TY - JOUR

T1 - Enhancement of Proton Conductivity in Nonporous Metal-Organic Frameworks

T2 - The Role of Framework Proton Density and Humidity

AU - Pili, Simona

AU - Rought, Peter

AU - Kolokolov, Daniil I.

AU - Lin, Longfei

AU - Da Silva, Ivan

AU - Cheng, Yongqiang

AU - Marsh, Christopher

AU - Silverwood, Ian P.

AU - García Sakai, Victoria

AU - Li, Ming

AU - Titman, Jeremy J.

AU - Knight, Lyndsey

AU - Daemen, Luke L.

AU - Ramirez-Cuesta, Anibal J.

AU - Tang, Chiu C.

AU - Stepanov, Alexander G.

AU - Yang, Sihai

AU - Schröder, Martin

PY - 2018/11/13

Y1 - 2018/11/13

N2 - Owing to their inherent pore structure, porous metal-organic frameworks (MOFs) can undergo postsynthetic modification, such as loading extra-framework proton carriers. However, strategies for improving the proton conductivity for nonporous MOFs are largely lacking, although increasing numbers of nonporous MOFs exhibit promising proton conductivities. Often, high humidity is required for nonporous MOFs to achieve high conductivities, but to date no clear mechanisms have been experimentally identified. Here we describe the new materials MFM-550(M), [M(HL1)], (H4L1 = biphenyl-4,4′-diphosphonic acid; M = La, Ce, Nd, Sm, Gd, Ho), MFM-550(Ba), [Ba(H2L1)], and MFM-555(M), [M(HL2)], (H4L2 = benzene-1,4-diphosphonic acid; M = La, Ce, Nd, Sm, Gd, Ho), and report enhanced proton conductivities in these nonporous materials by (i) replacing the metal ion to one with a lower oxidation state, (ii) reducing the length of the organic ligand, and (iii) introducing additional acidic protons on the MOF surface. Increased framework proton density in these materials can lead to an enhancement in proton conductivity of up to 4 orders of magnitude. Additionally, we report a comprehensive investigation using in situ 2H NMR and neutron spectroscopy, coupled with molecular dynamic modeling, to elucidate the role of humidity in assembling interconnected networks for proton hopping. This study constructs a relationship between framework proton density and the corresponding proton conductivity in nonporous MOFs, and directly explains the role of both surface protons and external water in assembling the proton conduction pathways.

AB - Owing to their inherent pore structure, porous metal-organic frameworks (MOFs) can undergo postsynthetic modification, such as loading extra-framework proton carriers. However, strategies for improving the proton conductivity for nonporous MOFs are largely lacking, although increasing numbers of nonporous MOFs exhibit promising proton conductivities. Often, high humidity is required for nonporous MOFs to achieve high conductivities, but to date no clear mechanisms have been experimentally identified. Here we describe the new materials MFM-550(M), [M(HL1)], (H4L1 = biphenyl-4,4′-diphosphonic acid; M = La, Ce, Nd, Sm, Gd, Ho), MFM-550(Ba), [Ba(H2L1)], and MFM-555(M), [M(HL2)], (H4L2 = benzene-1,4-diphosphonic acid; M = La, Ce, Nd, Sm, Gd, Ho), and report enhanced proton conductivities in these nonporous materials by (i) replacing the metal ion to one with a lower oxidation state, (ii) reducing the length of the organic ligand, and (iii) introducing additional acidic protons on the MOF surface. Increased framework proton density in these materials can lead to an enhancement in proton conductivity of up to 4 orders of magnitude. Additionally, we report a comprehensive investigation using in situ 2H NMR and neutron spectroscopy, coupled with molecular dynamic modeling, to elucidate the role of humidity in assembling interconnected networks for proton hopping. This study constructs a relationship between framework proton density and the corresponding proton conductivity in nonporous MOFs, and directly explains the role of both surface protons and external water in assembling the proton conduction pathways.

KW - COORDINATION POLYMERS

KW - WATER-MOLECULES

KW - DIFFUSION

KW - SORPTION

KW - SITES

UR - http://www.scopus.com/inward/record.url?scp=85056604299&partnerID=8YFLogxK

U2 - 10.1021/acs.chemmater.8b02765

DO - 10.1021/acs.chemmater.8b02765

M3 - Article

AN - SCOPUS:85056604299

VL - 30

SP - 7593

EP - 7602

JO - Chemistry of Materials

JF - Chemistry of Materials

SN - 0897-4756

IS - 21

ER -