In-situ synthesis of NiS2 nanoparticles/MoS2 nanosheets hierarchical sphere anchored on reduced graphene oxide for enhanced electrocatalytic hydrogen evolution reaction

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).

Laser-Induced Co-Doped FePS3 with Massively Phosphorus Sulfur Vacancies Nanosheet for Efficient and Highly Stable Electrocatalytic Oxygen Reaction

Purposely optimizing material structure to reduce the energy change of the rate-determining step (RDS) for promoting oxygen evolution reaction (OER) catalytic performance is a major strategy to enhance the energy efficiency of electrocatalytic water splitting. Density functional theory (DFT) simulations indicate that creating a large number of defects on or inside the 2D FePS3 is very beneficial for its catalytic reaction of OER, especially when there are more defects, the structural diversity of the surface is more conducive to the adsorption and reaction of intermediates. In particular, when Co-doped FePS3 surfaces produce a large number of S and P defects and expose metallic Fe as active sites, its catalytic performance, especially the catalytic stability, is significantly enhanced. A facile and efficient laser-ablation-in-liquid method is then designed to combine Co with 2D layered crystal FePS3. Amazingly, the laser-induced (Fe0.53Co0.46)PS3 sample exhibits excellent OER performance, with an overpotential at 288 mV and a small Tafel slope of 58.3 mV dec-1. Moreover, (Fe0.53Co0.46)PS3 operates stably for 138 h at 10 mA cm-2 and 27 h at 100 mA cm-2, which shows that the stability of (Fe0.53Co0.46)PS3 far exceeds that of most of OER catalysts of Fe─Co system so far, and the comprehensive OER performance is in the first echelon of transition metal catalyst systems. This work proposes an in-depth understanding of the structural mechanism design of massive phosphorus sulfur vacancies by laser-induced manufacturing and will shed new light on promoting the stability of transition metal-based OER catalysts without any precious alternatives.

Growth of MoS2 Nanosheets on Brush-Shaped PI-ZnO Hybrid Nanofibers and Study of the Photocatalytic Performance

The design and preparation of advanced hybrid nanofibers with controllable microstructures will be interesting because of their potential high-efficiency applications in the environmental and energy domains. In this paper, a simple and efficient strategy was developed for preparing hybrid nanofibers of zinc oxide-molybdenum disulfide (ZnO-MoS2) grown on polyimide (PI) nanofibers by combining electrospinning, a high-pressure hydrothermal process, and in situ growth. Unlike simple composite nanoparticles, the structure is shown in PI-ZnO to be like the skeleton of a tree for the growth of MoS2 "leaves" as macro-materials with controlled microstructures. The surface morphology, structure, composition, and photocatalytic properties of these structures were characterized using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis spectroscopy. The ultra high-volume fraction of MoS2 can be grown on the brush-shaped PI-ZnO. Decorating ZnO with nanosheets of MoS2 (a transition metal dichalcogenide with a relatively narrow band gap) is a promising way to increase the photocatalytic activity of ZnO. The hybrid nanofibers exhibited high photocatalytic properties, which decomposed about 92% of the methylene blue in 90 min under visible light irradiation. The combination of MoS2 and ZnO with more abundant surface-active sites significantly increases the spectral absorption range, promotes the separation and migration of carriers, and improves the photocatalytic characteristics.

Efficient Electrocatalytic Nitrogen Reduction to Ammonia with Electrospun Hierarchical Carbon Nanofiber/TiO2@CoS Heterostructures

As a sustainable alternative technology to the cost- and energy-intensive Haber-Bosch method, electrochemical nitrogen (N2) reduction offers direct conversion of N2 to NH3 under ambient conditions. Direct use of noble metals or non-noble metals as electrocatalytic materials results in unsatisfactory electrocatalytic properties because of their low electrical conductivity and stability. Herein, three-dimensional flexible carbon nanofiber (CNF/TiO2@CoS) nanostructures were prepared on the surface of CNF by using electrospinning, a hydrothermal method, and in situ growth. We investigated the behavior of CNFs/TiO2@CoS as an electrocatalytic material in 0.1 M sodium sulfate. The highest ammonia yield of the material was 4.61 × 10-11 mol s-1 cm-2 at -0.45 V vs. RHE, and the highest Faraday efficiency, as well as superior long-term durability, was 8.3% at -0.45 V vs. RHE. This study demonstrates the potential of firecracker-shaped nanofiber templates for loading varied noble metals or non-noble metals as a novel development of hybrid composites for electrocatalytic nitrogen reduction.

