Erbium Single Atom Composite Photocatalysts for Reduction of CO₂ under Visible Light: CO₂ Molecular Activation and 4f Levels as an Electron Transport Bridge

Abstract

It is still challenging to design a stable and efficient catalyst for visible‐light CO2 reduction. Here, Er3+ single atom composite photocatalysts are successfully constructed based on both the special role of Er3+ and the special advantages of Zn2GeO4/g‐C3N4 heterojunction in the photocatalysis reduction of CO2. Especially, Zn2GeO4:Er3+/g‐C3N4 obtained by in situ synthesis is not only more conducive to the tight junction of Zn2GeO4 and g‐C3N4, but also more favorable for g‐C3N4 to anchor rare‐earth atoms. Under visible‐light irradiation, Zn2GeO4:Er3+/g‐C3N4 shows more than five times enhancement in the catalytic efficiency compared to that of pure g‐C3N4 without any sacrificial agent in the photocatalytic reaction system. A series of theoretical and experimental results show that the charge density around Er, Ge, Zn, and O increases compared with Zn2GeO4:Er3+, while the charge density around C decreases compared with g‐C3N4. These results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO2 molecular activation of Er3+ single atom and 4f levels as electron transport bridge are fully exploited. The pattern of combining single‐atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.

Single-atom catalysts for photocatalytic energy conversion

“…The authors have attributed the greatly improved photocatalytic activity of MOF-525-Co to the boosted separation efficiency of electron-hole pairs in porphyrin units after the Co introduction. Since then, many research works of photocatalytic CO 2 reduction into CO or CH 4 fuel gas have been reported over various single-atom photocatalysts along with the production of H 2 , where H 2 O provides the hydrogen resource 59,[74][75][76]114,[155][156][157][158][159][160][161][162][163][164][165][166]. Li et al have created a unique Fe-N 4 O site supported on nitrogen-rich carbon for photocatalytic CO 2 reduction via a facile top-down strategy (Figures 10A-…”

Towards single‐atom photocatalysts for future carbon‐neutral application

“…Rare‐earth metals also show broad application prospects in CO 2 reduction 194 . Wang et al 195 prepared a single‐atom Er 3+ composite photocatalyst (Zn 2 GeO 4 :Er 3+ /g‐C 3 N 4 ), and without a sacrificial agent, the photocatalytic efficiency is five times higher than that of g‐C 3 N 4 . Through XPS and DFT, the authors proved that the 4f energy level of Er 3+ can serve as an electron transfer bridge at the interface between Zn 2 GeO 4 and g‐C 3 N 4 , thereby promoting the activation of CO 2 (Figure 14F).…”

“…Rare-earth metals also show broad application prospects in CO 2 reduction. 194 Wang et al 195 prepared a single-atom Er 3+ composite photocatalyst (Zn 2 GeO 4 :Er 3+ / g-C 3 N 4 ), and without a sacrificial agent, the photocatalytic efficiency is five times higher than that of g-C 3 N 4 .…”

Single-atom-based catalysts for photoelectrocatalysis: challenges and opportunities

“…Similarly, Ag, Au, Pt, Co and Er SAs supported by g-C 3 N 4 , MOFs/covalent organic frameworks (COFs), TiO 2 , CdS and other semiconductor nanomaterials could boost the photocurrent density and the total photocatalytic performance compared to their counterparts without single metal active sites. 30,49,[75][76][77][78][79][80][81][82][83] From these few cases, SACs have demonstrated their potentials in PEC applications. The rational deployment and fundamental investigation of SACs in PEC deserve further study.…”