Photoelectrochemical Water Splitting Reaction System Based on Metal-Organic Halide Perovskites

Abstract

In the development of hydrogen-based technology, a key challenge is the sustainable production of hydrogen in terms of energy consumption and environmental aspects. However, existing methods mainly rely on fossil fuels due to their cost efficiency, and as such, it is difficult to be completely independent of carbon-based technology. Electrochemical hydrogen production is essential, since it has shown the successful generation of hydrogen gas of high purity. Similarly, the photoelectrochemical (PEC) method is also appealing, as this method exhibits highly active and stable water splitting with the help of solar energy. In this article, we review recent developments in PEC water splitting, particularly those using metal-organic halide perovskite materials. We discuss the exceptional optical and electrical characteristics which often dictate PEC performance. We further extend our discussion to the material limit of perovskite under a hydrogen production environment, i.e., that PEC reactions often degrade the contact between the electrode and the electrolyte. Finally, we introduce recent improvements in the stability of a perovskite-based PEC device.

Keywords: metal-organic halide perovskite; passivation; photoelectrochemical reaction; water splitting.

Figure 1

Intrinsic crystal structure and optical properties of perovskite materials. (a) A typical perovskite crystal structure. (b) Crystal structure of B cation and X anion (B cation is located at the octahedral site of X anion). (c) Crystal structure of A cation and X anion (A cation is located at the octahedron site of X anion. (d) UV-vis spectra for the APbI₃ perovskites formed, where A is either cesium (Cs), methylammonium (MA) or formamidinium (FA). (e) UV-vis absorption spectra FAPbI_yBr_3-y perovskites. (f) Temperature dependence of the absorption coefficient of methylammonium lead iodide (MAPbI₃) extracted from photoluminescence (PL) spectra. (g) Near-bandgap absorption and photoluminescence spectra at room temperature mixed-organic perovskites [39,40,43,44].

Figure 2

Photoelectrochemical processes involved in (a) water reduction and (b) water oxidation. (c) Proposed mechanistic pathways for H₂ generation at a metal center of Mⁿ⁺. (d) Two mechanistic pathways to form an O–O bond for the molecular catalysts. (ref. [61]).

Figure 3

The operating mechanism of perovskite-based photoelectrochemical device (a) n–i–p configuration, (b) p–i–n configuration.

Figure 4

Examples of the n–i–p configuration of perovskite-based PEC cells. (a) Schematic illustration of the photoelectrochemical test of a Ni-coated perovskite photoanode in a PEC cell using a standard three-electrode system and energy diagram of each material. (b) Photocurrent densities of the compact TiO₂ layer (black curve) and CH₃NH₃PbI₃ photoanodes without (blue curve) and with Ni surface layer (red curve). Comparison of photocurrent densities of CH₃NH₃PbI₃ photoanodes (with and without Ni surface layer). (c) Schematic illustration of the integrated photoelectrolysis cell with perovskite photoelectrode. (d) Voltammogram of perovskite photoanode with 10 μm Ni catalyst under simulated illumination (0.7 sun; red curve), under dark (dashed curve), and on metallic Ni electrode (blue curve) as reference. Electrolyte was K-borate solution (pH 9.2) and 1.0 M KOH solution (pH 14) respectively [79,80].

Figure 5

Examples of the n–i–p configuration of perovskite-based PEC cells. (a) Schematic illustration of the perovskite photoanode for PEC water splitting in a standard three-electrode system. (b) Voltammogram of perovskite photoanodes with SC paint layer (red curve) and without SC paint layer (black curve) under simulated illumination and in the dark (green curve), with the CC paste electrode (blue curve) as a reference. (c) Schematic illustration of perovskite photoanode device used CsPbBr₃, TiO₂ (electron collecting), m-carbon (hole collecting). (d) Linear sweep voltammetry (LSV) of a TiO₂|CsPbBr₃|m-c|GS and a TiO₂|CsPbBr₃|m-c|GS|WOC measured at a scan rate of 20 mV s⁻¹, in a 0.1 M KNO₃ electrolyte solution with pH 2.5 (pH adjusted with H₂SO₄) [81,82].

