Electrochemical activation-induced surface-reconstruction of NiOx microbelt superstructure of core-shell nanoparticles for superior durability electrocatalysis

Multi-layered heterogeneous interfaces created in Co0.85Se@Ni3S4/NF to enhance supercapacitor performances by multi-step alternating electrodeposition

Heterogeneous interface construction is of far-reaching significance to optimize the electrochemical performance of electrodes. Herein, a multi-step alternating electrochemical deposition (MAED) method is proposed to alternately deposit Co0.85Se and Ni3S4 nanosheets on a nickel foam (NF), forming a special alternate layer-by-layer structure with multi-layered heterogeneous interfaces. The creation of the multi-layered heterogeneous interfaces provides a large interfacial area for redox reactions with optimum interstitials facilitating ion diffusion, thus greatly improving the electrochemical energy storage efficiency. With the increase in the layer number, the material exhibits increasingly better energy storage performance, and 8L-Co0.85Se@Ni3S4/NF exhibits the highest specific capacitances of 2508 F g-1 and 1558 F g-1 at a scan rate of 2 mV s-1 and a current density of 1 A g-1. The 8L-Co0.85Se@Ni3S4/NF//polypyrrole (PPy)/NF asymmetric supercapacitor provides a maximum operation potential window of 1.55 V and energy densities of 76.98 and 35.74 W h kg-1 when the power densities are 775.0 and 15 500 W kg-1, respectively, superior to most of the related materials reported. Through MAED, the deposited phase and the layer number can be accurately controlled, thus providing an efficient strategy for interface construction so as to increase the electrochemical activity of the energy storage materials.

Controllable Phase Separation Engineering of Iron-Cobalt Alloy Heterojunction for Efficient Water Oxidation

The tailor-made transition metal alloy-based heterojunctions hold a promising prospect for the electrocatalytic oxygen evolution reaction (OER). Herein, a series of iron-cobalt bimetallic alloy heterojunctions are purposely designed and constructed via a newly developed controllable phase separation engineering strategy. The results show that the phase separation process and alloy component distribution rely on the metal molar ratio (Fe/Co), indicative of the metal content dependent behavior. Theoretical calculations demonstrate that the electronic structure and charge distribution of iron-cobalt bimetallic alloy can be modulated and optimized, thus leading to the formation of an electron-rich interface layer, which likely tunes the d-band center and reduces the adsorption energy barrier toward electrocatalytic intermediates. As a result, the Fe0.25Co0.75/Co heterojunction exhibits superior OER activity with a low overpotential of 185 mV at 10 mA cm-2. Moreover, it can reach industrial-level current densities and excellent durability in high-temperature and high-concentration electrolyte (30 wt % KOH), exhibiting enormous potential for industrial applications.

Recent progress of Ni-based nanomaterials for the electrocatalytic oxygen evolution reaction at large current density

The precise design and development of high-performing oxygen evolution reaction (OER) for the production of industrial hydrogen gas through water electrolysis has been a widely studied topic. A profound understanding of the nature of electrocatalytic processes reveals that Ni-based catalysts are highly active toward OER that can stably operate at a high current density for a long period of time. Given the current gap between research and applications in industrial water electrolysis, we have completed a systematic review by constructively discussing the recent progress of Ni-based catalysts for electrocatalytic OER at a large current density, with special focus on the morphology and composition regulation of Ni-based electrocatalysts for achieving extraordinary OER performance. This review will facilitate future research toward rationally designing next-generation OER electrocatalysts that can meet industrial demands, thereby promoting new sustainable solutions for energy shortage and environment issues.

P-doped Co3S4/NiS2 heterostructures embedded in N-doped carbon nanoboxes: Synergistical electronic structure regulation for overall water splitting

