A metal-vacancy-solid-solution NiAlP nanowall array bifunctional electrocatalyst for exceptional all-pH overall water splitting

The development of active and durable bifunctional electrocatalysts for overall water splitting in a wide pH range is highly desirable for industrial water electrolysis. Herein, we develop a new type of 3D metal-vacancy solid-solution NiAlP nanowall array synthesized by a combination of selective alkali-etching and phosphorization strategies as a highly-active and earth-abundant all-pH bifunctional electrocatalyst for efficient overall water splitting. These metal-vacancy NiAl_δP nanowall arrays as both the anode and cathode are highly efficient in overall-water-splitting catalysis, realizing 10 mA cm^-2 at quite low cell voltages of 1.50-1.70 V for pH = 0-14. In particular, the NiAl_δP nanowall arrays could achieve an outstanding overall water splitting activity in acidic electrolyte (pH = 0) with high turnover frequencies of ∼11:000 H₂ per h and ∼5000 O₂ per h at 50 and 300 mV overpotentials for the HER and OER, respectively, far exceeding those of the best noble-metal-free catalysts and the Pt/C-RuO₂ combination.