Fe2P encapsulated in carbon nanowalls decorated with well-dispersed Fe3C nanodots for efficient hydrogen evolution and oxygen reduction reactions

Regulating the thickness of the carbon coating layer in iron/carbon heterostructures to enhance the catalytic performance for oxygen evolution reaction

The exploration of high-performance electrocatalysts for the oxygen evolution reaction (OER) is crucial and urgent for the fast development of green and renewable hydrogen energy. Herein, an ultra-fast and energy-efficient preparation strategy (microwave-assisted rapid in-situ pyrolysis of organometallic compounds induced by carbon nanotube (CNT)) is developed to obtain iron/carbon (Fe/C) heterogeneous materials (Fe/Fe₃C particles wrapped by carbon coating layer). The thickness of the carbon coating layer can be adjusted by changing the content and form of carbon in the metal sources during the fast preparation process. Fe/Fe₃C-A@CNT using iron acetylacetonate as metal sources possesses unique Fe/C heterogeneous, small Fe/Fe₃C particles encapsulated by the thin carbon coating layer (1.77 nm), and obtains the optimal electron penetration effect. The electron penetration effect derives from the redistribution of charge between the surface carbon coating layer and inner Fe/Fe₃C nanoparticles efficiently improving both catalytic activity and stability. Therefore, Fe/Fe₃C-A@CNT shows efficient OER catalytic activity, just needing a low overpotential of 292 mV to reach a current density of 10 mA cm^-2, and long-lasting stability. More importantly, the unique control strategy for carbon thickness in this work provides more opportunity and perspective to prepare robust metal/carbon-based catalytic materials at the nanoscale.

Heterogeneous Ni3P/Ni nanoparticles with optimized Ni active sites anchored in N-doped mesoporous nanofibers for boosting pH-universal hydrogen evolution

Developing low-cost, environmentally friendly and efficient non-precious metal electrocatalysts as alternatives to noble metals for the hydrogen evolution reaction (HER) is highly essential for the sustainable advancement of green hydrogen energy. Herein, a novel heterostructured Ni₃P/Ni nanoparticle anchored in nitrogen-doped mesoporous carbon nanofibers (Ni₃P/Ni@N-CNFs) is prepared by a facile solid-phase calcination protocol. The results demonstrated that benefiting from the intensive electronic coupling effect at the interface of the Ni₃P/Ni heterostructure, the electron configuration of the Ni active site is optimized and thus the favorable HER activity. Furthermore, the N-doped carbon nanofiber scaffold with an extensive mesoporous structure endows Ni₃P/Ni@N-CNFs with abundant electrochemically active sites together with excellent conductivity and stability, contributing to fast electron/mass transport. As expected, the resultant Ni₃P/Ni@N-CNF electrocatalyst exhibited exceptional HER catalytic properties under universal pH conditions, driving a current density of 10 mA cm^-2 at pretty low overpotentials of 121 mV, 145 mV and 187 mV in acidic, basic and neutral solutions, respectively, and retaining the catalytic stability for over 60 h. This intriguing work represents a fresh perspective for designing and exploiting highly advanced phosphide electrocatalysts for green hydrogen fuel production.

Vanadium doped FeP nanoflower with optimized electronic structure for efficient hydrogen evolution

Reasonable design of hydrogen evolution reaction (HER) electrocatalyst from the perspective of electronic structure is a vital way to optimize the catalytic activity. Mono-metallic iron-based phosphates have been shown to be active toward HER, but their performance remains unsatisfactory despite their abundant reserves and low preparation cost. Here, guided by the d-band center and band structure theories, V-doped FeP nanoflower grown directly on iron foam are constructed. Combining the density functional theory (DFT) simulations with physical characterizations reveal that the enhanced HER activity is mainly attributed to the lowed d-band central position, increased water dissociation capacity, decreased hydrogen formation energy barrier and reduced charge transfer impedance. As a HER catalyst in 1 M KOH, the obtained V-FeP shows low overpotentials of ∼149, ∼246 and ∼290 mV to deliver the current densities of 100, 500 and 1000 mA cm^-2 with at least 24 h. When coupled with other highly active oxygen evolution reaction (OER) catalyst (NiFe-LDH/IF), the NiFe-LDH/IF⁽⁺⁾ || V-FeP/IF^(-) pair also performs a low cell voltage and over 100-h stability at high current density of 1000 mA cm^-2, which endows it a large potential in the practical electrolytic water industry. Our work may provide a reference for the enhancement of inert and low-cost HER-active iron phosphide.