Ru-P pair sites boost charge transport in hematite photoanodes for exceeding 1% efficient solar water splitting

Rui-Ting Gao¹, Lijia Liu², Yanbo Li³, Yang Yang^{4

5

6

7

8}, Jinlu He¹, Xianhu Liu⁹, Xueyuan Zhang¹⁰, Lei Wang¹, Limin Wu^{1

11}

Affiliations

¹ College of Chemistry and Chemical Engineering, College of Energy Material and Chemistry, Inner Mongolia University, 010021 Hohhot, China.
² Department of Chemistry, Western University, London, ON N6A5B7, Canada.
³ Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, 610054 Chengdu, China.
⁴ NanoScience Technology Center, University of Central Florida, Orlando, FL 32826.
⁵ Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32826.
⁶ Department of Chemistry, University of Central Florida, Orlando, FL 32826.
⁷ Renewable Energy and Chemical Transformation Cluster, University of Central Florida, Orlando, FL 32826.
⁸ The Stephen W. Hawking Center for Microgravity Research and Education, University of Central Florida, Orlando, FL 32826.
⁹ Key Laboratory of Materials Processing and Mold, Ministry of Education, Zhengzhou University, 450002 Zhengzhou, China.
¹⁰ School of Materials Science and Engineering, China University of Petroleum (East China), 266580 Qingdao, China.
¹¹ Department of Materials Science and State Key Laboratory of Molecular Engineering of Polymers, Fudan University, 200433 Shanghai, China.

PMID: 37364112
PMCID: PMC10319015
DOI: 10.1073/pnas.2300493120

Ru-P pair sites boost charge transport in hematite photoanodes for exceeding 1% efficient solar water splitting

Rui-Ting Gao et al. Proc Natl Acad Sci U S A. 2023.

. 2023 Jul 4;120(27):e2300493120.

doi: 10.1073/pnas.2300493120. Epub 2023 Jun 26.

Authors

Rui-Ting Gao¹, Lijia Liu², Yanbo Li³, Yang Yang^{4

5

6

7

8}, Jinlu He¹, Xianhu Liu⁹, Xueyuan Zhang¹⁰, Lei Wang¹, Limin Wu^{1

11}

Affiliations

¹ College of Chemistry and Chemical Engineering, College of Energy Material and Chemistry, Inner Mongolia University, 010021 Hohhot, China.
² Department of Chemistry, Western University, London, ON N6A5B7, Canada.
³ Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, 610054 Chengdu, China.
⁴ NanoScience Technology Center, University of Central Florida, Orlando, FL 32826.
⁵ Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32826.
⁶ Department of Chemistry, University of Central Florida, Orlando, FL 32826.
⁷ Renewable Energy and Chemical Transformation Cluster, University of Central Florida, Orlando, FL 32826.
⁸ The Stephen W. Hawking Center for Microgravity Research and Education, University of Central Florida, Orlando, FL 32826.
⁹ Key Laboratory of Materials Processing and Mold, Ministry of Education, Zhengzhou University, 450002 Zhengzhou, China.
¹⁰ School of Materials Science and Engineering, China University of Petroleum (East China), 266580 Qingdao, China.
¹¹ Department of Materials Science and State Key Laboratory of Molecular Engineering of Polymers, Fudan University, 200433 Shanghai, China.

PMID: 37364112
PMCID: PMC10319015
DOI: 10.1073/pnas.2300493120

Abstract

Fast transport of charge carriers in semiconductor photoelectrodes are a major determinant of the solar-to-hydrogen efficiency for photoelectrochemical (PEC) water slitting. While doping metal ions as single atoms/clusters in photoelectrodes has been popularly used to regulate their charge transport, PEC performances are often low due to the limited charge mobility and severe charge recombination. Here, we disperse Ru and P diatomic sites onto hematite (DASs Ru-P:Fe₂O₃) to construct an efficient photoelectrode inspired by the concept of correlated single-atom engineering. The resultant photoanode shows superior photocurrent densities of 4.55 and 6.5 mA cm^-2 at 1.23 and 1.50 V_RHE, a low-onset potential of 0.58 V_RHE, and a high applied bias photon-to-current conversion efficiency of 1.00% under one sun illumination, which are much better than the pristine Fe₂O₃. A detailed dynamic analysis reveals that a remarkable synergetic ineraction of the reduced recombination by a low Ru doping concentration with substitution of Fe site as well as the construction of Ru-P bonds in the material increases the carrier separation and fast charge transportation dynamics. A systematic simulation study further proves the superiority of the Ru-P bonds compared to the Ru-O bonds, which allows more long-lived carriers to participate in the water oxidation reaction. This work offers an effective strategy for enhancing charge carrier transportation dynamics by constructing pair sites into semiconductors, which may be extended to other photoelectrodes for solar water splitting.

