2D materials modulating layered double hydroxides for electrocatalytic water splitting

Regulation of electron density redistribution for efficient alkaline hydrogen evolution reaction and overall water splitting

The rational design of morphology and heterogeneous interfaces for non-precious metal electrocatalysts is crucial in electrochemical water decomposition. In this paper, a bifunctional electrocatalyst (Ni/NiFe LDH), which coupling nickel with nickel-iron layer double hydroxide (NiFe LDH), is synthesized on carbon cloth. At current density of 10 mA cm-2, the Ni/NiFe LDH exhibits a low hydrogen evolution reaction (HER) overpotential of only 36 mV due to the accelerated electrolyte penetration, which is caused by superhydrophilic interface. Moreover, an alkaline electrolyzer is formed and provide a current density of 10 mA cm-2 with a voltage of only 1.49 V. It is confirmed by the density functional theory (DFT) that electron from the Ni layer is transferred to NiFe LDH layer, redistributing the local electron density around the heterogeneous phase interface. Thus, the Gibbs free energy for hydrogen adsorption is optimized. This work provides a promising strategy for the rational regulation of electrons at heterogeneous interfaces and the synthesis of flexible electrocatalysts.

Interface-Engineered 3D porous MoS2-ReS2 in-plane heterojunction as efficient hydrogen evolution reaction electrocatalysts

Constructing in-plane heterojunctions with high interfacial density using two-dimensional materials represents a promising yet challenging avenue for enhancing the hydrogen evolution reaction (HER) in water electrolysis. In this work, we report that three-dimensional porous MoS2-ReS2 in-plane heterojunctions, fabricated via chemical vapor deposition, exhibit robust electrocatalytic activity for the water splitting reaction. The optimized MoS2-ReS2 in-plane heterojunction achieves superior HER performance across a wide pH range, requiring an overpotential of only 200 mV to reach a current density of 10 mA cm-2 in alkaline seawater. Thus, it outperforms standalone MoS2 and ReS2. Furthermore, the catalyst exhibits remarkable stability, enduring up to 200 h in alkaline seawater. Experimental results coupled with density functional theory calculations confirm that electron redistribution at the MoS2-ReS2 heterointerface is likely driven by disparities in in-plane work functions between the two phases. This leads to charge accumulation at the interface, thereby enhancing the adsorptive activity of S atoms toward H* intermediates and facilitating the dissociation of water molecules at the interface. This discovery offers valuable insights into the electrocatalytic mechanisms at the interface and provides a roadmap for designing high-performance, earth-abundant HER electrocatalysts suitable for practical applications.

Nanozyme-Enhanced Electrochemical Biosensors: Mechanisms and Applications

Nanozymes, as innovative materials, have demonstrated remarkable potential in the field of electrochemical biosensors. This article provides an overview of the mechanisms and extensive practical applications of nanozymes in electrochemical biosensors. First, the definition and characteristics of nanozymes are introduced, emphasizing their significant role in constructing efficient sensors. Subsequently, several common categories of nanozyme materials are delved into, including metal-based, carbon-based, metal-organic framework, and layered double hydroxide nanostructures, discussing their applications in electrochemical biosensors. Regarding their mechanisms, two key roles of nanozymes are particularly focused in electrochemical biosensors: selective enhancement and signal amplification, which crucially support the enhancement of sensor performance. In terms of practical applications, the widespread use of nanozyme-based electrochemical biosensors are showcased in various domains. From detecting biomolecules, pollutants, nucleic acids, proteins, to cells, providing robust means for high-sensitivity detection. Furthermore, insights into the future development of nanozyme-based electrochemical biosensors is provided, encompassing improvements and optimizations of nanozyme materials, innovative sensor design and integration, and the expansion of application fields through interdisciplinary collaboration. In conclusion, this article systematically presents the mechanisms and applications of nanozymes in electrochemical biosensors, offering valuable references and prospects for research and development in this field.

