Vacancy engineering activates π-d conjugated coordination polymers for CO2 reduction: an ab initio study

Abstract

π-d conjugated coordination polymers (CCPs) represent an emerging class of two-dimensional (2D) materials with distinctive physicochemical properties. Their extended π-d conjugation and the presence of redox-active metal centers endow these materials with promising potential for energy storage applications. However, their applicability in energy conversion processes, particularly in the electrochemical reduction of CO₂ (CO₂RR) as a pathway for carbon mitigation, remains largely unexplored. Identifying efficient and selective catalysts for CO₂RR is critical for advancing sustainable CO₂ utilization technologies. In this work, we investigate the CO₂RR performance of pristine and nitrogen-vacancy-engineered M-tetraaminobenzoquinone (M-TABQ; M = Mn, Fe, Co) π-d CCPs using spin-polarized density functional theory (DFT) calculations. Pristine M-TABQ systems exhibit negligible CO₂ activation, whereas nitrogen-vacancy-engineered M(N_v)-TABQ structures show pronounced CO₂ activation. All vacancy-engineered systems demonstrate strong adsorption of the *COOH reaction intermediate, with Mn(N_v)-TABQ exhibiting the strongest binding affinity. Thermodynamic analysis reveals CO selectivity across all investigated systems, with Mn(N_v)-TABQ exhibiting the lowest overpotential of 1.08 V. In addition, linear scaling relationships illustrate correlations between ΔG_*COOH and ΔG_*CO, as well as between ΔG_*CHO and ΔG_*CO, suggesting coupled adsorption energetics across key reaction intermediates. These findings highlight the critical role of vacancy engineering in enabling π-d CCPs to function as efficient and tunable catalysts for CO₂ electroreduction, while providing practical design principles that can guide experimental researchers in the rational synthesis and optimization of functional π-d CCP electrocatalysts.