An in situ phosphorization strategy towards doped Co ₂ P scaffolded within echinus-like carbon for overall water splitting

Eco-environmental synthesis of non-expensive electrocatalysts such as transition-metal phosphides (TMPs) is critical to advancing renewable hydrogen fuel. TMP nanostructures prepared typically by introducing additional conventional phosphorus sources are suggested as promising durable and low-cost electrocatalysts. Herein, an eco-efficient guest/host precursor-based synthesis route is demonstrated to prepare doped Co₂P scaffolded within echinus-like carbon ((M_0.2Co_0.8)₂P@C, M = Fe and Ni) as electrocatalysts for overall water splitting. (Fe_0.2Co_0.8)₂P@C is derived by directly pyrolyzing a precursor of sodium dodecyl phosphate-intercalated CoFe-layered double hydroxide (CoFe-LDH), without introducing any additional phosphorus source. Electrocatalytic testing shows that (Fe_0.2Co_0.8)₂P@C requires overpotentials of 290 and 130 mV at a current density of 10 mA cm^-2 for oxygen and hydrogen evolution reactions (OER and HER) in an alkaline electrolyte, respectively. Furthermore, a different (Ni_0.2Co_0.8)₂P@C composite, obtained only by altering a NiCo-LDH host, exhibits better electrocatalytic activities than those of Fe-doped (Fe_0.2Co_0.8)₂P@C. In particular, the (No_0.2Co_0.8)₂P@C||(Ni_0.2Co_0.8)₂P@C electrolyzer affords a current density of 10 mA cm^-2 at a decent voltage of 1.62 V for overall water splitting. Electron energy-loss spectroscopy (EELS) observations show the oxyhydroxide layer formed on the surface, and density functional theory (DFT) calculations reveal that Fe-/Ni-doping lowers the Gibbs free energy barrier for the OER and the HER, both underpinning the enhancements.