Electrochemical conversion of CO2 is a promising way to utilize this virtually free feedstock material. Carbon-supported Co(II) porphyrins are excellent catalysts for electroreduction of CO2 to CO in aqueous medium, however their efficient immobilization on the electrode surface is still a challenge to answer. In this work we present covalent ligation of Co(II) tetraphenylporphyrin (CoTPP-cov) to carbon cloth as a superior heterogenisation tool which improves electron transfer rate onto catalytically active centre and maximizes amount of electrochemically active catalyst. Formation of covalent link with carbon surface was attained via electroreduction of porphyrin diazonium salt followed by metalation with Co(OAc)2 in organic solvent. CoTPP-cov exhibits excellent CO2 reduction rate with TOF of 10.8 and CO faradic yield of 69% at the potential of -1.05 V vs NHE outperforming noncovalent analogue by far. Cumulative TON of 3.9 105 observed in a prolonged electrolysis is one of the highest to date. Electrokinetic studies revealed that the charge transfer onto catalytically active centre plays a key role at low overpotentials and π-conjugated linker with the support facilitates charge transfer through the electrode-catalyst interface. Proton relay effect does not appear in case of Co(II) porphyrins in strong contrast to Fe(III) analogues excluding possibility of intermediate protonation being rate-determining step. Variation of substituents around porphyrin core showed that tetraphenylporphyrinate is the most active catalyst. Competitive hydrogen evolution was found to take place on carbon rather than on the porphyrin itself. Based on experimental data, we proposed plausible mechanism implying rate determining step to be dependent on the electrode potential.

Improvement of Co porphyrin CO2 electroreduction activity via its covalent immobilization on the surface of carbon cloth electrodes

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.