Metal‐Complex/Semiconductor Hybrid Photocatalysts and Photoelectrodes for CO₂ Reduction Driven by Visible Light

Abstract

CO2 reduction to carbon feedstocks using heterogeneous photocatalysts is an attractive means of addressing both climate change and the depletion of fossil fuels. Of particular importance is the development of a photosystem capable of functioning in response to visible light, which accounts for the majority of the solar spectrum, representing a kind of artificial photosynthesis. Hybrid systems comprising a metal complex and a semiconductor are promising because of the excellent electrochemical (and/or photocatalytic) activity of metal complexes during CO2 reduction and the ability of semiconductors to efficiently oxidize water to molecular O2. Here, the development of hybrid photocatalysts and photoelectrodes for CO2 reduction in combination with water oxidation is described.

Molecular Junctions on Polymeric Carbon Nitrides with Enhanced Photocatalytic Performance

“…The time curves of CO and H 2 evolution of BINA 4 ‐CN were also tested (Figure S18). The accumulated product of a 5 h reaction was 41.5 μmol, representing a catalytic turnover number of 41.5 with respect to Co(bpy) 3 2+ , revealing the catalytic nature and good stability of the reaction …”

“…The accumulatedp roduct of a5hr eaction was 41.5 mmol, representing ac atalytic turnover number of 41.5 with respectt o Co(bpy) 3 2 + ,r evealing the catalytic nature and good stability of the reaction. [23] In summary,w eh ave developed an efficient andr obust photocatalyst system for H 2 generation and CO 2 reduction by linking am olecular catalyst (MC), Co(bpy) 3 2 + ,w ith light-harvesting/electron-donating polymeric carbon nitride (PCN) nanosheets. The resultsshowedt hat PCN nanosheets covalently connected with Co(bpy) 3 2 + exhibited ah igh H 2 activity with ar ate of 8.8 mmol h À1 and ah igh CO 2 reduction activity with a rate of 8.1 mmol h À1 ,w hich are 12.5 and 16 times higher than those of the unboundCo(bpy) 3 2 + and PCN, respectively.Photoluminescence and electrochemical measurements revealed that the excellent photocatalytic activity of Co(bpy) 3 2 + /BINA-CN assembly was attributed to the high efficiency interfacial electron transfer from PCN to Co(bpy) 3 2 + .U ndoubtedly,t he close contact and strong interaction between photosensitizer and MC plays akey role in the hybrid system for photocatalytic water splitting and photocatalytic CO 2 reduction.…”

Selective CO2 reduction into formate using Ln–Ta oxynitrides combined with a binuclear Ru(II) complex under visible light

“…Catalytic conversion of anthropogenic CO 2 into energy rich chemicals with the aid of visible light energy could be a potential means of addressing the shortage of carbon resources and global warming issues [1][2][3][4][5][6][7][8]. Hybrid materials that consist of visible-light-absorbing semiconductors and (photo)catalytically active metal complexes have been reported to function as good photocatalysts for CO 2 reduction under visible light [2,7,8]. For example, a binuclear Ru(II) complex having a photosensitizer and catalyst units in one molecule (RuRu', see Fig.…”

“…1) works as an efficient homogeneous photocatalyst for CO 2 reduction, but requires a relatively strong electron donor for operation because of its low photooxidation ability. Combining the RuRu' with a visible-light-absorbing semiconductor that has strong oxidation ability enables one to accomplish CO 2 reduction even with the use of a weak electron donor [7]. In some photoelectrochemical systems constructed from a similar binuclear metal complex and a semiconductor, sacrificial reagent-free CO 2 reduction has been achieved [9][10][11].…”

“…Focusing on the semiconductor component, various semiconductor materials including TaON [12], Ta 3 N 5 [13], GaN:ZnO [14], and Li 2 LaTa 2 O 6 N [15], C/N polymers [16] and Pb 2 Ti 2 O 5.4 F 1.2 [17] have been reported to become active semiconductor components for the Z-scheme CO 2 reduction with the aid of RuRu'. It has been also shown that for efficient CO 2 reduction, the potential of the conduction band minimum (CBM) of a semiconductor applied to the Z-scheme system has to be more negative than -1.3 V (vs Ag/AgNO 3 ), which is equivalent to the excited-state oxidation potential of the photosensitizer unit in RuRu', because suppression of back electron transfer from RuRu' to the semiconductor is essential [7]. Although several non-oxide materials have been reported to work as the semiconductor component in the hybrid photocatalyst with RuRu' for visible-light-driven CO 2 reduction, it is still important to search for a new semiconductor material for the application.…”