Predictive fabrication of Ni phosphide embedded in carbon nanofibers as active and stable electrocatalysts

Abstract

Although numerous first-principle studies have suggested candidate materials that may be used as enhanced electrocatalysts, the synthesis of such materials is quite another challenge. Furthermore, it has been still necessary to combine the active material with a supporting matrix in an optimized structure for stability and surface accessibility. Herein, we report a predictive fabrication method for the system where NiP₂ nanoparticles has beenevenly embedded in carbon nanofibers (CNFs), which is expected to be superior by theoretical calculation but not successfully made so far. Through thermodynamic considerations on the inter-component reactions against processing variables, such as temperature, partial pressure of oxygen and phosphorus (pO₂, pP₄), a suitable two-step synthesis route consisting of successive pO₂-controlled carbonization and pP₄-controlled phosphidation was deduced. The obtained NiP₂/CNFs had the desired electrocatalytic properties as well as physical features, including maximized surface area and well-combined structure. Consequently, the catalysts had overpotentials of only 71 mV at 10 mA cm⁻² and long-term stability of over 100 hours with less than 10% degradation under the operating conditions.