Halide Perovskites for Photoelectrochemical Water Splitting and CO2 Reduction: Challenges and Opportunities

Abstract

Photoelectrochemical water splitting and CO₂ reduction provide an attractive route to produce solar fuels while reducing the level of CO₂ emissions. Metal halide perovskites (MHPs) have been extensively studied for this purpose in recent years due to their suitable optoelectronic properties. In this review, we survey the recent achievements in the field. After a brief introduction to photoelectrochemical (PEC) processes, we discussed the properties, synthesis, and application of MHPs in this context. We also survey the state-of-the-art findings regarding significant achievements in performance, and developments in addressing the major challenges of toxicity and instability toward water. Efforts have been made to replace the toxic Pb with less toxic materials like Sn, Ge, Sb, and Bi. The stability toward water has been also improved by using various methods such as compositional engineering, 2D/3D perovskite structures, surface passivation, the use of protective layers, and encapsulation. In the last part, considering the experience gained in photovoltaic applications, we provided our perspective for the future challenges and opportunities. We place special emphasis on the improvement of stability as the major challenge and the potential contribution of machine learning to identify the most suitable formulation for halide perovskites with desired properties.

Figure 1

Schematics illustrating the band gap energetics involved in the water oxidation and CO₂ reduction reactions in PEC and the role of the activation catalyst in thermodynamic and kinetic terms. The symbols “*” and “‡” represent the activated state and the transition state of CO₂ by adsorption on the cathode surface, respectively. Reproduced with permission from ref (68). Copyright 2019 American Chemical Society.

Figure 2

(a) Unit cell of deal cubic ABX₃ perovskite, and (b) ABX₃ cubic perovskite crystal structure. Reproduced with permission from ref (112). Copyright 2018 Wiley. (c) Crystal structure of A₂B′BX₆ double perovskites. Orange for B, gray for B′, turquoise for A, and brown for X. Reproduced with permission from ref (113). Copyright 2016 American Chemical Society. (d) Crystal structure of the A_aB_bX_x halide rudorffites. Reproduced with permission from ref (104). Copyright 2017 Wiley. (e) Crystal structure of 0D A₃B₂X₉ nonperovskite. (f) 2D layered structure of A₃B₂X₉ vacancy-ordered perovskite. Orange for A, green for X, and blue for B. Reproduced with permission from ref (109). Copyright 2015 American Chemical Society. (g) UV–vis absorption spectra of mixed halide lead perovskite (MAPb(I_1–xBr_x)₃) films. The numbers 1–7 denote samples corresponding with increasing bromine content (X) within the films. Reproduced with permission from ref (81). Copyright 2014 Royal Society of Chemistry.

Figure 3

(a) SEM cross-sectional image of the MAPbI₃-based photoanode. (b) Photocurrent density vs time graph of perovskite photoanode under illumination (0.7 sun) and bias (1.0 V vs SHE). Reproduced with permission from ref (131). Copyright 2016 American Chemical Society. (c) Schematic illustration (left) and photo (right) of the perovskite photoanode configuration for PEC O₂ evolution. (d) Top left: Photocurrent density; top middle: applied bias photon-to-current conversion efficiency (ABPE), and top right: faradaic efficiency of the FAMAPbI₃-based photoanode. Bottom: Photocurrent density vs time graph under 1 sun illumination at 1.23 V_RHE of the FAMAPI₃-based photoanode. Reproduced with permission from ref (134). Copyright 2022 American Chemical Society. (e) Amperometric I–t curves of the CsPbBr_xI_3–x NC/carbon nanotube at −0.4 V. Reproduced with permission from ref (135). Copyright 2019 Royal Society of Chemistry. (f) Current densities of different halide perovskite nanocrystal-based PEC systems. Reproduced with permission from ref (137). Copyright 2021 Wiley-VCH.

Figure 4

(a) Photocurrent density vs applied bias graph of the MAPbI₃-based photocathode. (b) Photocurrent density vs time graph recorded at 0 V_RHE. Reproduced with permission from ref (121). Copyright 2016 Nature. (c) Schematic structure and the cross-sectional SEM image of the CsPbBr₃-based photocathode. Reproduced with permission from ref (141). Copyright 2018 Royal Society of Chemistry.

Figure 5

(a) CB and VB positions of various halide perovskite compositions, with respect to both vacuum and NHE levels. The CO₂ redox levels are also present. Reproduced with permission from ref (21). Copyright 2020 American Chemical Society. (b) PEC setup of the In_0.4Bi_0.6-coated halide perovskite photocathode in a standard three-electrode system. The photocathode is illuminated from the FTO side. The direction of electron or hole flow in the cell is shown. (c) Stability test of the perovskite/In_0.4Bi_0.6 photocathode under 1 sun illumination at −0.6 V vs RHE. Reproduced with permission from ref (150). Copyright 2019 American Chemical Society.

Figure 6

Screening flowchart employed by Gao et al. for lead-free inorganic double perovskites. Adopted from ref (196). Copyright 2021 Elsevier.