducting medium. In most superprotonic conductive MOFs with high ( � 10 À 1 S cm À 1 order) proton conductivity, highly acidic molecules such as H 2 SO 4 are being used in an ex situ fashion as proton sources.…”

Syntheses and High Proton Conductivities of Two 3D Zr(IV)/Hf(IV)-MOFs from Furandicarboxylic Acid

“…As pointed out by Kitagawa and Lim, the papers about such kinds of MOFs have radically increased from a few/per year in 2006 to 140/per year in 2020 . According to the latest results of our search from the Web of Science, the number of related papers is close to 300/year in 2021 and 2022, indicating that the investigation on these MOFs is gaining more and more attention and becoming a new highlight in the field of energy as well as electrochemistry. − Up to now, several reviews have summarized and outlined the preparation strategies of proton-conducting MOFs, proton-conducting enhancement strategies, − post-modification strategies, proton-conducting MOFs based on different organic ligands (e.g., phosphonic acid, sulfonic acids, − carboxylic acids, aza-carboxylic acids, etc. ), and proton-conducting MOFs based on different metal nodes in a more comprehensive and in-depth manner. , …”