Figure 6

Examples of the p–i–n configuration of perovskite-based PEC cells. (a) Material and electronic configuration of the perovskite-based photocathode. (b) Linear sweep voltammetry of the perovskite-based photocathode at a scan rate of 5 mV s⁻¹. (c) Schematic illustration of the sandwich-like CH₃NH₃PbI₃ photocathode for PEC H₂ evolution in a standard three-electrode system. (d) Current density–potential curves for the Pt–Ti/CH₃NH₃PbI₃ photocathode [83,84].

Figure 7

Examples of the p–i–n configuration of perovskite-based PEC cells. (a) Schematic representation of a CsPbBr₃-based photocathode. (b) Performance of all-inorganic LHP photocathode under AM 1.5 G simulated sunlight conditions. Current density–potential curves. (c) Cross-sectional schematic of a photocathode stabilized against corrosion in 0.5 M H₂SO₄(aq) via a hybrid ETL comprising PC₆₁BM with TiO₂ deposited by ALD. Photogenerated electrons are conducted through the TiO₂ to the Pt catalysts, where electrons are used to reduce protons to hydrogen. (d) Photoelectrochemical behavior of the photocathode in the dark and under continuous and chopped illumination reveals the time scale (ms) and magnitude (>10 mA/cm²) of the photocurrent response [85,86].

Figure 8

Degradation pathway of metal-organic halide perovskite materials in water.

Figure 9

DFT calculation of perovskite’s degradation pathway in water. (a) Formation enthalpies of vacancy point and pair defects as a function of the Fermi energy (E_F) under I-poor (Pb-, MA-rich) conditions (left) and I-rich (Pb-, MA-poor) conditions (right). (b) Band alignment and thermodynamic transition levels in MAPbI₃, water-intercalated MAPbI₃_H₂O, and monohydrate MAPbI₃·H₂O, where deep-lying Pb 5d levels are used as a reference for the VBM and CBM of each phase [92].

Figure 10

Cases of improving stability by passivation. (a) Chronoamperometric trace recorded at an applied potential of 0 V vs. RHE. An aqueous buffer solution (0.1 M borate, pH 8.5), chopped solar light irradiation (AM 1.5 G, 100 mW/cm², λ > 400 nm). (b) Stability analysis at 0 V_RHE. (c) Current vs. time graph of perovskite photoanode under illumination (0.7 sun) and bias (1.3 V vs. RHE) in KOH solution (pH 14). (d) Faradaic efficiency for hydrogen evolution on the Pt–Ti/CH₃NH₃PbI₃ photocathode with Pt and SCE as the counter and reference electrodes, respectively, in 0.5 M H₂SO₄ solution [80,83,84,85].

Figure 11

Cases of improving stability by passivation. (a) Current versus time graph of a perovskite photoanode at an applied potential of 1.23 V versus RHE under simulated AM 1.5 G solar illumination (100 mW/cm²) in 1 M KOH solution. (b) Photocurrent density versus time of a photocathode with a nominally 15 nm thick Pt catalyst under continuous illumination. The electrode potential was held at 0 V vs. RHE during continuous illumination of 0.5 Sun. (c) Chronoamperometric trace recorded at an applied potential of 1.23 V_RHE in KOH electrolyte solution at pH 12.5, under chopped simulated solar light irradiation (AM 1.5 G, 100 mW/cm²) [81,82,86].

Figure 12

Cases of improving stability by using inorganic perovskites. (a) The photocurrent density curve of the Cs₂SnI₆ compound using a three-electrode system with a 0.3 M NaCl electrolyte and the inserted picture shows the working principle of the system. (b) PEC water splitting performance of a Ba₂Bi_1.4Nb_0.6O₆ photoanode. LSV curves of PEC water oxidation in 1 m KOH solution of Ba₂Bi_1.4Nb_0.6O₆ film and Co₃O₄ coated Ba₂Bi_1.4Nb_0.6O₆ film (Pt, as counter electrode and cathode). (c) Durability test of the Ba₂Bi_1.4Nb_0.6O₆ film at 1.23 V (vs. RHE) [98,99].