Fe2P/reduced graphene oxide/Fe2P sandwich-structured nanowall arrays: a high-performance non-noble-metal electrocatalyst for hydrogen evolutionElectronic supplementary information (ESI) available: Fig. S1-S9 and Table S1. See DOI: 10.1039/c7ta01791j

Transition metal phosphides (TMPs) have been one of the ideal candidates as low-cost and high-efficiency catalysts for hydrogen evolution reactions (HERs). We report herein a novel TMP architecture, Fe 2 P nanoparticles/reduced graphene oxide (rGO) nanosheets/Fe 2 P nanoparticles (Fe 2 P@rGO) sandwich-structured (Fe 2 P@rGO) nanowall arrays on a Ti plate. This nanostructure was easily prepared via one-step electrodeposition followed by a low-temperature phosphidation reaction. The Fe 2 P@rGO nanowall array film is featured with maximally exposed catalytic sites, fast electron and mass transport, and robust structure stability, and therefore it behaves as an excellent HER electrocatalyst. The Fe 2 P@rGO shows a low overpotential of 101 mV at a current density of 10 mA cm −2 and a small Tafel slope of 55.2 mV dec −1 with a large exchange current density of 0.146 mA cm −2 . Furthermore, the catalyst exhibits superior durability evidenced by about 87% catalytic activity retention against about 55% for the commercial Pt/C catalyst after a 12 h test. The study presents a new nanoengineering strategy for high-performance TMP-based HER catalysts. Vertical sandwich-like architectures of Fe 2 P@rGO were constructed and performed well in terms of excellent HER activity and high stability simultaneously.