N-doped carbon armored metal phosphides were anchored in-situ on backbones of nickel foam (NF), by using polydopamine as both carbon source and targeted precursor delivery vehicle. The product served as a highly efficient chainmail bi-functional catalyst toward electrolytic water splitting, requiring small operating cell voltages of only 1.65, 1.73, and 1.79 Vat 50, 100, and 250 mA/cm(2), respectively for overall water splitting. More importantly, the product catalyst also possessed excellent long-term stability, even tested at 250 mA/cm2. The excellent activity and durability may be ascribed to the positive synergistic effects between well-mixed metal phosphides, advantageous nanostructure of interwoven thin vertical nanosheets, protective and conductive N-doped carbon matrix, hydrophilic and aerophobic characteristics, and well dispersed and utilized active materials on skeleton surfaces of the highly conductive NF. This synergistic effect boosting and protective layer armored design for highly efficient and stable electrocatalysts is unique and scalable, suitable for large-scale applications not only in the field of electrocatalysis, but also in other heterogeneous catalysis. (C) 2019 Elsevier Inc. All rights reserved.