A Review of Stoichiometric Nickel Sulfide-Based Catalysts for Hydrogen Evolution Reaction in Alkaline Media

Efficient and cost-effective catalysts for hydrogen evolution reaction (HER) are essential for large-scale hydrogen production, which is a critical step toward reducing carbon emissions and advancing the global transition to sustainable energy. Nickel sulfide-based catalysts, which exist in various stoichiometries, show promise for HER in alkaline media. However, as single-phase materials, they do not demonstrate superior activity compared to Pt-based catalysts. This review highlights recent strategies to enhance the HER performance of nickel sulfides, including heteroatom doping, heterostructure construction, and vacancy engineering, tailored to their different stoichiometric ratios. The study also examines synthesis methods, characterizations, and their impact on HER performance. Furthermore, it discusses the challenges and limitations of current research and suggests future directions for improvement.

Enhancing Rapid Li+/Na+ Storage Performance via Interface Engineering of Reduced Graphene Oxide-Wrapped Bimetallic Sulfide Nanocages

Transition-metal sulfide is considered to be an admirable transformational electrode material due to low cost, large specific capacity, and good reversibility in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, the reduced graphene oxide-wrapped open bimetallic sulfide (NiS2-Co3S4@rGO) nanocage, derived from nickel-cobalt Prussian blue, was obtained by two-step calcination. There are luxuriant pore structures in the nanocage composite with a specific surface area of 85.28 m2 g-1, which provides plentiful paths for rapid transmission of Li+/Na+ and alleviates the volume stress caused by insertion and extraction of alkali metal ions. The excellent interface combination of bimetallic sulfide wrapped in reduced graphene oxide improves the conductivity and overall performance of the battery. Thanks to the special interface engineering, the open NiS2-Co3S4@rGO nanocage composite displays rapid lithium storage properties with an average diffusion coefficient of 8.5 × 10-13 cm2 s-1. Moreover, after 300 cycles, the reversible capacity of the composite is 1113.2 mAh g-1 at 1 A g-1. In SIBs, the capacity of the open NiS2-Co3S4@rGO composite is 487.9 mAh g-1 when the current density is 5 A g-1. These preeminent performances demonstrate the enormous development prospects of bimetallic sulfide nanocage as anode material in LIBs and SIBs.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

In Operando X-ray Spectroscopic and DFT Studies Revealing Improved H2 Evolution by the Synergistic Ni-Co Electron Effect in the Alkaline Condition

The different electrolyte conditions, e.g., pH value, for driving efficient HER and OER are one of the major issues hindering the aim for electrocatalytic water splitting in a high efficiency. In this regard, seeking durable and active HER electrocatalysts to align the alkaline conditions of the OER is a promising solution. However, the success in this strategy will depend on a fundamental understanding about the HER mechanism at the atomic scale. In this work, we have provided thorough understanding for the electrochemical HER mechanisms in KOH over Ni- and Co-based hollow pyrite microspheres by in operando X-ray spectroscopies and DFT calculations, including NiS2, CoS2, and Ni0.5Co0.5S2. We discovered that the Ni sites in hollow NiS2 microspheres were very stable and inert, while the Co sites in hollow CoS2 microspheres underwent reduction and generated Co metallic crystal domains under HER. The generation of Co metallic sites would further deactivate H2 evolution due to the large hydrogen desorption free energy (-1.73 eV). In contrast, the neighboring Ni and Co sites in hollow Ni0.5Co0.5S2 microspheres exhibited the electronic interaction to elevate the reactivity of Ni and facilitate the stability of Co without structure or surface degradation. The energy barrier in H2O adsorption/dissociation was only 0.73 eV, followed by 0.06 eV for hydrogen desorption over the Ni0.5Co0.5S2 surface, revealing Ni0.5Co0.5S2 as a HER electrocatalyst with higher durability and activity than NiS2 and CoS2 in the alkaline medium due to the synergy of neighboring Ni and Co sites. We believe that the findings in our work offer a guidance toward future catalyst design.

Electronic redistribution over the active sites of NiWO4-NiO induces collegial enhancement in hydrogen evolution reaction in alkaline medium

The activity-enhancement of a new-generation catalyst focuses on the collegial approach among specific solids which exploit the mutual coactions of these materials for HER applications. Strategic manipulation of these solid interfaces typically reveals unique electronic states different from their pure phases, thus, providing a potential passage to create catalysts with excellent activity and stability. Herein, the formation of the NiWO₄-NiO interface has been designed and synthesized via a three-step method. This strategy enhances the chance of the formation of abundant heterointerfaces due to the fine distribution of NiWO₄ nanoparticles over Ni(OH)₂ sheets. NiWO₄-NiO has superior HER activity in an alkaline (1 M KOH) electrolyte with modest overpotentials of 68 mV at 10 mA cm^-2 current density. The catalyst is highly stable in an alkaline medium and negligible change was observed in the current density even after 100 h of continuous operation. This study explores a unique method for high-performance hydrogen generation by constructing transition metal-oxides heterojunction. The XPS studies reveal an electronic redistribution driven by charge transfer through the NiWO₄-NiO interface. The density functional theory (DFT) calculations show that the NiWO₄-NiO exhibits a Pt-like activity with the hydrogen Gibbs free energy (ΔG_H*) value of 0.06 eV compared to the Pt(ΔG_H* = -0.02 eV).