Electrochemical CO2 reduction from NH4HCO3 in ammonia-based carbon capture: Comparison of external and in-situ carbon sources

Abstract

Combining ammonia-based carbon capture technology with electrocatalytic reduction powered by excess energy from power plants enables efficient use of captured carbon products while avoiding energy-intensive CO₂ release and compression process. Revealing the impact of in-situ carbon sources on reaction activity and product selectivity is crucial in the direct electrocatalytic reduction of ammonium bicarbonate (NH₄HCO₃). This study compares the reduction performance of in-situ and external carbon source systems via potentiostatic reduction on Ag-based electrodes in Ar- or CO₂-saturated bicarbonate electrolytes. We found that high NH₄HCO₃ concentrations in the in-situ system enhance CO₂ and intermediate adsorption on Ag-based catalysts, achieving CO production efficiencies comparable to external carbon sources, with a peak CO Faradaic efficiency of 62.2 % at −0.6 V and a current density of 9.84 mA·cm⁻² at −0.8 V. NH₄⁺ has a larger ionic radius, which increases local CO₂ concentration and proton availability, enhancing CO yield and catalytic efficiency over K⁺ in in-situ carbon source systems. It also promotes hydrogen evolution reactions (HER), enabling efficient syngas production via dual-reaction synergy. We hope these findings provide theoretical support and guidance for system control strategies in the ammonia-based carbon capture coupled with electrocatalytic conversion technology.