Crystalline Ni-Fe phosphide/amorphous P doped Fe-(oxy)hydroxide heterostructure as a multifunctional electrocatalyst...

Hydrogen production by electrocatalytic water splitting is considered to be an effective and environmental method, and the design of an electrocatalyst with high efficiency, low cost, and multifunction is of great importance. Herein, we developed a crystalline NiFe phosphide (NiFeP)/amorphous P-doped FeOOH (P-FeOOH) heterostructure (defined as P-NiFeO_xH_y) as a high-efficiency multifunctional electrocatalyst for water electrolysis. The NiFeP nanocrystals provide remarkable electronic conductivity and plenty of active sites, the amorphous P-FeOOH improves the adsorption energy of oxygen-containing species, and the crystalline/amorphous heterostructure with superhydrophilic and superaerophobic surface generates synergistic effects, providing plentiful active sites and efficient charge/mass transfer. Benefiting from this, the designed P-NiFeO_xH_y displays ultralow overpotentials of 159.2 and 20.8 mV to achieve 10 mA cm^-2 for oxygen evolution reaction and hydrogen evolution reaction, and also shows the superior performance of urea oxidation reaction with a low voltage of 1.37 V at 10 mA cm^-2 in 1 M KOH with 0.33 M urea. In-situ Raman spectra and ex-situ XPS analysis were also used to investigate the catalytic process and reveal the surface structure evolution of P-NiFeO_xH_y under electrochemical oxidation. Accordingly, the designed P-NiFeO_xH_y is employed as both cathode and anode to assemble into the urea-assisted water electrolysis device, which can reach 10 mA cm^-2 with a low 1.36 V and could be further driven by a solar cell. The work reveals a design of superior activity, cost-effective and multifunctional electrocatalysts for water splitting.