Crystalline-Amorphous Interface Coupling of Ni3S2/NiPx/NF with Enhanced Activity and Stability for Electrocatalytic Oxygen Evolution

Design and synthesis of autogenous growth NiFe bimetallic phosphide catalysts on a nickel iron foam-like substrate for efficient overall water splitting

The design of low-cost, highly active, and stable electrocatalysts is pivotal for advancing water electrolysis technologies. In this study, carbonyl iron powder (CIP) was anchored within the pores of nickel foam (NF) by electroplating nickel, creating nickel iron foam-like (NFF-L) substrates. Subsequently, nickel-iron hydroxide (NiFe-OH) was synthesized on the NFF-L substrate employing an autogenous growth strategy, followed by a phosphating treatment that produced a nanoflower-like NiFe bimetallic phosphide heterostructure catalyst (Fe2P-Ni2P@NFF-L). This novel method of substrate filling enhanced space utilization, while the presence of micropores and mesopores on the nanosheet surfaces facilitated electrolyte infiltration and ion diffusion, thereby significantly increasing the specific surface area. The formation of a two-phase heterointerface accelerated electron transmission and transfer, enhancing water dissociation and the adsorption of hydrogen adatoms (Had). In addition, under anodic oxidation conditions, the dynamic surface reconstruction facilitated a synergistic interaction between the highly active β-NiOOH and α-FeOOH phases, which significantly contributed to the catalyst's exceptional intrinsic activity for the oxygen evolution reaction (OER).

An efficient hydrogen evolution catalyst constructed using Pt-modified Ni3S2/MoS2 with optimized kinetics across the full pH range

Electrocatalyst materials play a crucial role in determining the efficiency of the hydrogen evolution reaction (HER), directly influencing the overall effectiveness of energy conversion technologies. Ni3S2/MoS2 heterostructures hold substantial promise as bifunctional catalysts, owing to their synergistic electronic characteristics and plentiful active sites. However, their catalytic efficacy is impeded by the relatively elevated chemisorption energy of hydrogen-containing intermediates, which constrains their functionality in different pH environments. In order to mitigate this limitation, trace amounts of Pt are introduced into the heterostructure, intending to enhance electronic transport and refining chemisorption energies, thereby facilitating significant enhancements in both HER and oxygen evolution reaction (OER) activities over a wide pH range. It is revealed that the Pt-modified catalyst achieves exceptional HER performance, requiring merely 64 mV and 83 mV overpotentials to attain a current density of 100 mA cm-2 in acidic and alkaline media, respectively. Furthermore, theoretical simulations corroborate that Pt modification optimizes local electronic configurations and augments electronic transfer, contributing to its superior catalytic performance. This investigation underscores the pivotal role of Pt modification in propelling the practical application of Ni3S2/MoS2 heterostructures as highly efficient and pH-universal bifunctional catalysts.

Fe,Ce Co-Doped Ni3S2/NiS Polymorphism Nanosheets With Improved Electrocatalytic Activity and Stability for Water Oxidation

Balancing the relationship between electrocatalytic activity and stability of sulfide catalysts during oxygen evolution reaction (OER) has been attracting extensive research interest. Here, a simple electrodeposition-vulcanization two-step route was designed to successfully construct nickel foam supported sheet-like Fe,Ce-codoped Ni3S2/NiS polymorphism catalyst (labeled as Fe,Ce-Ni3S2/NiS/NF). Electrochemical measurements showed that the as-obtained Fe,Ce-Ni3S2/NiS/NF electrode presented excellent OER electrocatalytic performances. In 1 M KOH solution, merely 173 and 234 mV of overpotentials were required to deliver the current densities of 10 and 100 mA cm-2, respectively. Further investigations revealed that the Fe,Ce co-doping regulated the electron density around Ni, which promoted the conversion of Ni towards the higher valence state and simultaneously, avoided the stability decrease of the catalyst caused by excessive oxidation corrosion. Moreover, the defects generated during vulcanization also contributed to promoting water oxidation. The present work provides a facile and feasible approach to balance the relationship between the stability and the activity of sulfide catalysts for OER.

Deep reconstruction of crystalline-amorphous heterojunction electrocatalysts for efficient and stable water and methanol electrolysis

During electrocatalytic water splitting, surface reconstruction often occurs to generate truly active species for catalytic reactions, but the stability and mass activity of the catalysts is a huge challenge. A method that combines cation doping with morphology control strategies and constructs an amorphous-crystalline heterostructure is proposed to achieve deep reconstruction of the catalyst during the electrochemical activation process, thereby significantly improving catalytic activity and stability. Amorphous iron borate (FeBO) is deposited on cobalt-doped nickel sulfide (Co-Ni3S2) crystals to form ultrathin nanosheet heterostructures (FeBO/Co-Ni3S2) as bifunctional electrocatalysts for the OER and methanol oxidation reaction (MOR). During the OER process, FeBO/Co-Ni3S2 is deeply reconstructed to form a NiFeOOH/Co-Ni3S2 composite structure with ultrathin nanosheets with abundant amorphous-crystalline interfaces to ensure structural stability. Furthermore, Co-Ni3S2 electrocatalysts were synthesized via nickel foam (NF) self-derivation, which resulted in strong adhesion between the catalyst and substrate and formed a hierarchical structure consisting of interconnected nanosheets with excellent mass transfer and abundant active sites to increase the activity and stability of the electrocatalyst. The dual-electrode electrolyzer requires cell voltages of 1.58 and 1.44 V to achieve water and methanol overall electrolysis at a current density of 10 mA cm-2 and keep working over 100 and 25 h, respectively. This strategy provides a new way to promote reconstruction to construct excellent bifunctional electrocatalysts.

