Theoretical insight on why N-vacancy promotes the selective CO2 reduction to ethanol on NiMn doped graphitic carbon nitride sheets

• Published in: Applied surface science 2022-09, Vol.595, p.153527, Article 153527
• Main Authors: Roongcharoen, Thantip, Mano, Poobodin, Jitwatanasirikul, Thanadol, Sikam, Pornsawan, Butburee, Teera, Takahashi, Kaito, Namuangruk, Supawadee
• Format: Article
• Language: English
• Subjects: C-C coupling; C2 product; CO2 reduction; Electronic structure; Graphitic carbon nitride
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2022.153527

[Display omitted] •MnNi doped on pristine and vacancy g-C3N4 for CO2 reduction are studied.•Vacancy can firmly trap NiMn which promotes the selective CC coupling to ethanol.•ICOHP along the reaction path reveals the evolution of the CC coupling process.•The most preferable C-C coupling pathway is found for *CO + *CHO to *COCHO.•Ni and Mn show fully-filled 3d10 and half-filled 3d5 configurations, respectively.•NiMn at vacancy site donates an excess electron to adsorbates during C-C coupling. To develop promising dual atom catalysts (DACs) for enhancing valuable C2+ products in CO2 electroreduction (CO2RR), we need a molecular level understanding of the interaction between reaction intermediates, metal atoms, and substrates. NiMn on graphitic carbon nitride (g-C3N4) was experimentally reported to be an efficient CO2RR catalyst. Here, we studied the origin of its activity. We used integrated crystal orbital Hamiltonian population (ICOHP) analysis along the reaction coordinate of the carbon–carbon (C-C) coupling reaction to understand how the electronic structures of NiMn doped on pristine (NiMn@g-C3N4) and N-vacancy graphitic carbon nitride (NiMn@V-g-C3N4) affect the reaction. NiMn@V-g-C3N4 selectively produces ethanol at low limiting potential −0.55 V and a low kinetic barrier (0.78 eV) for *CO+*CHO→*COCHO. At this step, electron donation from the NiMn in the N-vacancy to the adsorbate is essential. Tricoordinated Ni atom at the vacancy site has a stable oxidation state 0 with a fully filled 3d10 configuration, while Mn atom takes +2 oxidation state with a half-filled 3d5 configuration. ICOHP shows that these electronic configurations result in a moderate binding strength of key intermediates near the Ni while facilitating the flexible change in Mn-C to Mn-O binding for producing *COCHO, thus promoting the formation of ethanol.