Facile construction of self-supported Fe-doped Ni3S2 nanoparticle arrays for the ultralow-overpotential oxygen evolution reaction

Interface Catalysts of Ni3Fe1 Layered Double Hydroxide and Titanium Carbide for High-Performance Water Oxidation in Alkaline and Natural Conditions

The electrocatalytic oxygen evolution reaction (OER) is important for many renewable energy technologies. Developing cost-effective electrocatalysts with high performance remains a great challenge. Here, we successfully demonstrate our novel interface catalyst comprised of Ni₃Fe₁-based layered double hydroxides (Ni₃Fe₁-LDH) vertically immobilized on a two-dimensional MXene (Ti₃C₂T_x) surface. The Ni₃Fe₁-LDH/Ti₃C₂T_x yielded an anodic OER current of 100 mA cm^-2 at 0.28 V versus reversible hydrogen electrode (RHE), nearly 74 times lower than that of the pristine Ni₃Fe₁-LDH. Furthermore, the Ni₃Fe₁-LDH/Ti₃C₂T_x catalyst requires an overpotential of only 0.31 V versus RHE to deliver an industrial-level current density as high as 1000 mA cm^-2. Such excellent OER activity was attributed to the synergistic interface effect between Ni₃Fe₁-LDH and Ti₃C₂T_x. Density functional theory (DFT) results further reveal that the Ti₃C₂T_x support can efficiently accelerate the electron extraction from Ni₃Fe₁-LDH and tailor the electronic structure of catalytic sites, resulting in enhanced OER performance.

Electrocatalytic Water Splitting: From Harsh and Mild Conditions to Natural Seawater

Electrocatalytic water splitting is regarded as the most effective pathway to generate green energy-hydrogen-which is considered as one of the most promising clean energy solutions to the world's energy crisis and climate change mitigation. Although electrocatalytic water splitting has been proposed for decades, large-scale industrial hydrogen production is hindered by high electricity cost, capital investment, and electrolysis media. Harsh conditions (strong acid/alkaline) are widely used in electrocatalytic mechanism studies, and excellent catalytic activities and efficiencies have been achieved. However, the practical application of electrocatalytic water splitting in harsh conditions encounters several obstacles, such as corrosion issues, catalyst stability, and membrane technical difficulties. Thus, the research on water splitting in mild conditions (neutral/near neutral), even in natural seawater, has aroused increasing attention. However, the mechanism in mild conditions or natural seawater is not clear. Herein, different conditions in electrocatalytic water splitting are reviewed and the effects and proposed mechanisms in the three conditions are summarized. Then, a comparison of the reaction process and the effects of the ions in different electrolytes are presented. Finally, the challenges and opportunities associated with direct electrocatalytic natural seawater splitting and the perspective are presented to promote the progress of hydrogen production by water splitting.

Modulating the Electronic Structure of Nickel Sulfide Electrocatalysts by Chlorine Doping toward Highly Efficient Alkaline Hydrogen Evolution

The exploration of indurative and stable low-cost catalysts for hydrogen evolution reaction (HER) is of great importance for hydrogen energy economy, but it still faces challenges. Herein, we report a Cl-doped Ni₃S₂ (Cl-Ni₃S₂) nanoplate catalyst vertically grown on Ni foam with outstanding activity and durability for HER, which only requires an overpotential of 67 mV to reach a current density of 10 mA cm^-2 in alkaline media and exhibits negligible degradation after 30 h of operation. Both the advanced X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculation validate that Cl doping can optimize the electronic structure and the intrinsic activity of Ni₃S₂. This study devoted to the revelation of the impact of ionic doping on the activity of catalysts at the atomic scale can provide the direction for the rational design of novel and advanced HER electrocatalysts.

Quasi-Parallel NiFe Layered Double Hydroxide Nanosheet Arrays for Large-Current-Density Oxygen Evolution Electrocatalysis

Designing advanced electrocatalysts for oxygen evolution at large current density (>500 mA cm^-2 ) is critical to practical water splitting applications. Herein, a novel quasi-parallel NiFe layered double hydroxide (NiFe LDH) nanosheet arrays with pattern alignment on Ni foam was developed. The initial α-Ni(OH)₂ layer induced effective coprecipitation between Ni²⁺ and Fe³⁺ for the formation of LDH phase, guaranteeing the electronic pulling effect among metal cations and enhancing the interaction between active materials and substrate for excellent adhesion and electrical conductivity. Quasi-parallel NiFe LDH nanoarrays exhibited outstanding oxygen evolution activity with a small Tafel slope of 30.1 mV dec^-1 and overpotentials of 196, 255, and 284 mV at a current density of 10, 500, and 1000 mA cm^-2 in 1.0 m KOH solution, respectively, and high stability over 40 h at 750 mA cm^-2 . This work presents a new strategy towards fabricating electrode materials with exceptional performance.

Sulfur defect rich Mo-Ni3S2 QDs assisted by O-C[double bond, length as m-dash]O chemical bonding for an efficient electrocatalytic overall water splitting

Developing earth-abundant and highly efficient electrocatalysts is critical for further development of a system. The metal (M) doping strategy and inorganic/organic composite are two common strategies to improve the performance of electrocatalysts for overall water splitting (OWS). In this paper, two strategies are subtly used to prepare Mo-Ni₃S₂ quantum dots (QDs) with rich sulfur defects through Moⁿ⁺ doping Ni₃S₂ and introduction of trisodium citrate by a two-step hydrothermal reaction. Results show that high sulfur defects can be controllably prepared as the lattice mismatch and active sites can be efficiently increased via Moⁿ⁺ doping. Moreover, the introduction of trisodium citrate with carboxyl functional groups not only enhances the degree of sulfur defects around the metal center, changes the morphology of sulfide to distribute the active centers evenly, but also endow the metal center with strong valence changing ability with organic characteristics. The in situ Raman study reveals that O-C[double bond, length as m-dash]O promotes the formation of the real active site M-OOH by the way of self-sacrifice during the OER process. Mo-Ni₃S₂ QDelectrocatalyst shows excellent performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), achieving a current density of 10 mA cm^-2 at the overpotentials of 115 mV and 222 mV with very good chemical stability, superior than that of most of the reported materials. The OWS reaction can provide a current density of 10 mA cm^-2 and 50 mA cm^-2, which only needs 1.53 V and 1.74 V with excellent industrial application prospects.

Novel heterostructure Cu2S/Ni3S2 coral-like nanoarrays on Ni foam to enhance hydrogen evolution reaction in alkaline media

We fabricated a heterostructure Cu2S/Ni3S2 nanosheet array, which can accelerate charge transfer and provide more active sites. This work provides a promising non-noble metal electrocatalyst for water splitting under alkaline conditions.