Thousand-fold increase in O2 electroreduction rates with conductive MOFs.
Ruperto G Mariano1, Oluwasegun J Wahab2, Joshua A Rabinowitz3
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
ACS Central Science
|August 1, 2022
Summary
Molecular materials, like conductive metal-organic frameworks (MOFs), show high oxygen reduction reaction (ORR) activity when mass transport limitations are overcome. This research reveals their true potential, exceeding previous estimates by orders of magnitude.
Area of Science:
- Electrochemistry
- Materials Science
- Catalysis
Background:
- Conductive metal-organic frameworks (MOFs) possess high active site densities but exhibit low reported oxygen reduction reaction (ORR) activity.
- Previous ORR activity measurements for MOFs were limited by multiscale mass transport challenges, leading to underestimation of their intrinsic catalytic performance.
Purpose of the Study:
- To investigate and overcome the multiscale mass transport limitations hindering the performance of molecular materials in electrocatalysis.
- To accurately determine the intrinsic electrocatalytic activity of conductive MOFs for the oxygen reduction reaction (ORR).
Main Methods:
- Utilized gas diffusion electrolyses and nanoelectrochemical measurements to address oxygen transport limitations.
- Employed scanning electrochemical cell microscopy to enforce maximal mass transport rates.
Main Results:
- The intrinsic ORR activity of Ni3(HITP)2, a model 2D conductive MOF, was found to be underestimated by over three orders of magnitude.
- When supported on a gas diffusion electrode (GDE), Ni3(HITP)2 achieved ORR activities exceeding -150 mA cm-2.
- Under optimal mass transport conditions, Ni3(HITP)2 demonstrated ORR current densities over -1200 mA cm-2 and significantly higher mass activity compared to GDEs.
Conclusions:
- Precise control over multiscale mass transport is critical for achieving high current densities in molecular electrocatalysts.
- Molecular materials, particularly conductive MOFs, possess significant untapped potential for high-performance electrocatalysis once transport limitations are addressed.
