Constructing Carbon-encapsulated NiFeV-based Electrocatalysts by Alkoxide-based Self-template Method for Oxygen Evolution Reaction
The development of green and sustainable water-splitting hydrogen production technology is conducive to reducing the over-reliance on fossil fuels and realizing the strategic goal of "carbon neutral". As one of the half reactions for water splitting, oxygen evolution reaction has suffered the problems of sluggish four-electron transfer process and relatively slow reaction kinetics. Therefore, exploring efficient and stable catalysts for oxygen evolution reaction is of critical importance for water-splitting technology. Metal alkoxides are a series of compounds formed by the coordination function of metal ions with alcohol molecules. Metal alkoxides possess the double advantages of organic materials and inorganic materials, which makes them reveal a promising application in the electrochemical field. In view of the poor activity and stability of the current oxygen evolution reaction electrocatalysts, this study has adopted the alkoxide-based self-template method to prepare the carbon-encapsulated NiFeV-based electrocatalysts through using the solid NiFeV-alkoxides as precursors. The organic components in solid metal alkoxides are employed to achieve the graphitized carbon encapsulation after the high-temperature calcination process, which is beneficial for improving the conductivity and corrosion resistance of catalysts. Through adjusting the V doping amounts and the calcination temperatures, the electronic structure of NiFe nanoparticles and carbon encapsulation are optimized, which are both key influence factors for oxygen evolution performances. As a result, the oxygen evolution catalysts with high activity and stability are obtained successfully in this work. The experimental results have shown that the NiFeV-based catalysts present a uniform spherical structure with carbon encapsulation. The current density of 20 mA·cm-2 can be obtained at the overpotential of only 381 mV as an electrocatalyst for oxygen evolution reaction in water electrolysis. After the continuous 10000 s durability test, the NiFeV-based catalyst exhibits a small reduction of current density and still maintains the catalytic activity almost similar to the initial test, revealing a good oxygen evolution stability. The excellent catalytic activity and stability of NiFeV-based catalysts are mainly attributed to the uniform spherical structure, the optimized regulation of V on the electronic structure and the protective effect of carbon encapsulation on metal particles. The V element in the catalysts exhibits the rich redox states of V3+, V4+ and V5+, which can effectively adjust the electronic structure of adjacent atoms and optimize the binding energy of oxygen reduction reaction intermediates, thus improving the electrocatalytic performance of catalysts. This work provides a useful guidance for improving the electrocatalytic performance of oxygen evolution catalysts through the V-doping and carbon encapsulation strategies.