posted on 2024-01-19, 14:03authored byElli Vichou, Yanis Adjez, Yun Li, Maria Gómez-Mingot, Marc Fontecave, Carlos M. Sánchez-Sánchez
The activity and selectivity of molecular catalysts for
the electrochemical
CO2 reduction reaction (CO2RR) are influenced
by the induced electric field at the electrode/electrolyte interface.
We present here a novel electrolyte immobilization method to control
the electric field at this interface by positively charging the electrode
surface with an imidazolium cation organic layer, which significantly
favors CO2 conversion to formate, suppresses hydrogen evolution
reaction, and diminishes the operating cell voltage. Those results
are well supported by our previous DFT calculations studying the mechanistic
role of imidazolium cations in solution for CO2 reduction
to formate catalyzed by a model molecular catalyst. This smart electrode
surface concept based on covalent grafting of imidazolium on a carbon
electrode is successfully scaled up for operating at industrially
relevant conditions (100 mA cm–2) on an imidazolium-modified
carbon-based gas diffusion electrode using a flow cell configuration,
where the CO2 conversion to formate process takes place
in acidic aqueous solution to avoid carbonate formation and is catalyzed
by a model molecular Rh complex in solution. The formate production
rate reaches a maximum of 4.6 gHCOO– m–2 min–1 after accumulating a total
of 9000 C of charge circulated on the same electrode. Constant formate
production and no significant microscopic changes on the imidazolium-modified
cathode in consecutive long-term CO2 electrolysis confirmed
the high stability of the imidazolium organic layer under operating
conditions for CO2RR.