Synchronous regulation of morphology and electronic structure of FeNi-P nanosheet arrays by Zn implantation for robust overall water splitting

FeNi-based phosphides are one of the most hopeful electrocatalysts, whereas the significant challenge is to achieve prominent bifunctional catalytic activity with low voltage for water splitting. The morphology and electronic structure of FeNi-based phosphides can intensively dominate effective catalysis, therefore their simultaneous regulating is extremely meaningful. Herein, a robust bifunctional catalyst of Zn-implanted FeNi-P nanosheet arrays (Zn-FeNi-P) vertically well-aligned on Ni foam is successfully fabricated by Zn implanting strategy. The Zn fulfills the role of electronic donor due to its low electronegativity to enhance the electronic density of FeNi-P for optimized water dissociation kinetics. Meanwhile, the implantation of Zn into FeNi-P can effectively regulate morphology of the catalyst from thick and irregular nanosheets to ultrathin lamellar structure, which generates enriched catalytic active sites, leading to accelerating electron/mass transport ability. Accordingly, the designed Zn-FeNi-P catalyst manifests remarkable hydrogen evolution reaction (HER) activity with low overpotentials of 55 and 225 mV at 10 and 200 mA·cm⁻², which is superior to the FeNi-P (82 mV@10 mA·cm⁻² and 301 mV@200 mA·cm⁻²), and even out-performing the Pt/C catalyst at a high current density > 200 mA·cm⁻². Moreover, the oxygen evolution reaction (OER) activity of Zn-FeNi-P also has dramatically improved (207 mV@10 mA·cm⁻²) comparable to FeNi-P (221 mV@10 mA·cm⁻²) and RuO₂ (239 mV@10 mA·cm⁻²). Noticeably, an electrolyzer based on Zn-FeNi-P electrodes requires a low cell voltage of 1.47 V to achieve 10 mA·cm⁻², far beyond the catalytic activities of FeNi-P||FeNi-P (1.51 V@10 mA·cm⁻²) and the benchmark RuO₂||Pt/C couples (1.56 V@10 mA·cm⁻²). This Zn-implanting strategy paves a new perspective for the development of admirable bifunctional catalysts.