Strained heterointerfaces in sandwich–like NiFe layered double hydroxides/Co1-xS for highly efficient and superior long–term durable oxygen evolution reaction

Efficient detection of carbendazim using an electrochemical sensor for a novel NiFeLDH@HsGY-NH2/MWCNTs heterostructure with lattice-strain

Carbendazim (CBZ) is widely used for crop protection and its residues threaten human health and the environment. Therefore, developing an effective electrocatalyst is important for the extremely sensitive detection of CBZ. Lattice-strain engineering is an effective strategy to change its electronic structure and ultimately optimize the catalytic performance of materials, which can be used as a modification method to improve the detection performance of electrochemical sensors. Herein, a NiFeLDH@HsGY-NH2/MWCNTs heterojunction with strain effect is prepared by the electrostatic self-assembly method. The structure, morphology, composition, crystallinity and electrochemical performance of NiFeLDH@HsGY-NH2/MWCNTs are analyzed using various instrumental techniques, in which geometric phase analysis (GPA) and X-ray diffraction (XRD) images confirm the lattice-strain generated in NiFeLDH@HsGY-NH2/MWCNTs. The results indicate that the prepared electrochemical sensor exhibited an excellent response for carbendazim (CBZ) in the linear range of 0.05-50.00 μM with a detection limit of 10.00 nM (S/N = 3) under the optimal detection conditions. By analyzing the reasons for the improvement of the catalytic performance of the composite material, it is found that the composite of MWCNTs not only improves the conductivity of NiFeLDH but also regulates the electronic structure of metal atoms through double effects. This study provides new insights into the design of efficient and low-cost catalysts to facilitate electrochemical sensor applications.

Lattice-Strain Engineering for Heterogenous Electrocatalytic Oxygen Evolution Reaction

The energy efficiency of metal-air batteries and water-splitting techniques is severely constrained by multiple electronic transfers in the heterogenous oxygen evolution reaction (OER), and the high overpotential induced by the sluggish kinetics has become an uppermost scientific challenge. Numerous attempts are devoted to enabling high activity, selectivity, and stability via tailoring the surface physicochemical properties of nanocatalysts. Lattice-strain engineering as a cutting-edge method for tuning the electronic and geometric configuration of metal sites plays a pivotal role in regulating the interaction of catalytic surfaces with adsorbate molecules. By defining the d-band center as a descriptor of the structure-activity relationship, the individual contribution of strain effects within state-of-the-art electrocatalysts can be systematically elucidated in the OER optimization mechanism. In this review, the fundamentals of the OER and the advancements of strain-catalysts are showcased and the innovative trigger strategies are enumerated, with particular emphasis on the feedback mechanism between the precise regulation of lattice-strain and optimal activity. Subsequently, the modulation of electrocatalysts with various attributes is categorized and the impediments encountered in the practicalization of strained effect are discussed, ending with an outlook on future research directions for this burgeoning field.

In-situ growth of 3D hierarchical γ-FeOOH/Ni3S2 heterostructure as high performance electrocatalyst for overall water splitting

Obtaining efficient, stable, and low-cost electrocatalysts is the key to realizing large-scale water splitting. In this work, three-dimensional (3D) hierarchical γ-iron oxyhydroxide (γ-FeOOH)/Ni₃S₂ electrocatalyst on Ni foam is constructed for electrochemical overall water splitting. The 3D γ-FeOOH/Ni₃S₂ heterostructure can effectively enhance active sites and charge transfer capability, also the heterostructure can benefit electronic effect at the interfaces and synergistic effect of multiple components. Therefore, the γ-FeOOH/Ni₃S₂ exhibits excellent electrocatalytic activity with low overpotentials of 279 mV at 50 mA⋅cm^-2 for oxygen evolution reaction and 92 mV at 10 mA⋅cm^-2 for hydrogen evolution reaction, respectively. In addition, only a potential of 1.66 V is needed to attain 10 mA⋅cm^-2 for the overall water splitting. In particular, the γ-FeOOH/Ni₃S₂ exhibits long-term stability for 120 h at 10 mA⋅cm^-2 without significant degradation. This work provides a valuable idea for obtaining low-cost and high performance bifunctional electrocatalysts for water splitting.

Recent Advances on Transition-Metal-Based Layered Double Hydroxides Nanosheets for Electrocatalytic Energy Conversion

Transition-metal-based layered double hydroxides (TM-LDHs) nanosheets are promising electrocatalysts in the renewable electrochemical energy conversion system, which are regarded as alternatives to noble metal-based materials. In this review, recent advances on effective and facile strategies to rationally design TM-LDHs nanosheets as electrocatalysts, such as increasing the number of active sties, improving the utilization of active sites (atomic-scale catalysts), modulating the electron configurations, and controlling the lattice facets, are summarized and compared. Then, the utilization of these fabricated TM-LDHs nanosheets for oxygen evolution reaction, hydrogen evolution reaction, urea oxidation reaction, nitrogen reduction reaction, small molecule oxidations, and biomass derivatives upgrading is articulated through systematically discussing the corresponding fundamental design principles and reaction mechanism. Finally, the existing challenges in increasing the density of catalytically active sites and future prospects of TM-LDHs nanosheets-based electrocatalysts in each application are also commented.

