Plasmonic Enhancement in Water Splitting Performance for NiFe Layered Double Hydroxide-N10 TC MXene Heterojunction

A brief review on the progress of MXene-based catalysts for electro- and photochemical water splitting for hydrogen generation

The development and generation of affordable and highly efficient energy, particularly hydrogen, are one of the best approaches to address the challenges posed by the depletion of non-renewable energy sources. Hydrogen energy, as a green and ecosystem-friendly source with zero carbon emission, can be generated through various methods, including water splitting (HER/OER) via either photo- or electrocatalytic reactions. To implement these reactions effectively in practical applications, it is highly desirable to develop extremely efficient and cost-effective catalytic materials that are comparable to contemporary catalysts. MXenes, a family of newly discovered 2D transition metal carbides, nitrides, or carbonitrides with surface termination groups, such as -OH, -O, and -F, have emerged as promising materials and substrates for photo- and electrocatalytic applications due to their unique characteristics. These include excellent conductivity provided by the transition metals, hydrophilic nature imparted by the surface termination groups, high mechanical stability, fast electronic transmission and extremely high surface area-to-volume ratios. In this review, we provide detailed insights into the synthesis, properties, and catalytic applications of MXenes. We systematically outline the photo- and electrocatalytic water splitting reactions carried out by various MXene-based heterostructures, supported by experimental data. A thorough deliberation on the structure-activity associations of reported catalysts and a basic understanding of the electrocatalytic applications of MXenes are also included. Furthermore, we offer an insight into the upcoming tasks, challenges, prospects and new research strategies for MXenes in water splitting applications. A noteworthy recognition of the design and optimization of extremely efficient MXene-based catalysts in water splitting applications is therefore offered in this review.

Subtle 2D/2D MXene-Based Heterostructures for High-Performance Electrocatalytic Water Splitting

Developing efficient electrocatalysts is significant for the commercial application of electrocatalytic water splitting. 2D materials have presented great prospects in electrocatalysis for their high surface-to-volume ratio and tunable electronic properties. Particularly, MXene emerges as one of the most promising candidates for electrocatalysts, exhibiting unique advantages of hydrophilicity, outstanding conductivity, and exceptional stability. However, it suffers from lacking catalytic active sites, poor oxidation resistance, and easy stacking, leading to a significant suppression of the catalytic performance. Combining MXene with other 2D materials is an effective way to tackle the aforementioned drawbacks. In this review, the focus is on the accurate synthesis of 2D/2D MXene-based catalysts toward electrocatalytic water splitting. First, the mechanisms of electrocatalytic water splitting and the relative properties and preparation methods of MXenes are introduced to offer the basis for accurate synthesis of 2D/2D MXene-based catalysts. Then, the accurate synthesis methods for various categories of 2D/2D MXene-based catalysts, such as wet-chemical, phase-transformation, electrodeposition, etc., are systematically elaborated. Furthermore, in-depth investigations are conducted into the internal interactions and structure-performance relationship of 2D/2D MXene-based catalysts. Finally, the current challenges and future opportunities are proposed for the development of 2D/2D MXene-based catalysts, aiming to enlighten these promising nanomaterials for electrocatalytic water splitting.

Engineering Heterostructures of Layered Double Hydroxides and Metal Nanoparticles for Plasmon-Enhanced Catalysis

Artificially designed heterostructures formed by close conjunctions of plasmonic metal nanoparticles (PNPs) and non-plasmonic (2D) lamellar nanostructures are receiving extensive interest. The synergistic interactions of the nanounits induce the manifestation of localized surface plasmon resonance (LSPR) in plasmonic metals in the specific environment of the 2D-light absorbing matrix, impacting their potential in plasmon enhanced catalysis. Specifically, layered double hydroxides (LDH) with the advantages of their unique 2D-layered structure, tuned optical absorption, ease of preparation, composition diversity, and high surface area, have emerged as very promising candidates for obtaining versatile and robust catalysts. In this review, we cover the available PNPs/LDH heterostructures, from the most used noble-metals plasmonic of Au and Ag to the novel non-noble-metals plasmonic of Cu and Ni, mainly focusing on their synthesis strategies toward establishing a synergistic response in the coupled nanounits and relevant applications in plasmonic catalysis. First, the structure–properties relationship in LDH, establishing the desirable features of the 2D-layered matrix facilitating photocatalysis, is shortly described. Then, we address the recent research interests toward fabrication strategies for PNPs/support heterostructures as plasmonic catalysts. Next, we highlight the synthesis strategies for available PNPs/LDH heterostructures, how these are entangled with characteristics that enable the manifestation of the plasmon-induced charge separation effect (PICS), co-catalytic effect, or nanoantenna effect in plasmonic catalysis with applications in energy related and environmental photocatalysis. Finally, some perspectives on the challenges and future directions of PNPs/LDHs heterostructures to improve their performance as plasmonic catalysts are discussed.

