Interfacial and electronic modulation of FeP–CoP on reduced graphene aerogel boosts bifunctional catalysis for overall water splitting

Abstract

Sustainable H₂ production demands efficient bifunctional water-splitting catalysts. We present a novel 3D flower-like architecture of reduced graphene aerogel (rGA)-confined FeP–CoP nanoarrays self-assembled on nickel foam (FeP–CoP@rGA/NF) via hydrothermal growth and phosphidation. This unique architecture enhances structural stability, prevents particle agglomeration, and facilitates rapid charge/mass transport. The catalyst shows excellent electrocatalytic performance, requiring only 36 mV@10 mA cm⁻² for HER and 241 mV@50 mA cm⁻² for OER in 1 M KOH, respectively, outperforming most bifunctional catalysts. Remarkably, FeP–CoP@rGA/NF drives overall water splitting in alkaline electrolyte at 1.635 V@50 mA cm⁻² with nearly 100% faradaic efficiency. For zinc–air batteries, a high open-circuit voltage (1.5 V), remarkable peak power density (120 mW cm⁻²), and excellent current density capability (300 mA cm⁻²) are achieved. Density functional theory (DFT) calculations show that the synergy between rGA and FeP–CoP significantly accelerates OER/HER by regulating the electronic structure. In situ surface-enhanced infrared spectroscopy reveals that rGA optimizes the interfacial water structure, thereby enhancing overall water splitting efficiency. These findings provide important guidance for the design of efficient bifunctional catalysts in water electrocatalysis and diverse electrochemical energy systems.