Jimmyc., Chinese University of Hong KongYu and Huang Bolong, The Hong Kong Polytechnic University, et alIt is reported that an asymmetrically coupled heteronuclear photocatalyst can overcome the bottleneck of low selectivity of C2+ products caused by the slow C-C coupling process in CO2 reduction reaction (CO2RR).The catalyst contains single atoms Ni and Co supported on TiO2 and exhibits 71% acetic acid selectivity during photocatalytic CO2 RR.
DFT calculations reveal the high photocatalytic activity of Nico-TiO2. The Ni and COSA sites are located at the surface Ti sites and show a consistent coordination environment, confirming the bonding and antibonding orbitals in NiCo-TiO2 close to the Fermi level (EF). It is worth noting thatThe surface bonding orbitals are dominated by Ni and COSA sites with strong orbital coupling, indicating a small electron transfer energy barrierPartial density of states (PDOS) further confirmed the efficient electron transfer in Nico-TiO2. Ni-3D and Co-3D orbitals show high electron densities near EF, indicating that they are the main active sites for efficient electron transfer
At the same time, these orbitals compensate for the band gap of electron transfer in the original TiO2, thereby improving the efficiency of electron transfer;The Ti-3D orbital and O-2P orbital cover the Ni-3D and Co-3D orbitals to ensure the stable electronic structure of the active site during photocatalysis.
In contrast,The original TiO2 exhibits an obvious potential barrier between the valence band maximum (VBM) and the conduction band minimum (CBM), and the large energy barrier leads to the decrease of the photocatalytic activity of CO2RR。The metals Ni and Nio exhibit different PDoS, in which the Ni-3D orbital clearly crosses the EF and EG-T2G** appearsIn Ni-TiO2 and Nico-TiO2, the Ni-3D orbital is more similar to NiO, while for metallic Co, the 3D orbital exhibits wide coverage and crosses EF. In COO, the Co-3D orbital shows a distinct peak near EF with the presence of EG-T2G**. The electronic structure confirms that both the CO and NISA sites show an oxidized structure, which is attributed to bonding to adjacent oxygen sites in TiO2.
The activation of C-C coupling further confirmed the important role of the dual-active site. C-C coupling is energetically easier on Nico-TiO2 due to the facilitation of the adjacent SA site. In contrast, the Sa sites in Co-TiO2 and Ni-TiO2 result in an energy barrier of 0 for C-C coupling50 and 042EV, explaining the absence of C2 products in photocatalysis。For the energy change of CO2RR, the study found that HCOO- had a higher energy barrier of 125EV, which is not conducive to the formation of acetic acid;The formation of CHO* and COH* shows a smaller energy barrier compared to the formation of CO and subsequent C-C coupling, resulting in lower amounts of C1 product generation for CH4 and CH3OH.
For the C2 pathway, CHCHO* is 0The high energy barrier of 86EV greatly limits the generation of CH3CH2OH and C2H4. In contrast, the generation of CH3COOH shows a very favorable reaction trend with a total energy release of -374 EV, revealing a high yield of CH3COOH on the experiment.
guangri jia, mingzi sun et al. asymmetric coupled dual-atom sites for selective photoreduction of carbon dioxide to acetic acid. adv. funct. mater. 2022, 2206817