A porous carbon layer wrapped Co3Fe7 alloy derived from a bimetallic conjugated microporous polymer as a trifunctional electrocatalyst for rechargeable Zn-air batteries and self-powered overall water splitting

Abstract

Herein, a N-doped porous carbon/Co₃Fe₇ alloy composite (FP-950) was prepared via direct carbonization of a cheap and readily available bimetallic conjugated microporous polymer (CMP), namely Fc–Por, composed of ferrocene (Fc) and Co–porphyrin (Co–Por), via the copolymerization of 1,1′-ferrocenedicarboxyaldehyde and pyrrole which could be manufactured in the industrial scale in the presence of cobaltous acetate. The special carbon encapsulation structure of nanohybrids promotes the synergistic effect of Co₃Fe₇ and Co_5.47N, which could protect the nanoparticles from the harsh environments. Moreover, the ultrahigh specific surface areas and the hierarchical pore structure are beneficial for the exposure of catalytically active sites. Hence, FP-950 exhibits a robust trifunctional electrocatalytic activity towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in alkaline media. For example, it exhibits an acceptable HER performance with an overpotential (E_over) of 299 mV at 10 mA cm⁻² and a small Tafel slope value of 144 mV dec⁻¹. Meanwhile, FP-950 also displays impressive activity towards the OER with a low operating overpotential of 346 mV and a small Tafel slope value of 89 mV dec⁻¹. Furthermore, FP-950 also presents acceptable ORR performance in alkaline environments which makes it an excellent catalyst for rechargeable Zn-air batteries with a high specific capacity of 792 mA h g_Zn⁻¹ and a super long life-time of 83 h (10 mA cm⁻²). By using FP-950 as the sole catalyst for full water splitting, an alkaline electrolyzer affords a cell voltage as low as 1.63 V at 10 mA cm⁻². Finally, this also revealed that FP-950 could be used for overall water splitting in a self-powered manner under ambient conditions with a high H₂ evolution rate of 569.5 μmol h⁻¹. This work paves the way for the rational fabrication of a low-cost trifunctional electrocatalyst which could be further applied in sustainable energy technologies.