NiFeCu phosphides with surface reconstruction via the topotactic transformation of layered double hydroxides for overall water splitting

Abstract

Regulating the crystal plane exposure of catalysts is an effective way of enhancing their oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities. Herein, we have synthesized ultrathin metal phosphide (NiFeCuP) nanosheets via the topotactic transformation of layered double hydroxide (LDH) precursors, based on their tunable composition and special layered structure. These as-prepared metal phosphides not only inherit the ultrathin nanosheet structure of LDHs, but also maintain metal atomic dispersion of the LDH precursors, thus exposing more active sites and increasing their internal activity. Moreover, the presence of the heteroatomic Cu atom in ultrathin NiFeCuP nanosheets regulates the exposed crystal plane, that is, it induces the (210) crystal plane exposure and tunes the electronic structure to enhance OER and HER performances. Experiments combined with calculations indicate that ultrathin NiFeCuP nanosheets with surface reconstruction and regulated electronic structures optimize the ΔG value of the intermediates during the water splitting process, thereby exhibiting obviously improved HER and OER performances, and excellent overall water splitting activity. The prepared bi-functional catalyst exhibits an HER overpotential of 86 mV and an OER overpotential of 156 mV at 10 mA cm⁻². This results in a low cell voltage of only 1.49 V to drive the overall water splitting in alkaline solutions. This work provides a new idea for the development of bi-functional catalysts exhibiting excellent performances by regulating the exposed crystal plane.