Electronic modulation of composite electrocatalysts derived from layered NiFeMn triple hydroxide nanosheets for boosted overall water splitting.

Herein, we report the synthesis of Fe and Mn co-doped Ni3S2 nanosheet arrays (FM-NS NSAs) as well as layered NiFeMn triple hydroxide (NiFeMn-LTH)/FM-NS hybrid NSAs (HNSAs) via an easily controllable sulfidation method with NiFeMn-LTH NSAs as the precursor, which can be employed as coupled oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrodes to achieve boosted overall water splitting performance. It is discovered that the incorporation of the dual Fe and Mn cations can simultaneously modulate the morphology and optimize the electron density of the obtained catalysts. As a result, the full sulfidation product of FM-NS NSAs display a much-enhanced activity for the OER at a current density of 10 mA cm-2 with an overpotential of 188 mV. The NiFeMn-LTH/FM-NS HNSAs obtained from partial sulfidation demonstrate an enhanced HER activity with a lower overpotential of 110 mV at 10 mA cm-2. The FM-NS NSA anode and the NiFeMn-LTH/FM-NS HNSA cathode were coupled in an alkaline medium for overall water splitting and exhibited a much lower cell voltage of 1.48 V at 10 mA cm-2, superior to most of the reported noble-metal-free electrocatalysts. Additionally, a battery-assisted electrolyzer (1.5 V) was assembled to explore the feasibility for practical energy-efficient water splitting.