Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal-Organic Framework

Hyunho Noh, Chung Wei Kung, Ken Ichi Otake, Aaron W. Peters, Zhanyong Li, Yijun Liao, Xinyi Gong, Omar K. Farha*, Joseph T. Hupp

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

102 Scopus citations

Abstract

The Zr6-based metal-organic framework NU-1000 was successfully functionalized with candidate catalysts - MoSx units - via SIM (solvothermal deposition in MOFs) of molybdenum(VI), followed by reaction with H2S gas. The structure of the material, named MoSx-SIM, was characterized spectroscopically and through a single-crystal X-ray diffraction measurement. These measurements and others established that the catalyst is monometallic, with mixed oxygen and sulfur coordination, and that it forms from a MOF-node-supported molybdenum-based cluster featuring only oxy ligands. Notably, the formal potential for the MOF-grafted complex, like that for the metal-sulfur active site of hydrogenase, is nearly coincident with the formal potential for the hydrogen couple. Its effective concentration within the mesoporous MOF is several hundred millimolar, and its porous-framework-based immobilization/heterogenization obviates the need for aqueous solubility as a condition for use as a well-defined catalyst. MoSx-SIM was evaluated as an electrocatalyst for evolution of molecular hydrogen from aqueous acid. Although the MoSx-functionalized framework exhibits catalytic behavior, the highly insulating nature of the support inhibits high electrocatalytic performance. Introduction of an archetypal redox mediator (RM), methyl viologen (MV2+), resulted in more than 20-fold enhancement in its catalytic performance on a turnover frequency basis, implying efficient RM-assisted electron transfer to otherwise electrochemically non-addressable MoSx moieties. Electrochemical kinetic studies with additional viologens as mediators reveal an unexpected square-root dependence of overall reaction rate on mediator concentration, as well as sensitivity to the strength of RM•+ as a reductant. These observations, together with observations of potential-dependent H/D isotope effects and potential-dependent pH effects, provide useful insights into the catalysis mechanism and help to explain how the MOF-affixed monometallic catalyst can effectively catalyze a two-electron reduction reaction, i.e., hydrogen evolution from acidified water.

Original languageEnglish (US)
Pages (from-to)9848-9858
Number of pages11
JournalACS Catalysis
Volume8
Issue number10
DOIs
StatePublished - Oct 5 2018

Funding

This work was supported by the ANSER Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC0001059. H.N. gratefully acknowledges support from the Ryan Fellowship program of the Northwestern University International Institute of Nanotechnology. C.-W.K. acknowledges support from the Postdoctoral Research Abroad Program (105-2917-I-564-046) sponsored by the Ministry of Science and Technology (Taiwan). We thank Prof. Michael R. Wasielewski and his lab group for the use of a gas chromatograph. This work made use of the IMSERC, J. B. Cohen X-ray Diffraction, EPIC, and KECK II facilities of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Materials Research Collaborative Access Team (MRCAT, Sectors 10ID) operations are supported by the U.S. Department of Energy and the MRCAT member institutions. This work was supported by the ANSER Center, an Energy Frontier Research Center funded by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC0001059. H.N. gratefully acknowledges support from the Ryan Fellowship program of the Northwestern University International Institute of Nanotechnology. C.-W.K. acknowledges support from the Postdoctoral Research Abroad Program (105-2917-I-564-046) sponsored by the Ministry of Science and Technology (Taiwan). We thank Prof. Michael R. Wasielewski and his lab group for the use of a gas chromatograph. This work made use of the IMSERC, J. B. Cohen X-ray Diffraction, EPIC, and KECK II facilities of Northwestern University's NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois through the IIN. Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Materials Research Collaborative Access Team (MRCAT, Sectors 10ID) operations are supported by the U.S. Department of Energy and the MRCAT member institutions.

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry

Fingerprint

Dive into the research topics of 'Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal-Organic Framework'. Together they form a unique fingerprint.

Cite this