BiVO₄/Cs₂PtI₆ Vacancy-Ordered Halide Perovskite Heterojunction for Panchromatic Light Harvesting and Enhanced Charge Separation in Photoelectrochemical Water Oxidation

Abstract

Photoelectrochemical water oxidation is a challenging reaction in solar water splitting due to the parasitic recombination process, sluggish catalytic activity, and electrode stability. Oxide semiconductors are stable in an aqueous medium but show huge charge carrier recombination. Creation of a heterojunction is found to be effective for extracting the photogenerated electrons/holes before they recombine to the ground state. In this work, we created a heterojunction of BiVO4 with vacancy-ordered halide perovskite Cs2PtI6 and used it as a photoanode in PEC water oxidation. Cs2PtI6 is the only halide perovskite that is found to be extremely stable even in strong acids and bases. We utilized the stability of this material and its panchromatic visible light absorption property and made the first unprotected heterojunction dual-absorber photoanode for PEC water oxidation. At 1.23 V (vs RHE), bare BiVO4 gave 0.6 mA cm–2 photocurrent density, whereas the BiVO4/Cs2PtI6 heterojunction shows 0.92 mA cm–2. With the addition of IrO x cocatalyst, at 1.23 V (vs RHE), the heterojunction gave ∼2 mA cm–2. To obtain 2 mA cm–2 photocurrent, pure BiVO4 requires 560 mV overpotential, whereas the heterojunction requires 250 mV. The increase in the photocurrent arises from the increase in the efficiency of charge separation from BiVO4 to Cs2PtI6 and the complementary absorption offered by the latter.

Acid‐ and Base‐Stable Cs2Pt(Cl,Br)6 Vacancy‐Ordered Double Perovskites and Their Core–Shell Heterostructures for Solar Water Oxidation

“…[38] In our previous reports, we have also shown that varying the A-site from Cs 2 PtI 6 (r Cs ¼ 1.88 Å, r Pt ¼ 0.625 Å) to Rb 2 PtI 6 (r Rb ¼ 1.72 Å) or varying B-site to Cs 2 SnI 6 (r Sn ¼ 0.69 Å) provide similar diffraction pattern but with a shift in peak to higher 2θ value for smaller A or B-site element. [23,25] The diffraction patterns of chloride-and bromide-based compounds were also found to be matching with the Joint Committee on Powder Diffraction Standards data (Figure S1, Supporting Information).…”

“…In our previous work, we have shown that Cs 2 PtI 6 is stable even in harsh acidic or basic conditions and can be employed as a photoanode for PEC water oxidation. [ 23,25 ] Similarly, a recent report on Cs 2 PtBr 6 nanocrystals also showed good PEC performance displaying a current density of 0.335 mAcm −2 . [ 31 ] These reports on PEC cells employed intrinsic materials without mixed halides or metal‐sites and have already shown excellent performance.…”

“…However, certain vacancy-ordered double perovskites such as Cs 2 PtI 6 and Cs 2 PdBr 6 showed intrinsic water stability without any protection layer allowing direct usage in PC/PEC application. [23][24][25] Vacancy-ordered double perovskites with the formula A 2 BX 6 have recently received a lot of attention in the perovskite community due to their excellent stability, good absorption coefficient, panchromatic absorption, and compositional tunability making…”

“…However, certain vacancy‐ordered double perovskites such as Cs 2 PtI 6 and Cs 2 PdBr 6 showed intrinsic water stability without any protection layer allowing direct usage in PC/PEC application. [ 23–25 ]…”

Evaluating the performance of Cs2PtI6−xBrx for photovoltaic and photocatalytic applications using first-principles study and SCAPS-1D simulation

“…For photocatalysis applications, good photocatalysis for water splitting or CO 2 reduction techniques should meet the requirement of (1) a suitable bandgap for absorption of the solar spectrum; (2) immediate electron-hole separation of the material; (3) high stability in aqueous medium against corrosion; (4) the redox potential of the material is suitable for H 2 generation and CO 2 reduction. Cs 2 PtI 6 is also used as a photoanode for the photoelectrochemical (PEC) water oxidation process [ 15 , 16 ] due to its stability even in an acidic or bases environment. In Jayanthan et al.…”