Unraveling Ni-Fe 2D nanostructure with enhanced oxygen evolution via in situ and operando spectroscopies

Ni-Fe-based materials are well known as one of the most active electrocatalysts for the oxygen evolution reaction (OER) in alkaline environments. In this study, we propose a facile and scaling up synthesis route using a surfactant for Ni-Fe 2D nanostructured electrocatalysts. Furthermore, we uncovered the hidden phase transformation mechanism of 2D Ni-Fe layered double hydroxide (LDH) electrocatalysts by combining various in situ and operando analyses. The Ni-Fe LDH underwent a chemically induced phase transformation in an alkaline environment without applied potential. The resulting phase transformation product persisted throughout the entire OER mechanism cycle, such that it played a dominant role in the process. The presence of high-valent Ni and Fe was observed on the surface; hence, the OER selectivity and catalytic turnover frequency were enhanced in the low-overpotential domain. Our study not only uncovers the fundamentals of Ni-Fe LDH but also expands the potential for practical alkaline water splitting.