Controlled synthesis of CeOx-NiCo2O4 nanocomposite with 3D umbrella-shaped hierarchical structure: A sharp-tip enhanced electrocatalyst for efficient oxygen evolution reaction over a broad pH region

Synergistic enhancement of oxygen vacancy enrichment and morphology regulation in CeO2-NiCo2O4 heterostructure catalysts for high-performance cathodes in direct borohydride-hydrogen peroxide fuel cells

Hydrogen peroxide (H2O2) emerges as a viable oxidant for fuel cells, necessitating the development of an efficient and cost-effective electrocatalyst for the hydrogen peroxide reduction reaction (HPRR). In this study, we synthesized a self-supporting, highly active HPRR electrocatalyst comprising two morphologically distinct components: CeO2-NiCo2O4 nanowires and CeO2-NiCo2O4 metal organic framework derivatives, via a two-step hydrothermal process followed by air calcination. X-ray diffraction and transmission electron microscopy analysis confirmed the presence of CeO2 and NiCo2O4, revealing the amalgamated interface between them. CeO2 exhibits multifunctionality in regulating the surface electronic configuration of NiCo2O4, fostering synergistic connections, and introducing oxygen deficiencies to enhance the catalytic efficacy in HPRR. Electrochemical measurements demonstrate a reduction current density of 789.9 mA·cm-2 at -0.8 V vs. Ag/AgCl. The assembly of direct borohydride-hydrogen peroxide fuel cell (DBHPFC) exhibits a peak power density of 45.2 mW·cm-2, demonstrating durable stability over a continuous operation period of 120 h. This investigation providing evidence that the fabrication of heterostructured catalysts based on CeO2 for HPRR is a viable approach for the development of high-efficiency electrocatalysts in fuel cell technology.

Anchoring Ni(OH)2-CeOx Heterostructure on FeOOH-Modified Nickel-Mesh for Efficient Alkaline Water-Splitting Performance with Improved Stability under Quasi-Industrial Conditions

Developing low-cost and industrially viable electrode materials for efficient water-splitting performance and constructing intrinsically active materials with abundant active sites is still challenging. In this study, a self-supported porous network Ni(OH)2-CeOx heterostructure layer on a FeOOH-modified Ni-mesh (NiCe/Fe@NM) electrode is successfully prepared by a facile, scalable two-electrode electrodeposition strategy for overall alkaline water splitting. The optimized NiCe0.05/Fe@NM catalyst reaches a current density of 100 mA cm-2 at an overpotential of 163 and 262 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1.0 m KOH with excellent stability. Additionally, NiCe0.05/Fe@NM demonstrates exceptional HER performance in alkaline seawater, requiring only 148 mV overpotential at 100 mA cm-2. Under real water splitting conditions, NiCe0.05/Fe@NM requires only 1.701 V to achieve 100 mA cm-2 with robust stability over 1000 h in an alkaline medium. The remarkable water-splitting performance and stability of the NiCe0.05/Fe@NM catalyst result from a synergistic combination of factors, including well-optimized surface and electronic structures facilitated by an optimal Ce ratio, rapid reaction kinetics, a superhydrophilic/superaerophobic interface, and enhanced intrinsic catalytic activity. This study presents a simple two-electrode electrodeposition method for the scalable production of self-supported electrocatalysts, paving the way for their practical application in industrial water-splitting processes.

Microplotter Printing of a Miniature Flexible Supercapacitor Electrode Based on Hierarchically Organized NiCo2O4 Nanostructures

The hydrothermal synthesis of a nanosized NiCo₂O₄ oxide with several levels of hierarchical self-organization was studied. Using X-ray diffraction analysis (XRD) and Fourier-transform infrared (FTIR) spectroscopy, it was determined that under the selected synthesis conditions, a nickel-cobalt carbonate hydroxide hydrate of the composition M(CO₃)_0.5(OH)·0.11H₂O (where M-Ni²⁺ and Co²⁺) is formed as a semi-product. The conditions of semi-product transformation into the target oxide were determined by simultaneous thermal analysis. It was found by means of scanning electron microscopy (SEM) that the main powder fraction consists of hierarchically organized microspheres of 3-10 μm in diameter, and individual nanorods are observed as the second fraction of the powder. Nanorod microstructure was further studied by transmission electron microscopy (TEM). A hierarchically organized NiCo₂O₄ film was printed on the surface of a flexible carbon paper (CP) using an optimized microplotter printing technique and functional inks based on the obtained oxide powder. It was shown by XRD, TEM, and atomic force microscopy (AFM) that the crystalline structure and microstructural features of the oxide particles are preserved when deposited on the surface of the flexible substrate. It was found that the obtained electrode sample is characterized by a specific capacitance value of 420 F/g at a current density of 1 A/g, and the capacitance loss during 2000 charge-discharge cycles at 10 A/g is 10%, which indicates a high material stability. It was established that the proposed synthesis and printing technology enables the efficient automated formation of corresponding miniature electrode nanostructures as promising components for flexible planar supercapacitors.

Boosting oxygen evolution electrocatalysis via CeO2 engineering on Fe2N nanoparticles for rechargeable Zn-air batteries

In the process of developing low-cost and high-performance bifunctional electrocatalysts, rational selection of catalytic components and tuning of their electronic structures to achieve synergistic effects is a feasible approach. In this work, CeO₂ was composited into Fe/N-doped carbon foam by a molten salt method to improve the electrocatalytic performance of the composite catalyst for the oxygen evolution reaction (OER). The results showed that the excitation of oxygen vacancies in CeO₂ accelerated the migration of oxygen species and enhanced the oxygen storage/release capacity of the as-prepared catalyst. Meanwhile, the size effect of CeO₂ particles enabled the timely discharge of gas bubbles from the reaction system and thus improved the OER kinetics. In addition, a large number of pyridine-N species were induced by CeO₂-doping and sequentially anchored in the carbon matrix. As a result, the Fe₂N active state was formed through the strengthened binding of Fe-N elements. Benefiting from the strong electronic interaction between Fe₂N and CeO₂ components, the optimal CeO₂-Fe₂N/NFC_-2 catalyst sample showed a good OER performance (E_j=10 = 266 mV) and ORR electrocatalytic activity (E_1/2 = 0.87 V). The practical feasibility tests indicated that the Zn-air battery assembled by the CeO₂-Fe₂N/NFC_-2 catalyst exhibited a large energy density and an excellent long-term cycling stability.

Interfacial electronic modification of bimetallic oxyphosphides as Multi-functional electrocatalyst for water splitting and urea electrolysis

Electrochemical water or wastewater splitting is a sustainable development approach for both hydrogen generation and pollutant elimination. Herein, an N-engineering ultrathin bimetallic oxyphosphides nanosheets on Ni foam (CoNiOP/NF) as a multi-functional binder-free electrode was synthesized for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The catalytic activity of the composites could be improved through introducing N-doping via an in-situ transformation and heterogeneous metals by ion exchange. Both theoretical calculation and experimental investigations confirmed that electrons transferred from metal centers to anion at the interface, which was favor to accelerate the phase transformation to electrochemically active species and optimize the intermediates adsorption dynamics, thus providing greatly enhanced electrocatalytic activities. Assembled an electrolyzer using UOR replaced OER, it required only 1.42 V to achieve 50 mA cm^-2 with long-term stability, 214 mV less than that required for HER‖OER. This work would be beneficial for the exploitation of non-noble metal-based electrocatalysts for simultaneous realization of energy-saving urea-assisted electrolytic hydrogen production and urea-containing wastewater purifying.