Simple preparation of Ni2P/Ni(PO3)2 inlayed in nitrogen-sulfur self-doped ultrathin holey carbon nanosheets with excellent electrocatalytic activities for water splitting

Highlights: • N/S-self doped ultrathin holey carbon nanosheets were simply prepared. • Highly dispersed Ni₂P/Ni(PO₃)₂ was in-situ inlayed in the carbon nanosheet. • The catalysts exhibit excellent bifunctional activities for HER, OER and overall water splitting. • Synergistic effects between Ni₂P and Ni(PO₃)₂ was exhibited. -- Abstract: In this work, composites of Ni₂P/Ni(PO₃)₂ inlayed in N/S self-doped ultrathin holey carbon nanosheets were facilely prepared using methyl orange (MO) as nitrogen and sulfur sources, in-situ produced Ni(OH)₂ nanosheet by hydrolysis of NiCl₂ as self-sacrificed template, followed by pyrolysis and phosphorization. Ni₂P/Ni(PO₃)₂ was highly dispersed in carbon nanosheets and supplied fruitful of exposed active sites, and thus endowed the as-prepared samples highly electrocatalytic activities for water splitting. In addition, the N/S self-doped carbon protected Ni₂P/Ni(PO₃)₂ from corrosion by the electrolyte and greatly enhanced the stabilities of the catalysts. As a result, the optimized composite 1:8-NPO/NS-C-420, derived from the precursor with 1:8 molar ratio of MO/Ni(II) and phosphorized at 420 °C, has exhibited excellent electrocatalytic activities for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting. As a result, 88 mV and 273 mV overpotential was obtained for HER and OER at 10 mA/cm² in acidic and alkaline electrolyte, respectively. As for the overall water splitting, only 1.63 V of cell voltage is needed to reach 10 mA/cm². The catalyst also exhibited high long-term stability in HER, OER and water splitting.