Noncovalent Immobilization of Pentamethylcyclopentadienyl Iridium Complexes on Ordered Mesoporous Carbon for Electrocatalytic Water Oxidation

Grayson Johnson,Sen Zhang,William A Goddard,Ana M Geer,Diane A Dickie,Christopher Webber,Cheng-Jun Sun,Hua Zhou,Chang Liu,Charles B Musgrave,T Brent Gunnoe

doi:10.1002/smsc.202100037

Abstract

The attachment of molecular catalysts to conductive supports for the preparation of solid‐state anodes is important for the development of devices for electrocatalytic water oxidation. The preparation and characterization of three molecular cyclopentadienyl iridium(III) complexes, Cp*Ir(1‐pyrenyl(2‐pyridyl)ethanolate‐κO,κN)Cl (1) (Cp* = pentamethylcyclopentadienyl), Cp*Ir(diphenyl(2‐pyridyl)methanolate‐κO,κN)Cl (2), and [Cp*Ir(4‐(1‐pyrenyl)‐2,2′‐bipyridine)Cl]Cl (3), as precursors for electrochemical water oxidation catalysts, are reported. These complexes contain aromatic groups that can be attached via noncovalent π‐stacking to ordered mesoporous carbon (OMC). The resulting iridium‐based OMC materials (Ir‐1, Ir‐2, and Ir‐3) were tested for electrocatalytic water oxidation leading to turnover frequencies (TOFs) of 0.9–1.6 s−1 at an overpotential of 300 mV under acidic conditions. The stability of the materials is demonstrated by electrochemical cycling and X‐ray absorption spectroscopy analysis before and after catalysis. Theoretical studies on the interactions between the molecular complexes and the OMC support provide insight onto the noncovalent binding and are in agreement with the experimental loadings.

Highlights

IntroductionTo transform the current energy landscape, it is increasingly have focused on the use of chemical oxidants (e.g., NaIO4 and ceric ammonium nitrate),[9,11,12,13,14,15,16,17,18,19,20,21,22,23,24] with perhaps fewer studies on electrochemically driven water oxidation.[25,26,27,28,29] For example, Crabtree and coworkers identified important to find a clean, renewable energy source to replace fos- the tris-aqua complex [Cp*Ir(H2O)3]2 (A) (Cp* 1⁄4 pentamethylsil fuels.[1] Artificial photosynthesis by water splitting has been cyclopentadienyl) and the complex bearing the 2-(2-pyridyl)-
Proposed as a promising alternative, and one approach is to 2-propanolate ligand, B, as molecular water oxidation catalyst use electrical power produced from renewable energy sources precursors at pH 7 and 1.7 V versus normal hydrogen electrode
Rational design of the structure of molecular catalysts is demonstrated as a methodological advance for integrating homogenous catalyst on heterogeneous support interface

Summary

Introduction

To transform the current energy landscape, it is increasingly have focused on the use of chemical oxidants (e.g., NaIO4 and ceric ammonium nitrate),[9,11,12,13,14,15,16,17,18,19,20,21,22,23,24] with perhaps fewer studies on electrochemically driven water oxidation.[25,26,27,28,29] For example, Crabtree and coworkers identified important to find a clean, renewable energy source to replace fos- the tris-aqua complex [Cp*Ir(H2O)3]2 (A) (Cp* 1⁄4 pentamethylsil fuels.[1] Artificial photosynthesis by water splitting has been cyclopentadienyl) and the complex bearing the 2-(2-pyridyl)-. Proposed as a promising alternative, and one approach is to 2-propanolate ligand, B, as molecular water oxidation catalyst use electrical power produced from renewable energy sources precursors at pH 7 and 1.7 V versus normal hydrogen electrode. Sun Advanced Photon Source Argonne National Laboratory Lemont, IL 60439, USA

Methods

Results

Conclusion