Dual-purpose nickel-iron layered double hydroxides by controlled lanthanide and phosphide incorporation for promoting overall water splitting efficiency

Abstract

Developing non-noble metal and binder-free bifunctional electrocatalysts is of paramount importance but challenging for simultaneously promoting oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes. In the work, we introduce the dual-purpose utilization of nickel-iron layered double hydroxides (LDH) by a lanthanide and phosphide incorporation strategy for highly efficient overall water splitting (OWS). The screening of lanthanides effect shows that the lanthanide dopants (Ce, La and Nd) greatly contribute to the layer lattice distortion of LDH host structure and strong electronic interaction with Fe2+ species, leading to the increment of OER active species content of α-Ni(OH)2 phase and Fe3+. Specially, the formation of Ce3+/4+ reversible redox species can significantly promote charge transfer efficiency, thus corporately attributing to the excellent OER activity (η10 = 207 mV) and durability (300 mA·cm−2 for 200 h). On the other hand, we found that with further phosphide anions engineering, the HER Volmer step is accelerated in lanthanide and phosphide co-doped LDH, as compared to the solely phosphide doped LDH. The present of co-doped lanthanide can modify the adsorption energy of hydrogen intermediates and the Ce3+/4+ reversible redox species also facilitate the formation of HER active Ni2P phase, resulting in the lowest η10 value of 134 mV. The dual-purpose configuration of the Ce LDH // Ce LDH-P electrodes, provides low OWS potentials of 1.638 and 1.839 V to reach current densities of 10 and 100 mA·cm−2, respectively. These findings could introduce a new way to integrate nonprecious-metal bifunctional electrocatalysts into an efficient OWS system.