Low-temperature pyrolysis enables FeNi₃ nanoparticle implanted N-doped carbon nanosheets as an efficient bifunctional electrocatalyst for overall water splitting

The creation of highly efficient and stable OER/HER bifunctional electrocatalysts is vital to advancing the practical application of electrocatalytic water splitting. Herein, we propose a facile yet reliable approach to produce FeNi₃ nanoparticle (NP) implanted N-doped carbon nanosheets (denoted as FeNi₃/NCS) as a powerful bifunctional catalyst towards electrocatalytic water splitting. Specifically, a melamine tube is first synthesized via a hydrothermal method, which is utilized as a self-supporting template to grow FeNi-LDH, yielding melamine tube@FeNi-LDH. Sequentially, the FeNi₃ NP embedded N-doped carbon nanosheets are achieved by low-temperature pyrolysis of melamine tube@FeNi-LDH at 400 °C. The resulting FeNi₃/NCS electrocatalyst displays outstanding OER/HER catalytic performance and stability in alkaline media. The overpotential for the OER is 260 mV, outperforming the control samples of NCT, FeNiO/C, FeNi/NC and even benchmark RuO₂ (300 mV). The HER overpotential is also significantly reduced compared with the control samples. The impressive bifunctional activity of FeNi₃/NCS is primarily attributed to the synergistic effect between FeNi₃ NPs and N-doped carbon, which is substantiated by both experimental results (i.e., overpotential and XPS) and DFT simulation (i.e., Gibbs free energy, electron density difference, etc.). The FeNi₃/NCS-assembled water splitting device requires only 1.53 V of cell voltage to drive a current density of 10 mA cm⁻², surpassing the counterparts of RuO₂-Pt/C, NCT, FeNiO/C, and various reported FeNi-containing electrocatalysts. The combination of hydrothermal and low-temperature pyrolysis strategies will shed light on the design and preparation of LDH-derived high-performance and stable bifunctional electrocatalysts for overall water splitting.