Hollow Nanosheet Arrays Assembled by Ultrafine Ruthenium–Cobalt Phosphide Nanocrystals for Exceptional pH-Universal Hydrogen Evolution

The development of high-efficiency electrocatalysts for pH-universal hydrogen evolution reaction (HER) is promising for constructing feasible water splitting systems at all pH values, but it remains challenging. Herein, we report a facile approach toward unique hollow nanosheet arrays assembled by ultrafine ruthenium–cobalt phosphide (Ru–CoxP) nanocrystals through conversion from metal–organic framework templates. The synergic effects of optimized electronic structure, increased active sites, and rapid charge/mass transfer endow the Ru–CoxP nanoarrays with outstanding electrocatalytic performance toward pH-universal HER. While exhibiting remarkably low overpotentials of 34.6 mV and 22.7 mV at 10 mA cm–2 in 1 M KOH and 0.5 M H2SO4, respectively, the Ru–CoxP nanoarrays show an extremely low overpotential of 21.6 mV at 10 mA cm–2 in 1 M phosphate buffer solution (PBS). Furthermore, they can stably drive a Pt-free neutral electrolyzer for overall water splitting at 10 mA cm–2 with a cell voltage as low as 1.557 V.