Porous Indium Tin Oxide-Supported NiFe LDH as a Highly Active Electrocatalyst in the Oxygen Evolution Reaction and Flexible Zinc-Air Batteries

Innovative InAg-carbon nanocomposites: mesoporous design for OER enhancement

To produce clean and sustainable hydrogen energy through water electrolysis, the sluggish oxygen evolution reaction (OER) needs to be accelerated sustainably by using stable and highly effective electrocatalysts. Bimetallic nanocomposites have been recently recognized as an interesting class of electrocatalysts because of their synergistic behaviour, tunable morphology, and high catalytic efficiency. Herein, InC, AgC, and InAgC nanocomposites were synthesised via a hydrothermal method using a mesoporous carbon support derived from the carbonisation of giant cane. The structural characterisation revealed that the InC composite has tetragonal In with a minor presence of cubic In2O3, whereas AgC and InAgC are well aligned with cubic Ag and tetragonal In. Electron microscopy revealed that InC has a 3D plate-like structure, while InAgC exhibits a spherical shape and is uniformly dispersed across the carbon surface. InAgC showed excellent activity and durability for the OER, with a notably low overpotential of 480 mV at a current density of 100 mA cm-2, a Tafel slope of 97 mV dec-1, and an oxygen production turnover frequency of 10.19 s-1. The chronoamperometric (i-t) study of InAgC at 1.58 V vs. RHE for 20 h in 1 M KOH indicates that the catalyst is highly stable for the OER in alkaline electrolytes. The electrochemical double-layer capacitance (Cdl) value in the non-faradaic potential region of InAgC is greater (52.14 mF cm-2) than those of mesoporous carbon (16.54 mF cm-2), AgC (33.10 mF cm-2), and InC (48.77 mF cm-2), which is attributed to InAgC having more accessible active sites for the OER. This work presents numerous possibilities for developing effective nanocomposites using giant cane as a natural carbon source.

Reconstructed Hydroxyl Coordination Field Enhances Mass Transfer for Efficient Electrocatalytic Water Oxidation

Mass transfer factor plays an indispensable role in high current density to accelerate the oxygen evolution reaction (OER) process, yet research on modulating reactant mass transport remains limited. Herein, by leveraging the dual acid-base properties of aluminum sites, both the activation of the electronic activity of the layer for layered double hydroxides (LDH) and construction of the interlayer hydroxide coordination field (IHCF) have been achieved through in situ electrochemical reconstruction. It not only facilitates charge transfer and the surface catalytic transformation of reaction intermediates but, most notably, the presence of the IHCF significantly enhances the mass transport of reactants. As a result, the overpotential of LDHs with IHCF is only 164 mV, significantly better than the reported Ni-based catalysts. Deuterium kinetic isotope effect experiments and pH-dependence measurements demonstrate that the IHCF effectively enhances substrate mass transport capability and structural stability, thereby accelerating the proton-coupled electron transfer process. To further validate the high mass transport characteristics, stability tests of the alkaline flow electrolyzer show that catalysts maintain over 1000 h of stability at a high current density. This work suggests that the IHCF effect can be utilized for further design and synthesis of efficient water oxidation catalysts for practical application.

Synergistic dual sites of Zn-Mg on hierarchical porous carbon as an advanced oxygen reduction electrocatalyst for Zn-air batteries

The development of cost-effective and high-performance non-noble metal catalysts for the oxygen reduction reaction (ORR) holds substantial promise for real-world applications. Introducing a secondary metal to design bimetallic sites enables effective modulation of a metal-nitrogen-carbon (M-N-C) catalyst's electronic structure, providing new opportunities for enhancing ORR activity and stability. Here, we successfully synthesized an innovative hierarchical porous carbon material with dual sites of Zn and Mg (Zn/Mg-N-C) using polymeric ionic liquids (PILs) as precursors and SBA-15 as a template through a bottom-up approach. The hierarchical porous structure and optimized Zn-Mg bimetallic catalytic centers enable Zn/Mg-N-C to exhibit a half-wave potential of 0.89 V, excellent stability, and good methanol tolerance in 0.1 M KOH solution. Theoretical calculations indicated that the Zn-Mg bimetallic sites in Zn/Mg-N-C effectively lowered the ORR energy barrier. Furthermore, the Zn-air batteries assembled based on Zn/Mg-N-C demonstrated an outstanding peak power density (298.7 mW cm-2) and superior cycling stability. This work provides a method for designing and synthesizing bimetallic site catalysts for advanced catalysis.