Sheet-Isolated MoS2 Used for Dispersing Pt Nanoparticles and its Application in Methanol Fuel Cells

It is highly challenging to activate the basal plane and minimize the π-π stacking of MoS2 sheets, thus enhancing its catalytic performance. Here, we display an approach for making well-dispersed MoS2 . By using the N-doped multi-walled carbon nanotubes (NMWCNTs) as an isolation unit, the aggregation of MoS2 sheets was effectively reduced, favoring the dispersion of Pt nanoparticles (noted as Pt/NMWCNTs-isolated-MoS2 ). Excellent bifunctional catalytic performance for methanol oxidation and oxygen reduction reaction (MOR/ORR) were demonstrated by the produced Pt/NMWCNTs-isolated-MoS2 . In comparison to Pt nanoparticles supported on MoS2 (Pt/MoS2 ), the MOR activity (2314.14 mA mgpt -1 ) and stability (317.69 mA mgpt -1 after 2 h of operation) on Pt/NMWCNTs-isolatedMoS2 were 24 and 232 times higher, respectively. As for ORR, Pt/NMWCNTs-isolated-MoS2 holds large half-wave potential (0.88 V) and high stability (92.71 % after 22 h of operation). This work presents a tactic for activating the basal planes and reducing the π-π stacking of 2D materials to satisfy their applications in electrocatalysis. In addition, the proposed sheet-isolation method can be used for fabricating other 2D materials to promote the dispersion of nanoparticles, which assist its application in other fields of energy as well as the environment.

Atomic Distance Engineering in Metal Catalysts to Regulate Catalytic Performance

It is very important to understand the structure-performance relationship of metal catalysts by adjusting the microstructure of catalysts at the atomic scale. The atomic distance has an essential influence on the composition of the environment of active metal atom, which is a key factor for the design of targeted catalysts with desired function. In this review, we discuss and summarize strategies for changing the atomic distance from three aspects and relate their effects on the reactivity of catalysts. First, the effects of regulating bond length between metal and coordination atom at one single-atom site on the catalytic performance are introduced. The bond lengths are affected by the strain effect of the support and high-shell doping and can evolve during the reaction. Next, the influence of the distance between single-atom sites on the catalytic performance is discussed. Due to the space matching of adsorption and electron transport, the catalytic performance can be adjusted with the shortening of site distance. In addition, the effect of the arrangement spacing of the surface metal active atoms on the catalytic performance of metal nanocatalysts is studied. Finally, a comprehensive summary and outlook of the relationship between atomic distance and catalytic performance is given.

Metal-Oxides- and Metal-Oxyhydroxides-Based Nanocomposites for Water Splitting: An Overview

Water electrolysis is an important alternative technology for large-scale hydrogen production to facilitate the development of green energy technology. As such, many efforts have been devoted over the past three decades to producing novel electrocatalysis with strong electrochemical (EC) performance using inexpensive electrocatalysts. Transition metal oxyhydroxide (OxH)-based electrocatalysts have received substantial interest, and prominent results have been achieved for the hydrogen evolution reaction (HER) under alkaline conditions. Herein, the extensive research focusing on the discussion of OxH-based electrocatalysts is comprehensively highlighted. The general forms of the water-splitting mechanism are described to provide a profound understanding of the mechanism, and their scaling relation activities for OxH electrode materials are given. This paper summarizes the current developments on the EC performance of transition metal OxHs, rare metal OxHs, polymers, and MXene-supported OxH-based electrocatalysts. Additionally, an outline of the suggested HER, OER, and water-splitting processes on transition metal OxH-based electrocatalysts, their primary applications, existing problems, and their EC performance prospects are discussed. Furthermore, this review article discusses the production of energy sources from the proton and electron transfer processes. The highlighted electrocatalysts have received substantial interest to boost the synergetic electrochemical effects to improve the economy of the use of hydrogen, which is one of best ways to fulfill the global energy requirements and address environmental crises. This article also provides useful information regarding the development of OxH electrodes with a hierarchical nanostructure for the water-splitting reaction. Finally, the challenges with the reaction and perspectives for the future development of OxH are elaborated.