Keywords: charge carrier transfer; electron-hole recombination; hematite photoelectrodes; metal and nonmetal pair sites; photoelectrochemical water oxidation.

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Conflict of interest statement

The authors declare no competing interest.

Figures

**Fig. 1.**
Characterization of DASs Ru-P:Fe₂O₃. (A) Schematic illustration for the preparation of DASs Ru-P:Fe₂O₃. (B) HAADF-STEM image. A large numbers of Ru atoms were atomically dispersed on the Fe₂O₃. *Inset* of the B shows the another angle of Ru single atoms. (C and D) high-resolution HAADF-STEM images. The *Inset* of the D shows the corresponding fast Fourier transform pattern, indicating the single crystallinity structure of hematite nanoflakes. (E and F) The lines represent the line profiles from the HAADF intensity analysis labeled in D. (G) STEM-EDS elemental mapping of Fe, O, Ru, and P. Scale bars in B, C, D, and G are 2 nm, 1 nm, 1 nm, and 50 nm, respectively.

**Fig. 2.**
Coordination environment analysis of SAs Ru:Fe₂O₃ and DASs Ru-P:Fe₂O₃. (A) Ru 3p XPS spectra, (B) P 2p XPS spectra, and (C) Raman spectra of Fe₂O₃, SAs Ru:Fe₂O₃, and DASs Ru-P:Fe₂O₃. (D) The normalized Ru K-edge XANES spectra of SAs Ru:Fe₂O₃ and DASs Ru-P:Fe₂O₃ as well as Ru foil, RuO₂, and RuP references. (E) The Ru K-edge Fourier transformed EXAFS spectra (R-space) of SAs Ru:Fe₂O₃ and DASs Ru-P:Fe₂O₃ as well as Ru foil, RuO₂, and RuP references. (F) The schematic models of SAs Ru:Fe₂O₃ and DASs Ru-P:Fe₂O₃. (*G–I*) WT-EXAFS plots of SAs Ru:Fe₂O₃, DASs Ru-P:Fe₂O₃, and RuP.

**Fig. 3.**
Photoelectrochemical activities of Fe₂O₃, SAs Ru:Fe₂O₃, and DASs Ru-P:Fe₂O₃. (A) *J-V* curves. (B) Chopped *J-V* curve of DASs Ru-P:Fe₂O₃. (C) ABPE values. (D) Surface charge separation efficiencies (ƞ_surface). (E) IPCE values in a Xe lamp. (F) OCP-derived carrier lifetimes. (G) PEIS at 1.23 V_RHE. Inset shows the corresponding circuit. (H) Stability measurement, (I) gas productions, and (I) Faraday efficiencies of DASs Ru-P:Fe₂O₃. All electrochemical measurements were performed in 1 M KOH under AM 1.5G illumination (100 mW cm⁻²).

**Fig. 4.**
Band edge energetics characterizations. (A) Mott–Schottky plots under dark, (B) UV-vis absorption spectra, and (C) UPS curves of Fe₂O₃, SAs Ru:Fe₂O₃, and DASs Ru-P:Fe₂O₃. Tauc plots of UV-vis absorption spectra are shown in the *Inset* of B. The blue dashed lines in C denote the area shown in the zoomed-in image in the *Inset* of C. (D) Band diagrams of corresponding photoanodes.

**Fig. 5.**
Photogenerated charge carrier dynamics. (A and B) Transient absorption decay curves at (A) 570 nm and (B) 620 nm for Fe₂O₃, SAs Ru:Fe₂O₃, and DASs Ru-P:Fe₂O₃. The fits for the decays were shown as solid lines, and the circles represent the experimental data. (C) Transient absorption spectra of DASs Ru-P:Fe₂O₃ when excited with 380 nm. (D) Charge transfer rate constants (k_trans), (E) charge recombination rate constants (k_rec), and (F) charge transfer efficiencies extracted from IMPS analysis for the corresponding photoanodes.

**Fig. 6.**
DFT analysis. (A) Side view of ELF and (B) PDOS of Fe₂O₃, SAs Ru:Fe₂O₃, and DASs Ru-P:Fe₂O₃. (C) Differential charge densities of SAs Ru:Fe₂O₃ and DASs Ru-P:Fe₂O₃. (D) Charge trapping and recombination, and (E) free energies of OER reaction steps of Fe₂O₃, SAs Ru:Fe₂O₃, and DASs Ru-P:Fe₂O₃. (F) The OER proceeding on the surfaces of SAs Ru:Fe₂O₃ and DASs Ru-P:Fe₂O₃.

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References

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Ru-P pair sites boost charge transport in hematite photoanodes for exceeding 1% efficient solar water splitting

Affiliations

Ru-P pair sites boost charge transport in hematite photoanodes for exceeding 1% efficient solar water splitting

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

References

LinkOut - more resources

Full Text Sources