P-Block Metal-Based Electrocatalysts for Nitrogen Reduction to Ammonia: A Minireview

Electrochemical nitrogen reduction reaction (NRR) to ammonia (NH₃ ) using renewable electricity provides a promising approach towards carbon neutral. What's more, it has been regarded as the most promising alternative to the traditional Haber-Bosch route in current context of developing sustainable technologies. The development of a class of highly efficient electrocatalysts with high selectivity and stability is the key to electrochemical NRR. Among them, P-block metal-based electrocatalysts have significant application potential in NRR for which possessing a strong interaction with the N 2p orbitals. Thus, it offers a good selectivity for NRR to NH₃ . The density of state (DOS) near the Fermi level is concentrated for the P-block metal-based catalysts, indicating the ability of P-block metal as active sites for N₂ adsorption and activation by donating p electrons. In this work, we systematically review the recent progress of P-block metal-based electrocatalysts for electrochemical NRR. The effect of P-block metal-based electrocatalysts on the NRR activity, selectivity and stability are discussed. Specifically, the catalyst design, the nature of the active sites of electrocatalysts and some strategies for boosting NRR performance, the reaction mechanism, and the impact of operating conditions are unveiled. Finally, some challenges and outlooks using P-block metal-based electrocatalysts are proposed.

Triethanolamine-assisted synthesis of NiFe layered double hydroxide ultrathin nanosheets for efficient oxygen evolution reaction

Water electrolysis is a promising technique for producing high-quality hydrogen, the application of which is impeded by the sluggish oxygen evolution reaction (OER) process. In this study, ultrathin nickel-iron layered double hydroxide (NiFe LDH) nanosheets were successfully synthesized through a facile hydrothermal reaction with the assistance of triethanolamine (TEA). Morphological and structural characterizations revealed that the presence of TEA modified the morphology of NiFe LDH, facilitated the synthesis of high-purity NiFe LDH, improved the crystallinity of NiFe LDH and resulted in a slight decrease in specific surface area. X-ray photoelectron spectroscopy (XPS) analysis demonstrated the modulation of the electronic structure engendered by the addition of TEA, with nickel and iron appearing in high valence state in the resulting NiFe LDH nanosheets. The as-prepared NiFe LDH nanosheets possessed outstanding OER activity with fast kinetics, exhibiting a low overpotential of 261 mV to achieve a current density of 10 mA cm-2 and a small Tafel slope of 32.5 mV dec-1 in 1 M KOH. The excellent OER performance and rapid OER kinetics are mainly attributed to the high-valence Ni and Fe rather than the modification in the morphology and microstructure.

In-site hydrogen bubble template method to prepare Ni coated metal meshes as effective bi-functional electrodes for water splitting

Metal substrates are frequently used as current collectors and supports for electrochemically active materials, but their effect on the physical and electrochemical performance of electrocatalysts is rarely investigated. In this study, the electrodeposition method was used to coat four different metal meshes with three-dimensional nickel porous structures using hydrogen bubbles as a template. The significant influence of the metal substrates on the morphology of deposited nickel was demonstrated. 3D porous structures formed on nickel, iron, copper, and titanium meshes via the hydrogen bubble template method varied significantly. It was found that differences in the physical adsorption of hydrogen and electrochemical hydrogen evolution on metal substrates are the fundamental reasons behind the diverse morphology of the coatings. Lattice matching of the substrate and the active material also plays an important role during the electrodeposition process. Electrocatalytic performance of the newly prepared materials in water electrolysis was evaluated using the hydrogen and oxygen evolution reactions (HER and OER). The results demonstrate the high electrocatalytic activity of Ni/FeM in the OER and HER, and the good stability of Ni/TiM in HER.

Layered FeCoNi double hydroxides with tailored surface electronic configurations induced by oxygen and unsaturated metal vacancies for boosting the overall water splitting process

Two-dimensional (2D) layered double hydroxides (LDH) with excellent hydrophilic ability and rapid hydroxyl insertion are regarded as one of the most promising electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) for overall water splitting to produce hydrogen. However, the electrocatalytic HER/OER activities can be restricted by the inert basal plane due to the poor conductivity, deficient active sites and inferior durability despite there being efficient active sites in the material edge. Thus, capturing many more exposed reactive sites to facilitate the rapid reaction kinetics is a crucial strategy. In this paper, both oxygen and unsaturated metal vacancies with FeCoNi LDH materials are generated through a surface activation approach by pre-covering of fluoride and a post-boronizing process. Such a material is grown on Ni foam to form an F-FeCoNi-Ov LDH/NF electrocatalyst. The activated surface of the electrocatalyst with oxygen vacancies and unsaturated metal sites shows enhanced electroconductivity for regulating the surface electronic structure and optimizing the surface adsorption energy for intermediates during HER/OER processes. As a result, this electrocatalyst exhibits excellent electrocatalytic performance for both the HER and OER with low overpotentials, small Tafel slopes and long durability. The enhancement mechanism is also studied deeply for fundamental understanding. For performance validation, an F-FeCoNi-Ov LDH/NF∥F-FeCoNi-Ov LDH/NF water splitting cell is fabricated and needs only 1.54 V and 1.81 V to reach current densities of 10 and 100 mA cm^-2, respectively. This work provides a practicable strategy to develop 2D LDH nanomaterials with boosted electrocatalytic activity for sustainable and clean energy storage systems.