Manufacturing technologies
Technology for energy production, Environmental materials

Development of function-Integrated catalytic system forsmall molecule conversion
Division of Applied Chemistry, Graduate School of Engineering
Associate Professor Mio Kondo
Researchmap https://researchmap.jp/mio_kondo?lang=en

Abstract
Four-electron oxidation of water (2H2O → O2 + 4H+ + 4e−) is an
important reaction for suppling the protons and electrons required
to generate reduced products (i.e., chemical energy) from abundant resources in a clean manner. In this study, inspired by the natural water oxidation system, we hypothesized that the integration of
catalytic centers and hole transporters into one material could be apromising strategy for obtaining efficient catalytic system for wateroxidation. Based on this strategy, a polymer-based catalytic system(Poly-1) was constructed by assembling catalytic center and holetransporter units. Poly-1 exhibited high hole transporting ability,and can promote water oxidation with a high faradaic efficiency
and a low overpotential. This performance of Poly-1 is of the highest class compared to the relevant systems.

which has a catalytic center surrounded by hole transporters. Ourstudy is a significant example of a molecule-based catalytic systemthat mimics the key features of the OEC. Collectively, the present
study offers a novel concept for obtaining efficient catalytic system
for water oxidation.

Manufacturing technologies▍ Background & Results
Demand for a sustainable society and clean energy production
has increased in recent years. In this context, the construction ofcatalytic system for artificial photosynthesis has attracted considerable attention. Water oxidation is regarded as a key reaction in
artificial photosynthesis, and the efficient catalyst for the reaction
is highly required. In this study, a novel approach for developing
an artificial catalytic system for water oxidation was demonstrated.
Inspired by the natural photosynthesis, we constructed an artificial
water oxidation system that have a catalytic center surrounded byhole transporting units. A metal-complex-based precursor composed of a tetranuclear cobalt moiety as a catalytic center andcarbazole ligands, was newly designed and synthesized. By theelectrochemical polymerization of the complex, carbazole moietiesof the complex dimerized to form biscarbazole moieties, which canact as hole transporter, and the polymer-based material (Poly-1)
was successfully obtained. Electrochemical impedance spectra ofPoly-1 and the cobalt cubane complex without biscarbazole moieties revealed that charge transfer ability is largely enhanced due tothe biscarbazole moieties embedded in Poly-1. Controlled potential electrolysis of Poly-1 resulted in the evolution O2 as confirmed.
The performance of our catalytic system (the overpotential (η =413 mV) and Faradaic efficiency (91.5%)) was found to be of thebest class compared to the relevant Co complex-based catalyticsystems. Note that the catalytic activity is almost suppressed when
the complex without biscarbazole moieties was used as a catalyst.
These results clearly demonstrate that the integration of two functions into one material is a key to develop the efficient water oxidation system.

▍ Significance of the research and Future perspective
In nature, the water oxidation is efficiently catalyzed by a metal-complex-based catalyst (the oxygen-evolving complex, OEC)
surrounded by hole-transporting amino acid residues. However, inartificial systems, there is no example of the water oxidation system

P a t e n tIwami, Hikaru; Kondo, Mio; Masaoka, Shigeyuki et al. Electrochemical Polymerization Provides a Function-Integrated System for Water Oxidation. Angew.
Chem. Int. Ed. 2021; 60: 5965-5969. doi: 10.1002/anie.202015174
UR
L https://www.chemistryviews.org/details/ezine/11284936/Artificial_Water_Oxidation_System.html
K e y w o r d artificial photosynthesis, metal complex, small molecule conversion
Tr e a t i s e