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

Integrating a bioelectrochemical system with CO2 electroreduction (CO2ER) 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 CO2ER catalyst with iron bonded to nitrogen atoms (Fe-Nx) 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 CO2-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-Nx based carbon materials for CO2ER. 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(cat)(-1) h(-1).

Automated summary

The CO2ER catalyst Fe SA-NC, prepared through a unique Fe-Nx molecular-confined pyrolysis strategy, exhibited superior performance in terms of low overpotential, small Tafel slope, and high Faradaic efficiency. Experimental results and theoretical calculations both demonstrated the crucial role of Fe-N-4 sites in enhancing reaction kinetics.