Fascinating Tin Effects on the Enhanced and Large-Current-Density Water Splitting Performance of Sn-Ni(OH)2

Ni(OH)₂-based materials are widely studied in oxygen evolution reaction (OER), but no related synthesis, electrocatalytic application, or theoretical analysis of Sn⁴⁺-doped Ni(OH)₂ has been reported. In this work, Sn-Ni(OH)₂ with a homogeneously distributed nanosheet array was synthesized through a one-step hydrothermal process. It displays a hugely enhanced catalytic activity compared to undoped Ni(OH)₂ throughout the OER and hydrogen evolution reaction (HER) processes. The overpotentials at 100 mA cm^-2 of Sn-Ni(OH)₂ are 312 mV (OER) and 298 mV (HER), which are lower than the corresponding 396 and 427 mV of Ni(OH)₂, respectively. In addition, Sn-Ni(OH)₂ can deliver stable large current densities (at ≈500 and ≈1000 mA cm^-2) for the long-term (>100 h) chronoamperometry testing. Moreover, Sn-Ni(OH)₂ illustrates catalytic activity comparable to that of a commercial Pt/C||RuO₂ electrode pair during the overall water splitting course. Both experimental phenomena and relevant computed theoretical data confirm that the enhanced water splitting activity is mainly due to the introduced Sn⁴⁺ site, which acts as the active center activates the nearby Ni sites during the OER, while acting as the most active reaction site that participates in the HER. Although the doped Sn⁴⁺ has two different effects on OER and HER proceedings, water splitting performance of Sn-Ni(OH)₂ has been conspicuously improved.

Light Scattering and Luminophore Enrichment-Enhanced Electrochemiluminescence by a 2D Porous Ru@SiO2 Nanoparticle Membrane and Its Application in Ultrasensitive Detection of Prostate-Specific Antigen

Electrochemiluminescence (ECL) by virtue of its controllability and versatility has emerged as a significant tool in bioassay, but how to integrate it with other (nano)materials and further break the limit of sensitivity for ultrasensitive detection still possess tremendous potential. Herein, a close-packed Ru@SiO₂ NP nanomembrane that serves as an enhanced substrate and luminophore enricher simultaneously was constructed by the liquid-liquid interface self-assembly method and applied for ECL-enhanced bioassay. The developed ECL electrode obtained ∼600-fold enhancement on ECL intensity compared with the bare ITO electrode and ∼21-fold enhancement compared with the SiO₂ NP nanomembrane electrode due to the dramatic light scattering of the 2D SiO₂ NPs and the enrichment of Ru(bpy)₃²⁺ molecules on the surface of the Ru@SiO₂ NP nanomembrane electrode. Based on the fascinating Ru@SiO₂ NP nanomembrane platform, we further constructed a label-free immunosensor for the detection of prostate-specific antigen (PSA). The as-fabricated Ru@SiO₂-nanomembrane ECL immunosensor exhibited good stability and performed ultrasensitive detection with an utmost low detection limit of 0.169 fg·mL^-1 (signal/noise = 3). Our work puts forward an effective solution benefiting for further improving ECL performance for ultrasensitive bioassays.

An Extreme Energy-Saving Carbohydrazide Oxidization Reaction Directly Driven by Commercial Graphite Paper in Alkali and Near-Neutral Seawater Electrolytes

The energy-saving anode with low oxidization potential has been an intriguing pursue for earth-abundant seawater electrolysis. In this paper, we first introduced a superior energy-saving carbohydrazide oxidization reaction catalysis system in the anode section, which can be driven by commercial graphite paper with good durability. Combining this catalysis reaction and common graphite paper, the lowest anodic potentials 0.63 V (vs RHE) and 1.09 V (vs RHE) were obtained for driving a 10 mA/cm² current density in alkali and near-neutral seawater electrolytes, respectively, outperforming all the as-reported alkali or near-neutral seawater catalysts accordingly to the best of our knowledge.