Polymetallic sulfide nanosheet arrays with composite structure as a highly efficient oxygen evolution electrocatalyst

Designing an earth-abundant and cost-effective electrocatalyst for oxygen evolution reaction (OER) is the crux to the hydrogen production by water electrolysis on industrial scale. Herein, we developed a trimetallic sulfide hybrid of CoS_1.097/Fe_1-xS/Ni₃S₂/NF nanoarrays by the combination of morphology optimization and interface modulation. The unique morphology of ultrathin nanosheets significantly enriches the reaction sites of the catalyst, while the abundant heterogeneous interfaces effectively regulate the local electron structure and thus intrinsically enhances the catalytic activity of the material. As a result, the catalyst delivers the superior OER performance with the ultralow overpotential of 229 mV at the current density of 50 mA cm^-2 and Tafel slope of 30.2 mV dec^-1. Furthermore, the current density of the material keeps constant for 50 h in 1.0 M KOH. This work proposes a strategy for the synthesis of polymetallic sulfide catalysts with composite structure as an efficient OER catalyst by morphology optimization and interface modulation.

Tuning the Interface of Co1-xS/Co(OH)F by Atomic Replacement Strategy toward High-Performance Electrocatalytic Oxygen Evolution

The construction of heterostructures is one of the most promising strategies for engineering interfaces of catalysts to perform high-efficiency oxygen evolution reaction (OER). However, accurately tuning heterostructures' interface during operation remains a challenge. Herein, we fabricated the needled-like heterostructure Co_1-xS/Co(OH)F supported on flexible carbon fiber cloth via an atomic substitution strategy, in which sulfur atoms are simultaneously grafted into F vacancies after the partial removal of F atoms from Co(OH)F during the electrodeposition, thus achieving the growth of cobalt sulfide on the interface of Co(OH)F. This electrocatalyst with such design exhibits the following advantages: (1) The lattice distortion caused by atomic substitution leads to the increase of active sites; (2) Co_1-xS constructed on the surface of Co(OH)F by the atomic replacement strategy optimizes the adsorption (OH^-) and desorption (O₂) energy in the OER process; (3) the needle-like structure possesses the tip-enhanced local electric field effect. As a result, the Co_1-xS/Co(OH)F/CC catalyst exhibits very high OER catalytic performance with an overpotential of 269 mV at a current density of 10 mA cm^-2 and a Tafel slope of 71 mV dec^-1. The asymmetric electrode shows superior catalytic activity and stability in overall water splitting. The catalytic mechanism of these highly efficient Co_1-xS/Co(OH)F/CC catalysts was investigated via DFT theoretical calculations and ex situ characterizations. This atomic substitution strategy displays universality for other transition metal sulfides (metal = Ni, Mn, Cu).

Introducing a Synergistic Ligand Containing an Exotic Metal in Metal-Organic Framework Nanoarrays Enabling Superior Electrocatalytic Water Oxidation Performance

Designing and fabricating well-aligned metal-organic framework nanoarrays (MOF NAs) with high electrocatalytic activity and durability for water oxidation at large current density remain huge challenges. Here the vertical NiFc-MOF NAs constructed from agaric-like nanosheets were fabricated by introducing a ligand containing an exotic Fe atom to coordinate with Ni ion using Ni(OH)₂ NAs as a self-sacrificing template. The NiFc-MOF NAs exhibited superior water oxidation performance with a very low overpotential of 161 mV at the current density of 10 mA cm^-2. Chronoamperometry was tested at an overpotential of 250 mV, which delivered an initial industrial-grade current density of 702 mA cm^-2 and still remained at 694 mA cm^-2 after 24 h. Furthermore, it possessed fast reaction kinetics with a small Tafel slope of 29.5 mV dec^-1. The superior electrocatalytic performance can be ascribed to the structural advantage of vertically grown agaric-like NAs and the synergistic electron coupling between Ni and Fe atoms, namely, electron transfer from Ni to Fe atoms in NiFc-MOF NAs. The exposed density and valence state of active Ni sites were synchronously increased. Furthermore, the energy barrier for the adsorption/desorption of oxygenated intermediates was ultimately optimized for water oxidation. This work provides a novelty orientation to accelerate electrocatalytic performance of MOF NAs by introducing self-sacrificing templates containing one metal and synergistic ligand containing dissimilar metal.

