Heteroatom-Doped Carbon-Encapsulated FeP Nanostructure: A Multifunctional Electrocatalyst for Zinc-Air Battery and Water Electrolyzer

The rational design and synthesis of efficient multifunctional electrocatalysts for renewable energy technologies is of significant interest. Herein, we demonstrate a novel approach for the synthesis of a nitrogen and phosphorus dual-doped mesoporous carbon-encapsulated iron phosphide (FeP@NPC) nanostructure and its multifunctional electrocatalytic activity toward an oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction for zinc-air battery (ZAB) and alkaline water-splitting applications. FeP@NPC is obtained by the carbothermal reduction of the precursor complex [Fe(bpy)(3)](PF6)(2) in the presence of melamine without any traditional phosphidating agent. The PF6- counteranion is used for the phosphidation of Fe. FeP@NPC obtained at 900 degrees C (FeP@NPC-900) exhibits excellent bifunctional oxygen electrocatalytic performance with a very low potential gap (Delta E = E-1/2(ORR) - E-j10(OER)) of 670 mV. The ZAB device delivers a peak power density of 190.15 mW cm(-2) (iR-corrected), specific capacity of 785 mA h g(zn)(-1), and energy density of 706.5 Wh kg(zn)(-1) at SO mA cm(-2). The ZAB exhibits excellent charge-discharge cycling stability for over 35 h with negligible voltaic efficiency loss (0.9%). Three CR2032 coin-cell-based ZABs made of an FeP@NPC-900 air cathode connected in series power 81 LEDs for 15 min. FeP@NPC-900 also has promising electrocatalytic activity toward water splitting in acidic as well as in alkaline pH. The benchmark current density of 10 mA cm(-2) is achieved with a two-electrode alkaline water electrolyzer at a cell voltage of 1.65 V. ZAB-powered water electrolyzer is made by integrating two rechargeable ZABs connected in series with the two-electrode water electrolyzer. The ZAB powers the electrolyzer for 24 h without a significant loss in the open-circuit voltage. The catalyst retains its initial structural integrity even after continuous water electrolysis for 24 h.

Automated summary

In this study, a nitrogen and phosphorus dual-doped mesoporous carbon-encapsulated iron phosphide nanostructure was synthesized, and its multifunctional electrocatalytic activity towards various reactions in renewable energy technologies was demonstrated. The material showed excellent performance in zinc-air batteries and alkaline water-splitting applications.