Recent Advances in Solar-Driven Carbon Dioxide Conversion: Expectations versus Reality

Abstract

Solar-driven carbon dioxide (CO₂) conversion to fuels and high-value chemicals can contribute to the better utilization of renewable energy sources. Photosynthetic (PS), photocatalytic (PC), photoelectrochemical (PEC), and photovoltaic plus electrochemical (PV+EC) approaches are intensively studied strategies. We aimed to compare the performance of these approaches using unified metrics and to highlight representative studies with outstanding performance in a given aspect. Most importantly, a statistical analysis was carried out to compare the differences in activity, selectivity, and durability of the various approaches, and the underlying causes are discussed in detail. Several interesting trends were found: (i) Only the minority of the studies present comprehensive metrics. (ii) The CO₂ reduction products and their relative amount vary across the different approaches. (iii) Only the PV+EC approach is likely to lead to industrial technologies in the midterm future. Last, a brief perspective on new directions is given to stimulate discussion and future research activity.

Figure 1

Number of papers published in the years of 2014–2019. Data collected from Web of Science Core Collection on 2020-03-06; topic: (photo* or solar) and (CO₂ or carbon dioxide) and (conversion or reduction).

Figure 2

Schematic illustration of (a) biophotosynthetic, (b) photothermal, (c) microbial-photoelectrochemical, (d) photosynthetic and photocatalytic (PS/PC), (e) photoelectrochemical (PEC), and (f) photovoltaic plus electrochemical (PV+EC) approaches for CO₂ conversion.

Figure 3

(a) Schematic illustration of N-bromosuccinimide treated cobalt oxide nanoparticles and (b) CH₄ formation rate over catalysts with different surface treatments. Reprinted with permission from ref (99). Copyright 2019 Royal Society of Chemistry. (c) Comparison of CO₂ reduction performances of different catalysts. Reprinted with permission from ref (102). Copyright 2019 Wiley-VCH. (d) Schematic illustration of CO₂ reduction using a Ru complex/C₃N₄ hybrid photocatalyst and (e) the turnover number of HCOOH production as a function of irradiation time using different photocatalysts and solvents. Reprinted with permission from ref (103). Copyright 2019 Wiley-VCH. (f) The turnover number of CO evolution as a function of irradiation time over modified iridium(III) photocatalyst. Reprinted from ref (104). Copyright 2017 American Chemical Society.

Figure 4

Statistical analysis of PS/PC CO₂ conversion studies: (a) product distribution, (b) normalized formation rate distribution, and (c) normalized formation rate distribution of different products.

Figure 5

(a) SEM image of reduced mesoporous Bi nanosheets. Reprinted with permission from ref (105). Copyright 2018 Wiley-VCH. (b) Full cell configuration containing In_0.4Bi_0.6-coated perovskite photocathode. Reprinted from ref (106). Copyright 2019 American Chemical Society. (c) Schematic of the PEC CO₂ reduction process involving protected Cu₂O photocathodes and a Re-based molecular catalyst. Reprinted with permission from ref (107). Copyright 2015 Royal Society of Chemistry. (d) Changes in E_cell and HCOOH production with a wired CuFeO₂/CuO and Pt couple under illumination without external bias. Reprinted with permission from ref (109). Copyright 2015 Royal Society of Chemistry. (e) The scheme of photoanode-dark anode configuration for CO₂ conversion. Reprinted from ref (9). Copyright 2016 American Chemical Society.

Figure 6

Statistical analysis of PEC CO₂ conversion studies: (a) product distribution, (b) FE distribution, (c) current density (under 1 Sun) distribution, and (d) FE distribution of different products.

Figure 7

(a) Energy diagram of each part in a redox-medium-assisted system. Reprinted with permission from ref (113). Copyright 2018 Springer Nature. (b) Illustration of a wire connection between the triple-junction cell and GDE cell and (c) CO Faradaic efficiency and solar-to-fuel efficiency over 20 h duration. Reprinted from ref (114). Copyright 2020 American Chemical Society.

Figure 8

Statistical analysis of PV+EC CO₂ conversion studies: (a) product distribution, (b) SFE distribution, and (c) SFE distribution of different products.

Figure 9

Comparisons of (a) product distribution, (b) light-to-fuel conversion efficiency, and (c) longest measurements in PS/PC, PEC, and PV+EC systems.

Figure 10

Typical timescale of different photoinduced processes in semiconductors, together with the methods that are employed to monitor them. PL, photoluminescence; IMPS/IMVS, intensity-modulated photocurrent/photovoltage spectroscopy.