Water splitting using transition metal sulfides as electrocatalysts has gained considerable attention in the field of renewable energy. However, their electrocatalytic activity is often hindered by unfavorable free energies of adsorbed hydrogen and oxygen-containing intermediates. Herein, phosphorus (P)-doped Co3S4/NiS2 heterostructures embedded in N-doped carbon nanoboxes were rationally synthesized via a pyrolysis-sulfidation-phosphorization strategy. The hollow structure of the carbon matrix and the nanoparticles contained within it not only result in a high specific surface area, but also protects them from corrosion and acts as a conductive pathway for efficient electron transfer. Density functional theory (DFT) calculations indicate that the introduction of P dopants improves the conductivity of NiS2 and Co3S4, promotes the charge transfer process, and creates new electrocatalytic sites. Additionally, the NiS2-Co3S4 heterojunctions can enhance the adsorption efficiency of hydrogen intermediates (H*) and lower the energy barrier of water splitting via a synergistic effect with P-doping. These characteristics collectively enable the titled catalyst to exhibit excellent electrocatalytic activity for water splitting in alkaline medium, requiring only small overpotentials of 150 and 257 mV to achieve a current density of 10 mA cm-2 for hydrogen and oxygen evolution reactions, respectively. This work sheds light on the design and optimization of efficient electrocatalysts for water splitting, with potential implications for renewable energy production.

Synergistically engineering of vacancy and doping in thiospinel to boost electrocatalytic oxygen evolution in alkaline water and seawater

Electronic structure engineering lies at the heart of the catalyst design, however, utilizing one strategy to modify the electronic structure is still challenging to achieve optimal electronic states. Herein, an advanced approach that incorporating both Ru dopants and sulfur vacancies into thiospinel-type FeNi2S4 to synergistically modulate the electronic configuration, is proposed. Deep characterizations and theoretical study reveal that the in-situ formed Ni3+ species are real active centers. Ru doping and sulfur vacancies synergistically tune the electronic states of Ni2+ sites to a near-optimal value, leading to the formation of abundant oxygen evolution reaction (OER)-active Ni3+ species via electrochemical reconstruction. Consequently, the optimized Ru-FeNi2S4 catalyst can exhibit superb electrocatalytic performance towards OER, delivering the overpotentials of 253 mV and 340.8 mV at 10 mA·cm-2 in alkaline water and seawater, respectively. The proper combination of vacancy and heteroatom doping in this work may unlock the catalytic power of conventional catalysts toward electrochemical reactions.

Densifying Crystalline-Amorphous Ni3S2/NiOOH Interfacial Sites To Boost Electrocatalytic O2 Production

The development of an efficient and low-cost electrocatalyst for oxygen evolution reaction (OER) is the key to improving the overall efficiency of water electrolysis. Here, we report the design of a three-dimensional (3-D) heterostructured Ni₉S₈/Ni₃S₂ precatalyst composed of unstable Ni₉S₈ and inert Ni₃S₂ components, which undergoes in situ electrochemical activation to generate an amorphous-NiOOH/Ni₃S₂ heterostructured catalyst. In situ Raman spectroscopy combined with ex situ characterizations, such as X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, reveals that during the activation, Ni₉S₈ loses the sulfur element to form nickel oxides and eventually transforms to amorphous NiOOH at O₂-evolving potentials, while the Ni₃S₂ component is rather inert that its majority in the bulk remains, thus forming a 3-D congee-like NiOOH/Ni₃S₂ heterostructure with the Ni₃S₂ crystalline particles randomly dispersed among amorphous NiOOH species. Unlike the sparse heterostructure that consists of a layer of NiOOH on top of Ni₃S₂, our unique congee-like NiOOH/Ni₃S₂ heterostructure provides plentiful reactive amorphous-crystalline interfacial sites. Moreover, the partial electron transfer between the NiOOH and remaining Ni₃S₂, benefiting from their dense interfacial sites, contributes to a higher valence state of the Ni³⁺ active centers in NiOOH, hence optimizing the adsorption of OER intermediates. Density functional theory calculations further disclose that the electronic structure regulation not only optimizes the Gibbs free energy of intermediate adsorption but also tunes the OH* absorption behavior to be exothermic, elucidating the spontaneous occurrence of OH* absorption and hence improves the OER. Therefore, a low overpotential of only 197 mV at an O₂-evolving current density of 10 mA/cm², a small Tafel slope of 38.8 mV/dec, and good stability are achieved on the amorphous-NiOOH/crystalline-Ni₃S₂ heterostructured catalyst.

Improved electrode kinetics of a modified Na3V2(PO4)3 cathode through Zr substitution and nitrogen-doped carbon coating towards robust electrochemical performance at low temperature

The substitution of V with Zr in a NASICON structure and an NC coating endow 0.1Zr-NVP/NC with excellent electrochemical performance at low temperature.