A yolk-shell structure construction for metal-organic frameworks toward an enhanced electrochemical water splitting catalysis

NiFe-based transition metal catalysts are widely used in electrocatalysis, especially in the field of water splitting, due to their excellent electrochemical performance. Herein, a simple method was designed to synthesize a Ni MOF based on nickel foam and it was modified with Fe. After the introduction of Fe, the resulting material exhibits an obvious yolk-shell structure, which greatly increases the specific surface area and facilitates the construction of active sites. At the same time, the synergy between Ni and Fe is conducive to optimizing the electronic structure and effectively improving the poor stability of the MOF. As a result, the synthesized Ni MOF-Fe-2 only needs an overpotential of 229 mV to achieve the OER at a current density of 10 mA cm^-2, which is better than most reported transition metal-based electrocatalysts. To our surprise, it showed extraordinary stability under the voltage used for water splitting.

Fundamental understanding of electrocatalysis over layered double hydroxides from the aspects of crystal and electronic structures

Layered double hydroxides (LDHs) composed of octahedral ligand units centered with various transition metal atoms display unique electronic structures and thus attract significant attention in the field of electrocatalytic oxygen evolution reactions (OER). Intensive experimental explorations have therefore been carried out to investigate the LDHs synthesis, amorphous control, intrinsic material modifications, interfacing with other phases, strain, etc. There is still the need for a fundamental understanding of the structure-property relations, which could hinder the design of the next generation of the LDHs catalysts. In this review, we firstly provide the crystal structure information accompanied by the corresponding electronic structures. Then, we discuss the conflicts of the active sites on the NiFe LDHs and propose the synergistic cooperation among the ligand units during OER to deliver a different angle for understanding the current structure-property relations beyond the single-site-based catalysis process. In the next section of the OER process, the linear relationship-induced theoretical limit of the overpotential is further discussed based on the fundamental aspects. To break up the linear relations, we have summarized the current strategies for optimizing the OER performance. Lastly, based on the understanding gained above, the perspective of the research challenges and opportunities are proposed.

Robust NiCoP@FeP derived from Prussian blue analog for efficient overall water splitting

The design of efficient, stable, and non-noble metal based bifunctional electrocatalysts remains a great challenge. The synergistic effect can adjust the local electronic structure to improve the catalytic performance. In...

Recent Advances in Alkaline Exchange Membrane Water Electrolysis and Electrode Manufacturing

Water electrolysis to obtain hydrogen in combination with intermittent renewable energy resources is an emerging sustainable alternative to fossil fuels. Among the available electrolyzer technologies, anion exchange membrane water electrolysis (AEMWE) has been paid much attention because of its advantageous behavior compared to other more traditional approaches such as solid oxide electrolyzer cells, and alkaline or proton exchange membrane water electrolyzers. Recently, very promising results have been obtained in the AEMWE technology. This review paper is focused on recent advances in membrane electrode assembly components, paying particular attention to the preparation methods for catalyst coated on gas diffusion layers, which has not been previously reported in the literature for this type of electrolyzers. The most successful methodologies utilized for the preparation of catalysts, including co-precipitation, electrodeposition, sol-gel, hydrothermal, chemical vapor deposition, atomic layer deposition, ion beam sputtering, and magnetron sputtering deposition techniques, have been detailed. Besides a description of these procedures, in this review, we also present a critical appraisal of the efficiency of the water electrolysis carried out with cells fitted with electrodes prepared with these procedures. Based on this analysis, a critical comparison of cell performance is carried out, and future prospects and expected developments of the AEMWE are discussed.

NiFe Layered-Double-Hydroxide Nanosheet Arrays on Graphite Felt: A 3D Electrocatalyst for Highly Efficient Water Oxidation in Alkaline Media

It is of great importance to rationally design and develop earth-abundant nanocatalysts for high-efficiency water electrolysis. Herein, NiFe layered double hydroxide was in situ grown hydrothermally on a 3D graphite felt (NiFe LDH/GF) as a high-efficiency catalyst in facilitating the oxygen evolution reaction (OER). In 1.0 M KOH, NiFe LDH/GF requires a low overpotential of 214 mV to deliver a geometric current density of 50 mA cm^-2 (η_{50 mA cm^-2} = 214 mV), surpassing that NiFe LDH supported on a 2D graphite paper (NiFe LDH/GP; η_{50 mA cm^-2} = 301 mV). More importantly, NiFe LDH/GF shows good durability at 50 mA cm^-2 within 50 h of OER catalysis testing and delivers a faradaic efficiency of nearly 100% in the electrocatalysis of OER.

Characterization and Electrochemical Behaviour of Nanoscale Hydrotalcite-Like Compounds toward the Reduction of Nitrate

In this research, nano Cu/Al–HTLCs, Co/Al–HTLCs and Cu/Co/Al–HTLCs were synthesized, characterized, and tested in electrolytic reduction nitrate. Experimental results showed that Cu/Al–HTLCs were less stable than Co/Al–HTLCs due to the Jahn–Teller effect. However, electrocatalytic activity of copper was superior to that of cobalt; thus, Cu/Co/Al–HTLCs were selected based on their stable crystalline structure and electrochemical activity. The optimized Cu₂CoAl–HTLC was highly active in nitrate reduction, with two peaks for nitrate and nitrite reduction, respectively. Ammonia, nitrite and N-containing gases were found to be the final products of constant potential electrolysis at −0.54 and −0.74 V.