Multiphase interface coupling of Ni-based sulfide composites for high-current-density oxygen evolution electrocatalysis in alkaline freshwater/simulated seawater/seawater

Constructing highly efficient electrocatalysts is vital to enhance oxygen evolution reaction (OER) performance at industrially relevant current densities. Herein, three-phase coupled Ni3S2/r-NiS/h-NiS composites are grown in situ on Ni foam (NNSN/NF) via a one-step solvothermal approach. The as-prepared composites need overpotentials of only 377 mV, 451 mV and 476 mV at 1000 mA cm-2 for the OER in alkaline freshwater, simulated seawater and seawater, respectively. In addition, the optimized catalyst exhibited long-term durability at 300 mA cm-2. Our work clarifies designing and preparing cost-effective Ni-based sulfide electrocatalysts for the OER in alkaline freshwater/simulated seawater/seawater under industrially relevant current densities.

Highly Efficient CoFeP Nanoparticle Catalysts for Superior Oxygen Evolution Reaction Performance

Developing effective and long-lasting electrocatalysts for oxygen evolution reaction (OER) is critical for increasing sustainable hydrogen production. This paper describes the production and characterization of CoFeP nanoparticles (CFP NPs) as high-performance electrocatalysts for OER. The CFP NPs were produced using a simple hydrothermal technique followed by phosphorization, yielding an amorphous/crystalline composite structure with improved electrochemical characteristics. Our results reveal that CFP NPs have a surprisingly low overpotential of 284 mV at a current density of 100 mA cm-2, greatly exceeding the precursor CoFe oxide/hydroxide (CFO NPs) and the commercial RuO2 catalyst. Furthermore, CFP NPs demonstrate exceptional stability, retaining a constant performance after 70 h of continuous operation. Post-OER characterization analysis revealed transformations in the catalyst, including the formation of cobalt-iron oxides/oxyhydroxides. Despite these changes, CFP NPs showed superior long-term stability compared to native metal oxides/oxyhydroxides, likely due to enhanced surface roughness and increased active sites. This study proposes a viable strategy for designing low-cost, non-precious metal-based OER catalysts, which will help advance sustainable energy technology.

Facile and scalable synthesis of Ni3S2/Fe3O4 nanoblocks as an efficient and stable electrocatalyst for oxygen evolution reaction

This study employed a one-step hydrothermal process to synthesize Ni3S2/Fe3O4 nanoblocks in situ on nickel foam (NF). The resulting Ni3S2/Fe3O4/NF catalyst demonstrates exceptional electrocatalytic activity for the oxygen evolution reaction (OER) and robust long-term stability. It achieves a low overpotential of only 220 mV for a current density of 10 mA cm-2 with a Tafel slope of 54.1 mV dec-1 and remains stable in 1.0 M KOH for 66 h. The binder-free self-supported three-dimensional nanoblocks enhance the reaction region and long-term stability. Electronic interactions between Fe3O4 and Ni3S2, coupled with heterogeneous interfaces, optimize the electronic structure, fostering the formation of highly reactive species. Density-functional theory (DFT) calculations confirm that Ni3S2/Fe3O4, with a heterogeneous interfacial structure, modulates the chemisorption of reaction intermediates on the catalyst surface, optimizing the Gibbs free energies (ΔG) of oxygen-containing intermediates. The synergistic effect between the two active materials within the heterogeneous structure enhances OER catalytic performance. This finding offers a valuable approach to designing efficient and stable OER electrocatalysts.

Application of Amorphous-Crystalline Coupling Materials in Electrocatalysis

Interface engineering has proven to be a highly efficient strategy for modulating the physicochemical properties of electrocatalysts and further enhancing their electrochemical performance in related energy applications. In this context, the newly proposed crystalline-amorphous (c-a) heterostructures with unusual atomic arrangements at interfaces show strong competitiveness. Nonetheless, few efforts have been made to reveal and summarize the structure-activity relationship at the two-phase interface and the corresponding electrocatalytic mechanism. This concept is devoted to comprehensively discussing the fundamental characteristics of crystalline-amorphous electrocatalysts and their application in the field of energy conversion with typical examples. In addition, the development prospects and opportunities of crystalline-amorphous heterostructure are summarized to provide potential development directions for other types of clean energy development.

3D nanostructured Ce-doped CoFe-LDH/NF self-supported catalyst for high-performance OER

Powder electrocatalysts for oxygen evolution reactions usually need adhesives for electrocatalytic performance tests, leading to the increase of resistance, reduction of catalyst loading, and easy stripping of the catalyst under long-time or high current operation. In this study, Ce-doped CoFe layered double hydroxides were uniformly grown on nickel foam by a one-step hydrothermal route. A nanostructured self-supported electrode Ce-CoFe-LDH/NF without adhesive was obtained directly, which has a regular nanoneedle morphology with a length of ∼1.2 μm and tip width of ∼20 nm. Adopting Ce3+ ions with a large radius to partially displace Fe3+ ions with a small radius produced lattice distortion and more defects in the host layer of CoFe-LDH, whereby possessing the great potential to enhance catalytic behaviors. Once used as an electrocatalyst for the oxygen evolution reaction, Ce-CoFe-LDH/NF shows an outstanding electrocatalytic performance, including an optimized overpotential of 225 mV at 10 mA cm-2, a decreased Tafel slope of 34.34 mV dec-1, and a low charge transfer impedance of 2.4 Ω in 1 M KOH electrolyte. Moreover, the overpotential of the working electrode increased by only 0.04 V after 24 hours and was maintained at a current density of 50 mA cm-2. These results demonstrate a low-cost strategy compared to using noble metal OER electrocatalysts. Thus, this study highlights a ready universal approach to fabricate high-performance supported catalysts for energy-related applications.