Ultrathin wrinkled NiFeP nanosheets enable efficient oxygen evolution electrocatalysis

Nanoflower-like FeVNi3S2-xas efficient electrocatalyst for alkaline oxygen evolution reaction

The development of low cost efficient catalysts for oxygen evolution reaction (OER) is still a obstacle to realize the commercialization of electrocatalytic water splitting. Herein, interface engineering and heteroatom doping is adopted to synthesize iron and vanadium doped nickel sulfide on nickel foam via hydrothermal method followed by hydrogen treatment to create sulfur defects. The optimized nanoflower-like FeVNi3S2-x/NF is an efficient OER electrocatalyst that outperforms many of the reported transition metals catalysts. Benefiting from abundant sulfur defects and the synergistic effect of heteroatom doping, FeVNi3S2-x/NF exhibits an ultralow overpotential of 230 mV to reach a current density of 100 mA cm-2, a rapid reaction kinetics with a small Tafel slope of 46.6 mV dec-1, and a stable long-term durability in 1 M KOH. Experimental results and characterizations confirm that sulfur vacancies together with the synergistic effect from multiple heteroatom doping can effectively regulate the electronic structure, resulting in increased electrical conductivity and electrochemically active surface area, thus enhancing OER performance. Furthermore,in situRaman spectroscopy reveals that, the reconstitution amorphous nickel oxyhydroxide (NiOOH) on the catalyst surface is responsible for catalyzing the OER reaction. This work represents a promising methodology to synthesize low-cost and highly active OER electrocatalysts.

Hierarchical Highly Wrinkled Trimetallic NiFeCu Phosphide Nanosheets on Nanodendrite Ni3S2/Ni Foam as an Efficient Electrocatalyst for the Oxygen Evolution Reaction

The sluggish oxygen evolution reaction (OER) and costly noble-metal oxide catalysts hinder the vast usage of environmentally friendly water splitting for hydrogen production. Elemental doping by partial replacing of parent metal elements with elements of higher electronegativity is considered to be one of the most efficient strategies to promote the electrocatalytic OER performance. In this work, we synthesize an efficient hierarchical highly wrinkled NiFeCu phosphide nanosheet on nanodendrite Ni₃S₂/NiF substrates through partial replacement of Cu instead of Ni and Fe in NiFeP@Ni₃S₂/NiF by using a facile electrodeposition method. The NiFeCuP@Ni₃S₂/NiF electrocatalyst needs only 230, 282, and 351 mV to reach 10, 50, and 100 mA × cm^-2, respectively. Notably, this electrocatalyst shows one of the lowest OER overpotentials at 10 mA/cm^-2 for metal phosphides and endured the OER at 20 mA × cm^-2 for 18 h with negligible voltage elevation. The X-ray photoelectron spectroscopy (XPS), double-layer capacitance (C_dl) plots, and electrochemical impedance spectroscopy show that the partial Cu doping in NiFeP@Ni₃S₂/NiF not only can change the electron density around Ni and Fe but also can increase the electrochemically active surface area and conductivity of electrocatalysts.

Nickel iron phosphide ultrathin nanosheets anchored on nitrogen-doped carbon nanoflake arrays as a bifunctional catalyst for efficient overall water splitting

Development of high-efficiency and Earth-abundant bifunctional catalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is desirable to realize an efficient overall water splitting process. In this work, a highly active and durable bifunctional catalyst of coral-like nickel iron phosphide ultrathin nanosheets anchored on nitrogen-doped carbon nanoflake arrays on carbon cloth (CC-NC-NiFeP) was fabricated by using metal organic framework (MOF) derived nitrogen-doped carbon nanoflake arrays as catalyst supports. Combined with the electronic structure regulation by bimetallic phosphides and using three dimensional nitrogen-doped carbon nanoflakes as supports that provide a large specific surface area as well as fast charge/mass transport, the as-prepared CC-NC-NiFeP yields excellent bifunctional electrocatalytic activity in both the HER and OER in an alkaline medium with an overpotential of 94 mV and 145 mV to reach a current density of 10 mA cm^-2, respectively. Meanwhile, the CC-NC-NiFeP can behave as both a cathode and anode simultaneously for overall water splitting, achieving a low cell voltage of 1.54 V to reach a current density of 10 mA cm^-2, which outperforms that of most of the non-precious metal based catalysts.