Ferric Oxide Nanocrystals‐Embedded Co/Fe‐MOF with Self‐Tuned d‐Band Centers for Boosting Urea‐Assisted Overall Water Splitting

Abstract

A novel semiconductive Co/Fe‐MOF embedded with Fe2O3 nanocrystals (Fe2O3@CoFe‐MOF) is developed as a trifunctional electrocatalyst for the urea oxidation reaction (UOR), oxygen evolution reaction (OER), and hydrogen evolution reaction for enhancing the efficiency of the hydrogen production via the urea‐assisted overall water splitting. Fe2O3@CoFe‐TPyP‐MOF comprises unsaturated metal‐nitrogen coordination sites, affording enriched defects, self‐tuned d‐band centers, and efficient π–π interaction between different layers. Density functional theory calculation confirms that the adsorption of urea can be optimized at Fe2O3@CoFe‐TPyP‐MOF, realizing the efficient adsorption of intermediates and desorption of the final product of CO2 and N2 characterized by the in situ Fourier transform infrared spectroscopy. The two‐electrode urea‐assisted water splitting device‐assembled with Fe2O3@CoFe‐TPyP‐MOF illustrates a low cell voltage of 1.41 V versus the reversible hydrogen electrode at the current density of 10 mA cm−2, attaining the hydrogen production rate of 13.13 µmol min−1 in 1 m KOH with 0.33 m urea. The in situ electrochemical Raman spectra and other basic characterizations of the used electrocatalyst uncover that Fe2O3@CoFe‐TPyP‐MOF undergoes the reversible structural reconstruction after the UOR test, while it demonstrates the irreversible reconstruction after the OER measurement. This work redounds the progress of urea‐assisted water spitting for hydrogen production.

Real Active Site Identification of Co/Co3O4 Anchoring Ni-MOF Nanosheets with Fast OER Kinetics for Overall Water Splitting

“…Based on the above results, the excellent OER performance of Ni NDC-Co/CP can be attributed to several factors: (1) The presence of rough nanosheets facilitated by Co 3 O 4 , which are modified to enhance the contact area with the electrolyte, thereby expediting electron transfer under an electric field . (2) The introduction of Co 2+ leads to the generation of Co–O–Ni–O–Co units in Ni NDC-Co, optimizing the d-orbitals of Ni 2+ and promoting the formation of Ni 3+ , thereby reducing the reaction energy barrier in the OER process. , (3) In situ growth avoids the use of binders and preserves the catalytic capacity of the catalyst as much as possible …”

“…64 (2) The introduction of Co 2+ leads to the generation of Co− O−Ni−O−Co units in Ni NDC-Co, optimizing the d-orbitals of Ni 2+ and promoting the formation of Ni 3+ , thereby reducing the reaction energy barrier in the OER process. 45,65 (3) In situ growth avoids the use of binders and preserves the catalytic capacity of the catalyst as much as possible. 66…”

Constructing CoNi-LDH/Fe MOF/NF Heterostructure Catalyst for Energy-Efficient OER and UOR at High Current Density

“…Therefore, UOR-assisted water splitting can significantly reduce the potential at the anode, which is very beneficial for reducing electrolytic energy consumption. 51 EIS was employed to analyze the reaction kinetics of CoNi-LDH/Fe MOF/NF at different potentials for OER and UOR, as can be seen in Figure 4c,e. The Nyquist plots demonstrate a gradual reduction in the radius of the semi arc as the applied potential increases, indicating a gradual decrease in the R ct of the catalytic reaction.…”

“…The overpotentials of UOR are significantly lower than those of the OER. Therefore, UOR-assisted water splitting can significantly reduce the potential at the anode, which is very beneficial for reducing electrolytic energy consumption …”

Metal–organic frameworks (MOFs) for hybrid water electrolysis: structure–property–performance correlation

“…For instance, Liu et al integrated CoFe-TPyP-MOF with Fe 2 O 3 to tune the d-band of the catalyst for improved UOR activity. 103 The resulting Fe 2 O 3 @CoFe-TPyP-MOF heterostructure featured unsaturated metal–nitrogen coordination sites, which led to enriched defects, self-tuned d-band centers, and efficient π–π interactions between different layers. 103 XPS and XAS studies confirmed the modulation of coordination and electronic properties of the catalyst due to the formation of the heterostructure.…”