Novel Strain Engineering Combined with a Microscopic Pore Synergistic Modulated Strategy for Designing Lattice Tensile-Strained Porous V2C-MXene for High-Performance Overall Water Splitting

Transition metal carbon/nitride (MXene) holds immense potential as an innovative electrocatalyst for enhancing the overall water splitting properties. Nevertheless, the re-stacking nature induced by van der Waals force remains a significant challenge. In this work, the lattice tensile-strained porous V₂C-MXene (named as TS₍₂₄₎-P₍₅₀₎-V₂C) is successfully constructed via the rapid spray freezing method and the following hydrothermal treatment. Besides, the influence of lattice strain degree and microscopic pores on the catalytic ability is reviewed and explored systematically. The lattice tensile strain within V₂C-MXene could widen the interlayer spacing and accelerate the ion transfer. The microscopic pores could change the ion transmission path and shorten the migration distance. As a consequence, the obtained TS₍₂₄₎-P₍₅₀₎-V₂C shows extraordinary hydrogen evolution reaction and oxygen evolution reaction activity with the overpotential of 154 and 269 mV, respectively, at the current density of 10 mA/cm², which is quite remarkable compared to the MXene-based electrocatalysts. Moreover, the overall water splitting device assembled using TS₍₂₄₎-P₍₅₀₎-V₂C as both anode and cathode demonstrates a low cell voltage requirement of 1.57 V to obtain 10 mA/cm². Overall, the implementation of this work could offer an exciting avenue to overcome the re-stacking issue of V₂C-MXene, affording a high-efficiency electrocatalyst with superior catalytic activity and desirable reaction kinetics.

Construction of 3D Hierarchical Co3O4@CoFe-LDH Heterostructures with Effective Interfacial Charge Redistribution for Rechargeable Liquid/Solid Zn-Air Batteries

Constructing three-dimensional (3D) hierarchical heterostructures is an appealing but challenging strategy to improve the performance of catalysts for electrical energy devices. Here, an efficient and robust flexible self-supporting catalyst, interface coupling of ultrathin CoFe-LDH nanosheets and Co₃O₄ nanowire arrays on the carbon cloth (CC/Co₃O₄@CoFe-LDH), was proposed for boosting oxygen evolution reaction (OER) in rechargeable liquid/solid Zn-air batteries (ZABs). The strong interfacial interaction between the CoFe-LDH and Co₃O₄ heterostructures stimulated the charge redistribution in their coupling regions, which improved the electron conductivity and optimized the adsorption free energy of OER intermediates, ultimately boosting the intrinsic OER performance. Besides, the 3D hierarchical nanoarray structure facilitated the exposure of catalytically active centers and rapid electron/mass transfer during the OER process. As such, the CC/Co₃O₄@CoFe-LDH catalyst achieved excellent OER catalytic activity in alkaline medium, with a small overpotential of 237 mV at 10 mA cm^-2, a low Tafel slope of 35.43 mV dec^-1, and long-term durability of up to 48 h, significantly outperforming the commercial RuO₂ catalyst. More impressively, the liquid and flexible solid-state ZABs assembled by the CC/Co₃O₄@CoFe-LDH hybrid catalyst as the OER catalyst presented a stable open circuit voltage, large power density, superb cycling life, and satisfactory flexibility, indicating great potential applications in energy technology. This work provides a good guidance for the development of advanced electrocatalysts with heterostructures and an in-depth understanding of electronic modulation at the heterogeneous interface.

Dicyandiamide-assisted synthesis of N-doped porous CoMn-Nx@N-C carbon nanotube composites via MOFs as efficient trifunctional electrocatalysts in the same electrolyte

The development of low-cost, long-term stability, and good oxygen reversible catalytic reaction (ORR/OER) and hydrogen evolution (HER) activity under the same electrolyte concentration of electrocatalytic materials has an important role in the construction of large-scale applications and more valuable sustainable energy systems. Among them, the representative CoMn-Nx@N-C-900-0.2 showed good ORR/OER/HER catalytic activity in 0.1 M KOH alkaline electrolyte, specifically manifested by its half-wave potential E = 0.84 V in the ORR test, which was better than that of commercial Pt/C. The total oxygen electrode activity index of OER/ORR was E = 0.79 V, and it also showed good HER performance. When the current density was 10 mA cm^-2, the operating potential was E = -0.266 V. The synergistic effects of the CoMn bimetallic alloy, tubular layered porous structure, which exposed more active area and various nitrogen species such as CoMn-Nx, were the main reasons for the improvement of the trifunctional catalytic performance of electrocatalytic materials. The synthesis strategy and analysis of the electrocatalyst performance provide a new reference for the development of multifunctional materials with high catalytic performance.