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<p>Recent studies have reported a variety of Mn bipyridine complexes as efficient electrochemical catalysts for the CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR). However, the catalytic reduction mechanism remains ambiguous, particularly regarding the influence of terminal bipyridine substituents and the role of weak acids on catalytic performance. In this work, density functional theory (DFT) calculations and microkinetic modeling (MKM) are carried out to gain intuitive thermodynamics and kinetics insights into catalytic CO<sub>2</sub>RR behaviors of [(bpy)Mn(CO)<sub>3</sub>]<sup>+</sup> (abbreviated as <b>[bpyMn]</b>) and [(mesbpy)Mn(CO)<sub>3</sub>]<sup>+</sup> (abbreviated as <b>[mesbpyMn]</b>), focusing on product selectivity control. The 2e-reduction of Mn(I) to active Mn(0)-mesbpy(−1) in a spin-polarized singlet state is associated with ligand-to-metal electron transfer induced by axial ligand departure (LMET-ALD), which is attributed to the low reduction potential of <b>[mesbpyMn]</b>. The complete cycles of producing CO, formic acid (FA), and H<sub>2</sub> show that the rate-determining steps are the second protonation and hydride formation, respectively. Structural similarity of transition states of hydride formation from various acids demonstrates that there is a correlation between the energy barrier for FA production and p<i>K</i><sub>a</sub> of acids. The terminal substituent <b>[mes]</b> serves a dual function: (1) elevating the singly occupied molecular orbital (SOMO) energy level through increasing the contribution of the empty <i>π</i>(mebpy), which favors electron transfer for hydride formation; and (2) acting as an “energy bridge” to mediate the degeneration of <i>d</i><sub><i>xy</i></sub> (Mn) with fully occupied <i>π</i>(mesbpy) orbitals, facilitating the second protonation step. These findings provide a comprehensive understanding of Mn-bipyridinecatalyzed CO<sub>2</sub>RR, offering valuable insights for the design of improved molecular catalysts for CO<sub>2</sub>RR.</p>

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Thermodynamics and kinetics insights into product selectivity in the electrochemical CO2 reduction catalyzed by manganese bipyridine complexes

  • 期刊论文

  • 发表日期：

    2026年1月4日

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  • Fei Wang,
  • Jingjing Zhang,
  • Aibing Chen,
  • Josep M. Poblet

摘要

Recent studies have reported a variety of Mn bipyridine complexes as efficient electrochemical catalysts for the CO2 reduction reaction (CO2RR). However, the catalytic reduction mechanism remains ambiguous, particularly regarding the influence of terminal bipyridine substituents and the role of weak acids on catalytic performance. In this work, density functional theory (DFT) calculations and microkinetic modeling (MKM) are carried out to gain intuitive thermodynamics and kinetics insights into catalytic CO2RR behaviors of [(bpy)Mn(CO)3]+ (abbreviated as [bpyMn]) and [(mesbpy)Mn(CO)3]+ (abbreviated as [mesbpyMn]), focusing on product selectivity control. The 2e-reduction of Mn(I) to active Mn(0)-mesbpy(−1) in a spin-polarized singlet state is associated with ligand-to-metal electron transfer induced by axial ligand departure (LMET-ALD), which is attributed to the low reduction potential of [mesbpyMn]. The complete cycles of producing CO, formic acid (FA), and H2 show that the rate-determining steps are the second protonation and hydride formation, respectively. Structural similarity of transition states of hydride formation from various acids demonstrates that there is a correlation between the energy barrier for FA production and pKa of acids. The terminal substituent [mes] serves a dual function: (1) elevating the singly occupied molecular orbital (SOMO) energy level through increasing the contribution of the empty π(mebpy), which favors electron transfer for hydride formation; and (2) acting as an “energy bridge” to mediate the degeneration of dxy (Mn) with fully occupied π(mesbpy) orbitals, facilitating the second protonation step. These findings provide a comprehensive understanding of Mn-bipyridinecatalyzed CO2RR, offering valuable insights for the design of improved molecular catalysts for CO2RR.