Computational Evaluation of N₈ Polynitrogen-Stabilized Single-Atom Catalysts for CO₂ Reduction

Single-atom catalysts (SACs) show significant promise for the electrochemical CO₂ reduction reaction (CO₂RR) owing to their unique structures and properties. Moreover, strong metal-support interactions mean that their activity is highly tunable by the substrate. Recently, a novel N₈ polynitrogen (PN) chain was successfully synthesized by a cyclic voltammetry approach; it has highly active lone pairs and acts as an electron donor, allowing for the enhancement of SACs stabilized on it, as evidenced by previous work showing its propensity toward selective hydrogenation of acetylene to ethylene. In this work, we use density functional theory (DFT) calculations to investigate the CO₂RR to C1 products (carbon monoxide, formic acid, methane, and methanol) on Pd and Ni SACs supported on N₈ PN. First, we find that under the traditional proton-coupled electron transfer mechanism, formic acid is the most likely product on both Pd-N₈ and Ni-N₈. We also investigate a pathway in which H₂ first preferentially adsorbs to the N₈ PN chain and splits, causing a spontaneous reconfiguration of PN and allowing for facile proton transfer. In both cases, if CO is formed, further reduction to methanol is likely. Finally, methane production is highly unfavorable due to the large energy barriers required to form the *C intermediate. Overall, this work provides insights into an important set of reactions on a novel, highly active catalyst material and demonstrates how the selectivity of the CO₂RR can be tuned by altering the SAC chemistry and substrate.