Ultrafine Co3O4 nanolayer-shelled CoWP nanowire array: a bifunctional electrocatalyst for overall water splitting

Large-scale sonochemical fabrication of a Co3O4-CoFe2O4@MWCNT bifunctional electrocatalyst for enhanced OER/HER performances

Herein, we have prepared a mixed-phase Co₃O₄-CoFe₂O₄@MWCNT nanocomposite through a cheap, large-scale, and facile ultrasonication route followed by annealing. The structural, morphological, and functional group analyses of the synthesized catalysts were performed by employing various characterization approaches such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The resultant samples were tested for bifunctional electrocatalytic activity through various electrochemical techniques: cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The prepared Co₃O₄-CoFe₂O₄@MWCNT nanocomposite achieved a very high current density of 100 mA cm^-2 at a lower (290 mV and 342 mV) overpotential (vs. RHE) and a smaller (166 mV dec^-1 and 138 mV dec^-1) Tafel slope in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, compared to Co₃O₄-CoFe₂O₄. The excellent electrochemical activity of the as-prepared electrocatalyst was attributed to the uniform incorporation of Co₃O₄-CoFe₂O₄ over MWCNTs which provides high redox active sites, a greater surface area, better conductivity, and faster charge mobility. Furthermore, the enhanced electrochemical active surface, low charge-transfer resistance (R_ct), and higher exchange current density (J₀) of the Co₃O₄-CoFe₂O₄@MWCNT ternary composite are attributed to its superior behavior as a bifunctional electrocatalyst. Conclusively, this study demonstrates a novel and large-scale synthesis approach for bifunctional electrocatalysts with a high aspect ratio and abundance of active sites for high-potential energy applications.

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.

Synergistically Coupled CoMo/CoMoP Electrocatalyst for Highly Efficient and Stable Overall Water Splitting

Finding reservoir-rich and efficient bifunctional electrocatalysts for water splitting is key to further sustainable energy development. Transition metal phosphides (TMPs) are extensively exploited as effective electrocatalysts, but the construction of strong coupling interfaces to improve catalytic performance by simple methods is still a bottleneck. Here, we designed and prepared a novel heterostructure electrocatalyst composed of cobalt-molybdenum (CoMo) alloy particles integrated with CoMoP nanosheets via the method of template-assisted conversion, followed by electrodeposition. Thanks to the strong interfacial coupling and synergistic effect between CoMo alloy particles and CoMoP nanosheets, the prepared CoMo/CoMoP/NF shows outstanding activity with overpotentials of only 29 mV for the hydrogen evolution reaction (HER) and 246 mV for the oxygen evolution reaction (OER) in 1 M KOH at a current density of 10 mA cm^-2. Furthermore, the assembled CoMo/CoMoP || CoMo/CoMoP electrode can attain 10 mA cm^-2 with a low battery voltage of 1.54 V. This study offers a valuable reference to the construction of bimetallic alloy/bimetallic phosphide heterostructure electrocatalysts, which applies to the large-scale application of electrocatalytic energy conversion technology.

Recent advances in the metal–organic framework-based electrocatalysts for the hydrogen evolution reaction in water splitting: a review

Water splitting is an important technology for alternative and sustainable energy storage, and a way for the production of hydrogen without generating pollution.