Steering artificial photosynthesis via photoinduced conversion of monometallic to bimetallic sites in FeCo nitroprussides

Abstract

Artificial photosynthesis provides an efficient strategy for solar energy storage via water splitting and CO₂ reduction, but it remains a challenge in tuning artificial photosynthesis between these two competing reactions. Herein, we demonstrate photoinduced conversion of monometallic to bimetallic sites in a Fe-Co nitroprusside (FeCo-NP) to steer the reaction path from H₂ evolution to CO₂ reduction. Monometallic Co sites achieve efficient H₂ production with 28.5 mmol g^-1 activity and 85.4% selectivity. Photoinduced release of nitrosyl groups from Fe sites generates bimetallic Fe-Co sites, which suppress H₂ evolution and enhance CO₂ reduction, yielding 31.5 mmol g^-1 activity and 87.3% selectivity for C1 products. Mechanistic investigations reveal that monometallic Co sites catalyze H₂ evolution via H₂O adsorption and O-H cleavage while bimetallic Fe-Co sites facilitate both H₂O and CO₂ adsorption and subsequent O and C hydrogenation for CO and HCOOH. This work uncovers a strategy to manipulate competing reaction pathways via photoinduced conversion of monometallic to bimetallic sites, which provides unique insights into addressing environmental issues and energy crises.

Fig. 1. Design of mono- and bi-metallic nitroprussides.

a Schematic illustration of photoinduced conversion of monometallic to bimetallic catalysts in the nitroprusside framework for PHE and CO₂RR, respectively. SEM images of b FeCo-NP and c FeCo-NP-24. The insets are particle size distribution of FeCo-NP and FeCo-NP-24, respectively. d EDS elemental mapping images of FeCo-NP-24. Source data for Fig. 1 are provided as a Source Data file.

Fig. 2. Characterization of nitroprussides.

a PXRD patterns and b FT-IR spectra of FeCo-NP-n. c Nitrogen sorption isotherms of FeCo-NP and FeCo-NP-24, and d Fe 2p XPS spectra of FeCo-NP and FeCo-NP-24. Source data for Fig. 2 are provided as a Source Data file.

Fig. 3. XAS Characterization.

a Fe K-edge XANES spectra and the zoomed-in pre-edge spectra (The inset is a partial enlarged view.). b The Fe K-edge k³-weighted Fourier transform (FT) and the fitting curves for FeCo-NP and FeCo-NP-24. The data are k³-weighted and not phase-corrected. The real components curve fitting in R-spaces of c FeCo-NP and d FeCo-NP-24. Wavelet transforms k³-weighted EXAFS spectra of e FeCo-NP and f FeCo-NP-24. Source data for Fig. 3 are provided as a Source Data file.

Fig. 4. Structural transformation and photocatalytic performance.

a Schematic illustration of nitrosyl group release via light irradiation. b Catalytic performance of FeCo-NP-n. c Recycle and catalyst stability of FeCo-NP-24 in photocatalytic CO₂RR. The error bars (standard deviation) in the Fig. 4a–d were obtained from three replicate experiments. d Recycle and catalyst stability of FeCo-NP in photocatalytic PHE. Photocatalytic experiments were performed in CO₂-saturated H₂O/CH₃CN solution (v: v = 1: 9) at room temperature (25 °C). Source data for Fig. 4 are provided as a Source Data file.

Fig. 5. Photocatalytic mechanism investigation.

a The decay of [Ru(bpy)₃]²⁺ absorption at 455 nm with and without the addition of FeCo-NP. b The decay of [Ru(bpy)₃]⁺ absorption at 510 nm following the addition of BIH or BIH with FeCo-NP. In situ FT-IR spectra collected during the photocatalytic CO₂RR and PHE over c, FeCo-NP-24 and d FeCo-NP. e Gibbs free energy diagram of PHE on monometallic Co sites. Source data for Fig. 5 are provided as a Source Data file.

Fig. 6. Bimetallic catalytic mechanism in FeCo-NP-24.

a The Gibbs free energy diagram for CO and HCOOH production on bimetallic Fe-Co sites. The red values stand for the reaction-free energies. b The reaction intermediate structures for CO and HCOOH production via the Fe path on bimetallic Fe-Co sites. Source data for Fig. 6 are provided as a Source Data file.