(Photo)electrocatalytic Versus Heterogeneous Photocatalytic Carbon Dioxide Reduction

Abstract

The present review summarizes some of the main results achieved in electrochemical, photocatalytic, and (photo)‐electrocatalytic systems for the reduction of carbon dioxide. After a preliminary survey of the electrocatalytic and photocatalytic systems in terms of materials used, efficiencies, operating conditions, and product distribution, it is shown how the combination of the two approaches affords often higher efficiency than the single technologies and allows better control of the product distribution. In fact, the peculiar energetic distribution at the interface of irradiated semiconductors under opportune electrical bias enables enhancement of the spatial separation of the photogenerated charges and minimization of the external energy required in electrochemical applications. Even though the efficiency of CO2 reduction is still far away from being industrially appealing, in some cases the photoelectrocatalytic systems are promising tools to be further investigated for sustainable green chemistry based CO2 utilization. The aim of this review is to examine the strengths and the weaknesses of the different approaches considering that sometimes one of the three methods can be used more successfully than the others, depending on the desired product(s) and the materials used as photocatalysts or as the (photo)electrode.

Photoelectrochemical CO2 Reduction Products Over Sandwiched Hybrid Ga2O3:ZnO/Indium/ZnO Nanorods

“…On the basis of the CO 2 reduction of major products, the simplified CO 2 reduction mechanism is depicted in Figure 8 ( Sohn et al, 2017 ; Wang et al, 2019 ; Song et al, 2020 ; Prabhu et al, 2020 ; Sun et al, 2021 ; da Silva Freitas et al, 2021 ; Ješić et al, 2021 ; Ochedi et al, 2021 ; Chen et al, 2021 ; Bellardita et al, 2021 ). In an NaHCO 3 electrolyte saturated with CO 2 , two processes are initially involved; H + + e − → H ad and CO 2 + H + + e − → HOOC ad .…”

“…In an NaHCO 3 electrolyte saturated with CO 2 , two processes are initially involved; H + + e − → H ad and CO 2 + H + + e − → HOOC ad . The surface H ad is liberated as gaseous H 2 via H ad + H + + e − → H 2 or H ad + H ad → H 2 ( Sohn et al, 2017 ; Wang et al, 2019 ; Prabhu et al, 2020 ; Song et al, 2020 ; Bellardita et al, 2021 ; Chen et al, 2021 ; da Silva Freitas et al, 2021 ; Ješić et al, 2021 ; Ochedi et al, 2021 ; Sun et al, 2021 ). This process became pronounced when the thickness of GZO was increased.…”

“…Inversely, the formate and H 2 production processes became reduced under light irradiation. CH 4 and C 2 H 2 were minor products and the net reactions are written as CO 2 + 8H + + 8e − → CH 4 + 2H 2 O and 2CO 2 + 10H + + 10e − → C 2 H 2 + 4H 2 O, respectively ( Sohn et al, 2017 ; Wang et al, 2019 ; Song et al, 2020 ; Prabhu et al, 2020 ; Bellardita et al, 2021 ; Chen et al, 2021 ; da Silva Freitas et al, 2021 ; Ješić et al, 2021 ; Ochedi et al, 2021 ; Sun et al, 2021 ). Some surface O≡C ad species may transform into HOC ad and H x C ad .…”

“…Producing recycled energy products using abundant CO 2 is another challenging project for future solutions for energy and environment ( Sohn et al, 2017 ; Wang et al, 2019 ; Prabhu et al, 2020 ; Song et al, 2020 ; Bellardita et al, 2021 ; Chen et al, 2021 ; da Silva Freitas et al, 2021 ; Ješić et al, 2021 ; Ochedi et al, 2021 ; Sun et al, 2021 ). Electrochemical CO 2 reduction is a promising method, and the development of electrodes is a major goal for approaching practical application in the industry.…”

Alternating Current Techniques for a Better Understanding of Photoelectrocatalysts

“…Usually, the applied potential is used to enhance the rate of the reaction which accelerates the accumulation of the product at the inner Helmholtz layer and the amount of product formed near the interface. The diffusion layer (δ) in PEC is thicker than that of PC; further, the photocorrosion encountered commonly in PC can also easily be controlled by the applied external bias in which it can be compared to that of cathodic protection. , In every aspect from the rate of H 2 production to the separation of produced H 2 , PEC is always better than PC, which is why PEC is intensively interrogated for possible scale up to enable large scale H 2 production these days with concurrent pollutant treatments and or value-added products synthesis. Perceiving such a mightiness of PEC, we provide our perspective on how well we could further understand the performance of catalysts used in PEC using electroanalytical and photoelectroanalytical techniques that use alternating current (AC) as the main source of perturbation for probing the PEC interfaces.…”