▎ 摘　　要

Water electrolysis is considered a key step in future hydrogen energy strategies. However, the current bottleneck of this technology lies in the cost and efficiency of electrocatalysts. To obtain non-precious metal-based catalysts with rationally designed structures towards high efficiency, herein, a structure of graphene-supported double-shelled hollow nanospheres derived from a metal-organic framework is synthesized. These sub-100 nm nanospheres are composed of a bimetallic Ni2P/FeP inner shell with a carbon outer skin, which, together with the conductive graphene support, provides a largely exposed active area, high conductivity and outstanding stability. This catalyst demonstrates excellent performance in the OER with an ultra-low overpotential of 211 mV to drive 10 mA cm(-2) and a small Tafel slope of 43 mV dec(-1), which outperforms the most recently reported OER catalysts. It also exhibits bi-functionality for both the HER and OER with remarkable stability, thus can be applied as an efficient electrocatalyst for overall water splitting with a low cell potential of 1.578 V for 10 mA cm(-2).