Recent Advances in Heterogeneous Photocatalytic CO₂ Conversion to Solar Fuels

Abstract

As a promising approach to achieving two objectives with one strategy, photocatalytic CO 2 conversion for C1/C2 "solar fuels" production can provide a package solution to the current global warming and growing energy demand by using inexhaustible solar energy and increasing atmospheric CO 2 . Although numerous efforts have been made to enhance the CO 2 conversion efficiency through developing photocatalysts and CO 2 reduction systems in recent years, some challenges still remain in improving the activity and selectivity of the CO 2 photoreduction reactions. This review gives an overview of fundamental aspects and recent research advances of heterogeneous photocatalytic CO 2 conversion systems in the last 3 years, and the catalysts are categorized as one-step excitation semiconductor systems, one-step excitation photosensitized semiconductor systems, and two-step excitation hybrid systems such as semiconductor heterojunction and Z-scheme systems. Also, some suggestions are given for further confirming that the carbon-containing "solar fuels" are derived from CO 2 rather than from the possible carbonaceous impurities in the photocatalytic system, because most of the papers cited in this review have not demonstrated that CO 2 is the actual carbon source for photoreduction through 13 CO 2 labeling or other techniques. Lastly, a short perspective on the challenges and new directions in this field is proposed, which would be of great interest for the further improvements of activity and selectivity of the CO 2 reduction reactions.

One‐Pot Synthesis of Cu‐Nanocluster‐Decorated Brookite TiO2Quasi‐Nanocubes for Enhanced Activity and Selectivity of CO2 Photoreduction to CH4

“…The present results demonstratet hat brookite TiO 2 would be ap otential effective photocatalyst for CO 2 photoreduction, and that Cu nanoclusters can act as an inexpensive and efficient co-catalyst alternative to the commonly used noble metals to improvet he photoactivity and selectivity for CO 2 reduction to CH 4 . not very good for photocatalytic CO 2 reduction because the high activity of H 2 generation may consumea ne xcesso fp hotogenerated electrons, and then leads to ad ecreased activity of CO 2 reduction to solar fuels.…”

“…As for Cu-BTN,t he V O sites can be neutralized by small amountso fC u 2 + instead of Ti 4 + ,w hich then leads to the disappearance of the IR peak at % 3726 cm À1 ,a nd the obviously enhanced HCO 3 À adsorption capacities compared to the pristine BTN and the Cu/BTN would be ab enefit to the selective CH 4 generation. Namely, the Cu-BTN products can promote the selectiveg eneration of CH 4 as compared to CO due to the surfaceo xygen vacancies and CO 2 /H 2 Oa dsorption behaviors differing from the pristine BTN and the Cu/BTN.…”

“…Although the two Cu-loaded BTN products have similar Cu species, particles ize, dispersity and loading content on BTN surfaces, the one-pot decorated Cu-BTN product shows significantly enhanced photoactivity and selectivity for CO 2 reduction to CH 4 as compared to the pristine BTN and the post-deposited Cu/BTN. Further investigations indicate that the resultantC u-BTN product showing selectiveg eneration of CH 4 as comparedt oC Oc an be due to the surface oxygen vacancy amount and CO 2 /H 2 Oa dsorption behavior differing from the pristineB TN and the post-deposited Cu/BTN. It is believed that this studydemonstrates somei nsight into non-noblem etallic Cu and brookite TiO 2 for promising low-cost photocatalytic CO 2 conversion applications.…”

“…is the irradiationt ime; c CO and c CH 4 are the produced CO and CH 4 concentration, respectively. As can be seen from Figure 7a,p ristine BTN showsr elatively poor production rates of CO/CH 4 (3.46/0.79 mmol g À1 h À1 )w ith an overall photoactivity (TCEN) of 13.2 mmol g À1 h À1 .A fter being decorated with metallic Cu nanoclusters, the corresponding Cu-BTN products exhibit as harply enhanced overall photoactivity (TCEN) with selective CH 4 production,e ven thought he CO production rate shows an unobvious change. For instance, 0.5 %C u-BTN gives CO/CH 4 production rates of 3.03/15.34 mmol g À1 h À1 (Figure 7a)w ith TCEN of 128.7 mmol g À1 h À1 (Figure 7b).…”

“…[3,4,11] The XPS spectra( Figure 2) indicate that all the regional XPS spectra of O1 s, Ti 2p and Cu 2p for1 .5 %C u-BTN after 10 hi rradiation show no obvious peak shift, demonstrating the relatively good stabilityo ft he presentC u-BTN during the CO 2 photoreduction processes. Figure S4 depicts the CO/ CH 4 production activities of 1.5 %C u-BTN in six consecutive runs of accumulatively 12 h( each run is 2h irradiation, and then the sample was dried at 70 8Cfor the next run).…”