An integrated bioelectrochemical system coupled CO2 electroreduction device based on atomically dispersed iron electrocatalysts

Abstract

Integrating a bioelectrochemical system with CO 2 electroreduction (CO 2 ER) can achieve recovery of resources and conversion of value-added chemicals, but it still faces challenge of high overpotential and poor selectivity. Herein, we report a CO 2 ER catalyst with iron bonded to nitrogen atoms (Fe-N x ) anchored hierarchical porous carbon (Fe SA-NC) by a molecular-confined pyrolysis strategy. Owing to the high surface area and atomic-level Fe-N 4 sites, Fe SA-NC possessed superior CO 2 -to-CO conversion performance with a low overpotential of 90 mV, a small Tafel slope of 92 mV dec −1 , and high Faradaic efficiency of 95.9% at −0.5 V, superior to almost all previously reported Fe-N x based carbon materials for CO 2 ER. Experimental results manifested the atomic-level Fe-N 4 sites in carbon frameworks with a single Fe atom coordinating four N atoms. Theoretical calculations revealed Fe-N 4 sites weaken the free energy for the formation of *COOH intermediate, and the short Fe-C bond length in the structure of *COOH absorbed on Fe-N 4 sites accelerated the electron transfer from Fe-N 4 centers to *COOH, thus boosting the reaction kinetics. An integrated device with cathodic Fe SA-NC and bioanode can recover energy and carbon resource from wastewater, delivering maximum current and CO production rate of 1.54 ± 0.05 mA and 33.66 ± 0.58 mmol g −1 cat h −1 . An integrated bioelectrochemical system with CO 2 electroreduction device for wastewater treatment based on an atomically dispersed Fe-N 4 site is developed. • The Fe SA-NC displayed outstanding electrocatalytic CO 2 -to-CO conversion performance. • Highly exposed Fe-N 4 sites weakened the free energy for formation of *COOH intermediate. • The short Fe‐C‒bond length in the structure of *COOH absorbed on Fe-N 4 sites accelerated electron transfer. • A novel integrated bioelectrochemical system coupled CO 2 ER device was constructed.